U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 130556 
Storm Prediction Center ac 130555 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1155 PM CST Wed Dec 12 2018 

Valid 131200z - 141200z 

..there is a slight risk of severe thunderstorms across portions of 
East Texas... 

Isolated strong to severe thunderstorms may impact parts of The 
Ark-la-tex region into the lower Mississippi Valley and central Gulf 
Coast vicinity today and tonight. Large hail should be the main 
threat in parts of East Texas late this afternoon and evening. 

A lead southern-stream shortwave trough will advance quickly 
eastward over the lower MS valley into the southeast today and 
tonight. Meanwhile, a more amplified upper trough will deepen and 
eventually close off over central Texas this afternoon and evening. A 
surface low will develop slowly eastward across central/East Texas in 
tandem with the upper low, while a weaker secondary low develops 
across the central Gulf Coast tonight into early Friday morning. 

..East Texas into the lower MS valley... 
Scattered thunderstorms will likely be ongoing this morning over 
parts of southeast Texas as continued low-level warm air advection and 
large-scale lift occurs ahead of the previously mentioned 
southern-stream shortwave trough. Although low-level moisture will 
likely remain limited with dewpoints in the upper 50s/lower 60s, 
modest diurnal heating should support weak instability from 
southeast Texas into parts of southern la through this morning. With 
30-40 kt of effective bulk shear forecast to be present over this 
region, isolated strong/gusty downdraft winds could occur. A tornado 
also cannot be ruled out, mainly near the coast where low-level 
moisture will be somewhat greater. 

As the primary upper trough/low moves across the Southern Plains 
this afternoon, a strong mid-level jet of 50-80+ kt will overspread 
much of East Texas. There still remains uncertainty regarding the 
degree of destabilization that will develop across this region in 
the wake of morning convection. Still, there will probably be enough 
of a gap through much of the afternoon to allow for some surface 
heating, and mid-level lapse rates will be steepening ahead of the 
upper low as mid/upper-level temperatures decrease. Forecast 
soundings from the NAM/rap suggest MLCAPE around 1000-1250 j/kg will 
develop in a narrow corridor arcing around the eastern periphery of 
the surface cyclone by 20-21z. The strong forcing associated with 
the mid-level jet and a cold front attendant to the surface low will 
likely initiate isolated to widely scattered convection by late 
afternoon in parts of East Texas. Although not much veering of the 
south-southwesterly winds with height is forecast, they will 
strengthen considerably through the troposphere. Long, nearly 
straight hodographs at mid levels suggest isolated large hail with 
supercells will probably be the main threat, although strong/gusty 
winds could also occur. A tornado or two may also be possible, 
primarily to the northeast of the surface low where low-level winds 
should be locally backed more southeasterly. 

..central Gulf Coast... 
The inland advance of a coastal warm front will likely be tempered 
until late tonight across coastal southeastern la, MS, al, and the 
western Florida Panhandle. Low-level warm/moist air advection will 
gradually increase overnight as the closed upper low over East Texas 
slowly approaches from the west and a secondary surface low forms 
and subsequently develops eastward across this region. With low to 
mid 60s dewpoints forecast to move only slightly inland ahead of the 
surface low, a marginal wind/tornado threat should generally remain 
confined along/near the coast where weak surface-based instability 
and strong low-level shear will be present. 

.Gleason/Cook.. 12/13/2018 


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