SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1234 PM CDT Mon Jul 29 2024
Valid 301200Z - 311200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MIDDLE MISSISSIPPI VALLEY AS WELL AS ACROSS THE CENTRAL
DAKOTAS...
...SUMMARY...
Scattered strong to severe storms will be possible across a broad
region from the northern Plains to the Midwest, Ohio Valley, and
Carolinas. A more concentrated severe threat is possible across
portions of the Middle Mississippi Valley as well as across the
central Dakotas.
...Synopsis...
Upper ridging is forecast to remain centered over the southern
Plains on Tuesday, with moderate westerly flow aloft extended
throughout much of the northern third of the CONUS. Several
shortwave troughs will be embedded within these westerlies, the
strongest of which is expected to be the shortwave progressing
across the northern Rockies and into the northern High Plains.
Another shortwave trough is expected to begin the period in the MN
vicinity, before progressing east-southeastward through WI and the
Mid MS Valley into Upper Great Lakes and lower/middle OH Valley. Yet
another shortwave trough is forecast to track slowly northeastward
across the upper OH Valley.
At the surface, a broad area of low pressure is expected to remain
over the Plains, with a moist airmass covering the central and
eastern CONUS to its east. The surface pattern will likely be free
of notable synoptic features, although a weak frontal zone,
demarcated predominantly by a wind shift, may extend from a weak low
near the northern IN/OH border southwestward into southern IL and
then back northwestward with a more warm-front-like character
through IA to another low in the SD/IA/MN border intersection
vicinity. Sharpening and/or progression of these boundaries will
depend largely on convective evolution of antecedent showers and
thunderstorms, leading to low forecast confidence. Two, potentially
three, convective clusters could be ongoing early Tuesday, including
one in the northern/central IA vicinity, which could then progress
into a very moist and buoyant airmass downstream while also
interacting with the warm front.
...Mid MS Valley into the Lower OH and TN Valleys...
As mentioned in the synopsis, thunderstorms will likely be ongoing
over the region Tuesday morning, likely in the northern/central IA
vicinity. Guidance varies on how these storms evolve, with much of
the CAM guidance suggesting the early storms weaken before then
restrengthening during the afternoon as the strongly buoyant airmass
downstream destabilizes. MLCAPE over 3000 J/kg is possible across
the Lower OH Valley, supporting very strong updrafts capable of
producing large hail. Shear will be modest, with most storms likely
remaining multicellular and outflow dominant. Damaging gusts will be
the primary risk with these storms. A supercell or two is still
possible, with low potential for a tornado along the warm front.
Another solution, which is offered by the NAM and ECMWF, suggests
these storms have organized into a linear MCS, which then continues
quickly southeastward, supported by the organized character of the
line and ample downstream moisture and buoyancy. Damaging gusts
would be the primary risk in this scenario, with a low-probability
tornado risk as well. Significant wind gusts over 65 kt would be
possible with the MCS solution, but forecast confidence is too low
to introduce an area with this outlook.
Additionally, overnight development is possible across IA amid
warm-air advection supported by a moderate low-level jet. Given the
uncertainty regarding the convection evolution throughout the day,
the thermodynamic environment that will be in place Tuesday night is
difficult to ascertain. There is some potential for preceding storms
to be far enough east and/or south that strong to severe storms can
be supported across IA overnight.
...Northern Plains...
Weak height falls amid moderate to strong instability may lead to
some thunderstorm development along a surface trough/dryline across
the Dakotas Tuesday afternoon. The shortwave trough will remain west
of the region, displacing the stronger mid-level flow to the west.
Even so, moderate westerlies atop southeasterly surface wind should
support moderate deep-layer vertical shear around 30 to 35 kt from
0-6 km. Strong buoyancy will likely be in place, with the resulting
combination of shear and buoyancy supporting a few organized storms
capable of both large hail and damaging gusts. A trend towards a
more outflow-dominant character is anticipated with eastern extent,
with damaging gusts becoming the most likely severe threat.
...Central Appalachians to the Carolinas...
Showers and thunderstorms will likely be ongoing from WV into
eastern TN early Tuesday morning. This storms (and associated
outflow) should progress southeastward throughout the day, with
additional development anticipated downstream across the western
Carolinas (and potential northern GA) as the airmass destabilizes.
Outflow-dominant storms could result in a few damaging gusts.
..Mosier.. 07/29/2024
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