Sunday, April 27, 2014

Rainy Week Shaping Up; Some Flooding Likely

Sunday (4/27) 4:30 pm
An interesting weather pattern is setting up to bring lots of rainfall to our area next week.  A surface low currently out across the central plains is slowly drifting northeast.  It's trailing cold front is bringing lots of severe weather issues over the southern plains the next few days.
Current Surface Map (2pm Sunday) via Intellicat
By Monday night, this low will be across the upper Missouri Valley.  The combination of counter-clockwise flow around this system and clockwise flow around a ridge out in the Atlantic will help draw in lots of both Gulf and Atlantic moisture up and down the eastern seaboard.  Waves of showers and thunderstorms will roll through the area Monday night through Thursday as this system continues to slowly drift northeast.

Surface Forecast Map 8am Tuesday via the WPC

The reason for the slow movement can be found looking at the 500 millibar map.  The low gets trapped under higher heights that cut it off from the best upper level flow (known as a Rex Block).
GFS 500 mb height anomaly for Tuesday 2pm via AccuWeather Pro

 It won't be until this blocking breaks down towards late week that this system will loosen it's grip on the eastern half of the country.  The trailing cold front will push through on Thursday as this system is finally allowed to exit northeast into Canada.  This will bring dry, cool conditions for the end of next week into the weekend.

Surface Forecast Map for Thursday 7am via the WPC
Between now and then, expect lots of very heavy rainfall.  Models are in good agreement that 1-3" will be likely across much of the area with some isolated amounts as high as 4-5". This will be more than enough to cause some flooding issues.  If you live in flood-prone zones, it'd probably be a smart idea to start taking precautions.  Models seem to like the area right along and east of the Blue Ridge mountains to the coast for heaviest rainfall.  On top of this, Wednesday and Thursday may bring a window for more severe weather across many of the same areas that saw some on Friday.  There's still a bit of uncertainty regarding the amount of instability, but that can be refined over the next couple days.  Just something else to keep an eye on right now.
GFS total rainfall through Thursday 8pm via AccuWeather Pro
Euro total rainfall through Thursday 8pm via AccuWeather Pro

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