U.S. Severe Weather Forecast (Sääkatsaus)

Day Three

acus01 kwns 151945 
Storm Prediction Center ac 151944 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0144 PM CST Fri Dec 15 2017 

Valid 152000z - 161200z 

..no thunderstorm areas forecast... 

no significant thunderstorm activity is expected over the contiguous 
United States through tonight. 


Other than the possibility of an isolated strike or two downwind of 
Lake Erie and Ontario later this evening associated with evolving 
lake effect snow bands, thunderstorm activity is not expected 
through tonight over the remainder of the country. 

.Dial.. 12/15/2017 

Previous discussion... /issued 1022 am CST Fri Dec 15 2017/ 

..synopsis and discussion... 
An upper low/trough over Ontario and the Great Lakes region will 
develop eastward across the mid-Atlantic/northeast and Quebec 
through the period. Positively tilted upper troughing extending 
southward from the upper low/trough across the Ohio Valley into the 
mid MS valley and Southern Plains will advance generally 
southeastward through tonight. Upper ridging over the western Continental U.S. 
Will deamplify today as another upper trough moves eastward over the 
Pacific northwest and California. A separate closed upper low over 
northwestern Mexico will make only slow eastward progress towards Texas 
through early Saturday morning. 

At the surface, a low is present just off the coast of the Outer 
Banks of NC, and a cold front extends southwestward from this low 
across the western Atlantic, northern Florida Peninsula, and Gulf of 
Mexico. This front will continue southeastward across the 
central/southern Florida Peninsula today before stalling late tonight. 
While a lightning strike or two cannot be completely ruled out along 
the immediate shores of Lake Erie and Ontario in western New York as lake 
effect snow bands become organized late this afternoon and evening, 
this potential appears highly conditional and short-lived. Overall, 
thunderstorm chances across the Continental U.S. Remain too low to justify a 
general thunderstorm area. 


Mesoscale Discussion

acus11 kwns 152243 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 152242 

Mesoscale discussion 1797 
National Weather Service Storm Prediction Center Norman OK 
0442 PM CST Fri Dec 15 2017 

Areas affected...portions of western New York and far northwestern 

Concerning...heavy snow 

Valid 152242z - 160245z 

Summary...a squall of heavy snow will continue to move ashore areas 
near Eastern Lake Erie this evening. Thereafter, lake effect snow 
bands will develop through the overnight. Snowfall rates upwards of 
two inches per hour will be possible. 

Discussion...along the cyclonic flank of a mid-level jet, broad 
ascent has fostered the development of a lake-enhanced snow squall 
over Eastern Lake Erie. This band should gradually move ashore over 
the next hour or so, aided by sufficient low-level instability and 
convergence. Kbuf dual-pol data suggest some enhancement of Crystal 
growth around -12 to -18 c, with subtle increases in kdp (upwards of 
0.4-0.6 deg/km) noted around 5000-6000 ft above radar level. 
Therefore, heavy snow is likely as the band continues to move 
onshore, and snowfall rates upwards of 2 inches per hour appear 
possible. Following the squall, lake-effect bands will likely 
organize later this evening, with continued localized heavy snow 

.Picca.. 12/15/2017 

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


Latitude...Lon 42118055 42997924 43347900 43417838 43297826 42687842 
42067905 41907963 41838010 41868039 41918050 42118055