U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 201956 
Storm Prediction Center ac 201954 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0254 PM CDT Fri Oct 20 2017 

Valid 202000z - 211200z 

..no severe thunderstorm areas forecast... 

isolated thunderstorms will remain possible over parts of East 
Texas, South Florida, and the Pacific northwest through this 
evening. Isolated/widely scattered storms are expected overnight 
from the Central Plains to Minnesota. 

Only very minor changes have been made to the ongoing general 
thunder areas. While a strong storm or two may develop late tonight 
near the mid Missouri Valley, the severe risk still appears too low 
for the introduction of marginal severe probabilities. 

.Picca.. 10/20/2017 

Previous discussion... /issued 1114 am CDT Fri Oct 20 2017/ 

Downstream from a progressive midlevel trough now moving over the 
Pacific northwest and northern Great Basin, Lee cyclogenesis across 
the northern High Plains will begin to draw low-level moisture 
northward from Texas across the plains. Isolated lightning strikes 
will be possible today from the Pacific northwest into parts of the 
northern rockies with the midlevel thermal trough and associated 
steep lapse rates. Otherwise, a lead shortwave trough over the 
Southern Plains has interacted with the primary moisture return 
corridor/weakening frontal zone across the Upper Texas coast, where 
thunderstorms have persisted through the overnight hours into this 
morning. A minor boost to storm coverage could occur inland with 
the diurnal heating cycle, but overall storm coverage should still 
decrease later this afternoon/evening as the lead shortwave trough 
ejects north-northeastward ahead of the moisture plume. Later 
tonight, some elevated convection will be possible from NE/South Dakota to Minnesota 
within the warm advection regime on the north edge of the returning 


Mesoscale Discussion

acus11 kwns 192021 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 192020 

Mesoscale discussion 1720 
National Weather Service Storm Prediction Center Norman OK 
0320 PM CDT Thu Oct 19 2017 

Areas affected...southwest New Mexico into a portion of far western 

Concerning...severe potential...watch unlikely 

Valid 192020z - 192245z 

Probability of watch issuance...5 percent 

Summary...stronger storms will remain capable of producing a few 
instances of downburst winds and hail through early evening. Overall 
threat is marginal, and coverage of severe events is not expected to 
become sufficient for a ww. 

Discussion...surface temperatures have climbed to near 80f with 
dewpoints in the mid to upper 40s in the presence of boundary-layer 
mixing, boosting MLCAPE to 400-800 j/kg. Storms over southern nm 
have increased in overall intensity during the last hour, and 
further increase in coverage may occur as forcing for ascent 
attendant to a progressive shortwave trough over Arizona spreads into 
western nm. No substantial increase in winds aloft is expected with 
the approach of the impulse, and vertical shear will remain weak and 
supportive of multicells. Nevertheless, the thermodynamic 
environment with steep lapse rates and inverted-v boundary layers 
will continue to promote a risk for a few instances of downburst 
winds and hail through early evening. 

.Dial.. 10/19/2017 

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


Latitude...Lon 31800602 31970707 32370817 33530845 33830682 33460584 
32500539 31800602