Monday, May 2, 2016

Monday May 2, 2016 Weather Briefing

When we last talked on Friday there was a severe weather outbreak underway in the Southern Plains.  The SPC did a nice job with its forecast although they could should  have extended the slight chance all the way into Alabama.
SPC Day 1 2 AM outlook with actual reports for Friday 4/29/16
The big story over the weekend and into today is heavy rainfall in Texas and Louisiana that has led to flash flooding.  As much as 5-10" of rain has already fallen according to radar estimates out of Lake Charles, LA
Estimated precip 920 PM Wednesday to now (image NOAA/NWS Lake Charles radar)
Currently there are some nasty thunderstorms just offshore.  If these were onshore than build an ark.  Still there is a threat for increasing showers and thunderstorms as the day goes on.
Lake Charles Loop 
This line of showers and storms will push towards New Orleans which is under a flash flood watch themselves.   We know the water trouble in New Orleans.  Even a heavy rain shower or thunderstorm that overstays it welcome in the Crescent City causes flooding problems.  So what is causing these slow moving thunderstorms?  First let's take a look at the surface chart.
WPC surface analysis 8 am 
We see the cold front which is responsible for the precipitation in Louisiana etends into the Ohio Valley where it is a messy stationary warm front with waves of low pressure on it.  The warm front will try to lift into New England but it will get caught up near the South Coast.  A wave of low pressure will move along the front bring a good soaking rain late this morning/early afternoon.  The rain clears later this afternoon but a rather miserable early evening results with drizzle and cool temperatures.  Baseball, softball and lacrosse practice will have a bite if the fields are puddle free.
16z HRRR 12 PM simulated radar (image Weatherbell)
Temperatures end up around 50 (give a few degrees south of Pike, take a few north of Pike).  This pattern will continue for the next several days.  The reason is a developing Omega block pattern over the US.  Right now there is a low pressure trough off the west coast, a low pressure trough in the northeast and a ridge of high pressure in the Rockies.  This has created congestion in the eastern half of the country as cold fronts are slow to exit.  As a result of this the severe threat today lines up well with the surface cold front.
SPC Day 1 Severe Thunderstorm Outlook 
The flash flooding risk also lines up well with this.
WPC excessive rainfall outlook 5/2/2016
Some high resolution guidance suggests some of the heavier rains are back towards Nashville and Western KY/TN so that is also something to keep an eye on.  In general a good 2-4" with locally higher amounts will fall.  In New England we are looking at up to 0.5" but generally around 0.25".

In terms of temperatures I've tried to avoid turning on my heat but it is raw outside.  Despite the rain in parts of the south temperatures still climb into the upper 60s low 70s.  If you want warmth Florida or the deserts of Arizona/California are the place to go.  In the Midwest/Plains it is seasonable if not slightly below average.
NWS NDFD national high temperature forecast Monday May 2 (image Weatherbell)
This Day in Weather History
The latest freeze on record occurred in parts of North Carolina damaging crops. Temperatures dropped to 29 in Raleigh and 32 in Greensboro on this day in 1963.  Source NWS Raleigh climate records page.

-Zack Green

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