U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 270544 
Storm Prediction Center ac 270542 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1242 am CDT Mon Mar 27 2017 

Valid 271200z - 281200z 

..there is an enhanced risk of severe thunderstorms for parts of 
western Kentucky into western and middle Tennessee and northern 

..there is a slight risk of severe thunderstorms for portions of 
the lower Mississippi Valley into parts of the Tennessee and lower 
Ohio valleys... 

..there is a marginal risk of severe thunderstorms surrounding the 
slight risk... 

Severe thunderstorms will be possible from parts of the lower 
Mississippi and Tennessee valleys northward to the Ohio Valley today 
into this evening. Hail and damaging winds will be the primary 
severe hazards with the stronger storms. 

A vigorous shortwave trough Sunday night on water-vapor imagery over 
the central Great Plains will move eastward into the lower Ohio Valley 
during the period. An associated strong belt of cyclonically curved 
mid-level flow will overspread the lower MS valley into the Tennessee and 
Ohio valleys. In the low levels, a northward advancing warm front 
will move through the Tennessee Valley. A weak surface low will develop 
east-northeast across the MS valley into the Ohio Valley as a cold 
front moves east across parts of the mid south before stalling over 
the lower MS valley. 

..portions of the Ohio-TN-MS valleys... 
Low-level moisture will return north into the mid south and Ohio 
Valley within a warm air advection regime associated with a 35-kt low level jet during the 
morning. Showers and isolated thunderstorms will likely be ongoing 
near the MS river at daybreak and move downstream into Tennessee and the 
lower Ohio Valley. There is some uncertainty regarding the magnitude 
of destabilization farther north near the Ohio River where clouds and 
early-day convection may limit destabilization. Nonetheless, models 
show a plume of upper 50s dewpoints near the Ohio River to the low-mid 
60s in the MS Delta. The increasing moisture coupled with diurnal 
destabilization south and west of early activity will probably 
result in 1000-1500 j/kg MLCAPE developing by mid afternoon with 
weak buoyancy forecast farther north near the Ohio River. Forcing for 
ascent provided by the mid-level wave in conjunction with 
convergence along the surface boundary over eastern Arkansas northward to 
the Ohio-MS river confluence will likely serve as a focus for storm 
development during the afternoon. Deep-layer shear is forecast to 
be strongest from Tennessee southward into northern MS/Alabama with effective 
shear magnitudes 35-50 kt. Cellular clusters of supercells and 
organized multicells are forecast with hail (perhaps very large with 
the most intense storm or two) and damaging winds the main threats. 

Farther southeast in the free warm sector over MS and al, weak 
(30-m) 500-mb height falls during the day coupled with heating and 
weakening convective inhibition may result in storms developing 
within confluence bands in absence of any well-defined boundary. 
Convection-allowing models suggest isolated to widely scattered 
storms and a risk for hail and wind damage will probably accompany 
the stronger storms. This activity over the deep south and Tennessee/Ohio 
valleys will likely weaken during the evening as it moves towards 
the Appalachians owing to the loss of heating and moving east of the 
instability axis. 

.Smith/marsh.. 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... 


Latitude...Lon 33329548 34259473 35279375 35289348 34949314 34239313 
33179342 32979421 33019551 33329548