SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1227 AM CDT Mon Sep 19 2022
Valid 191200Z - 201200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHEAST AND PORTIONS OF THE FAR NORTHERN PLAINS...
...SUMMARY...
Thunderstorms capable of producing strong wind gusts will be
possible today over parts of the Northeast. Isolated wind and hail
producing storms will be possible near the Canadian border region of
northeastern North Dakota and northwestern Minnesota.
...Synopsis...
A large-scale upper-level anticyclone, accompanied by surface high
pressure, will promote mass subsidence across much of the central
and southern CONUS today as a mid-level cyclone meanders along the
West Coast. Multiple mid-level perturbations will pivot around the
upper-level anticyclone, promoting enough deep-layer ascent to
support at least scattered thunderstorms across the far northern
Plains (near the Canadian border) and across much of the Northeast.
In both locations, adequate shear and buoyancy may result in strong
to potentially isolated severe thunderstorm development.
...Northeast...
Widespread showers and embedded thunderstorms should be ongoing at
the start of the period over eastern parts of the OH Valley into the
Appalachians. As a pronounced mid-level trough and associated
surface trough continues to advance eastward through the day,
deep-layer ascent will promote increased convective coverage. Some
insolation may occur across the Hudson Valley by late morning/early
afternoon, contributing to surface temperatures rising into the 70s
F amid low 60s F dewpoints. When overspread by 6 C/km mid-level
lapse rates, a tall, skinny CAPE profile should materialize, with
around 1000 J/kg MLCAPE possible. Largely unidirectional vertical
wind profiles with some speed shear will result in 40 kts of
effective bulk shear. A mix of cellular clusters and linear
structures should be the dominant modes of convection. Damaging
gusts are the main threat with the stronger storms. Severe gusts
should be isolated, warranting the introduction of Category
1/Marginal probabilities.
...North Dakota/Minnesota/International Border...
Weak surface low development is expected by afternoon across North
Dakota as a 500 mb speed max overspreads the far northern Plains.
While deep-layer ascent will not be particularly strong, the
combination of strong surface heating and modest upper support
should favor the development of at least a few thunderstorms by mid
to late afternoon. Surface temperatures/dewpoints in the 80s/upper
50s F beneath 8+ C/km mid-level lapse rates support 1000+ J/kg
MLCAPE. Low-level hodograph curvature and elongation above 3 km
suggests that a couple of supercells with large hail and perhaps
severe wind gusts may develop. Given limited low-level moisture
though, the severe threat is expected to be isolated, with Category
1/Marginal probabilities introduced.
..Squitieri.. 09/19/2022
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