Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
SPC AC 120057
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0657 PM CST Thu Nov 11 2021
Valid 120100Z - 121200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
PENNSYLVANIA INTO THE DELMARVA...
...SUMMARY...
A couple strong to severe thunderstorms may occur across the Mid
Atlantic by early morning, towards the end of the period.
...Synopsis...
A strong mid-level cyclone will continue to deepen while progressing
eastward across the Upper Mississippi Valley through 12Z (the end of
the forecast period). While the associated mid/upper level longwave
trough deepens, a belt of 60-90 kt 500 mb flow will pivot around the
trough and overspread a 50-70 kt southerly 850 mb jet centered over
the Hudson Valley in the 07-12Z period. At the surface, strong
convergence along a lee-trough axis/cold front will promote the
development and organization of low-topped convection capable of
producing strong wind gusts.
...Mid Atlantic...
As the surface cold front crosses the Appalachians and approaches
the lee trough, low-level convergence is expected to increase as the
50-70 kt low-level jet materializes and modest theta-e advection
ensues. The 00Z GSO and WAL observed soundings depict upper 50s F
surface dewpoints, but overall shallow moisture in the surface-850
mb layer. As such, buoyancy is expected to remain quite marginal
when warm-air advection occurs, with MLCAPE likely remaining under
500 J/kg on a widespread basis. Nonetheless, a narrow, low-topped
squall line is expected to develop along the immediate lee of the
surface trough axis around 07-09Z. Point forecast soundings across
portions of eastern PA southward towards Delmarva suggest that 50 kt
southerly winds may occur as low as 400-500 m AGL. Despite the lack
of buoyancy, any mechanically driven downward momentum transport
within the line may support a couple strong wind gusts, with an
instance or two of tree/power-line damage possible with the stronger
gusts, hence the introduction of Category 1/MRGL probabilities. The
damaging-gust threat is expected to persist past 12Z into the Day 2
period east of the current MRGL risk area.
..Squitieri.. 11/12/2021
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0600Z
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