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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