137
ACUS01 KWNS 041938
SWODY1
SPC AC 041936

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0236 PM CDT Thu Jul 04 2024

Valid 042000Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MISSISSIPPI VALLEY...AND FROM THE SOUTHERN PLAINS TO THE OHIO
VALLEY...

...SUMMARY...
Scattered severe thunderstorms will be possible through this evening
across parts of the upper Mississippi Valley, and from the southern
Plains to the lower Ohio Valley.

...20z Update...

Severe probabilities have been trimmed across parts of MN/IA in-line
with the current location of the surface cold front. Otherwise, only
minor changes have been made to the 10 percent general thunderstorm
line. Overall forecast thinking remains similar to the previous
outlook. However, coverage of severe storms across parts of southern
IL into the Ohio Valley (outside of WW 505) is uncertain the
remainder of the period. However, a very moist and unstable airmass
resides across the area. Additional storms may develop this
evening/overnight along the surface front, and any other storms that
can develop through evening would pose severe gust potential,
precluding a downgrade in probabilities at this time.

For information on short term severe potential across the Upper MS
Valley and the southern Plains, reference MCDS 1534 and 1535.

..Leitman.. 07/04/2024

.PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Jul 04 2024/

...Synopsis...
An upper trough over the northern/central Plains will move generally
eastward today across the Upper Midwest and mid MS Valley. A
separate, convectively augmented mid-level vorticity maximum is
present over southern IA/northern MO late this morning. This MCV and
associated convection across the OH Valley will move
east-northeastward across the OH Valley/Midwest through this
evening. At the surface, a weak low should develop eastward across
parts of the Upper Midwest in tandem with the large-scale upper
trough. Another weak surface low should also track northeastward
over the OH Valley with the remnant MCV. A convectively reinforced
front draped from the southern Plains northeastward into the mid MS
and OH Valleys will likely serve as a focus for strong to severe
thunderstorms this afternoon and evening.

...Mid Mississippi Valley into the Ohio Valley and Mid-Atlantic...
Mostly elevated thunderstorms are ongoing late this morning across
the lower OH Valley. The rather moist low-level airmass along/south
of a front will continue to gradually destabilize through the
afternoon. Although mid-level lapse rates will remain poor, moderate
instability has already developed downstream of activity moving
across southern IN and western KY. Additional intensification of
this convection will probably occur through early afternoon across
parts of central/eastern KY and perhaps southern OH ahead of the
MCV. Even though stronger mid-level flow may tend to remain
displaced to the north of the front, modest but sufficient
deep-layer shear should be present to support multicell clustering.
Scattered damaging winds occasionally reaching severe thresholds
should be the main threat with this activity as it spreads eastward
across the lower OH Valley this afternoon and evening. Low-level
flow is forecast to remain generally modest and veered to
southwesterly. Still, sufficient speed shear will be present to
support some threat for updraft rotation and perhaps a tornado or
two, especially if any supercells can develop and persist. Isolated
hail may also occur with more robust cores. Confidence in strong
convection moving off the Blue Ridge Mountains in the Mid-Atlantic
is relatively low. But, any thunderstorms that do form across this
region could produce locally damaging winds.

...Southern Plains to the Ozarks...
The portion of the cold front extending across the southern Plains
into the Ozarks is forecast to make only slow southward progress
through this evening. Even with some mid/high-level clouds
persisting across these areas, robust daytime heating along/south of
the front will likely encourage surface temperatures to warm into
the 90s and low 100s. Even though low/mid-level flow will remain
fairly weak, rather large surface temperature/dewpoint spreads (up
to 30-40 degrees F) and steepened low-level lapse rates should
foster a threat for mainly severe/damaging winds with any
thunderstorms that can develop this afternoon and evening. Robust
convection appears probable along/near the front by 22-00Z, and
there appears to be some potential for an organized cluster to
develop over the Ozarks/southern MO vicinity and sweep
east-southeastward through the late evening.

...Upper Mississippi Valley...
A focused area of ascent associated with the upper trough will
overspread southern MN and northern IA today. While cloud cover
remains prevalent over much of this region late this morning, there
has been some recent clearing on the western edge of the cloud deck.
A relatively small area of modest destabilization is still
anticipated, with MLCAPE around 1000-1500 J/kg possible. A 45-60 kt
mid-level jet attendant to the upper trough will overspread the
developing warm sector through the afternoon. This jet will aid
sufficiently strong deep-layer shear to support supercells with an
associated threat for severe hail. Some clustering/upscale growth
may eventually occur, which would support a greater threat for
severe/damaging winds. This activity should weaken by late evening
into WI and northern IL as it encounters a less unstable airmass.

$$