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    Day 2 Outlook >
May 24, 2024 1300 UTC Day 1 Convective Outlook
Updated: Fri May 24 12:55:06 UTC 2024 (Print Version | 20240524 1300Z Day 1 shapefile | 20240524 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 241255

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Fri May 24 2024

   Valid 241300Z - 251200Z


   Enhanced threat corridors exist for severe thunderstorm gusts this
   morning from eastern Iowa over northern Illinois, and hail (some
   very large) this afternoon and evening from eastern Oklahoma to
   north Texas.

   In mid/upper levels, a progressive shortwave train should continue
   within a belt of mostly westerly flow aloft over the CONUS.  The
   strongest of these shortwave troughs is evident in moisture-channel
   imagery over the northern Great Plains, with an embedded 500-mb low
   over northwestern SD.  The low should follow a cyclonically curving,
   net northeastward path to the northeastern corner of ND by 00Z, with
   trough roughly southward along the western border of MN then over
   eastern NE.  By 12Z tomorrow, the CONUS part of the trough should
   arc from western Lake Superior across eastern WI and northern IL. 
   Over the Southeast, a broad area of difluent mid/upper flow is
   expected, with numerous embedded vorticity lobes (some convectively
   generated or enhanced).  Fairly unperturbed west-southwesterly flow
   is expected from the Arklatex region across the southern Plains and
   Desert Southwest, downstream from a trough off coastal CA. 

   The surface analysis at 11Z showed a low over southeastern ND, with
   occluded/cold front arching across southwestern MN, western IA,
   east-central KS, west-central OK, TX between PVW-LBB, and
   northeastern NM.  A warm front was drawn from the leading edge of a
   severe MCS over eastern IA, southeastward across central IL.  The
   low should occlude and shift northward over southeastern MB through
   the period.  By 00Z, the frontal triple point should reach southern
   WI, with cold front across western IL, southwestern MO, southeastern
   OK and north-central to west-central TX, becoming a warm front over
   east-central/northeastern NM.  The warm front will move
   northeastward to southern WI and southwestern Lower MI, though its
   definition may be compromised by the effects of MCS activity.  A
   dryline was apparent from its frontal intersection over northwest TX
   south-southwestward to the Big Bend region.  This boundary will mix
   eastward today while the front overtakes it from the north, and
   should reach the eastern Edwards Plateau/western Hill Country by
   late afternoon. 

   ...Southern Plains to Mid-South...
   Scattered thunderstorms -- including supercells -- are expected to
   develop near the front this afternoon, to the east and northeast of
   the dryline.  Dryline storm-initiation potential is more conditional
   and isolated.  Once development occurs, updraft growth and storm
   evolution may occur very rapidly, given the strong surface heating,
   abundant moisture (70s F dewpoints common), steep deep-layer lapse
   rates and intense buoyancy (4000-5000 J/kg MLCAPE) that should

   Low-level flow and hodograph size will be modest, amidst a lack of
   substantial mid/upper-level perturbations to force greater mass
   response.  However, ambient mid/upper winds will be strong enough to
   support supercells (left- and right-moving), with effective-shear
   values near 50 kt.  Large to very large hail should be common in the
   first few hours after initiation, and locally severe gusts are
   expected as well.  Airmass recovery is possible into southeastern
   and east-central OK in the zone of warm/moist advection ahead of the
   front, and behind last night's southeastern OK activity.  A
   relatively dense and enhanced concentration of hail potential from
   eastern OK into north-central TX is expected, with hailstones
   greater than 2 inches in diameter likely, and some hail perhaps
   exceeding 3 inches.  Otherwise, deep, precip-loaded downdrafts will
   provide most of the wind potential early, with some upscale
   clustering and cold-pool aggregation possible to maintain damaging-
   wind potential into late evening, before activity generally weakens.

   Enhanced potential for severe gusts, along with a risk of a few
   brief/embedded tornadoes, may persist for a few more hours with an
   ongoing complex of thunderstorms crossing portions of eastern IA and
   northern MO, as this activity moves into IL and perhaps southern WI.
   A well-developed rear-inflow jet of 60-80 kt has been sampled by DMX
   radar VAD wind profiles.  The northern part of the complex is
   expected to weaken as it penetrates deeper into the cool sector
   (north of the warm front), while the middle part may persist for
   several hours near the front and across IL. See SPC Severe
   Thunderstorm Watch 300-301 and related mesoscale discussions for
   near-term details. 

   The outflow boundary from this complex was analyzed ahead of the
   cold front across parts of northwestern MO into northeastern KS, and
   should be laid down through the remainder of the morning across the
   rest of northern MO and parts of northern IL.  Given the deep and
   well-organized nature of its cold pool, severe probabilities may be
   more associated with the present activity.  Later development
   becomes more doubtful with northward extent from the boundary, which
   may retreat somewhat northward into southeastern IA and toward the
   WI/IL line later this afternoon, prior to frontal passage. 
   Probabilities mainly reflect the ongoing hazard, however, given
   great uncertainties regarding airmass recovery behind it.

   Farther southwest along/ahead of the front, widely scattered to
   scattered afternoon thunderstorms are possible, offering damaging
   gusts and large hail, as well as marginal tornado potential.  A
   substantial uncertainty regarding airmass recovery also is present
   in this regime, because of trajectories emanating from a pronounced
   theta-e deficit in AR and eastern OK produced by prior overnight
   convection.  A narrow corridor of sufficient boundary-layer moisture
   to support 2500-3500 J/kg MLCAPE may develop just ahead of the
   front.  Some relative flow weaknesses progged in parts of the
   mid/upper troposphere may render somewhat messy storm structures
   after early supercell mode.  Still, any storm(s) interacting with
   the outflow boundary will have locally greater potential for
   supercell longevity, and some risk for large to significant hail and
   a tornado.

   ..Edwards/Goss.. 05/24/2024



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