U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 270100 
Storm Prediction Center ac 270059 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0759 PM CDT Wed Apr 26 2017 

Valid 270100z - 271200z 

..there is a slight risk of severe thunderstorms across portions of 
the lower MS valley and vicinity... 

..there is a slight risk of severe thunderstorms across portions of 
northern in and Northwest Ohio... 

..there is a marginal risk of severe thunderstorms from portions of 
the southern Great Lakes region to the north-central Gulf Coast... 

Severe thunderstorms will remain possible from portions of the 
north-central Gulf Coast region northward to the southern Great 
Lakes region into tonight. Widely scattered damaging wind gusts and 
perhaps a couple of tornadoes may accompany storms moving across 
parts of the lower Mississippi Valley and vicinity into the 
overnight hours, while a cluster of storms moving across portions of 
northern Indiana and Northwest Ohio may produce widely scattered 
damaging winds into the evening hours. 

..portions of the north-central Gulf Coast region northward to the 
southern Great Lakes region... 
a corridor of convective bands extends from the lower Ohio Valley to 
the north-central Gulf Coast vicinity. The northern portion of this 
activity is pinching off the northernmost extent of more appreciable 
moisture return, which 00z observed soundings suggest resides closer 
to the coast. While poleward return of more substantially modified 
maritime air will occur ahead of the convection, the Richer moisture 
and related substantive buoyancy (mlcape around 500-1500 j/kg) 
should remain generally near and south of western/middle Tennessee. This is 
where sufficient deep shear (45-65 kt of effective bulk shear) will 
also exist in favor of continued quasi-linear convective modes 
capable of widely scattered damaging winds. This activity will 
spread into western Alabama through the overnight hours, and sufficient 
low-level shear may exist for occasional line-embedded and 
line-preceding supercell structures to support a couple of 
tornadoes. Some isolated severe risk could extend even farther east 
later in the night. 

Farther north, a sustained cluster of storms continues advancing 
northeastward across northern in, and may eventually affect parts of 
Northwest Ohio before weakening in Southern Lower Michigan this evening. 
Moderately steep midlevel lapse rates around 7.3 c/km, based on the 
Detroit 00z sounding, will support sufficient buoyancy amid modest 
moisture return for some severe risk persisting in the short-term. 

Relatively weaker low-level lapse rates and limited moisture return 
between the slight risk areas suggest that the severe risk should 
remain more isolated across parts of the Lower/Middle Ohio Valley 
region and vicinity. However, locally damaging wind gusts may 
accompany the most pronounced bowing convective line segments. 

.Cohen.. 04/27/2017 


Mesoscale Discussion

acus11 kwns 270036 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 270036 

Mesoscale discussion 0568 
National Weather Service Storm Prediction Center Norman OK 
0736 PM CDT Wed Apr 26 2017 

Areas affected...western Tennessee...northern Mississippi 

Concerning...Severe Thunderstorm Watch 166... 

Valid 270036z - 270200z 

The severe weather threat for Severe Thunderstorm Watch 166 

Summary...a risk for primarily potentially damaging wind gusts 
continues at least another couple of hours with the squall line 
advancing across northern Mississippi and portions of western 
Tennessee. This may include areas in close proximity to, but east 
of watch 166, before activity weakens, but it is not yet certain 
that a new watch will be needed. 

Discussion...as the significant short wave trough approaching the 
lower Mississippi Valley takes on an increasing negative tilt, 
stronger low-level convergence and mid-level forcing for ascent 
likely will become focused across northern Mississippi northward 
into the lower Ohio Valley during the next few hours. This is 
forecast to coincide with further strengthening of southerly 850 mb 
flow to 50+ kt ahead of the ongoing pre-frontal squall line which is 
now advancing east of the Mississippi River. However, the northward 
return of Richer boundary layer moisture is becoming increasingly 
cut-off from this region, and the maintenance of vigorous boundary 
based storm development beyond the next couple of hours is 
increasingly unclear. The segment of the squall line north of 
Greenville MS into the vicinity of the Mississippi/Tennessee state 
border seems to provide the greatest risk for potentially damaging 
wind gusts through the 01-03z time frame, with at least some 
northeastward acceleration possible. 

.Kerr.. 04/27/2017 

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


Latitude...Lon 36158881 36488844 36418745 34788792 33908807 33508891 
33628998 34278996 34808962 36158881