U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 251225 
Storm Prediction Center ac 251224 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0624 am CST Sat Feb 25 2017 

Valid 251300z - 261200z 

..there is a slight risk of severe thunderstorms this afternoon 
from central/eastern New York to north central North Carolina... 

..there is a marginal risk of severe thunderstorms surrounding the 
slight risk area...from western New England to North Carolina... 

Thunderstorms capable of producing damaging winds and isolated large 
hail are forecast from New York and western New England southward to 
North Carolina this afternoon. 

A strong mid-upper trough over the Great Lakes/Ohio Valley will 
progress eastward today, as an associated surface cold front crosses 
the Appalachians this morning and approaches the mid-Atlantic coast 
this evening. Some destabilization during the day ahead of the cold 
front, as well as increasing vertical shear with the approach of the 
midlevel trough, will support a risk of severe thunderstorms this 
afternoon from central/eastern New York to north central NC. 

..central/eastern New York to north central NC this afternoon... 
Thunderstorm development is expected by midday-early afternoon along 
the surface cold front from central New York and eastern PA southward 
across Virginia into at least north central NC. Warmer surface 
temperatures to the south (70s from Virginia into nc) and boundary layer 
dewpoints in the mid-upper 50s will drive weak-moderate 
surface-based buoyancy (mlcape of 500-1000 j/kg), along with steep 
low-level lapse rates. This thermodynamic regime will aid in 
downward momentum Transfer and damaging wind potential in organized 
line segments. Additionally, semi-discrete supercells will be 
possible given sufficient buoyancy and effective bulk shear near 50 
kt, which will support a risk for large hail in the presence of 
lingering steep midlevel lapse rates and seasonably cool midlevel 
temperatures (near -17 c at 500 mb). 

Strong linear forcing for ascent will support a more solid line of 
convection farther north into PA/New York along the cold front, where 
cooler surface temperatures will tend to limit buoyancy. Damaging 
winds will be the main severe risk this afternoon, before convection 
weakens this evening after overturning any remaining buoyancy. 

.Thompson/Kerr.. 02/25/2017 


Mesoscale Discussion

acus11 kwns 250250 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 250250 

Mesoscale discussion 0209 
National Weather Service Storm Prediction Center Norman OK 
0850 PM CST Fri Feb 24 2017 

Areas affected...parts of southern/eastern Kentucky...middle/eastern 
Tennessee...and northern Alabama 

Concerning...severe potential...watch possible 

Valid 250250z - 250415z 

Probability of watch issuance...60 percent 

Summary...thunderstorms should continue to increase in coverage 
ahead of a cold front, with some threat for large hail and damaging 
winds with the strongest storms. Severe Thunderstorm Watch issuance 
is possible if storms strengthen further. 

Discussion...a broken line of thunderstorms extends from southern Kentucky 
into middle Tennessee and northern Alabama along a pre-frontal trough as of 
0245z. As large-scale forcing for ascent overspreads this area from 
the west with an approaching mid to upper-level trough, convection 
should continue to increase in coverage over the next several hours. 
02z rap mesoanalysis indicates MLCAPE around 500 j/kg is located 
across middle Tennessee and surrounding vicinity, as relatively steep 
mid-level lapse rates (around 7.5 degrees c/km) are present per the 
00z sounding from Nashville, Tennessee. Even with the limited buoyancy, a 
veering wind profile and strong mid-level winds are supporting 40-50 
kt of effective bulk shear. An isolated large hail and damaging wind 
threat should develop with this broken line of storms through the 
remainder of the evening hours, and a Severe Thunderstorm Watch may 
be needed if convection continues to strengthen. 

.Gleason/guyer.. 02/25/2017 

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


Latitude...Lon 34878737 35858677 37168538 37188415 36938361 35908454 
35008564 34388639 34468709 34878737