U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 120539 
Storm Prediction Center ac 120537 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1137 PM CST Tue Dec 11 2018 

Valid 121200z - 131200z 

..no severe thunderstorm areas forecast... 

thunderstorms are expected to develop across portions of southwest 
Texas today and portions of southeast and East Texas into the lower 
Mississippi Valley Wednesday night. 

A positive-tilt shortwave trough will migrate eastward from Baja 
California, reaching south Texas by 10z Thursday while taking on 
negative tilt. Meanwhile, a more powerful shortwave initially over 
Idaho will amplify dramatically while migrating southeastward toward 
the Texas South Plains, with impressive 200+ dm 500 hpa height falls 
across that region during the forecast period. At the surface, a 
low will organize across southeastern Colorado and migrate 
southeastward toward western North Texas overnight. Low-level warm 
advection ahead of the low will result in 50s f dewpoints reaching 
the Red River in Texas and low-60s f dewpoints across southeast 
Texas. Areas of thunderstorms are expected to develop across West 
Texas today and eastward into portions of Arkansas and Louisiana 

..southeast Texas... 
Models suggest that thunderstorms should increase overnight in 
response to moistening low levels and lift associated with the 
advancing southern-stream mid-level trough. Strengthening wind 
profiles should support updraft rotation with any 
persistent/organized cellular convection, although weak instability 
(250-600 j/kg mucape) rooted just above the boundary layer within 
the pre-convective environment suggest that convection will likely 
remain slightly elevated. At this time, the severe threat appears 
to be too low for even 5%/marginal probabilities, but will increase 
if higher dewpoints can reach the Texas coast - most likely after 
the end of the forecast period. 

.Cook/Peters.. 12/12/2018 


Mesoscale Discussion

acus11 kwns 091734 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 091734 

Mesoscale discussion 1705 
National Weather Service Storm Prediction Center Norman OK 
1134 am CST sun Dec 09 2018 

Areas affected...portions of northern NC into southern WV and 
central/southern Virginia 

Concerning...heavy snow 

Valid 091734z - 092230z 

Summary...heavy snow will continue for a few more hours across parts 
of northwest NC and the higher terrain of southern WV and and 
western Virginia. Heavier snowfall also will continue to spread northeast 
into parts of central Virginia into early evening. A mix of snow and 
freezing rain and/or sleet also is possible across north-central NC 
into south-central Virginia the next few hours. 

Discussion...expansive area of moderate to heavy snowfall continues 
across parts of NC, WV and Virginia early this afternoon. The surface low 
is currently located just offshore the SC coast, and will continue 
to shift northeast near the NC coast through this evening. Midlevel 
moisture wrapping around the low level cyclone and forcing for 
ascent ahead of the approaching shortwave trough (currently over the 
Tennessee valley) will maintain wintry precip into the afternoon. A dry 
slot noted in WV imagery will continue to stream across NC and into 
eastern Virginia and some warming will occur over this area. As a result, 
snow may mix with freezing rain and/or sleet at times across 
north-central NC into south-central Virginia. 

Otherwise, cold air damming with a well-established cold conveyor is 
evident in observations across the Piedmont. Moderate to heavy snow 
will persist in this regime across the higher terrain and spread 
northeast into parts of central Virginia through the afternoon. Snowfall 
rates will generally be around 1 inch per hour, though heavier 
bursts approaching 2 inches per hour are possible. Precipitation 
will gradually wane from southwest (across nc) to northeast (wv and 
parts of va) late this afternoon into this evening. 

.Leitman.. 12/09/2018 

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


Latitude...Lon 35917922 35728036 35938125 36128151 36458188 36858190 
37438177 37808142 38068060 38447893 38507830 38447756 
38297706 38097673 37747670 37307681 37017694 36487754