U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 201244 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0644 am CST Tue Nov 20 2018 

Valid 201300z - 211200z 

..no severe thunderstorm areas forecast... 

a few thunderstorms are possible today across the Florida Peninsula, 
and late tonight in the vicinity of southern New Mexico. 

..FL peninsula today.. 
a low amplitude shortwave trough over the northeastern Gulf of 
Mexico will progress eastward across North Florida today. Along and 
south of a slow moving front, boundary-layer dewpoints mainly in the 
60s and surface heating within cloud breaks will support MLCAPE up 
to 1000 j/kg. A few thunderstorms will be possible along and just 
south of the front as it moves across central Florida this afternoon. 
Despite relatively strong flow in the upper troposphere, the threat 
for severe storms will be limited by rather modest midlevel lapse 
rates and weak low-level flow. By late evening, the thunderstorm 
threat across Florida is expected to diminish. 

..far West Texas/southeast nm after 06z... 
A southern-stream shortwave trough now approaching northern baja 
will move eastward to far West Texas by the end of the period. Some 
low-midlevel moistening is expected in the zone of ascent preceding 
this trough by the time it reaches far West Texas/southern nm by 
tonight, though the NAM appears to be too aggressive with the 
moistening/destabilization. Still, weak buoyancy (rooted near or 
just above 700 mb) will be possible overnight, when a few lightning 
flashes may occur with weak elevated convection. 

.Thompson.. 11/20/2018 


Mesoscale Discussion

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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 160856 

Mesoscale discussion 1652 
National Weather Service Storm Prediction Center Norman OK 
0256 am CST Fri Nov 16 2018 

Areas affected...portions of the mid-Atlantic and New England 

Concerning...heavy snow 

Valid 160856z - 161500z 

Summary...one area of heavy snow with rates in excess of 1 inch per 
hour will develop northeastward across northern New England this 
morning. Another area of moderate to locally heavy snow, with rates 
up to 1 inch per hour, will move across eastern PA into southern New 

Discussion...within large-scale upper troughing encompassing much of 
the central and eastern conus, a compact shortwave trough will 
continue moving quickly northeastward over the mid-Atlantic and New 
England regions this morning. A deepening surface low associated 
with this shortwave trough will likewise develop northeastward along 
the coast of southern New England. A band of moderate to heavy snow 
is occurring over western/northern NY, attendant to strong forcing 
for ascent and a mid-level deformation zone immediately ahead of the 
shortwave trough. Snowfall rates in excess of 1 inch per hour will 
likely continue for at least the next several hours as this band 
develops into northern New England. 

Across parts of central/eastern PA, northern NJ, southern NY, and 
southern New England, a mix of snow, sleet, and freezing rain have 
all been observed recently as strong low-level warm air advection 
has allowed for at least some melting of hydrometeors. However, a 
quick transition back to mainly snow is likely from west to east 
this morning as cold mid/upper-level temperatures embedded within 
the core of the shortwave trough overspread these areas. Forecast 
soundings from the NAM and rap both suggest that there will be 
sufficient wrap-around moisture remaining within the dendritic 
growth zone and steepening mid-level lapse rates to support moderate 
to locally heavy snow for a couple of hours. Snowfall rates up to 1 
inch per hour may occur. This scenario is well supported by recent 
high-resolution guidance, including most href members. A rapid 
decrease in snowfall intensity/coverage will likely be noted from 
west to east through the morning, as strong subsidence and mid-level 
drying behind the shortwave trough passage suppress precipitation 

.Gleason.. 11/16/2018 

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


Latitude...Lon 43667018 42917138 42457230 41937334 40907478 40407593 
40217652 40257704 41037762 41687752 43387669 44457594 
45047489 45087164 45387140 45447091 45837051 46087035 
46257028 46417018 46566969 46536828 46286771 45706771 
45216802 44626873 43996958 43667018