U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 161606 
Storm Prediction Center ac 161605 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1005 am CST Fri Nov 16 2018 

Valid 161630z - 171200z 

..no thunderstorm areas forecast... 

the risk for thunderstorms appears negligible across the U.S. Today 
through tonight. 

Downstream of blocking within the mid-latitude westerlies over the 
eastern Pacific, mid/upper flow across much of the U.S., While not 
particularly amplified, appears likely to remain broadly confluent 
and cyclonic. 

Strongest mid-level height falls, associated with a pair of vigorous 
short wave perturbations within this regime, are in the process of 
spreading from southeastern Canada and the northeast toward the 
northwestern Atlantic. As this continues, an associated deepening 
surface cyclone is forecast to migrate northeast of Cape Cod into 
areas near/east of the Canadian Maritimes. A cold front trailing 
from this feature has already advanced well south/east of the Gulf 
and Atlantic coasts, including the Florida Straits. 

In the wake of the front, cold surface ridging remains a prominent 
influence across much of the Gulf of Mexico and Gulf Coast region. 
While the center of this ridge may shift from the north central Gulf 
Coast into the vicinity of the central Appalachians by early 
Saturday, a significant reinforcing cold intrusion is expected to 
nose southeastward to the Lee of the northern rockies. 

In response to these developments, generally stable conditions will 
prevail across the U.S., With negligible (less than 10 percent) risk 
for thunderstorm activity. 

..northern New England coast... 
Models do suggest that strong differential thermal advection and 
forcing for ascent at mid-levels may contribute to a corridor of 
weak destabilization near coastal downeast Maine early this 
afternoon. Forecast soundings indicate that moist parcels 
contributing to weak cape will be based near/above 700 mb, where 
thermal profiles will generally be entirely below freezing, and the 
risk for charge separation supportive of lightning appears 

..northern intermountain region/rockies... 
Beneath strong mid-level cooling, insolation may contribute to weak 
boundary layer destabilization across the mountains of central Idaho 
and Wyoming through the Black Hills vicinity by late this afternoon. 
This may support scattered low-topped convective development, but 
forecast soundings suggest that the potential for charge separation 
supportive of lightning is negligible. 

.Kerr/Wendt.. 11/16/2018 


Mesoscale Discussion

acus11 kwns 160857 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 160856 

Mesoscale discussion 1652 
National Weather Service Storm Prediction Center Norman OK 
0256 am CST Fri Nov 16 2018 

Areas affected...portions of the mid-Atlantic and New England 

Concerning...heavy snow 

Valid 160856z - 161500z 

Summary...one area of heavy snow with rates in excess of 1 inch per 
hour will develop northeastward across northern New England this 
morning. Another area of moderate to locally heavy snow, with rates 
up to 1 inch per hour, will move across eastern PA into southern New 

Discussion...within large-scale upper troughing encompassing much of 
the central and eastern conus, a compact shortwave trough will 
continue moving quickly northeastward over the mid-Atlantic and New 
England regions this morning. A deepening surface low associated 
with this shortwave trough will likewise develop northeastward along 
the coast of southern New England. A band of moderate to heavy snow 
is occurring over western/northern NY, attendant to strong forcing 
for ascent and a mid-level deformation zone immediately ahead of the 
shortwave trough. Snowfall rates in excess of 1 inch per hour will 
likely continue for at least the next several hours as this band 
develops into northern New England. 

Across parts of central/eastern PA, northern NJ, southern NY, and 
southern New England, a mix of snow, sleet, and freezing rain have 
all been observed recently as strong low-level warm air advection 
has allowed for at least some melting of hydrometeors. However, a 
quick transition back to mainly snow is likely from west to east 
this morning as cold mid/upper-level temperatures embedded within 
the core of the shortwave trough overspread these areas. Forecast 
soundings from the NAM and rap both suggest that there will be 
sufficient wrap-around moisture remaining within the dendritic 
growth zone and steepening mid-level lapse rates to support moderate 
to locally heavy snow for a couple of hours. Snowfall rates up to 1 
inch per hour may occur. This scenario is well supported by recent 
high-resolution guidance, including most href members. A rapid 
decrease in snowfall intensity/coverage will likely be noted from 
west to east through the morning, as strong subsidence and mid-level 
drying behind the shortwave trough passage suppress precipitation 

.Gleason.. 11/16/2018 

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


Latitude...Lon 43667018 42917138 42457230 41937334 40907478 40407593 
40217652 40257704 41037762 41687752 43387669 44457594 
45047489 45087164 45387140 45447091 45837051 46087035 
46257028 46417018 46566969 46536828 46286771 45706771 
45216802 44626873 43996958 43667018