U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 180557 
Storm Prediction Center ac 180555 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1155 PM CST Thu Jan 17 2019 

Valid 181200z - 191200z 

..there is a marginal risk of severe thunderstorms across parts of 
East Texas/OK into the arklatex and lower MS valley... 

Isolated strong to severe thunderstorms capable of producing mainly 
large hail may occur from parts of East Texas and Oklahoma to the 
arklatex late this afternoon into tonight. Strong to locally 
damaging winds and perhaps a tornado may occur overnight into early 
Saturday morning from East Texas into the lower Mississippi Valley. 

An amplifying upper trough will eject eastward from The Rockies 
across the central and Southern Plains today. A 50-80+ kt mid-level 
southwesterly jet will overspread parts of the Southern Plains to 
the lower MS valley beginning this afternoon and continuing through 
tonight. A surface low initially over the Central High plains is 
forecast to develop southeastward to the OK/Texas border vicinity by 
this evening, and then continue developing eastward across the lower 
MS valley through the remainder of the period. 

..East Texas/arklatex into the lower MS valley... 
Low-level moisture transport will occur ahead of the upper trough 
and surface low through the day across parts of central/East Texas. 
With a prior frontal passage having shunted Richer moisture 
southward over the Gulf of Mexico, recovery of the low-level airmass 
across this region will likely be delayed until at least late this 
afternoon when sufficient low-level moisture can be transported far 
enough northward to support convective initiation. Forecast 
soundings across East Texas and the arklatex region suggest this 
initial activity will likely be slightly elevated, with MUCAPE of 
generally 500-1250 j/kg. Long, straight hodographs, effective bulk 
shear of 40-50 kt supporting mid-level storm rotation, and 
steepening mid-level lapse rates with the approach of the upper 
trough all suggest that isolated large hail should be the primary 
threat with these elevated thunderstorms. The hail threat across 
eastern OK and western/central Arkansas should be constrained by 
decreasing moisture/instability with northward extent, even through 
strong forcing for ascent and cold mid-level temperatures ahead of 
the upper trough will be present. 

Greater thunderstorm coverage should eventually occur from late this 
evening into tonight across East Texas and la along an eastward-moving 
cold front that will extend southward from the surface low. Even 
though surface dewpoints will likely remain in the upper 50s to 
lower 60s, strong low-level warm and moist air advection will occur 
ahead of the front across the lower MS valley overnight owing to a 
40-55 kt southwesterly low-level jet. While low-level lapse rates 
will be weak, forecast soundings from most short-term guidance show 
some potential for surface-based thunderstorms across this region, 
mainly in the 06-12z time frame. Given the strength of the low-level 
flow, strong to locally damaging winds could occur with a 
consolidating line of thunderstorms, and plentiful low-level shear 
may support an embedded tornado or two as well. The lack of greater 
low-level moisture across the warm sector limits confidence in any 
more than marginal risk probabilities at this time. 

.Gleason/Dean.. 01/18/2019 


Mesoscale Discussion

acus11 kwns 130855 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 130854 

Mesoscale discussion 0019 
National Weather Service Storm Prediction Center Norman OK 
0254 am CST sun Jan 13 2019 

Areas affected...central Virginia and Maryland...including southern 
portions of the Washington D.C./Baltimore Metro area 

Concerning...heavy snow 

Valid 130854z - 131300z 

Summary...moderate to heavy snow now developing across parts of 
central Virginia and Maryland is expected to persist through mid to 
late morning, with rates (around or in excess of 1 inch per hour) 
likely maximizing in the 6-10 am EST time frame. 

Discussion...a broadly cyclonic 50-70+ kt 500 mb jet streak 
continues to gradually develop eastward across the northern Gulf 
Coast states, with its exit region now beginning to nose to the Lee 
of the southern Appalachians, toward the southern mid Atlantic coast 
through mid to late morning. It appears an associated broad area of 
strong upward vertical motion will include a period of strengthening 
lower/mid-tropospheric frontogenesis across Virginia and adjacent 
portions of the mid Atlantic. 

Across central Virginia into adjacent portions of central Maryland, 
where temperature profiles are expected to remain entirely below 
freezing, models indicate that lift may begin to become maximized 
within the favorable mixed-phase layer for dendritic ice Crystal 
growth by daybreak, and continue through mid to late morning. Aided 
by relatively high precipitable water content (up to around .70 
inches), one or more bands of heavy snow, at rates around or in 
excess of 1 inch per hour, appear possible. Forecast soundings 
suggest that this may persist for a 3-4 hour period at any 
particular location, generally in a narrow corridor from the 
vicinity of the Blue Ridge, north of Roanoke VA, east/northeastward 
through southern portions of the greater Washington D.C./Baltimore 
metropolitan area. 

.Kerr.. 01/13/2019 

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


Latitude...Lon 38287888 38517861 38657841 38977644 38497624 37937809 
37697891 37767939 38087930 38287888