U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 201235 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0735 am CDT Fri Oct 20 2017 

Valid 201300z - 211200z 

..no severe thunderstorm areas forecast... 

scattered thunderstorms are possible during the day today over 
eastern Texas, with more isolated activity overnight into parts of 
the Central Plains and Midwest. A few strong storms are possible, 
but the severe thunderstorm risk is expected to be low. 

A deep large-scale upper trough will shift slowly eastward across 
central and western Continental U.S. Today, while an upper ridge will remain in 
place over the southeast. Within the large-scale trough, a strong 
embedded shortwave is expected to move from the Pacific northwest 
into the northern plains by Saturday morning, while multiple 
smaller-scale vorticity maxima over New Mexico and Texas this 
morning will move quickly northeastward into the plains and Midwest 
by tonight. At the surface, a deepening cyclone is expected to move 
eastward across the southern Canadian prairie provinces, as an 
attendant cold front moves into the central and northern plains by 
the end of the period. Ahead of the front, moisture return will 
continue, with 60f dewpoints advancing northward into the Central 
Plains as the low-level jet increases through the period. 

..East Texas... 
Ongoing deep convection near the Upper Texas coast will likely 
persist into at least the early afternoon, supported by a 
low-amplitude midlevel trough and rich low-level moisture. Some 
enhancement to low-level hodographs within the broad warm advection 
regime may support brief organization with the strongest cells, but 
generally modest instability and deep-layer shear should tend to 
limit the severe thunderstorm risk. 

..eastern Nebraska...Western/central Iowa... 
as low-level moisture continues to increase beneath a plume of 
steepening midlevel lapse rates, elevated thunderstorm development 
is possible late tonight across portions of the central/northern 
plains into the Midwest. Some hail potential will exist with the 
strongest cells across Iowa and eastern NE, given forecast MUCAPE of 
750-1500 j/kg. However, with effective shear expected to remain 
marginal for elevated parcels and considerable uncertainty regarding 
convective Mode and coverage, no severe hail probabilities are 
warranted at this time. 

.Dean/Edwards.. 10/20/2017 


Mesoscale Discussion

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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