From the ABC 7 Weather team

Severe Storms Possible Sunday and Monday

July 25, 2014 - 03:07 PM
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There is a good chance of severe weather to end the weekend and to start the next work week!

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.

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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.

 

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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:

 

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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.

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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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