U.S. Severe Weather Forecast (Convective Outlook)

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acus01 kwns 151945 
swody1 
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


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acus11 kwns 151850 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 151850 
nyz000-njz000-paz000-152245- 


Mesoscale discussion 1796 
National Weather Service Storm Prediction Center Norman OK 
1250 PM CST Fri Dec 15 2017 


Areas affected...parts of southern/eastern New Jersey and Long 
Island 


Concerning...heavy snow 


Valid 151850z - 152245z 


Summary...moderate snow is developing, with a 1-2 hour period of 
heavy snow possible across parts of southern and eastern New Jersey, 
mainly between 4-7 PM EST. 


Discussion...large-scale lift supported by low-level warm advection 
appears to be increasingly saturating sub-freezing thermodynamic 
profiles across the northern mid Atlantic coast region. Guidance 
has been persistent in suggesting that increasing mid-level forcing 
for ascent associated with an approaching short wave trough will 
eventually contribute to increasing lift through the mixed-phased 
layer most conducive to large dendritic ice Crystal growth. This is 
expected to support increasing snow rates through mid to late 
afternoon. 


Heaviest snow rates may focus across portions of southern and 
eastern New Jersey during the 21-23z time frame, perhaps aided by 
lower/mid tropospheric frontogenetic forcing which is forecast to 
strengthen while shifting off the coast, generally south of Long 
Island, by early evening. Coupled with at least a modest increase 
in moisture (precipitable water increasing in excess of .4 inches), 
it appears possible that snow rates could approach or exceed 1 inch 
per hour for a 1 or 2 hour period at a particular location. This 
seems most probable across New Jersey coastal areas from Atlantic 
City through Toms River/Lakewood in the 21-23z time frame, but 
portions of the greater Philadelphia metropolitan area may also be 
impacted, as well as perhaps portions of Long Island by early this 
evening. 


.Kerr.. 12/15/2017 


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


Attention...WFO...okx...phi... 


Latitude...Lon 40007515 40637344 40667225 39337326 38987471 39397544 
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