SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1253 AM CDT Wed Sep 21 2022
Valid 211200Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WESTERN UTAH TO
SOUTHERN IDAHO AND ACROSS THE UPPER OH RIVER VALLEY TO THE LOWER
GREAT LAKES...
...SUMMARY...
Scattered thunderstorms capable of severe hail, wind, and a few
tornadoes, are expected this afternoon and evening across the Upper
Ohio River Valley and the lower Great Lakes region. Isolated to
scattered severe gusts are also possible across portions of the
Great Basin this afternoon.
...Synopsis...
An upper wave over the upper MS River Valley/western Great Lakes
will gradually deepen over the next 24 hours amid continued cold air
advection across the Midwest behind a southeastward moving cold
front. Across the western CONUS, a closed low off the coast of
northern CA will shift east into central OR, supporting a broad
region of ascent across the Great Basin.
...Upper OH River Valley and Lower Great Lakes...
The surface cold front, currently draped from central WI into the
central Plains, will continue to migrate to the southeast as the
synoptic surface low consolidates across southeast Canada through
the day. Increasing southwesterly winds ahead of the front will
advect rich boundary layer moisture (dewpoints in the upper 60s/low
70s) from IL/IN into OH and far western PA by early afternoon.
Combined with modestly steepening mid-level lapse rates, buoyancy is
currently expected to increase to around 2000 J/kg MLCAPE
along/ahead of the front across IN/OH, decreasing with northeastern
extent into NY/VT. The deepening of the synoptic wave will also
support increasing flow in the 850-700 mb layer to near 30-45 knots
and yield improving helicity in the lowest 1-2 km across northern OH
to far western PA.
Strong lift along the cold front combined with weak
boundary-orthogonal storm motions should favor quick upscale growth
from initially discrete cells/clusters capable of large hail to
linear segments. The overall kinematic and thermodynamic
environments will be supportive of an organized severe threat,
including the potential for scattered damaging to severe gusts and a
few brief, embedded tornadoes within linear segments. Increased wind
probabilities were considered across northeast OH to western PA
where latest CAMs show the best signal for an organized line;
however, the potential for lingering morning convection along the
warm front and poor run-to-run consistency in the spatial coverage
of the threat limits confidence in the location/coverage of the best
wind potential.
...Great Basin...
Deep-layer flow is expected to increase through the day across UT
into ID as the closed low moves east into the region. Ascent ahead
of the wave coupled with increasing diffluence aloft should support
a broad region of ascent with elongated hodographs featuring 0-6 km
bulk shear values near 50-60 knots. Despite the dry conditions
sampled by the 00 UTC SLC sounding, latest GOES precipitable water
imagery shows a plume of higher PWAT values across the Four Corners
region. The western periphery of this moisture will likely advect to
the north/northwest as low to mid-level flow becomes more
meridional, supporting increasing buoyancy through the late
afternoon. However, the degree of destabilization remains somewhat
uncertain with some spread in guidance noted. Regardless, the strong
kinematics/lift should support organization of
discrete/semi-discrete cells. Strong to severe gusts appear possible
- especially if morning cloud cover remains limited and supports
steep low-level lapse rates by the afternoon.
..Moore/Gleason/Weinman.. 09/21/2022
Read more CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/SYjVTj
