U.S. Severe Weather Forecast (Przegląd konwekcyjny)

Day Three

acus01 kwns 271247 
Storm Prediction Center ac 271245 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0745 am CDT Mon Mar 27 2017 

Valid 271300z - 281200z 

..there is an enhanced risk of severe thunderstorms middle-south to 
central Kentucky/middle Tennessee... 

..there is a slight risk of severe thunderstorms lower Ohio Valley to 
central MS/al... 

..there is a marginal risk of severe thunderstorms middle Ohio Valley 
to lower MS valley... 

Scattered to numerous severe thunderstorms are expected across the 
lower Mississippi and Ohio valleys into the Tennessee Valley this 
afternoon and evening. Very large hail, damaging winds, and a couple 
tornadoes will be possible. 

A shortwave trough along the Kansas/MO border will move east to the 
Cumberland Plateau by early Tuesday. Attendant surface cyclone will 
track from the Ozark Plateau into the middle Ohio Valley, weakening 
late in the period. A cold front will shift east across the 
mid-south this afternoon with trailing portion stalling tonight over 
the lower MS valley. 

..lower MS/Ohio and Tennessee valleys... 
Two storm clusters are ongoing across southern Illinois/western Kentucky and 
separately over northwest Arkansas. The 27/00z WRF-NSSL and hrw-arw appear 
to have the best reflection of these clusters compared to other 
cams. The eastern cluster should slow destabilization north of the 
Ohio River today where surface dew points are predominately in the 40s 
as of 12z. Meanwhile, low-level moisture will continue to advect 
northeast ahead of the northwest Arkansas cluster into the mid-south 
within a broad 30-40 kt low level jet. This should result in a plume of lower 
60s surface dew points nosing towards the MS/Ohio River confluence, 
with middle 60s maintained across the lower MS valley. The 
increasing moisture coupled with diurnal destabilization will likely 
result in MLCAPE of 1000-2000 j/kg developing by mid afternoon. 
Low-level warm air advection ahead of the Arkansas cluster in conjunction with 
convergence along the impinging cold front should serve as a focus 
for increasing afternoon storm development. 

With effective shear magnitudes of 35-45 kt, several supercells are 
anticipated, especially with southern extent in the open warm 
sector. Large hail, a couple tornadoes, and isolated damaging winds 
are most probable with this activity centered on the mid-south. Some 
of the hail may be significantly severe owing to steep mid-level 
lapse rates sampled by 12z Jackson, Shreveport, and Little Rock 
raobs. A few of these supercells will likely organize into one or 
more east-moving line segments axis, with damaging winds becoming 
the predominant hazard towards middle Tennessee/central Kentucky/northwest Alabama. 

Farther south into central portions of MS/al, weak 500-mb height 
falls during the day coupled with heating and weakening convective 
inhibition should result in at least isolated storms developing 
within confluence bands in the absence of any well-defined boundary. 
A risk for hail and wind damage should accompany the stronger 

.Grams/Gleason.. 03/27/2017 


Mesoscale Discussion

acus11 kwns 270544 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 270544 

Mesoscale discussion 0341 
National Weather Service Storm Prediction Center Norman OK 
1244 am CDT Mon Mar 27 2017 

Areas affected...parts of northeast Texas...far southeastern OK...and 
southwestern Arkansas 

Concerning...Severe Thunderstorm Watch 88... 

Valid 270544z - 270645z 

The severe weather threat for Severe Thunderstorm Watch 88 

Summary...an isolated damaging wind and large hail threat continues 
across northern portions of Severe Thunderstorm Watch 88. A brief 
tornado also remains possible. An eastward extension in area of the 
watch may be needed based on current radar trends. 

Discussion...several clusters of thunderstorms with occasional 
bowing characteristics are moving northeastward around 40 kt across 
far southeastern OK/northeast Texas into southwestern Arkansas as of 0540z. 
While the airmass downstream is not overly unstable (mlcape up to 
500 j/kg), continued strong low-level warm air advection associated 
with a 40-50 kt low-level jet and effective bulk shear around 45-50 
kt will probably be sufficient to support continued maintenance of 
these clusters for the next few hours. Isolated damaging winds 
should be the main threat given the storm Mode and recent radar 
trends, although some large hail and perhaps a brief tornado cannot 
be ruled out. Given the current track on ongoing strong/severe 
convection, an extension in area of Severe Thunderstorm Watch 88 
into more of southwestern Arkansas may be warranted soon. 

.Gleason.. 03/27/2017 

..please see www.Spc.NOAA.Gov for graphic product... 


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