U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 180044 
Storm Prediction Center ac 180042 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0642 PM CST Sat Feb 17 2018 

Valid 180100z - 181200z 

..no severe thunderstorm areas forecast... 

a few lightning strikes remain possible tonight mainly over the 
Pacific northwest coastal areas. 

..Pacific northwest coast... 

Steepening lapse rates with cold mid-level temperatures accompanying 
an upper low circulation moving south southeastward through the 
Pacific northwest will result in weak instability (mlcape at or 
below 300 j/kg) within Post-frontal regime along coastal Washington and or. 
This environment may become at least marginally sufficient for 
scattered low-topped convection to produce a few lightning strikes 

..southwest Texas... 

A weak warm-advection regime will evolve across southwest Texas 
resulting in weak destabilization. A few elevated showers and 
possibly a lightning strike or two may occur in this environment 
late tonight. However, coverage of any thunderstorms is expected to 
remain less than 10%. 

.Dial.. 02/18/2018 


Mesoscale Discussion

acus11 kwns 172333 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 172332 

Mesoscale discussion 0069 
National Weather Service Storm Prediction Center Norman OK 
0532 PM CST Sat Feb 17 2018 

Areas affected...southeastern Pennsylvania...northern New 
Jersey...southern New York...and western Connecticut 

Concerning...heavy snow 

Valid 172332z - 180330z 

Summary...snowfall rates around or in excess of 1 inch per hour are 
possible for the next few hours this evening from southeastern 
Pennsylvania into the New York City vicinity. 

Discussion...an approaching mid/upper-level shortwave trough and 
low-level warm advection are contributing to ascent across the 
region. As precipitation spreads east-northeastward across the 
area, melting/evaporating hydrometeors will eventually saturate and 
cool the low-level profiles, resulting in snow reaching the ground. 
The latest high-resolution numerical guidance generally supports 
snowfall rates around or exceeding 1 inch per hour for the next few 
hours, as the system moves rapidly to the east-northeast. 

.Jirak.. 02/17/2018 

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


Latitude...Lon 40407601 41007525 41767390 42007330 41817284 41257290 
40837350 40267456 40027502 39747566 39847600 40407601