ACUS01 KWNS 291233
SWODY1
SPC AC 291232

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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ACUS01 KWNS 301251
SWODY1
SPC AC 301249

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Sat Mar 30 2024

Valid 301300Z - 311200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
EASTERN INDIANA TO PARTS OF WEST VIRGINIA AND SOUTHWESTERN
PENNSYLVANIA...

...SUMMARY...
Isolated severe hail and/or damaging gusts may occur across parts of
the Ohio Valley into West Virginia this afternoon/evening.

...Synopsis...
The mid/upper-level pattern over the western CONUS will remain
dominated by troughing related to a synoptic-scale cyclone --
centered initially off the CA coast about 150 nm west of SFO. The
cyclone will dig southeastward through the period, with its center
remaining just offshore, but elongating northeastward as several
vorticity lobes pivot into the northeastern quadrant of the gyre.
Meanwhile, a northern-stream trough now over southern Yukon and
northern BC will dig southward to the inland Pacific Northwest.
This will cause a phasing of northern and southern streams into a
more full-latitude, positively tilted trough by the end of this
period and early day 2, from the northern Rockies across southern
CA, to Pacific waters well west of northern Baja. Associated cold
air aloft and marginal (but adequate) low/middle-level moisture will
support isolated thunderstorm potential over much of CA and
northern/western NV.

Downstream, southwest flow aloft will spread across most of the
Intermountain West and Rockies, with several embedded/low-amplitude perturbations -- one of which may contribute enough instability
aloft to support isolated thunder over the central High Plains.
East of the Rockies, largely zonal mid/upper flow is forecast, with
the most convectively consequential perturbation now evident in moisture-channel imagery over portions of Lower MI, Lake Michigan,
IL, and IN. This feature is somewhat elongated in the flow, with
western and eastern components -- a general geometry that should be
maintained as it shifts eastward to the northern Mid-Atlantic region
through this evening.

Surface analysis at 11Z revealed a frontal-wave low over
northwestern IL, with cold front southwestward over western OK and
the TX Panhandle. A warm front was drawn east-southeastward from
the low near an IND-CVG-HTS line, to a weak low between LYH-CHO.
Though initially slowed somewhat by outflow from morning/midday
precip over the Ohio Valley region, the warm front should advance
northeastward into parts of OH and western PA today, as the main low
moves eastward to eastern OH by 00Z. At that time, the cold front
should extend from the low over southern parts of IN/IL/MO, to what
by then should be a stationary to warm front across northern OK into southeastern CO.

...Ohio Valley and WV...
An ongoing area of precip and isolated, embedded, non-severe
thunderstorms is apparent in radar animations from WI southeastward
to OH, in the combined zones of large-scale ascent related to warm
advection and DCVA (preceding the mid/upper perturbation). This
activity and its cloud shield are expected to proceed eastward
through the central/northern Appalachians and Mid-Atlantic today.
Favorable boundary-layer destabilization is most probable behind
that activity, as the western lobe of the mid/upper perturbation
approaches and passes over the area.

Clearing, insolation, theta-e advection, and mass convergence near
the cold front/low should overcome remaining MLCINH by mid/late
afternoon, supporting widely scattered thunderstorms. Activity
should move eastward to southeastward, offering isolated severe hail
and damaging gusts. Though low-level moisture still will be on the
weak side, and tempered somewhat by boundary-layer mixing, surface
dewpoints should reach the mid 40s to low 50s F by that time,
combining with steep low/middle-level lapse rates to enable 500-1500
J/kg MLCAPE. The well-mixed boundary layer will support strong to
marginally severe downdrafts with the most intense cells. Also, and
despite somewhat veered/southwesterly surface winds, low-level and
deep shear still will support some supercell potential with large
hail. Forecast soundings reasonably depict 45-55-kt effective-shear
magnitudes over the region. Activity should weaken east of the
higher terrain this evening, as it moves over a progressively
deeper, more-stable boundary layer.

..Edwards/Leitman.. 03/30/2024

$$

= = =
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