U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 180048 
Storm Prediction Center ac 180047 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0747 PM CDT Fri Aug 17 2018 

Valid 180100z - 181200z 

..there is a slight risk of severe thunderstorms across portions of 
the northeast... 

Strong to locally damaging wind gusts may continue for a few more 
hours this evening across parts of the northeast. Isolated strong 
gusts are also possible across parts of the northern rockies through 
the remainder of the evening. 

..Southern Plains to the northeast... 

Clusters of storms will continue to pose a damaging wind threat for 
a couple more hours this evening. Downstream 00z radiosonde observation from gyx shows 
weakening deep layer shear and loss of daytime heating will result 
in a rapidly stabilizing boundary layer. Maintaining probs mainly 
for forward propagating cluster over northern New Jersey and across western 
Massachusetts that still indicates some potential for strong gusts. 

Further south and west, probabilities have been removed from 
southeast OK across the mid-south and central Appalachians. Weak 
deep layer shear and nocturnal boundary layer stabilization will 
quickly diminish any lingering threat. 

..central/southern High Plains... 

The overall trend over the last hour has been weakening, 
progressively disorganized convection. An isolated strong wind gust 
may be possible for another hour or two across southeast Colorado into 
northeast nm, but the threat is quickly diminishing with loss of 
heating, and the marginal risk has been removed. 

..northern rockies... 

Only minor adjustments have been made to the marginal risk. 
Convection is ongoing across the region and a 64 mph gust was 
recently recorded near Craters of the Moon in southern Idaho. Isolated 
threat of strong wind gusts will continue for a few hours into this 

.Leitman.. 08/18/2018 


Mesoscale Discussion

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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 172331 

Mesoscale discussion 1314 
National Weather Service Storm Prediction Center Norman OK 
0631 PM CDT Fri Aug 17 2018 

Areas affected...parts of eastern Pennsylvania and northern New 
Jersey into the lower Hudson Valley 

Concerning...Severe Thunderstorm Watch 340... 

Valid 172331z - 180100z 

The severe weather threat for Severe Thunderstorm Watch 340 

Summary...storms may continue to produce frequent cloud to ground 
lightning, with increasing potential for damaging wind gusts 
possible into the 8-10 PM EDT time frame. 

Discussion...a small but sustained cluster of vigorous thunderstorms 
now northwest of Philadelphia PA seems to provide the most 
substantive continuing severe weather potential through 00-02z. 
Within surface troughing across the northern mid Atlantic region, 
the boundary layer air mass ahead of it remains warm, very moist and 
characterized by moderately large cape in excess of 2000 j/kg. 
Inflow of this air provides potential for further intensification of 
this convection, along with the possible evolution of a 
strengthening surface cold pool. Perhaps aided by modest vertical 
shear associated with a belt of 20-30 kt southwesterly lower/mid 
tropospheric flow, this could still be accompanied by an increasing 
risk for damaging wind gusts north of Philadelphia through northern 
New Jersey and portions of the lower Hudson Valley this evening. 

Otherwise, thunderstorm activity elsewhere across Severe 
Thunderstorm Watch 340 and surrounding areas seems likely to 
gradually diminish with decreasing severe weather potential. 

.Kerr.. 08/17/2018 

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


Latitude...Lon 40957505 41337454 41167374 40187411 39797522 40077580 
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