SPC AC 061602

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1102 AM CDT Mon May 06 2024

   Valid 061630Z - 071200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS FROM CENTRAL AND
   NORTHERN OKLAHOMA INTO SOUTH-CENTRAL KANSAS...

   ...SUMMARY...
   A regional outbreak of severe weather with multiple intense (EF3+),
   long-tracked tornadoes, as well as very large hail and severe
   thunderstorm gusts, is expected over parts of the south-central
   Plains from this afternoon through evening.

   ...NE/KS/OK to north TX...
   Water-vapor imagery late this morning shows a potent mid- to
   upper-level trough/low over the central Rockies with a speed max
   moving through the base of the trough and into the southern and
   central High Plains.  This negatively tilted mid level trough will
   continue northeast to near the Black Hills by this evening while its
   southern portion overspreads the KS/OK corridor.  The 12z Amarillo,
   TX raob showed the leading edge of stronger 700-600 mb southwesterly
   flow nosing eastward into the High Plains.  A cyclone near the NE
   Panhandle this morning will deepen as it moves north-northeast to
   the SD/ND border early Tuesday morning.  An associated Pacific front
   will push east into the High Plains and overtake the northern
   portion of the dryline across parts of the central High Plains this
   afternoon into this evening.  Farther south, a dryline will mix east
   into western OK by late this afternoon with a broad moist/unstable
   warm sector across the southern Great Plains and becoming
   increasingly pinched in spatial width farther north into the
   north-central Great Plains.  An attendant warm front will advance
   northward from OK into the lower MO Valley by early evening and
   later into the mid MS Valley.  

   Visible satellite imagery shows considerable low stratus and
   stratocumulus from north TX into the central Great Plains.  The 12z
   Fort Worth, TX raob sampled the richer low-level moisture (15 g/kg
   lowest 100mb mean mixing ratio) compared to areas farther north. 
   Surface analysis late this morning shows rapid northward transport
   of moisture into OK with 65-70 deg F dewpoints advecting northward
   through OK to the KS border.  This plume of richer moisture will
   continue northward today beneath an EML and lead to moderate
   destabilization over NE with a very to extremely unstable airmass
   forecast to develop farther south over the southern half of KS into
   OK and adjacent north TX.  

   Initial thunderstorm development is likely as the upper forcing
   impinges on the northwestern periphery of the moist/unstable sector
   across the central High Plains (western KS/NE) and northward into SD
   with time.  Steep 700-500 mb lapse rates and strengthening flow
   becoming more meridional with time will favor organized storms,
   including supercells and bands of storms with an associated isolated
   to scattered risk for hail/wind and perhaps a few tornadoes. 
   Farther south, the erosion of the cap is expected initially over the
   KS portion of the dryline and perhaps into northwest OK by the mid
   afternoon.  Strengthening flow through the column combined with
   strong to extreme buoyancy (2500-4500 J/kg MLCAPE) --from I-70 in
   central KS to I-40 in central OK-- will strongly favor supercell
   development.  Strong upper-level diffluence across the central Great
   Plains and intensifying southwesterly to westerly 250-mb flow, which
   will result in very long hodographs, will strongly favor discrete
   storm modes, at least initially.  Large to giant hail (3-4 inches in
   diameter) is possible with the more robust supercells.  The LLJ is
   forecast to be strongest over KS northward into the north-central
   Plains through 21z.  During the 21-00z timeframe, the flow
   associated with the LLJ will strengthen over OK acting to enlarge
   hodographs.  Climatologically large combinations of deep-layer
   shear, buoyancy, and SRH will result in extreme values of composite
   indices (STP 6-12) during the 22z-06z timeframe across the Moderate
   to High Risks.  Several discrete supercells are expected to traverse
   across a large portion of the Moderate and High-Risk equivalent
   tornado probabilities.  Tornadoes, some of which can be intense
   (EF3+), are forecast late this afternoon and well into the evening. 
   Some model guidance shows regenerative supercell development across
   central OK this evening.  Have extended the High Risk slightly
   farther south to account for this possibility.  

   ...Lower MO Valley/Ozarks/mid MS Valley late...
   As greater storm coverage and merging occurs this evening across KS
   into northern OK, large-scale ascent will further promote upscale
   growth into a severe squall line across eastern KS and moving into
   the lower MO Valley and western part of the Ozarks.  Have upgraded
   severe-wind probabilities and this resulted in a slight spatial
   extension of the Moderate Risk to the east across southeast
   KS/northeast OK.  A severe risk will probably continue east to the
   MS River overnight with an attendant wind risk and perhaps an
   isolated risk for a tornado.  

   ...Northern Plains...
   No appreciable change from previous forecast thinking for severe
   potential across the northern Plains.  A prefrontal corridor of
   favorable moisture and diurnal destabilization will become quite
   narrow with north and northwestward extent.  Nonetheless, it should
   support scattered thunderstorms in northward-shifting plume, curving
   from the western Dakotas (and perhaps parts of extreme northeastern
   WY and southeastern MT) southeastward to central NE, and connecting
   to the northern part of the central Plains severe threat.  With
   strong large-scale lift, cooling aloft, rapidly weakening MLCINH,
   and robust low-level mass response/shear expected ahead of the
   ejecting shortwave trough, confidence is growing that an arc of
   strong-severe thunderstorms will develop, offering large hail,
   severe gusts and at least marginal tornado potential.  Even with 50s
   to low 60s F surface dewpoints and limited time for substantial
   diabatic heating, the net steepening of low/middle level lapse rates
   should support peak MLCAPE near or slightly above 1000 J/kg.  Deep
   shear may not be particularly intense in a regime of strongly
   difluent flow aloft, but still should be adequate for supercell
   potential given large lowest-km hodographs possible, and effective
   SRH in the 150-300 J/kg range.  Severe potential should diminish
   after about 00Z.

   ...West-central/southwest TX...
   Model guidance continues to indicate isolated thunderstorms are
   possible in mid/late afternoon along/ ahead of the dryline over
   northwest to southwest TX.  Although large-scale/mid-upper forcing
   will be negligible (displaced to the north), any pockets of
   relatively persistent/maximized low-level lift may aid in local
   erosion of the cap and convective initiation.  Mid/upper 60s to low
   70s F surface dewpoints and steep low/middle-level lapse rates will
   contribute to 3000-4000 J/kg MLCAPE amidst enough deep shear for
   supercells.  A conditional significant-hail and marginal tornado
   threat exists with sustained supercell(s) -- if any can form. 
   Coverage concerns preclude more than marginal categorical outlook at
   this time.

   ...Mid South/TN Valley into the southern Appalachians...
   A mid-level shortwave trough over TN this morning will continue to
   move east into the southern Appalachians today.  An enhanced belt of
   westerly mid-level flow accompanying this impulse will overspread
   this general region.  In wake of decaying morning convection over
   the southern Appalachians, ample heating of a moist boundary layer
   will result in moderate destabilization by early-mid afternoon. 
   Storm redevelopment is forecast this afternoon along and north of a
   trailing/diffuse convective boundary over the TN Valley.  Scattered
   thunderstorms will probably develop by early to mid afternoon. 
   Effective shear magnitudes 25-30 kt will support  some organization
   in the form of clusters and perhaps transient supercells.  Marginal
   Risk equivalent severe probabilities have been added to highlight
   this isolated severe threat.

   ..Smith/Moore.. 05/06/2024

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