SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1216 PM CDT Tue Sep 14 2021

Valid 151200Z - 161200Z


Isolated strong to severe storms are possible across the Ohio Valley
with scattered severe storms possible into the Northeast Wednesday
afternoon and evening. Damaging winds, large hail, and a few
tornadoes will be possible.

...Northeast into the Upper Ohio Valley...

Latest water-vapor imagery depicts a mid-level short-wave trough
over SD. This feature is forecast to advance to a position from
lower MI into eastern IL by mid day Wednesday. Subsequently, this
feature will move into the lower Great Lakes/OH Valley by 16/00z as
strongest 500mb flow translates across northern New England into
southeast Canada. Associated surface front will progress into
upstate NY early in the period, trailing across the northern Hudson
Valley-western PA by 18z. Strongest mid-level height falls will
remain north of the international border, thus frontal
convergence/boundary-layer heating will prove instrumental in
convective development through the period. Latest guidance suggests
the strongest heating will be noted across the central Appalachians
into eastern PA where surface-3km lapse rates could approach 7.5
C/km by early afternoon. Northeast extent of this more buoyant air
mass will stretch into the Hudson Valley prior to frontal passage.

NAM forecast sounding at 17z for ALB depicts an uncapped surface
parcel with 2700 J/kg MLCAPE and 45kt of surface-6km bulk shear.
Scattered thunderstorms should easily develop within this
environment and organized robust updrafts are expected given these
conditions. Supercells are certainly possible prior to storm mergers
and possible line segment development. Greatest tornado potential
should extend along a corridor from the Hudson Valley across
southern VT/NH into extreme southern ME. Otherwise, more isolated,
less sheared, convection should extend southwest along the front
across PA into WV. More unstable thermodynamic environment across
this region will however support at least a threat for damaging
winds and some hail.

...Central Gulf Coast...

Remnants of Tropical Cyclone Nicholas will drift east across the
upper TX Coast into southern LA during the day2 period. Poor lapse
rates, due to extensive cloud cover, will greatly reduce buoyancy
where low-level shear is maximized. Forecast soundings suggest
southern MS into the western part of the FL Panhandle may experience
the greatest combination of low-level shear with at least marginal
surface heating. For these reasons, have adjusted the eastern edge
of the MRGL Risk a bit east across the FL Panhandle.

..Darrow.. 09/14/2021

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