From the ABC 7 Weather team

Archive for March 2013

Fact: March is a windy month - What gives?

March 14, 2013 - 11:04 AM
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March winds. Ugh! March is a fickle month. It can be warm, it can be cold. We can see thunderstorms and highs approaching 80 one day (yes, three 80 degree days happened last year by this point), and the next day we have wind chills in the 20s with snow showers—maybe even a blizzard!

No doubt the month of March has its mood swings. However, the most noticeable and consistent weather factor in March seems to be the strong winds. Every other day it seems that we as forecasters are calling for a “breezy/gusty/windy” day in the region…..okay, so what gives? Why the heck does March seem so windy compared to other months out of the year?

Well March is a transition month—obviously. We are heading out of the cold short days of winter into the longer and much warmer days of spring and summer. Cold air is situated north while warm air is trying to approach from the south. 

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Temperatures during the month of March are more extreme over shorter distances PLUS we have the heat of the sun finally at an angle that can actually warm up the surface quicker.

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With the sun heating up the Earth’s surface, pockets of warm air form. These pockets of warm air start moving towards the cold dense air that is still hanging out, leftover from the winter months. The difference in the air mass temperatures (between the warm air and cold air) create differing pressures, which in turn create winds.

The greater the difference in the high and low pressures, the stronger the force of the winds. Also, the distance between an area of high pressure and an area of low pressure will also determine the speed of the moving air. This is how we are set up for Thursday March 14th: An area of high pressure is hanging out over the Mississippi Valley while low pressure sets up shop in Eastern Canada. Winds flow around an area of high pressure clockwise while winds around low pressure move counter-clockwise. Considering these two pressure are pretty close together,  combined they cause a tight pressure gradient an allow a pretty fast northwest wind to flow right into the Mid-Atlantic.
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For Friday, the high pressure will float to the southeast, into the Gulf of Mexico and the low will move to the east across Canada and track across the upper Great Lakes. The distance between these two pressures becomes farther apart. Still expecting a breezy day for your Friday but this time winds will be coming from the southwest from the ridge of high pressure along the Gulf.

As we continue through this erratic month of March, the Earth will continue it's rotation to give us more sunshine in the Northern Hemisphere. This will moderate our temperatures, sending the cold air back to the north as we head into April which in turn will finally create less of these breezy, windy, gusty days we experience in the month of March. 

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The Comet: Chance to see again and where to look

March 13, 2013 - 04:42 PM
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Here are some great local pictures just after sunset yesterday of the comet panSTARRS.  

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From WTOP's Dave Dilldine and from a viewer in Warrenton.

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The clouds are clearing so another chance to try and see it again, or for the first time this evening  7:30-7:45.  Here is where to look.   

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And another chance Thursday evening.

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Thanks to Fred Espenak for the great diagrams.  Fred also created this wonderful timelapse of the comet just after sunset a few days ago in Arizona.

Comet PanSTARRS - The Movie from Fred Espenak on Vimeo.

Fred still calculates all the times of eclipses and is a retired NASA Goddard scientist.  Visit his Mr. Eclipse page for more great astronomical information.  And try and "catch a comet" before clouds and some wet weather this weekend.

 

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20th anniversary of the 1993 Storm of the Century

March 13, 2013 - 04:00 AM
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Today is the 20th anniversary of the 1993 "Storm of the Century" which came through the D.C. area on March 13, bringing with it a fair amount of snow and gusty winds.

While it wasn't the worst snow storm the D.C. area has ever seen, it's massive size and widespread damage it left in its wake through the remainder of the country made for its legendary status in weather history.

The low rapidly deepened in the Gulf of Mexico on the 12th, causing a 12-foot storm surge on the western coast of Florida in Taylor County. More than 100 boats called in to the Coast Guard with distress signals and 11 tornadoes were spawned in Florida. Thunderstorms formed along a line which extended south all the way to Cuba where damaging winds were also recorded.

At the same time, heavy snow was falling in Alabama in the Deep South and eventually spread to northeast. Twenty states recorded snowfall totals of 10 inches or more, which extended from Alabama all the way to Maine. Mount LeConte, Tenn. recorded 60 inches of snow and Mount Mitchell, N.C. recorded 50 inches of snow with 14 foot drifts!

Find out more about reported snowfall totals, highest wind gusts and storm related deaths below.

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Comet Watching: Possible to see around Washington tonight

March 12, 2013 - 03:16 AM
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A reasonably bright comet that is sometimes described as the "icy snowball" of our solar system has made a rare naked eye appearance in the evening sky.  This is a great image of the comet named "pan-STARRS" (named after telescopes not humans this time) as seen in the southern hemisphere earlier in March.  

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This great picture is courtesy of Michael Goh.

Now the comet has passed behind the sun by "only" 26 million miles and as it heads back to deep space will be visible here in the northern hemisphere and D.C. area.  BUT we need clear skies and a clear view of the western horizon.  I think there is a chance to see the comet this evening. 

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The rain and cold front will pass us this afternoon and if our hyperlocal futurecast shows some clearing around 7-8pm which will the best time to try and see the comet.  Here (thanks to Sky and Telescope) is where to look. 

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If the skies are clear shortly after sunset 7:20-7:45PM look to the west for the very, very thin cresent moon as shown in this diagram below from EarthSky.org.  Pan-STARRS should look like a blur above the moon.  
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Try and find a really good view of the western horizon and with binoculars (no need for a telescope) you should be able to clearly see it.  Let me know.  I'll try myself this evening (if my "clearing" forecast is correct) and let you know.  Good luck comet watchers. If not this evening we'll try later in the week, but this evening the very thin crescent moon is a good guide where to look.

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Comet visible: Will you see it?

March 12, 2013 - 02:23 AM
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Great simulation of were to look for the comet panSTARRS from Fred Espenak.  Fred created this about 1 month ago.  Now we need clear skies and good view of the western horizon.  The comet will get higher in the sky but a bit dimmer each evening over the next 2 weeks.  We'll keep you posted of best viewing weather

 

Visibility Simulation of Comet Panstarrs (C/2011 L4) from Fred Espenak on Vimeo.

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Tuesday is Tornado Preparedness Day in Virginia

March 11, 2013 - 03:38 PM
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In the past 5 years, the state of Virginia reported 131 tornadoes, which comes out to an average of 26 tornado reports per year. Tuesday at 9:45am, Virginia will have a statewide tornado drill which included schools and colleges and is encouraged for businesses, organizations and families across the state.

Above is a youtube video of a tornado that touched down at Longwood University in Farmville, VA on April 27, 2011. It's a stark reminder that tornadoes often do occur in Virginia and that you should be prepared coming in to the new severe weather season.

List of historical tornadoes by county in Virginia

This is the perfect time to review your severe weather action plan with your coworkers and family. Something easy to think about is last years derecho. Think about how long you were without power and what you wished you had at the time and be sure to include that in your severe weather safety kit. Obvious items include water, flashlights and batteries, non-perishable food items and a first aid kit. It's always best to be prepared.

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February temperatures slightly cooler than average for D.C.

March 11, 2013 - 10:49 AM
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With 2012 being the hottest year on record for the D.C. area, all signs were pointing to more above-average temperature trends to continue. This was the case when January 2013 ended 4.3 degrees above normal, but cooler weather has been the story since. Temperatures were below normal for the second time in the past 4 months in February, and through early March, temperatures have continued to buck the trend, at 1.4 degrees below normal for the month through the first 10 days.

February ended 0.7 degrees below normal for Reagan National airport, with an average temperature of 38.3 degrees, slightly below the normal average of 39 degrees for the month. With temperatures so close to the normal, it didn't rank in the top 50 coolest or warmest months since 1871. It was basically middle of the road.

Months with below average temperatures since January 2010

With temperatures above to well-above average over the past few years, it is significant that 2 of the past 4 months have experienced the opposite. Since January 2010, only 7 out of 38 months have seen temperatures below normal. That means temperatures in D.C. have only been below normal 18% of the time.

Through the first 10 days of March, temperatures have averaged over a degree below normal. Temperatures look to continue to be below average through at least the middle of the month with the exception of this past weekend and today. Only time will tell if cooler temperatures will hang around our area in 2013, but climate records over the past few years show this as highly unlikely. Enjoy it while it lasts!

We will be sure to post an update when the National Climatic Data Center (NCDC) publishes their findings on what February ranked for temperature and precipitation in the U.S. and globally.

 

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Snow Storm: A bust here and snowy bust for New England

March 8, 2013 - 05:03 PM
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Great two day NASA GOES Project high res satellite loop of the big storm that formed to our southeast and moved out over the Atlantic.  The circulation that brought warm air in the ocean and keep our snow as rain, also continues to pump in moisture over New England with record snows.  I missed the forecast by 6-8".  My colleagues in Boston missed by 10-14".  That is 10-14" too low. :>)  Ah, the challenges of forecasting.  Watch.  The Boston NWS forecast yesterday.

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  Still snowing and 24" near Boston.

 

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Pattern Change Means Weekend Warmup

March 7, 2013 - 08:57 PM
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March has started off a bit cooler than average, but that's all about to change.  Just as we spring forward and switch back to daylight saving time, temperatures start to climb.  Get ready for some spring fever in D.C.; and what better time for it to arrive than for the weekend!

Temperatures across the country are running much milder than average in the southern Plains and southwest, but cooler than average over the parts of the east.  Check out the highs from Thursday.

The ridge in the west will move east and will push some of that milder air into our area.  Adam Caskey created the maps below that do a nice job explaining this pattern change.

The average high temperature in D.C. in early March is 53°.  This weekend will be a few degrees above average and the trend for milder temperatures continues into early next.  Not a bad second weekend of March if you ask me!

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Washington Snow Storm: Really "Wrong"? Why?

March 7, 2013 - 12:01 AM
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Northeast Washington got a quick hit of snow early Wednesday, but after that, it was almost nothing. Photo: Jennifer Donelan

It's true - the forecast for 3 to 6 inches of wet snow in D.C. itself was a bust.  The District got some snow, but only enough for a brief white coating until quickly turning to rain.

In fact, the more than 1 inch of rain would have made for 5 to 8 inches of heavy, wet snow. So, why was the forecast for possible "major" storm wrong?

Well, 1) It was and is a major storm. Look at the snow accumulations. Here's a great picture form Adam Caskey of the ground and snow from the Iwo Jima Memorial (near sea level) and 4 miles west (about 200 feet higher).

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Elevation does, and can make a big difference in snow forecasts.  We know  the air near the ground was warm after the strong March sunshine of Tuesday. 

The forecasting tools we now use are largely based on "Numerical Weather Prediction." But for us "oldtimers," we also rely on experience.  Most of the signals I saw told me this would be a "dynamic" storm. 

Rapid development in just the "right" spot in the lower Chesapeake Bay could have drawn in cold air, and with rapid rising air, it should have overcome the low mild air and changed early rain to snow. 

One of the "what could go wrong" parts was the strong east winds shown on these simulations.

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The prediction during the Tuesday evening forecast for the Wednesday morning rush hour and snow amounts was right on!

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I should have kept that all day.  But I also remembered the famous Veteran's Day storm of November 1987. Several days before that storm it was 70°, but the "dynamics" in the atmosphere made for a historic snow, even if the calendar said November.

I knew the rain/snow line would be close. The late Tuesday vertical profiles of the air above us for Wednesday showed enough cold air for snow.  But that low level east wind was there.

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Our local hyperlocal microcast model/simulation was the "outlier" from everything else, but proved to be reasonably correct about the snowfall.

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The storm formed in the "perfect" area for a big snow around D.C., which is in the lower part of the Bay.

The only other "weak link" was the lack of real cold air to our north. I thought the snow forming above us (all the rain that fell was snow until 1,000 to 2,000 feet up) would be intense enough to "beat"  the mild air near the surface. Even with at mild east wind,  the morning rain around D.C. should have changed to snow. 

Wrong. 

But look at the snowfall reports in the area:

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So would I make the same forecast again?  Probably not. That east wind did turn to the northeast and heavy snows continued not far away. 

But I sure will look for colder air to our north and try harder next time.

Apologies?  No. I did my best just like you do. We'll edo more homework and study a bit more.

Here is a quick look at our hyperlocal simulation that for several days was showing more rain than snow. It proved pretty good. I also explain why this "outlier" was hard to go with.

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Live Blog: D.C. March Snowstorm

March 6, 2013 - 04:21 AM
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LIVE DOPPLER RADAR | CLOSINGS | STORMWATCH  7 FACEBOOK

Twitter: @Jacquijeras    @adamcaskey    @ABC7Brian    @alexliggitt

@BobRyanABC7    @DougHillABC7    @EileenABC7   @SteveRudinABC7

@DevonLucie   @LaurynRicketts

6:50PM:  Last update of the evening.  Snow did fall in parts of the region.  Here are a few snow totals from both Maryland and Virginia.  Too much warm air in and around D.C. and east of the I-95 corridor left a lot of snow lovers disappointed. 

5:35PM:  As storm starts to wind down, what exactly happened with the busted forecast in D.C.?  Bob Ryan just posted a new blog on our weather homepage.

4:38PM: Wind advisory in effect until 11 PM for DC, Prince William, Montgomery, Stafford, Spotsylvania and points East.

4:20PM: Winter Weather Advisory now canceled for all locations with the exception of Caroline County and south. All Watches/Warnings canceled for our viewing area.

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2:53pm:  Great side by side comparison showing the difference 4 miles makes with this storm.  Thanks to Adam Caskey for sharing!


2:30pm:  Winter storm warnings have been downgraded to winter weather advisory.  The storm is becoming more and more of a rain and wind event in D.C. and especially over southern MD. 


2:18pm:  Check out the waves along the Delaware beaches from the coastal storm.  Flooding a big concern along the beaches of the Eastern Shore. Latest wind gust at Rehoboth Beach was 71mph.

Wayne Wilkins

1:50pm:  Great snowman picture from Chantilly, VA - wet snow is the best for making snowmen!

Patrick Seaby - Chantilly, VA

1:40pm:  Snow still falling in Winchester where Facebook friend Mark Cappo measured 9".  Heavy wet snow combined with gusty winds means possible downed trees and power lines. 


1:30pm:  Still looking at mainly rain outside the ABC7 studio in Arlington.   Travel a little farther west and snow totals grow quickly!  Latest snow totals from Sterling NWS.


12:45pm:  Updated snow totals reflect the slow transition to all snow in the D.C. metro area.  Colder air will spill in over the next few hours and everyone will transition to snow, as the storm system moves farther out of the region.  Because the rain/snow mix is lingering in the metro area, snow totals are a bit lower.  West of Washington still looks on point to receive the highest snow totals.


12:11pm: A Winter Weather Advisory replaces the Winter Storm Warning in Calvert and St. Mary's Counties in Southern Maryland. The National Weather Service continues the Winter Storm Warning for the metro area until 3AM but late trends and movement of the storm indicate most of the snow (and rain S&E) will be pretty much over by this evening.

11:42am: Heaviest snowfall totals...

Rocky Bar, VA (Rockingham County):  17.8"

Massanutten, VA (Rockingham County):  17"

Charlottesville, VA (Albermarle County): 15.5"

City of Waynesboro, VA:  12.2"

11:32am: Wind gusts are starting to increase across the D.C. area. On the Eastern Shore in Easton, MD, a local storm report showed a tree fell on a house there. Here are the current local wind gusts. The highest gust I've seen so far is 61 mph from a buoy by Lewes, DE.

11am Wind Gusts

11:18am: It's crazy how location dependant the snow is as in Rosslyn, VA (At ABC 7 Studios right by the Key Bridge) there is currently nothing, but 4 miles away near Ballston in Arlington, there are a couple inches of snow. Looking at traffic cameras, we have also seen snow in NW D.C. in terrain that is only a few hundred feet higher. It's that one to two hundred feet of atmosphere that is currently the difference between rain and snow.

10:38am: There is still a very sharp gradient between snow and rain across the D.C. Metro. Currently, I've seen reports of snow in Vienna and even north Arlington, whereas it is raining in Rosslyn and the District itself. Surface temperatures here are still in the mid 30s, sitting at 36 at Reagan National.

This will not allow for any kind of accumulations unless the colder air finally makes it far enough east and accumulations are heavy enough. Snowfall totals east of D.C. may be well below where they were originally forecast. It appears totals just west of D.C. will be close to the forecast amount though as it has remained snow through the duration.

10:10am: Another great picture from Ashburn, VA (more west of D.C.!) from Erin Reidy.


9:57am: Wet snow continues to fall in the D.C. Metro, but at least in Arlington it hasn't been heavy enough to overcome the wet roads and wet grounds.

9:17am: More pictures keep rolling in to the Stormwatch 7 Facebook page. Keep them coming!

Courtesy: Kelly Gaitten in Hamilton, VA

8:55am: Here are some of the latest snowfall totals for the area.

Frederick, MD:  4.3"      Columbia, MD:  1.6"      Germantown, MD: 2.6"

Waynesboro, VA:  12.2"      Harrisonburg, VA:  9.2"      Winchester, VA: 8"

Culpeper, VA:  5.8"      Burke, VA:  1.8"      Ashburn, VA:  3.3"

8:41am: Heavy snow has now moved into the majority of the D.C. Metro with some rates of 1-2" per hours in the heaviest bands. Here's a live look at the Capitol this morning in this streaming camera.

8:07am: Current trends are showing rain now changing back to snow in the D.C. Metro but it's still hanging on as rain east of D.C. As the low continues to push east and intensify, more cold air will be brought into the system and snow will become the primary form of precipitation.

Current "rough depiction" of the Rain/Snow line

7:29am: Jefferson, MD has snow this morning as well as some hungry birds at the feeder! Thanks to Patti Carbaugh! She has seen about 6 inches so far with more coming down.


7:18am: Here are some of the latest snowfall totals for the region. Snow is extremely wet and heavy west of D.C., but in the city and east, roads and grounds are mainly wet with a lot of rain mixed in thus far.


7:13am: Here's a great picture from Mark Cappo this morning in Winchester, VA. I just had another picture of a ruler taken by Mark showing just over 7 inches so far.

Snow in Winchester, VA

6:55am: A fair amount of rain has mixed in and now taken over through much of the immediate D.C. Metro and even points west of D.C. as well. As the low moves off the east coast we are expecting precipitation to change back over to snow over the next couple of hours.

5:57am: Many of you want to know when the snow looks to exit the D.C. area. Here's a look at one of the models (NCEP Rapid Refresh) showing a finish time after sunset closer to 9pm in the D.C. area (earlier to the west).

(Credit: WeatherBell Models)

5:39am: This isn't expected to be the heaviest snow storm in March for the D.C. area but it may be close to the top ten. Be sure to check out Lauryn Ricketts blog on some of the top snowstorms in March.

Top March Snowstorms

5:21am: Here's a picture from Culpeper, VA at 3am this morning with the roads covered and snow coming down heavy from Kelly Stepp.

Courtesy Kelly Stepp

5:09am: Here's a picture out our window in Arlington of the snow plows lined up at a stoplight, though as you can see the roads are just wet at this point.


4:52am: Here is a picture from Dumfries, VA sent to us by Susan Billings through our Facebook page.

Dumfries early this morning (Susan Billings)

4:15am: Snow is coming down through the majority of the D.C. area this morning with exception of right along the western shore of the Chesapeake Bay and Southern Maryland where rain is falling. Please send us any reports (preferably measured by a ruler if you have one!) and pictures to us on our Stormwatch 7 Facebook Page, our twitter accounts listed above, or iwitness@wjla.com.

Doppler as of 4:10am

1:48am:  Snow coming down pretty good in parts of the region.  Here's a picture from north Bethesda of snow covered grass and cars.  Roads are just wet, but a little slick.


1:00am:  Road temperatures remain slightly above freezing, for now.  Snow will stick to the grass first and then will eventually start to the stick to the roadways, especially bridges, overpasses, and side streets next.  Here's a great site to monitor road temperatures.

12:50am:  Here's the latest water vapor image.  This gives you an idea of the energy that's helping to develop this major coastal storm.  I've circled the area of interest.  The pink represents colder cloud tops and precipitation, where as the orange indicates drier air.  The dynamics between the two generates a cyclonic spin in the atmosphere, which will further develop the low off the VA coast.  What does that mean for us?  A big snow storm.  Enough cold air for heavy snow and strong winds.

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12:41 am:  A winter storm warning is in effect for the entire viewing area through 3am Thursday.  Heavy snow is expected across the region with strong winds through late Wednesday night.


12:12am:  Precipitation filling in on radar across much of the metro area.  Looking outside the studio in Arlington, just light rain.  Numerous reports of heavy snow farther west into Winchester and Front Royal.  Snow reported near Potomac, MD from ABC7 reporter Tom Roussey. 


2013 March Snowstorm - Live Blog

It starts now with continuous updates on the mid-Atlantic snow storm.  The most up-to-date snow totals, updated warnings, pictures, and all other relavent information to this potentially historic March snow. 

Follow along and send us updates from where you are!  It's extremely helpful to hear from you and what conditions are like in your neighborhood.  Send us your pictures and weather updates to our Stormwatch7 Facebook page.  Also, check out our WeatherBug roof cameras across the viewing area. 

On Twitter?  These are the people to follow!

Stormwatch 7  Doug Hill  Bob Ryan  Jacqui Jeras  Adam Caskey  Brian van de Graaff  Steve Rudin  Devon Lucie  Alex Liggitt  Eileen Whelan  Lauryn Ricketts 

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D.C. Snow Storm: Latest of what, when and how much

March 5, 2013 - 09:45 PM
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10:30 PM update: More snow reports coming in and latest trends now favoring more snow earlier in metro area.  Will have new timeline posted soon and upping the snow totals for AM rush and noon.  Major snow storm for D.C. area 6-12" likely closer to D.C.

9:45 update:  First reports of snow and rain to the south of D.C.  all late information continues to support a major snow storm in the region.  No significant changes to our earlier timing and total snow fall.

Tuesday's temperatures of 50° and higher and road temperatures in the 60s that everything still points to heavy wet snow to hit us late Tuesday and Wednesday. 

The National Weather Service has much of metro area in a winter storm warning..  

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The storm track, winds and temperatures at the ground and in the air above us are critical to determining what will happen. Here is a look at a tonights very late simulation of the storm tomorrow afternoon.   

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I've drawn in where the center is which is near lower Chesapeake Bay. 
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Winds from the east are likely to keep a rain/snow mix right along the Interstate 95 corridor until about midday Wednesday as the storm moves east, becomes stronger and drawing in cold air from strong north to northeast winds. 

Look at the likely wind field in the mid-Atlantic Wednesday afternoon. 

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This will be a serious storm and, unfortunately, include very strong winds with beach erosion in the shore areas of New Jersey devestated by Sandy.

Here is our latest thinking on how much snow will be on the ground for the morning rush, noon and by the evening rush. 

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The storm won't really wind down until Wednesday night, and here is what to expect to see and shovel by Thursday morning. 

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The greatest threat is this will be a heavy wet snow with high winds, meaning likely power outages and very wet slippery driving. 

Also, take your time shoveling.  Wet snow will be very heavy and slow shoveling is more healthy than trying to do everything at once. Schools will likely be closed. Travel disruptions will definitely occur. We will keep you posted.

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Believe it or not: DC has its fairshare of some harsh snowstorms in March

March 5, 2013 - 01:34 PM
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Snow storms in March (although may seem like a rarity based on recent memory of Winter's in the Washington D.C. region) do happen. I remember being out of school for at least 2 weeks in Winchester, VA with the Blizzard of 1993 that happened on March 13th. DC only received 6.6" of snow with storm coined "The Superstorm." Locations west of DC, (Dulles saw 14.0" of snow, while a foot to a foot and a half of snow was measured along the foothills to the Blue Ridge).

 

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There was also a more recent March, 9th 1999 that snow event that dropped 8.4" on the DC area.


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However, since 1999 we have only had 8.7" of snow (most of that number is attributed to 5.5" DC saw on March 1st and 2nd of 2009).
With that being said, DC has had their share of snowstorms in March. Here are the major ones:

 

3/27/1891 - 12.0"

3/28/1942 - 11.5" (Palm Sunday Snowstorm)
3/7/1941 - 10.7"
3/15/1900 - 10.0"
3/3/1909 - 9.8"
3/9/1999 - 8.4"
3/14/1937 - 8.0"
3/2/1960 - 7.9"
3/7/1911 - 7.4"
3/13/1993 - 6.6"

 

Looks like there is a chance to to add to this list by the time we get into early Thursday morning:

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Wednesday Snow Storm: Rain before snow

March 5, 2013 - 12:13 AM
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12:30AM Tuesday update:  The late trends are still all for a major Wednesday storm.  But there is some hint that the secondary storm may form a bit more to the north than it looked earlier Monday.  If this trend continues, this would mean more rain for D.C. before any change to snow and the change would be later in the day Wednesday.  A late ensemble for the storm and precipitation around it Wednesday morning.

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With the current trend, I think by Tuesday most forecasts will be more about rain Wednesday ending as snow in D.C. with the lower 3" amount more likely (60% chance) but still a major snow storm for the Blue Ridge and Shenandoah where 6-12" is still likely

 

 

It's been more than two years since D.C. has even had 1" of snow and almost 15  years since a "big" March snowstorm.  The storm coming our way is still on track to be a big winter storm here, but the impacts are now likely to begin by Tuesday evening.  Here is the late satellite image showing the clouds and general weak storm in the middle part of the country.  

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 All the simulations of what will happen continue to converge that the primary storm to our west will reform near the Virginia Capes Tuesday night and then "wrap around" moisture will pull warm Atlantic air over cold air at the surface and produce very big (12" or more) snow in the Blue Ridge and Shenandoah area west of the D.C. area.  Here is the latest  ensemble showing the storm and precipitation track from Tuesday at 10PM (upper left) thru Wednesday afternoon (lower right) from data from the great PSU weather wall.  

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 The dashed orange line is roughly were the rain snow line will be.  It now is likely (70% chance) that the storm will begin as rain for the Tuesday evening rush.  This is a problem for road crews since pretreatments will likely be washed away.  Overnight Tuesday a wet snow continues well west of D.C. and then as the Wednesday morning rush approaches, the rain changes to a wet snow in the metro area.  (lower left image above). Heavy wet snow is likely Wednesday afternoon (70% chance) and Wednesday evening rush is likely to be a slippery, slushy mess.  Here is our latest "odds" outlook for snowfall in the immediate D.C. area. 

 

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Expect more than that far western suburbs and it is likely (60% chance) that the high elevations of northern Montgomery-Frederick County Maryland and south along the Blue Ridge and the Shenandoah Valley will see 8-12"+ of wet snow. Here's our latest storm total map

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 The risk continues to be tree damage from the weight of the snow and power outages. A nice discussion of the analogies of this storm is here with the Capital Weather Gang.   We'll update later this evening and include a detailed timeline.

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Snow Storm Wednesday: Yes, more likely

March 4, 2013 - 03:23 PM
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D.C. Blizzard of 1922.

3:20 p.m. Monday: The latest probability map from the National Weather Service and the Hydrometeorological Prediction Center shows areas west of D.C., especially the Blue Ridge - Shenandoah Valley region, in the bullseye for 8 inches of snow or more. 

The orange color means an 80 percent chance of 8 inches or more. New complete blog coming soon.

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A Winter Storm Watch will take effect in many areas of the D.C. region starting Tuesday evening.

The Winter Storm Watch encompasses the District of Columbia and every county/city in the Maryland/Virginia suburbs.

Everything I see leaves us still on track for a "big" storm Wednesday.  But the other big risk/threat from this storm is again coastal flooding in New Jersey. 

Everything continues to indicate a "significant," if not major, coastal storm. It will move from the Virginia/North Carolina coast northeast out to sea but winds along the Mid-Atlantic coast could reach 30-50 mph Wednesday afternoon. The dark red areas on the map indicate possible winds of 40-50 mph.

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This past weekend, I said a "big" snow in March in Washington is rare.  The Wednesday storm is now looking more and more likely (70 percent chance, I believe, for the area, especially west and north of D.C.) to be one of those rarities. 

The last time we had 6 inches of snow or more in March was 14 years ago.  So, why am I more confident than yesterday that the Washington area will see a winter storm Wednesday? Continuity, convergence and the cast.

Here's the simulation of the winds and the big wave at the jet stream Saturday for Wednesday:

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and Sunday:

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They're pretty close. You know I don't really fully trust any one model or mathematical/physical simulation of the future weather; I prefer ensembles.

Here is a look at the latest from the U.S. ensemble system showing a storm Wednesday just off the Virginia coast:

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and the European ensemble:

ZZZZZAgain, the models are pretty close, although the dark colors near us also indicate fairly high uncertainty.  Here is a look at the local mid-Atlantic ensembles for the storm track early Wednesday through Wednesday evening from the great weather site at PSU
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What does it show? The cast of characters. Everything has to be perfect staging in the atmosphere if you will for any big snow (or for snow lovers, the "big show") in the Washington area. 

Wednesday will feature cold air for sure, so whatever falls will snow.  But strong winds from the south, southeast and east need to bring in moisture to feed the storm.

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But, as shown in this simulation above of the storm center just southeast of D.C. and air temperature at about 1 mile up, the storm track has to be enough to the south to not allow the mild moist air to win over the cold air. The staging has to be perfect, and remember, the show is still a few days away. Here are my odds for Wednesday's storm

Major snow storm with more than 6 inches in the metro area 70 percent
Morning rain changes to afternoon wet snow in the metro area 60 percent
Heavy wet snow (6-12 inches) north and west of D.C. 70 percent
Rain south and east, ending as 2-4 inches of wet snow 60 percent
A complete miss ~0 perecent

That should bring more excitement for snow lovers, and right now it does look like it will be a wet snow with possible tree damage, power outages and very slippery going for the Wednesday afternoon commute.

Finally, here is the snow probability map from the National Weather Service for snow greater than 8 inches Wednesday.

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This storm will be not only a challenge for us forecasters (here's another great discussion from my friend Wes Junker and the Capital Weather Gang) and you, but a challenge for highway crews also this time because pre-salting won't help. The storm is likely to be a rain-snow event so salt will wash away before the wet snow comes. 

More updates to come but it is still  days now away.  Stay tuned and for more great historic Washington snow storm pictures look at the gallery Steve Rudin put together here.

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Snow Storm Wednesday: The Latest

March 2, 2013 - 03:48 PM
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Big snow storms in March in Washington are rare.  As we know, any snowstorm in Washington in the last two winters is rare. . .meaning none.  But, there is more and more evidence that a storm will form in the Midwest and move to the East Coast by Wednesday but the forecast of what impact that storm MAY have on Washington is a challenge and still very uncertain.  Here's why.  Here is where the "storm" is now. 

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Can you see it? It's just entering the Pacific Northwest and  I've circled the wave in the atmosphere as seen in observations of water vapor from the NOAA GOES satellite. 

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Predicting storms and weather is really predicting the movement, and changes of waves in the atmosphere.  Look at the wave with this storm at the level of the jet stream about 5 miles up in the air. 

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Here is a simulation/projection of where that wave will be Wednesday morning.  Very high confidence that this general pattern will happen, a storm at the surface associated with this wave will be in the Southeast. 

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But what will the storm track be and how close to Washington and what does it mean for snow?  One of the best ways to try and figure this out is to look at a number of simulations of the future, not just one.  An "ensemble" and here is one solution from the U.S. computers

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And one from the european solutions. 

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Similar, but I've also circled the colored areas that show the areas of highest variability or uncertainty. 

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Everything has to be "just right" for a big March snow in Washington.  Right now with the trends of the simulations and the "storm" just coming into area where more accurate measurements are made, (not many weather stations in the North Pacific) any risk/chance of a "big" snow Wednesday for Washington I think is low.  Right now less than 20%.  The chance of light-moderate snow (1-4" range) or rain-snow mix I think is moderate (50% chance) and the chance of nothing at all is also low (30% chance).  Yes it adds up to 100%. Here is the latest surface map forecast from the National Weather Service.

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As the storm develops, moves into the Rockies and Midwest Sunday into Monday and more observations get taken and a better "trend" develops, we can give more confidence to the Wednesday forecast.  For now don't get hopes up snow lovers, and snow haters . . . don't worry too much either.  More to come.

 

the last 2 winters

 

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Snow storm for the D.C. area next week? Not so fast...

March 1, 2013 - 12:19 PM
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You may have heard, "A winter storm will bear down on the East Coast 5 days from now, bringing heavy, wet snow and gusty winds with up to 6 to 12 inches possible by the time it ends Thursday."

This same statement could have been said numerous times this winter, as plenty of opportunities graced the region this far out, but you can tell by the snow we've received so far how many of these scenarios panned out. The past two winters resulted in a whopping 3.5 inches of snow, from the potential of well over 100 inches in the 5 day or more forecast period.

(I wish I had actual facts to back this up, just an observation)

GFS forecast for Saturday afternoon with the energy for this storm still over the Pacific

The energy we are talking about that will eventually have the chance to create this storm is still located over the Pacific. It will cross the Rockies by Monday and get to the Mississippi River by Tuesday. The question remains whether or not the trough will amplify over the East Coast, helping steer this system and its energy back over the D.C. area.

Over the past few days, a few models didn't show this and the storm tracked south of D.C. This is just the normal variability you would see in forecasts this far out in time.

Above is a look at the GFS spaghetti plot model consensus forecast, showing where the models think the 1004mb low would be on Friday. There's not much of a consensus just yet, with the low existing anywhere from off the Carolina coastline, to the Atlantic, to right over D.C.

This is something we showed on our Facebook page earlier today, and it got a few good responses.

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Meteorological Winter Ends. Hello Meteorological Spring!

March 1, 2013 - 05:00 AM
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I can't believe how fast time flies!  It's already the first of March, which also marks the start of meteorological spring!  You may be asking what the difference is between meteorological spring and astronomical spring (the one that always starts around the 20th or 21st of March). 

Meteorological spring is how climate data is measured.  It's easier for meteorologists to group the seasons into months.  It's broken down like this: meteorological spring includes March, April, and May; meteorological summer: June, July, August; meteorological fall: September, October, November; and meteorological winter: December, January, February, and March. 

Astronomical seasons begin when the spring and fall equinox occur and at the summer and winter solstice.  These times are determined based on the sun's tilt and alignment over the equator

Since yesterday was the last day of meteorological winter, I thought it would be interesting to look back at December, January, and February to see what stood out.  Both December and January ended above average.  December averaged 5.6° higher than average and January was 4.3° milder than average.  February; however, was 0.7° below average.  This makes February only the 3rd month, in the past 23 months, below average. 

On to the snow.  Sorry snow-lovers.  It was a very uneventful snow season in Washington.  The average snowfall for meteorological winter in D.C. is 13.6".  Between December, January, and February, D.C. got a whopping 1.5" (yes, a bit of sarcasm there).  This total actually ties for the 6th lowest meteorological winter snowfall. The lowest snowfall in a December, January, February period was back in the winter of 1972-1973 with 0.1".  So I guess it could be worse, snow-lovers.

This doesn't mean since we're switching the calendar to march and meteorological season to spring that we can't get any snow.  Remember the blizzard of '93?  Colleague Alex Liggitt wrote up a great blog on all the March averages and extremes from precipitation, to temperatures, and even severe weather.  Check it out!

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