U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 241935 
Storm Prediction Center ac 241933 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0233 PM CDT Mon Sep 24 2018 

Valid 242000z - 251200z 

..there is a marginal risk of severe thunderstorms over a small 
portion of the Central High plains... 

Isolated strong to severe storms remain possible this 
afternoon/evening across a part of the north-Central High plains. 


No changes have been made to the marginal risk area as previous 
forecast remains valid. Deeper forcing for ascent resulting from a 
progressive shortwave trough is spreading eastward through the 
Central High plains coincident with steep lapse rates but with 
limited low-level moisture and instability. A few strong storms with 
a threat for hail and gusty wind are possible within this weakly 
unstable but strongly sheared environment this afternoon, but 
overall threat is expected to remain marginal. 

.Dial.. 09/24/2018 

Previous discussion... /issued 1126 am CDT Mon Sep 24 2018/ 

An initial cold front is moving southeastward from eastern Colorado to 
northwestern Minnesota in association with the passage of a lead shortwave 
trough. An upstream trough over the northern rockies will progress 
eastward toward the northern High Plains tonight, driving a 
re-enforcing cold frontal surge across the Central Plains and upper 
MS valley. For a period this afternoon/evening, low-level upslope 
flow will establish from extreme southeastern Wyoming/northeastern Colorado 
into the western NE Panhandle, where residual low-level moisture and 
cloud breaks will support weak surface-based buoyancy. Given strong 
deep-layer vertical shear and lingering steep midlevel lapse rates, 
a couple of low-end supercells may be capable of producing 
marginally severe hail and/or strong outflow gusts. 

Otherwise, the warm sector will gradually spread northward across 
the Ohio Valley toward mi, downstream from the amplifying mid-upper 
trough over the northern plains. A series of diffuse midlevel 
vorticity maxima will eject northeastward this afternoon across the 
lower Ohio Valley, and will be preceded by modestly enhanced low-level 
flow (30-35 kt from the south-southwest). Midlevel lapse rates are 
poor after many prior days of convection, and clouds will tend to 
slow surface heating across Tennessee/Kentucky where the low-level flow/shear 
will be a little stronger. The overall scenario appears to be quite 
marginal, such that severe wind/tornado probabilities are too low to 
warrant an outlook area. 


Mesoscale Discussion

acus11 kwns 242055 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 242054 

Mesoscale discussion 1496 
National Weather Service Storm Prediction Center Norman OK 
0354 PM CDT Mon Sep 24 2018 

Areas affected...portions of central Tennessee and northern Alabama 

Concerning...severe potential...watch unlikely 

Valid 242054z - 242300z 

Probability of watch issuance...5 percent 

Summary...a few stronger/organized storms could develop over middle 
Tennessee and northern Alabama through this evening. Overall, the 
severe threat will remain isolated if it materializes. 

Discussion...a shortwave trough is moving over the southeast and 
Ohio River valley helping to spread ascent over the region. Within 
the warm sector including across Mississippi, Alabama, and most of 
Tennessee, a moist/unstable airmass is present and supportive of 
developing convection. MLCAPE of 750-1500 j/kg over middle 
Tennessee/northern Alabama with effective srh of 75-150 and bulk 
shear of 25-30 knots per mesoanalysis/rap soundings indicate the 
potential for a few weakly rotating storms. Bna radar has depicted a 
few storms with broad/weak rotation in the last hour across portions 
of middle Tennessee. A few stronger/organized storms are possible, 
but the overall severe threat remains marginal at best, thus a watch 
issuance is not expected. 

.Nauslar/Thompson.. 09/24/2018 

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


Latitude...Lon 35388699 35888682 36298650 36598615 36718558 36688530 
36548514 36288515 35918529 35508544 35128564 34858592 
34658612 34558634 34518659 34558689 34638716 34748719 
35208705 35388699