U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 240514 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1114 PM CST Tue Jan 23 2018 


Valid 241200z - 251200z 


..no severe thunderstorm areas forecast... 


... 
isolated thunderstorms will be possible across coastal areas of the 
Pacific northwest through tonight. 


... 


The western upper ridge will progress eastward across The Rockies to 
the plains this period, while an upper trough moves onshore the 
Pacific coast. As the trough moves towards the coast, an intense jet 
streak will overspread coastal or and California and midlevel cooling will 
occur. Concurrently at the surface, a weak cold front will move 
inland over the Pacific northwest and northern California and modest 
steepening of low to midlevel lapse rates will occur. Forecast 
soundings indicate very weak, albeit adequate, instability for 
isolated lightning strikes along the coast and perhaps into portions 
of the Willamette Valley. Of note, background flow will be strong as 
this system moves inland and may produce damaging winds. However, 
these winds will not be convective in nature, thus precluding the 
need for severe probs. 


.Leitman.. 01/24/2018 


$$ 

Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 231103 
mez000-231500- 


Mesoscale discussion 0045 
National Weather Service Storm Prediction Center Norman OK 
0503 am CST Tue Jan 23 2018 


Areas affected...northern Maine 


Concerning...winter mixed precipitation 


Valid 231103z - 231500z 


Summary...heavy snowfall with rates of up to 1 inch per hour will be 
possible across northern Maine over the next 3 to 4 hours. A mix of 
snow, freezing rain and sleet is likely after daybreak from near 
Caribou westward to the Canadian border. 


Discussion...the latest water vapor imagery shows a strong 
upper-level system from the Great Lakes southward into the Ohio and 
Tennessee valleys. Southwest anticyclonic flow exists ahead of the 
system across the northeast. A plume of low to mid-level moisture 
was moving across New England with a vorticity Max analyzed by the 
rap in far western Maine near the Maine-Canadian border. In 
addition, the exit region of a 50 to 60 kt low-level jet is analyzed 
over northern New England. These factors along with backed easterly 
low-level flow is contributing to strong isentropic ascent across 
northern Maine favorable for heavy snow. The greatest potential for 
heavy snow will be from Caribou, ME and Edmundston, Canada westward 
to the Canadian border where snowfall rates could reach 1 inch per 
hour. 


Further south, the core of a strong low-level jet will result in 
considerable warming around 850 mb in central and northern Maine 
this morning. As a result of the related melting-layer depth 
increase, snowfall should become mixed with freezing rain and sleet 
after daybreak. This changeover should gradually progress northward 
across north-central Maine this morning. 


.Broyles/Edwards.. 01/23/2018 


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


Attention...WFO...car... 


Latitude...Lon 47496841 47576922 46767004 46177016 45996804 46306754 
47126770 47496841