U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 210442 
Storm Prediction Center ac 210440 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1140 PM CDT Thursday Oct 20 2016 

Valid 211200z - 221200z 

..no severe thunderstorm areas forecast... 

severe thunderstorms are not expected across the contiguous United 
States today. 

A highly amplified upper trough over the eastern Continental U.S. Will progress eastward 
toward the coast today while acquiring a slight negative tilt over 
New England by late this evening. At the surface...a large area of weak 
low pressure extending from New York to NC should consolidate near the 
Delaware-Maryland-Virginia peninsula/New Jersey late this afternoon...with an attendant cold 
front likewise moving eastward across the Middle-Atlantic States and 
Carolinas. A warm front will lift northward over New England through this 
evening. Upper ridging will prevail over much of the western/central 
Continental U.S....with surface high pressure firmly established over the central 
states. A shortwave trough will approach the coast of the Pacific 
northwest by this afternoon. 

Surface dewpoints in the low to middle 60s will likely characterize the 
low-level airmass downstream of the eastward advancing cold front. 
However...poor middle-level lapse rates and widespread cloudiness 
should greatly limit the degree of destabilization that will be 
realized this afternoon from the middle-Atlantic to the Carolinas. At 
this time...the most favorable location for isolated thunderstorms 
appears to be across parts of southern New England...where a surge of 
moist sub-tropical air may allow for enough instability to support 
charge separation and lightning strikes. Even with a favorable 
kinematic field across much of the eastern states along/east of the 
front...forecast instability appears too limited to include any 
probabilities for organized severe thunderstorms. 

Across the Pacific northwest...isolated thunderstorms may occur 
mainly this afternoon in association with a shortwave trough. 
Generally weak low-level wind fields and marginal instability will 
likely preclude a severe threat with this activity. 

.Gleason/Jewell.. 10/21/2016 


Mesoscale Discussion

acus11 kwns 210301 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 210301 

Mesoscale discussion 1805 
National Weather Service Storm Prediction Center Norman OK 
1001 PM CDT Thursday Oct 20 2016 

Areas affected...N-cntrl PA...central New York 

Concerning...severe potential...watch unlikely 

Valid 210301z - 210400z 

Probability of watch issuance...20 percent 

Summary...threat for strong to marginally severe wind gusts may extend 
beyond Severe Thunderstorm Watch 499 expiration time of 03z across parts of 
north-central PA and central New York over the next 1-2 hours. 

Discussion...relatively highest wind gust potential remains focused 
across north-central PA...where a well-organized line segment is currently 
moving into Sullivan and Bradford counties PA. Vwp data from bgm and 
ccx are sampling strong low-level flow of 20-30 knots. A narrow 
corridor of instability aligned with the ongoing convective line 
should continue to support strong wind gust potential over the next 
1-2 hours...but this line will encounter an increasingly stable air 
mass to the North/East where cooler temperatures in the upper 50s and lower 
60s f are observed. 

.Rogers/Hart.. 10/21/2016 

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


Latitude...Lon 42057506 41097612 40587681 40637740 40837788 41377752 
42337648 42477579 42367515 42057506