ACUS02 KWNS 150601
SWODY2
SPC AC 150559

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Mon Apr 15 2024

Valid 161200Z - 171200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN PARTS OF
SOUTHERN IA...NORTHERN MO...AND WEST-CENTRAL IL...

...SUMMARY...
Scattered severe thunderstorms are likely from Tuesday morning into
the evening across a portion of the central states from the Corn
Belt to the Ozark Plateau. The most concentrated area of significant
severe hail and tornado potential is forecast over southern Iowa
into northern Missouri and west-central Illinois.

...Synopsis...
A seasonably deep surface cyclone should be located over central NE
at 12Z Tuesday. This cyclone should gradually progress eastward and
slowly weaken in IA Tuesday night. An initially intense mid-level
jetlet (in excess of 80 kts) should become centered from the Ozark
Plateau into the Mid-MS Valley by afternoon, before pronounced
dampening occurs as it shifts east across the Mid-South to Lower OH
Valleys. The initially north/south-oriented dryline/Pacific cold
front to the south of the surface cyclone will progress into the
Mid-MS Valley by 12Z Wednesday, with its trailing portion stalling
by late afternoon before reaching the Ark-La-Tex.

...Corn Belt/Lower MO and Mid-MS Valleys...
A broad spectrum of potential outcomes is evident ranging from
mainly a large hail and few tornadoes day to a more substantial
tornadic threat. The degree of tornado threat will be dependent on
multiple uncertainties becoming more resolved, with the hail
forecast the more confident of the three hazards.

Within the left-exit region of the aforementioned mid-level jet, a
synoptically favorable corridor for mid-afternoon to early evening
supercells is evident. Evening guidance varies in the degree of
warm-conveyor convection that should be ongoing and how it evolves
through midday, with the 00Z HRRR notably more aggressive. This
early-day activity will have impacts on the degree of boundary-layer destabilization ahead of the dryline/cold front. At the other end of
the spectrum, the 00Z NAM and NAM-NEST suggest a more substantial
gap will occur between the warm conveyor activity and afternoon
redevelopment along the dryline/front. Other guidance is somewhere
in between these two scenarios, and even the HRRR does indicate
isolated redevelopment occurring by late afternoon.

Confidence is high that pronounced boundary-layer heating will occur
behind the surface front and a plume of steep mid-level lapse rates
attendant to the shortwave trough will overspread the northwest
portion of the surface warm/moist sector during the afternoon.
Backed low-level flow and veering of the wind profile with height
should support supercells capable of producing significant severe
hail and tornadoes. The NAM has been consistently farther west with
the placement of the front by late afternoon with most guidance
mixing the boundary more aggressively east in IA/MO.

...Mid-South...
NCEP guidance is highly insistent that convective coverage should be
isolated at best and is substantially less than indicated by the
ECMWF. This appears to be related to a lack of more pronounced
boundary-layer heating, but also due to fairly warm and very dry
mid-level profiles to the south side of the intense but eventually
weakening mid-level jet. With the surface front stalling or even
advancing back west late, large-scale ascent appears to be weak
outside of low-level warm theta-e advection. As such, have begun
reducing probabilities from south to north. Still, the deep-layer
shear profile and rich boundary-layer moisture will conditionally
support supercell potential during the period.

..Grams.. 04/15/2024

$$
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ACUS02 KWNS 061730
SWODY2
SPC AC 061728

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 PM CDT Mon May 06 2024

Valid 071200Z - 081200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
INDIANA INTO NORTHWEST AND CENTRAL OHIO...

...SUMMARY...
Scattered severe thunderstorms will be possible Tuesday from the
Mid-South northeastward into the Ohio Valley. A few tornadoes, large
to very large hail, and severe/damaging winds all appear possible,
particularly from northeast Indiana into northwest and central Ohio.

...Synopsis...
A mid/upper cyclone is forecast to remain largely in place over the
western Dakotas while continuing to occlude. A convectively
augmented shortwave trough will likely move through the base of this
cyclone, progressing from the Mid MS Valley quickly northeastward
into the Upper Midwest and Upper Great Lakes during the day. Primary
surface low will occlude beneath the parent cyclone, but a secondary
low will likely develop at the triple point, moving from the MN/IA
border vicinity east-northeastward across central/southern MN into
Lower MI. The cold front extending southward from this secondary low
is forecast to push eastward across the Mid MS and OH Valleys, while
the warm front shifts northeastward into Lower MI and the Upper OH
Valley.

...Mid-South/Mid Mississippi Valley into the Ohio Valley...
A decaying convective line will likely extend from southern WI
through western IL and into western portions of the Mid-South early
Tuesday morning. Buoyancy will be modest ahead of this line, which
will likely limit the severe potential. Even so, there is still a low-probability chance for a few instances of hail and/or damaging
gusts, particularly along the southern end of the convective line in
the Mid-South vicinity where buoyancy is greatest.

The convective line is expected to make quick northeastward
progress, clearing the through the Lower OH Valley by the late
morning and much of the Middle OH Valley by the early afternoon. The
air mass is expected to recover quickly in its wake, with mid to
upper 60s dewpoints advecting in from the southwest. Additional
thunderstorm development is expected around 17-18Z across IL,
supported by both warm-air advection and increasing large-scale
ascent attendant to the approaching shortwave trough. This initial
activity will likely be elevated, but shear is strong enough to
support some more organized structures capable of hail. As the
downstream airmass across OH and IN destabilizes, these initial
storms will likely trend towards becoming more surface-based. Given
the strong vertical shear in place, the potential for supercells
will increase as storms become surface based. All severe hazards
will be possible with these supercells, including large hail and
tornadoes. The tornado threat is expected to maximize from northeast
IN into western and central OH during the late afternoon/early
evening, where the proximity to the warm front will contribute to
better low-level shear.

...Upper Midwest...
Despite relatively cool surface temperatures, cooling mid-levels
coupled with modest low-level moisture are expected to result in
airmass destabilization and modest buoyancy ahead of the triple
point and associated surface boundaries. Thunderstorm development is anticipated both near the triple point, as well as along and
north/northeast of the occluded front. Much of the activity in the
vicinity of the occluded front will likely be elevated, but a few
stronger updrafts capable of hail are still possible. More
surface-based storms are possible near the triple point across
southern WI. Here, isolated hail and gusty winds may occur with the
more robust cores, and a brief tornado or two also appears possible.

...Mid-Atlantic...
Isolated to perhaps widely scattered thunderstorms may develop
Tuesday afternoon across parts of VA/NC, generally along/east of a
weak surface lee trough. Sufficient forecast instability and shear
should be present to support some threat for hail and strong winds
with any thunderstorms that form. The overall severe threat is
expected to remain fairly isolated/marginal.

...Lower Mississippi Valley/Deep South...
This region will be displaced south of the stronger forcing for
ascent, but moderate buoyancy and vertical shear still suggest there
is isolated severe potential with any storms that do form. Current
guidance suggests the greatest probability of storms exists across
MS and AL where the low-level moisture convergence is greatest.

...Central Texas...
The severe thunderstorm threat remains highly conditional across
parts of central TX Tuesday afternoon along/near a low-level
moisture gradient/sharpening dryline. Large-scale ascent will be
negligible, with thunderstorm initiation relying on surface
convergence. If any thunderstorms can form and persist, they
could become severe given a strongly unstable airmass. This scenario
remain too uncertain to add low severe probabilities with this
outlook.

..Mosier.. 05/06/2024

$$
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