SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0732 AM CDT Fri Mar 29 2024
Valid 291300Z - 301200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE MIDWEST TONIGHT...
...SUMMARY...
Marginally severe hail is possible over portions of the Midwest
tonight.
...Synopsis...
The mid/upper-level pattern will feature strong, progressive troughs
-- each with an accompanying synoptic-scale cyclone -- near the East
and West Coasts, and low-amplitude, large-scale ridging in between.
The western low -- quite prominent in moisture-channel imagery now
west of Cape Mendocino -- should move southeastward and stay
offshore from CA through the period. However, downstream southwest
flow and several embedded vorticity lobes/shortwaves will move over
the Intermountain West. Portions of the central and northern
Rockies, as well as the Pacific Coast, should reside beneath enough
midlevel cooling/instability and low/middle-level moisture to
support isolated thunderstorms. Downstream, a leading shortwave
trough is evident from southern SK across eastern MT to central WY.
This feature should move eastward across the northern Plains today,
reaching the eastern Dakotas by 00Z, and crossing the upper
Mississippi Valley around 12Z tomorrow.
At the surface, 11Z analysis showed a frontal-wave low near HLC,
with short cold front southwestward over western KS, and warm front
across northern MO, south-central IL, to near CVG, and northern WV.
Another low was apparent over southeastern SK, with a trough
connecting these lows across the western Dakotas and central NE.
By 00Z, the southern low should reach southwestern/central IA, with
cold front southwestward over southwestern KS, and warm front across
central IL to southern IN. A trough -- with some reinforcement
related to the mid/upper perturbation -- still should extend from
that low to the northern one, by then near the southern SK/MB line.
By 12Z, the southern low should approach the southwestern shore of
Lake Michigan (near the IL/WI line), with cold front to northern MO,
northern OK and the TX Panhandle. The warm front should extend from
the low across southwestern Lower MI to western/southern OH.
...Midwest...
During the day, the central Plains to Midwest should remain capped
for substantial, surface-based convection, the result of a
combination of advection of EML air aloft from higher terrain in the
West, with insufficient moisture and lift. However, with continued
moist/warm advection in the increasing LLJ, and the approach of
large-scale DCVA/lift aloft related to the mid/upper trough,
convective potential will increase this evening north of the warm
front over parts of IA/IL. Isentropic lift to LFC will occur as
parcels saturate in the 700-850-mb layer and MUCINH erodes rather
quickly. Resulting elevated thunderstorms should shift eastward
into southern WI and central/northern IL, then late overnight, the
Michiana/northwest OH area.
Greatest inflow-layer buoyancy and hail potential should be with
relatively discrete cells in the early stage of the convective
process across IA/IL, then mainly the southern part of the
thunderstorm area as it crosses IL. Expect MUCAPE of around 500-700
J/kg developing from southern IA to central IL, decreasing to under
300 J/kg over much of southern WI. In forecast soundings,
effective-shear magnitudes vary a lot with CAPE depth, but generally
should be in a 30-40 kt range to support some thunderstorm
organization. Locally strong gusts cannot be ruled out either,
given a relatively dry subcloud layer present in forecast soundings,
and potential for downdraft winds to penetrate a relatively shallow,
near-surface stable layer. However, severe-gust potential still
appears too uncertain and unfocused for a wind area to be added at
this time.
..Edwards/Leitman.. 03/29/2024
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