U.S. Severe Weather Forecast (Convective Outlook)

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swody1 
Storm Prediction Center ac 211247 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0647 am CST Wed Nov 21 2018 


Valid 211300z - 221200z 


..no severe thunderstorm areas forecast... 


... 
isolated thunderstorms are possible today from coastal into central 
California, and across parts of southeast Texas. 


... 
No changes to the previous outlook. A weak southern-stream 
shortwave trough will move eastward to the northwest Gulf Coast by 
tonight, in advance of a larger-scale trough that will progress 
inland over California. Steepening low-midlevel lapse rates with the California 
trough, as evidenced by the area of convection and isolated 
lightning strikes near 130 W, will support a threat for isolated 
thunderstorms from about midday into tonight. Along the Texas coast, a 
modifying low-level air mass and a low-level warm advection regime 
will contribute to weak destabilization atop a coastal front. A few 
elevated thunderstorms will be possible from this afternoon into 
tonight. 


.Thompson/Peters.. 11/21/2018 


$$ 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 160856 
mez000-nhz000-maz000-vtz000-ctz000-nyz000-njz000-paz000-161500- 


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 
England. 


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 
potential. 


.Gleason.. 11/16/2018 


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


Attention...WFO...car...gyx...box...btv...okx...aly...phi...bgm... 
buf...ctp... 


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