From the ABC 7 Weather team

Archive for category Severe Weather July 2014

Severe Storms Possible Sunday and Monday

July 25, 2014 - 03:07 PM
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Say goodbye to the beautiful weather of Friday and hello again to summer in Washington, D.C. for the weekend. That means a return of heat and humidity as well as a return of summertime thunderstorms. Saturday will feature very warm temperatures, right around 90 degrees for a daytime high with increasing clouds and increasing humidity late in the day. Another thing that will increase on Saturday will be the chances of showers and thunderstorms. Albeit, it is only a slight chance of showers and thunderstorms through the PM and overnight hours on Saturday, but still a chance.


An upper level piece of energy will approach the region on Saturday night. Mainly our western areas will be the breeding ground for any action, but by Sunday, we all have equal chances to see showers and thunderstorms across the area as that disturbance passes through the D.C. area.

ZZZZZ

 

Also what we are watching after Sunday’s disturbance is a very strong cold front will be dropping out of the upper Midwest and down into the region for Monday. Therefore, we have a chance of showers and thunderstorms Saturday night – Monday, some of which could be strong to severe.
Above graphic, at the top, shows the slight risk area for severe weather Saturday through Monday. The risk moves from the Ohio Valley Saturday to our area on Sunday and Monday. On the bottom of the graphic, the surface features show an area of high pressure overhead bringing us very pleasant on conditions on Friday. Then through 8 p.m. Saturday, the area of high pressure scoots off the coast giving us a southerly flow bringing humid air from the south and transporting it right here into the D.C. area as a warm front approaches the region. By Sunday and Monday morning, the strong cold front is still to the north and west of the area.


So now that we know what is going on, what can we except through the weekend? Well considering that warm front is just to the south on Saturday night, lift from warm advection around the warm front and the piece of energy approaching us from westerly flow aloft will give us that about a 20% chance of storms on Saturday afternoon and evening continuing through the overnight hours. There will be a good chance of severe weather across our area through the day on Sunday as that disturbance moves through the region. One thing that still remains a question is temperatures on Sunday. Right now I have temperatures fairly warm, nearing 90 degrees. But, if we get some thunderstorms in the morning hours, that could down our temperatures for the afternoon and lessen the instability in the atmosphere. Either way, it will still be very muggy outside through the day on Sunday with mainly clouds hanging around. Some of our models do suggest that we get some thunderstorms during the first part of the day on Sunday.

 

ZZZZZ

 

Caption: Showers and thunderstorms around the region weaken slightly as they travel to our area from the north and west. This is around 11a.m. on Sunday.

We do know that any of these storms could produce damaging winds, possible hail and heavy rain. There will certainly be substantial moisture around the region given the nice southerly flow, therefore localized flash flooding is definitely a concern. Take a look at our precipitable water values:

 

ZZZZZ

 

You may have heard this term or “PWATS” quite a bit this summer. Really what preciptable water values are are the amount of water within a vertical column above the surface if it were all precipitated out. These values are over 2.00” in some spots and when we see that, we know there is enough moisture available to create flooding conditions.


By Monday, the chance of showers and storms remains through the day as the cold front finally travels through the region. Again, some of there could be strong to severe but by Tuesday, we are in for another treat.

ZZZZZ

A nice refreshing airmass moves into the region bringing low humidity and refreshing temperatures. Daytime highs on Tuesday are in the upper 70s to lower 80s! We just got to make it through some summertime storms to get the reward by mid-next week!

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Cherrystone tornado rated EF-1

July 25, 2014 - 11:46 AM
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The National Weather Service office in Wakefield, VA surveyed the damage from yesterday morning's storm in Northhampton County in southeastern Virginia and determined the damage was due to a tornado, straight line wind, and a large swath of hail.

Path of the tornado, straight line wind and large hail

Above is a look at the path of the tornado, wind and large hail. The tornado originated in the Chesapeake Bay as the storm rapidly intensified. The EF-1 tornado had estimated maximum wind speeds of 80 to 100 mph and was on the ground for 8 miles over a span of 15 minutes. It's maximum width was 150 yards. The tornado wasn't the only feature that caused damage in this storm.

A downburst resulting in straight line winds was observed in the yellow wind damage swath. Wind speeds were estimated between 65 and 75 mph and downed numerous trees and even contributed to overturning several camping trailers in the Cherrystone Campground.

The hail core fell mainly within the blue lines (first image above) in the size of golfballs to a few reports of baseball size. This caused considerable tree and leaf debris, crop damage and siding damage on homes in the path.

The storm caused 36 injuries and 2 fatalities.

See the rest of the preliminary storm survey here.

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Severe Storms Likely Monday and Tuesday

July 13, 2014 - 06:39 PM
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We've reached the climatological hottest time of the year in D.C. with our average high now 89°.  Some big changes on the horizon, as a strong cold front approaches the area.  This cold front will bring a welcome drop in the heat and humidity by Wednesday, but it will come with the price of severe weather for Monday and Tuesday.

Ahead of the front, our airmass remains very hot and humid.  Forecast high temperatures Monday are in the low to mid 90s.  Factor in the humidity and it will feel closer to the 100 degree mark.

The cold front will slide farther east Monday increasing the atmospheric dynamics for severe weather.  Take a look at the surface features, as of Sunday night.

The viewing area will remain under the very warm and moisture laden air until the cold front passes late Tuesday night.  That will help fuel the fire for the strong and severe storms.  The Storm Prediction Center has the entire vewing area (shaded in yellow in the image below) under a 'Slight' risk for severe storms Monday.   This means damaging winds (60+mph), large hail, and isolated tornadoes will be possible with any storms that develop.

Storm Prediction Center

A big dip in the jet stream will allow temperatures and humidity to drop off significantly by Wednesday and the rest of the week.  The clash of airmasses; however, is what is causing this elevated risk for severe weather.  Check out an upper level map (500mb level) that clearly shows the large trough digging into the area.  The brighter colors indicate higher wind speeds, which leads to increased wind shear.  Wind shear can cause damaging wind gusts and tornadoes.

WeatherBell - European Model 500mb heights and wind speed/direction

As mentioned, behind the front much cooler and drier air.  Take a look at the difference in forecast dewpoint temperatures on Monday and Wednesday.  Dewpoints will go from the mid 70s Monday afternoon to the low 50s Wednesday.  You will certainly feel the difference by midweek.

WeatherBell ECMWF Dewpoint Temperature Monday
WeatherBell ECMWF Dewpoint Temperature Wednesday

Remember to stay updated with the StormWatch7 weather team for the latest weather updates.  We also encourage you to download the free StormWatch7 weather app.  You'll have access to Live Super Doppler within the app, so you can track storms on the go.

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Cooler Air, but Not Cold Air Infiltrating the D.C. Area Next Week

July 12, 2014 - 05:10 PM
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Once we get through the possibility of severe storms on Monday and Tuesday, cooler air will move right into our region for the end of next week.


Classification. Yes, we are a society that likes to name things: Snowmaggedon, Commutergedon, SnowGuinness, etc. Where a squall line is a “derecho” and where a spill of cold air from the north is coined the “polar vortex.” I get it. I really do. Classification of tornadoes or hurricanes is absolutely necessary, however, to call every snowstorm a “blizzard” just makes me shake my head-but then move on with my life.


Before 2012, we had NEVER heard of the term “derecho” and now it seems every storm that comes through during the summer is classified as that. Before last winter, we NEVER EVER heard the term “polar vortex” used before and now, several months later, we gravitate right to it.


It is all in the eye of the beholder and left up to interpretation amongst professionals in the meteorology field. Although I didn’t want to touch this subject with a ten foot pole, I feel that we are forced to say something. The storm on Tuesday night left so many people wondering whether a “derecho” in fact hit the area that we had to reach out to the Storm Prediction Center to include their thoughts. So now onto the “polar vortex” or let’s just say the “unusual pattern setting up for Mid-July.”


All in all, we do know that next week unseasonably cold air will migrate out of the north and into the United States, spreading out into the Mid Atlantic. There is so much misuse of several weather terms throughout the year that I thought we should revisit the term “polar vortex”.


Our friends at the National Weather Service in New York made this graphic after the hysteria in social media yesterday about “the return of the polar vortex.” They reminded everybody on their Facebook page that “the most basic definition for “polar vortex” is that it is a piece of energy that comes from the polar region. It is generated by the large difference in temperature between the tropics and the poles. The temperature gradient is strongest during the winter; therefore it is more likely to affect mid-latitudes (our area) in the winter. However, it can affect us in the summer, but it is not nearly as strong as it is in the winter.”

NWS

There are differing opinions in the meteorology field on whether this is a “true polar vortex’ and that is why you will see so many different articles ALL OVER the internet on whether this is or it is not. This is what the Weather Prediction Center put out yesterday:\


“A DEEP UPPER LOW... NOT THE POLAR VORTEX AS ITS ORIGINS ARE FROM THE NE PACIFIC... WILL SWING THROUGH THE GREAT LAKES EARLY NEXT WEEK WITH AN IMPRESSIVE COLD SHOT OF AIR INTO THE CENTRAL AND THEN SOUTHERN PLAINS AND THE MIDWEST.”


Great. So in the grand scheme of things I ask myself “does it really matter to the general public what we coin this?” The answer I give myself is “no”.
So here is what we know. We have some unseasonably cold air coming down from the north and spilling into the region. The Midwest will get the brunt of the cold weather where temperatures could be as much as 20-25 degrees below normal! That is very impressive for summertime climate. Our normal temperature in the D.C. area for this time of year is a warm 89 degrees. The Climate Prediction Center has given us about a 40%-50 of seeing below normal temperatures next week.

Climate Prediction Center

Now, I got to tell you, if you are expecting temperatures in the 50s/60s then you have to travel to the north and west of here. Temperatures next week (starting Wednesday) are going to fall below normal but we are still talking 70s/80s. Here is a look at our 7-day forecast:

However, before we even get to that cooler air moving in, as you notice on the 7-day we are heating up! Temperatures on Sunday, Monday and Tuesday will have no problem reaching into the 90s. With the added July humidity, we are talking about heat indicies approaching 100 degrees all with the added threat of severe weather each day. The Storm Prediction Center has ALREADY outlined us in an area for a shot at severe weather on Monday into Tuesday:

Storm Prediction Center

So all in all, are we cooling down slightly for the end of next week? Yes. Are we going to have to deal with heat and humidity and severe storms at the beginning of next week? Yes. It is going to be a roller coaster week and we will certainly welcome the cooler air by the end of next week, not matter what we want to call it.

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Flash Flood Watch for the D.C. area until Midnight

July 10, 2014 - 03:48 PM
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DOPPLER RADAR  |  WATCHES/WARNINGS  |  STORMWATCH 7 FACEBOOK

A Flash Flood Watch is in effect through Midnight tonight for the majority of the D.C. area. Showers and storms along a frontal boundary are moving extremely slow, allowing for a prolonged period of heavy rainfall. Baltimore experienced its own storm earlier today which dropped a radar estimated 2.5 inches of rain. Additional storms may do the same for parts of the D.C. area through tonight.

Flash Flood Watch in effect until Midnight

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Storms possible through this evening in the D.C. area

July 9, 2014 - 03:35 PM
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LIVE DOPPLER RADAR  |  HD CAMERAS  |  WATCHES/WARNINGS

A Severe Thunderstorm Watch has been posted for much of the D.C. area until 10pm. This comes out after the Storm Prediction Center stated a watch would be unlikely for the D.C. area about an hour ago. After a few storms exhibited damaging winds, it appears they've changed their minds and decided to post one for the region through this evening and early tonight!

Severe T-Storm Watch until 10pm

Showers and thunderstorms will continue to be possible through the afternoon and evening, so please listen for the latest on where they are located and be sure to check Live Doppler Radar before going outside.

Storms will have the potential for heavy rainfall, frequent lightning and gusty winds. We will cover them live on ABC 7 News at 5pm and 6pm.

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Severe Thunderstorm Watch in the D.C. area Tuesday

July 8, 2014 - 07:06 PM
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As expected, a Severe Thunderstorm Watch has now been expanded to include the entire ABC 7 News viewing area until 11:00 p.m. Storms will likely bring periods of heavy rain, gusty winds and small hail. Wind gusts may exceed 70 miles per hour in some storms.The watch for western Maryland will expire at 8:00 pm. For the counties included, click here. Stay with ABC 7 News for additional update.

LIVE DOPPLER RADAR HERE

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Severe Thunderstorm Watch until 9 p.m. Thursday

July 3, 2014 - 01:24 PM
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LIVE DOPPLER RADAR

A Severe Thunderstorm Watch is in effect for the majority of the D.C. area until 9 p.m. tonight. Storms will continue to develop mainly southwest of D.C. and move into the region closer to the evening rush around 5 p.m. to 6 p.m. Very heavy rainfall will be possible in storms, which is why the National Weather Service also put the entire area under a Flash Flood Watch. Be sure not to cross any flooded roadways.

(Severe Thunderstorm Watch until 9 p.m.)

Storms will linger through late this evening but should diminish overnight. A few showers will be possible through the morning hours as the front continues to move through the region and Hurricane Arthur approaches from the south.

Find the latest on Hurricane Arthur here.

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Hurricane Arthur: First Hurricane of the Atlantic Season

July 3, 2014 - 06:14 AM
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As of the 8am update from the National Hurricane Center,  Arthur is now a Category 1 hurricane with max winds of 80 mph and moving north/northeast at 8 mph.  Check out the storm via satellite and radar.   

NOAA
Intellicast Radar

The storm is currently bringing rain to eastern South Carolina and is expected to pass over eastern NC later tonight.   Mandatory evacuations are already in place for Hatteras Island, NC.   Hurricane warnings are in effect for these areas, as heavy rain, gusty winds, coastal flooding, and dangerous surf are expected. 

NWS Morehead City, NC

Arthur is projected to brush the Carolina coast tonight and be off the mid-Atlantic coast by midday tomorrow.  Check out the latest track map from the National Hurricane Center.

National Hurricane Center.

Our local impact from Arthur will occur today.  As a cold front approaches from the west, and tropical moisture from Arthur feeds into our area, severe storms and flash flooding will be possible this afternoon and evening.  The Storm Prediction Center has our area in an elevated risk for severe storms with damaging winds.  The National Weather Service has also issued a flash flood watch for later today, as well.

Storm Prediction Center
NWS Sterling, VA

The cold front will slide east tomorrow morning and help push Arthur farther out to sea.  Drier air will slide in from west to east through the day tomorrow.  It should be rather delightful for the fireworks displays tomorrow evening with low humidity, comfortable temperatures, and a nice breeze.

The rest of the holiday weekend forecast looks great.   Have fun and be safe!

 

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Severe thunderstorm watch until 8 p.m. Wednesday

July 2, 2014 - 01:11 PM
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High heat and humidity combined with an upper-level disturbance moving through the region will create the possibility for severe weather this afternoon. Strong to severe thunderstorms will be possible with the potential for damaging winds and large hail.

(Severe thunderstorm watch until 8 p.m.)

The watch continues until 8pm this evening. In addition, a Heat Advisory is still in effect for the majority of the D.C. area through 7pm this evening. Heat index values may approach 105°F this afternoon so please try to limit your time outdoors if possible.

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