The Memorial Day holiday weekend will be a sunny but chilly one in the Washington area but don’t let that fool you. There is a hidden danger to be aware of on sunny, cool summer days.

High pressure will bring plenty of sunshine to the Washington area and points south this extended holiday weekend. Even though temperatures will be well-below average in the 60s and 70s with gusty winds at times through the first half of the weekend, the sun angle is very high this time of the year. As a matter of fact, the weather will be so chilly and brisk across the region, it’ll be very easy to forget packing the sunblock but don’t!

The UV Index is forecast to increase this weekend to 7 to 8 across the Mid-Atlantic and get as high as 9 to 13 across the Southeast.

What do these numbers mean? A UV index from 7 and above means you can burn in 20 minutes or less (especially if you are fair skinned). An SPF sunscreen of 30 is highly recommended. The sun's rays are strongest between 10 am to 4 pm.

The worst combination is a wind burn (because northwest winds will be rather brisk this weekend in the Washington area) and a sunburn, so be careful when outside this holiday weekend!

For more on the consequences of sun exposure, click here. Have a safe and enjoyable weekend!

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After such a memorable hurricane season last year which featured Hurricane Sandy, many of us will be taking note of the National Hurricane Center's Atlantic hurricane season outlook which they issued today. Here is a quick look at the number of named storms, hurricanes and major hurricanes (Category 3 or higher) they expect this season.

NOAA Article Here

From NOAA,

"For the six-month hurricane season, which begins June 1, NOAA's Atlantic Hurricane Season Outlook says there is a 70 percent likelihood of 13 to 20 named storms (winds of 39 mph or higher), of which 7 to 11 could become hurricanes (winds of 74 mph or higher), including 3 to 6 major hurricanes (Category 3, 4 or 5; winds of 111 mph or higher).

These ranges are well above the seasonal average of 12 named storms, 6 hurricanes and 3 major hurricanes."

Reasons for the above-average activity are warmer than average sea-surface temperatures in the tropical Atlantic, near-normal sea surface temperatures in the equatorial Pacific, and the continuation of the overall atmospheric climate pattern responsible for the high activity era since 1995.

How does this compare to last season? Here was the National Hurricane Center's 2012 season recap.

"For the 2012 Atlantic season, 19 named storms formed, of which 10
became hurricanes. One of those hurricanes, Michael, reached major hurricane status. Activity fore 2012 was well above the 30-year (1981-2010) average for named storms and hurricanes, and below average for major hurricanes. The 1981-2010 seasonal averages for the Atlantic Basin are 12 named storms, 6 hurricanes and 3 major hurricanes."

Above is a look at the storm names for the 2013 Atlantic Hurricane Season. You can find the list of storm names for the next few years here.

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With advancements in radar technology, forecasters have a greater ability to analyze storm structures.  Even though there is still much more to be researched and explored, meteorologists can get a good indication of the height, size, and intensity of a particular storm cell, which then leads to better warnings to the public.  The 3D visuals in the video below recap the evolution of the devastating tornado in Moore, OK Monday. 

The Moore, OK tornado, at one point, reached the highest tornado classification, EF5 status.  EF4 and EF5 tornadoes make up only 1% of all the tornadoes in the U.S.

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The August 2011 earthquake in Washington caused significant damage to the Washington Monument and has been closed to the public, as repairs are being done. 

If you've been around town, you've likely seen the scaffolding growing up the side of the monument, as crews work hard to make sure the structual integrity of the monument is up to standard.  This process has been going on since March 2013.  Take a minute to watch this incredible timelapse over the past 54 days of the rising scaffolding and the changing weather over the two month period.  Incredible!

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While the Atlantic Hurricane season is still two weeks away, today marks the beginning of hurricane season in the Eastern Pacific Ocean.  And, already things are starting to develop. 

Investigation 90

 
 The National Hurricane Center has identified a cluster of thunderstorms hundreds of miles south of the Mexican Coast as having the potential of developing into the first named storm of the season.  If so, it would be named Alvin.  Here's a complete list of hurricane names for 2013. (I always like looking to see if my name is on there, it never is!) This chart of forecast models show that if Alvin develops it should stay away from land. 

Computer Model Track

 
The large majority of hurricanes here travel from East to West or Northwest. The Eastern Pacific season on average is busier than the Atlantic season which can impact us here in D.C.  

Average Tropical Cyclones East Pacific

On average there are 15 named storms, 8 of them becoming hurricanes and 4 of those becoming major hurricanes (cat 3 or stronger).  We are expecting it to be a near average to slightly below average Eastern Pacific season in terms of numbers of cyclones.  One of the reasons for this has to do with the temperature of waters in the equatorial pacific. Notice they are slightly below average in blue.

Sea Surface Temperature Anomoly

We look to that El Nino phenomenon for clues.   El Nino Southern Oscillation (ENSO) is the unusual warming of equatorial waters in the Pacific Ocean. When temps are warm and winds are calm, it can make for a busy hurricane season in the Pacific. This year, we are in a "neutral" phase of El Nino and should stay that way through the summer, making for a trickier forecast.  More detailed ENSO info here. So, why should we care about this in D.C? The ocean and atmosphere are a continuum of currents and patterns. And, when it's warm in the Pacific, it is often cool in the Atlantic and vice versa.  With a near normal to below average season in the Pacific, we are seeing parts of the Atlantic warm up, especially off the coast of Africa.

Atlantic Sea Surface Temperatures

 
 Notice the cooler temperatures hugging the East Coast of the U.S. where we have had a cool May.  It's also a bit cool in the northern Gulf of Mexico.  Water temperatures need to be 80 degrees to support the "fuel" needed for a hurricane. The Atlantic Season may very well end up a busy one as many hurricane experts are predicting. We are coming off three consecutive "busy" seasons with 19 named storms each of those years.  We'll talk and blog more about the Atlantic Season in the next few weeks.

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An unseasonably cool airmass will creep into the region Monday morning and hang around through Tuesday behind this weekend's cold front. Here is a reason why you should wait until mid-May to plant many of your flower beds or your garden: Areas of frost and potentially sub-freezing temperatures will be possible in parts of the area.

Forecast Surface Map Tuesday Morning (COD Models)

Here's the set up. High pressure will enter the region Monday and Tuesday making for clear skies and light winds. Temperatures aloft and humidity levels at the surface will also be quite low, allowing for the maximum potential for radiational cooling. At this point in time, the potential exists for portions of our area to see morning low temperatures Monday night into Tuesday morning in the 30's and possibly even 20's in the mountains.

Forecast lows Tuesday morning (WeatherBell Models)

This will allow for some areas to develop frost around the D.C. Metro and potentially freezing conditions along and west of the Blue Ridge through the Shenandoah Valley. I have introduced that beautifully hand-drawn blue line to denote the freezing line, with temperatures forecast to be at or below freezing along and west of the line. This model does show, however, temperatures in the mid 30's closer to D.C. and upper 30's closer to the Chesapeake Bay. D.C. itself may see lows closer to the 40 degree mark.

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The weather pattern across the D.C. area, and much of the East Coast, has been plagued by this pesky upper level low the couple of days.  Clouds, showers, and muggy conditions.  Today the metro region finally broke out into some sunshine, but with unstable conditions, heavy showers and thunderstorms developed.  Even though there was some very heavy rain and even reports of small hail, these storms did give way to some neat looking skies.  Check out this timelapse from the WeatherBug camera on top of our ABC7 studios in Arlington.

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After an absolutely gorgeous first weekend of May, the start of the work week weather took a turn in the opposite direction.  Unfortunately, for those of you not a fan of the grey skies and showers, this weather pattern is here to stay... at least for a good chunk of the work week.  So why the unsettled weather?  Let's explore.

Check out yesterday's satellite image.  Notice the big "swirl" from space.

GOES

I went ahead and drew the features that are present from this system.  The 'L' represents the area of low pressure that is spinning, counterclockwise, over the southeast US.  The blue arrows indicate the onshore, or easterly, flow bringing in Atlantic moisture to the mid-Atlantic.  Air circulates around the low in this counterclockwise fashion.

The low will track northeast over the coming days, but will be slow to do so.  Take a look at the upper level low from about 18,000 ft (500mb).  This is a simulation of where the low will be later this afternoon. 

NCEP

As the low tracks northeast, cloudy and damp weather will persist across the region.  It won't be a complete washout each day this week, but scattered showers will be possible through at least Thursday.  Check out the Weather Prediction Center's quantitative precipitation forecast through Thursday evening.  This forecast shows between 1 and 2 inches of rain over our region, with locally higher amounts over southwestern VA.

WPC

With moderate rain possible over an extended period of time, the National Weather Service has issued a flood watch for parts of the Shenandoah valley through late tonight.  Remember, if you encounter standing water, never drive through it. The latest Flood Watch was extended north into Clarke, Frederick (VA), Hampshire and Mineral Counties as well.

By late Thursday, the low weakens its grip and gets caught back in the overall pattern.  Compare the 500mb heights in this forecast (below) for Thursday night to the same map shown above.  Notice there is a slight dip in the wave pattern, but nothing cut-off (like in the similar image a few graphics up). 

NCEP

For us, this means a less unsettled weather pattern.... sort of, for Friday at least. High temperatures will climb to near 80 degrees by the end of the week, which could initiate a few airmass thunderstorms to develop, but nothing widespread.  A cold front will then slide through this weekend bringing continued chances for showers but drier and slightly cooler air can be expected for early next week. 

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Spring is here and that means many of us are spending a lot more time outdoors.  We may have gotten out of the habit of applying sunscreen over the winter.  Here's a common conversation at my house:  "But Mom... it's not even sunny out. Why do I have to wear sunscreen?"  I admit it. My kids absolutely hate slathering on the thick white lotion that protects them from harmful ultra violet rays.  It's even a battle some days. But, I make them do it anyway, and we wear it year round.  Today is Melanoma Monday, as declared by the American Academy of Dermatology. They would like you to "Spot the Orange" and wear that color today to remind others to protect themselves. Did you know that skin cancer is the most common form of cancer?  And, it's highly preventable. Here's is today's forecast Ultra Violet Index. 

UV Forecast May 6th

 
 Wear sunscreen with UVA and UVB proction with an SPF of 30 or greater and apply it every few hours.  If at the beach, make sure it is waterproof.  On a day when the UV Index is "Extreme" it takes less than 15 minutes to get burned. Here is a chart to calculate sun exposure/burn times.  

Sun Exposure/Burn Times Chart

 
You can get your own personalized UV forecast by entering your zip code here.  The sun's rays are strongest from 10a until 2p.  Avoid prolonged exposure during this time.  Staying in the shade or taking shade "breaks" is recommended, so is wearing light weight long sleeves and pants if you're going to be in direct sun at length.  A hat can cover and protect your head and face. And sunglasses with UV protection are a must.  Remember white sandy beaches and water reflect the rays and can double your exposure.  Memorial Day weekend is just a few weeks away. Check out the average UV Index for May.

Average May Ultra Violet Index

 
  Did I mention that sun damage makes you look OLD?  Ever heard of sun spots? Sun damage in your younger years can translate to darker discoloration of your skin. Check out this image from the Mayo Clinic. 

Photo of Sun Damage from The Mayo Clinic

 
 Not a lot of sun expected until Friday in the D.C. area.  Make sure you pull out the sunscreen now, and check if its expired.  If so, time to freshen up and stay sun safe.

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Happy May Day everyone.  The month known for blooming flowers after April showers is upon us.  When I think about the month of April, my mind was thinking "cool" just like March.  But, when I took a look at climate records, we were actually a bit on the plus side. The month ended up 2 degrees above average.  The 91 degree day on April 10th helped to skew us on the plus side.  15 days in April were above average and 14 days were below.  As we turn the calendar to the month of May, we are right on track.  

May Averages

The average high for May first is 71 degrees and we will be near that all week.  By the end of the month, we warm up with an average high of 80.  Longer days help bump up the temps this month. Here's a look at the sun on the horizon around 5:30 this morning.

WJLA Rooftop View at 5:30 a.m.

 Sunrise was officially at 6:10a.m. Today, we will get 13 hours and 51 minutes of sunshine with sunset after 8:00 P.M.  While April is known for it's showers, May actually gets more rain on average around 4" for the month.  In addition, it's time to start thinking about severe weather safety plans and rules.  May, June and July are the peak severe weather months in the Mid-Atlantic. The Stormwatch 7 team of meteorologists will always be here to help keep you safe when dangerous weather approaches.

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