SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0238 PM CDT Wed Sep 06 2023
Valid 062000Z - 071200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
THE TENNESSEE VALLEY AREA WEST-SOUTHWESTWARD TO PARTS OF ARKANSAS
AND NORTHERN LOUISIANA...
...SUMMARY...
Strong/locally severe storms remain possible ahead of a
weak/advancing cold front -- potentially most numerous over parts of
the Tennessee and Lower Mississippi Valleys and vicinity.
...Discussion...
Aside from minor line adjustments to reflect ongoing and anticipated
convective evolution, changes appear unnecessary at this time as
prior reasoning continues to reflect current expectations for
evolution of severe-weather potential this afternoon and evening.
..Goss.. 09/06/2023
.PREV DISCUSSION... /ISSUED 1115 AM CDT Wed Sep 06 2023/
...Synopsis...
Amplified, but weak, mid-level troughing lingers offshore of the
Atlantic Seaboard, with a modest cyclone, slowly migrating
northeastward to the south of Nova Scotia, the most prominent
embedded perturbation. Upstream, models indicate that mid-level
troughing may also begin to amplify across and east of the
Mississippi Valley, downstream of building short wave ridging to the
north of a prominent subtropical high centered over southeastern New
Mexico.
The amplifying trough will include one generally weakening short
wave impulse progressing across the Great Lakes region today through
tonight, while an additional couple of perturbations dig within
northwesterly flow southeast of the Black Hills vicinity through the
Ozark Plateau/lower Mississippi Valley. Stronger wind fields are
becoming largely confined to the northwesterly regime upstream of
the evolving larger-scale mid-level trough axis, though a remnant
belt of modest southwesterly flow (including 30+ kt in the 850-700
mb layer) downstream of the trough axis is forecast to nose
northeast of lower Michigan through Ontario by mid/late afternoon.
The latter speed maximum will accompany a weakening migratory low
within weak surface troughing, along a cold front forecast to slowly
advance eastward across the upper Great Lakes region, Ontario and
central Quebec. An initial cold frontal surge already has reached
the lower Ohio Valley, Ozark Plateau and Texas South Plains
vicinity. Across parts of western Kentucky and Tennessee into
northeastern Arkansas, the front is preceded by a remnant MCV and
convective outflow associated with a dissipating cluster of
thunderstorms.
...Great Lakes through southern Great Plains...
While deep-layer mean wind fields and vertical shear have generally
weakened ahead/south of the cold front, modestly steep lapse rates
in lower through mid-levels, coupled with residual boundary-layer
moisture, may contribute to areas of sizable mixed-layer CAPE in
excess of 2000 J/kg by late afternoon. From the Tennessee Valley
into the Great Lakes region, this may be more sparse in nature due
to early day cloud cover and weak low-level focus for convective
development. However, it seems probable that a more prominent zone
of differential surface heating, across parts of central Arkansas
into western Tennessee, will become a focus for at least scattered
strong thunderstorm development by late this afternoon.
Given thermodynamic profiles characterized by large CAPE and a very
warm well-mixed boundary layer, various guidance has been suggestive
that an upscale growing cluster could eventually evolve along
consolidating, south/southwestward propagating cold pools into this
evening. If this occurs, a hail/downburst threat in stronger
initial storms may transition to a more widespread marginal severe
wind threat.
Other more widely scattered strong thunderstorm development is
possible west-southwestward into a hotter, drier and more deeply
mixed boundary layer across parts of west central Texas.
Read more
