U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 181606 
Storm Prediction Center ac 181605 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1005 am CST Tue Dec 18 2018 

Valid 181630z - 191200z 

..no severe thunderstorm areas forecast... 

severe thunderstorms are not forecast today or tonight across the 
contiguous United States. 

..western Washington... 
A powerful upper jet Max and associated surface cold front are 
moving ashore along the Washington coast, resulting in widespread 
precipitation. Several lightning strikes have been noted well 
offshore. Forecast soundings suggest the unstable layer will be 
sufficiently deep to support isolated lightning through much of the 
afternoon in vicinity of the Washington coastal ranges. There is a low 
potential for a lightning strike farther inland across Washington into ID, 
but that risk appears to be less than 10%. 

..southeast Texas... 
A second strong shortwave trough is digging southeastward across 
southern nm. Strengthening southerly low level winds ahead of the 
system will help to moisten/destabilize the air mass over southeast 
Texas. This will lead to increasing coverage of showers and a few 
embedded thunderstorms later tonight. No severe storms are 

.Hart/Cook.. 12/18/2018 


Mesoscale Discussion

acus11 kwns 170704 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 170703 

Mesoscale discussion 1714 
National Weather Service Storm Prediction Center Norman OK 
0103 am CST Mon Dec 17 2018 

Areas affected...southern and eastern Maine 

Concerning...winter mixed precipitation 

Valid 170703z - 171300z 

Summary...snow, perhaps mixed with freezing rain or sleet, will 
remain possible through the overnight hours. 

Discussion...frontogenesis in the 850-700-millibar layer within the 
warm-conveyor belt has resulted in a band of heavy precipitation 
along the southeast coast of Maine. This band will continue to pivot 
northwest through the overnight hours. In the vicinity of this band, 
surface temperatures have fallen below 32f, despite rap forecasts 
suggesting temperatures would remain near or above 32f. Modifying 
the rap soundings for the observed colder surface temperatures, wet 
snow is likely, but given the strength of the warm-air advection 
within the warm-conveyor belt, temperatures within the 
850-700-millibar layer may approach, or even exceed, 0c. As such, 
precipitation may mix with, or change to, freezing rain or sleet 

.Marsh/Goss.. 12/17/2018 

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


Latitude...Lon 44197086 45246936 45826711 44936676 44246739 43256962 
43007082 44197086