U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 251956 
Storm Prediction Center ac 251955 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0155 PM CST Sat Feb 25 2017 

Valid 252000z - 261200z 

..there is a slight risk of severe thunderstorms from a portion of 
the middle Atlantic into eastern New York and western New England... 

..there is a marginal risk of severe thunderstorms from eastern 
North Carolina through a portion of New England... 

Thunderstorms capable of producing isolated damaging wind and large 
hail will persist through early evening from North Carolina through 
Virginia and Maryland. Threat for mainly isolated damaging wind, 
hail and a brief tornado or two exists farther north from eastern 
Pennsylvania through eastern New York and western New England. 

..eastern North Carolina through Virginia and the northeastern 

Primary change to current outlook has been to trim from the west and 
introduce a 15% hail category over eastern VA, Maryland and southeast PA 
where discrete supercells have developed within zone of stronger 
boundary-layer destabilization. These storms will continue to pose a 
risk for isolated damaging wind as well as large hail. Farther north 
across eastern New York into western New England, a dominant linear 
Mode will promote a risk for mainly isolated damaging wind into 
early evening, but a brief tornado cannot be ruled out. 

.Dial.. 02/25/2017 

Previous discussion... /issued 1013 am CST Sat Feb 25 2017/ 

..NY/Vermont into NC... 
A strong upper trough is rotating across the mid MS and Ohio valleys 
today, with the associated surface cold front extending from western 
New York/PA southward into western NC. A band of showers and isolated 
thunderstorms is present ahead of the front. This activity is 
moving into an area where breaks in the clouds and dewpoints in the 
50s will yield marginal cape values and the potential for 
intensification. Strong winds aloft and focused forcing along the 
front, coupled with model consensus of a broken squall line later 
today, suggest a risk of a few storms intensifying to severe levels 
this afternoon. Fast-moving bowing structures capable of locally 
damaging winds would be the main threat, although hail may also 
occur in the strongest cores. 


Mesoscale Discussion

acus11 kwns 251725 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 251724 

Mesoscale discussion 0211 
National Weather Service Storm Prediction Center Norman OK 
1124 am CST Sat Feb 25 2017 

Areas affected...Maryland...central and eastern Virginia and 
northern North Carolina 

Concerning...severe potential...watch possible 

Valid 251724z - 251930z 

Probability of watch issuance...60 percent 

Summary...thunderstorms are expected to increase in coverage and 
intensity this afternoon ahead of a cold front. Locally damaging 
winds are possible, along with hail in the strongest cells. A watch 
may be needed if it is clear storms will become severe. 

Discussion...rapid surface heating continues across the region ahead 
of the cold front which extended from northwestern Virginia into western 
NC as of 17z. Dewpoints were holding in the mid to upper 50s 
suggesting a well-mixed and unstable boundary layer with MUCAPE to 
around 1000 j/kg. 

Satellite and radar show a few weak thunderstorms already forming 
over the higher terrain near the front, and a general upward trend 
is expected through the afternoon as it progresses east. By 18-19z, 
some storms may be severe. Wind profiles will continue to 
strengthen, especially in the mid to upper levels, with long 
hodographs favoring long-lived storms. Damaging winds appear to be 
the main threat with a broken line of cells or small bows. The cold 
air in the mid to upper levels would support the formation of hail. 
However, a relatively warm layer exists above 700 mb, and updrafts 
may struggle. As a result of this warm layer, storms may be slow to 
become severe, but with time, long-acting shear may overcome this, 
especially over eastern Virginia into MD, and northeastern NC later this 

The tornado threat is low, but not zero. Although storms could 
remain cellular, and low-level shear is in the sufficient category 
with 0-1 srh near 100 m2/s2, strong boundary layer mixing will be a 
detriment, as will be the warm layer aloft hampering vertical 
updraft accelerations in the lower parts of the storm. 

.Jewell/Hart.. 02/25/2017 

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


Latitude...Lon 37997518 37457556 37037585 36707636 36497718 36377824 
36457905 36887910 37257891 37657868 38207835 38657805 
39117772 39627728 39737666 39627590 39267550 38877524 
38427508 37997518