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    Day 2 Outlook >
Jul 20, 2024 1300 UTC Day 1 Convective Outlook
Updated: Sat Jul 20 12:52:28 UTC 2024 (Print Version | 20240720 1300Z Day 1 shapefile | 20240720 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 201252

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0752 AM CDT Sat Jul 20 2024

   Valid 201300Z - 211200Z


   Strong to isolated severe thunderstorms are possible over parts of
   the Southeast and central to southern High Plains, mainly from
   mid-afternoon to evening.

   The large-scale pattern in mid/upper levels will continue to feature
   longwave troughing over eastern North America, and ridging in the
   West.  The latter will be anchored by an anticyclone -- now centered
   over AZ -- that will retrograde slowly northwestward through the
   period.  This process -- and a broad field of minor shortwaves and
   vorticity lobes in northerly/northwesterly flow -- will contribute
   to net height falls over much of the central CONUS.  A downstream
   shortwave trough was evident in moisture-channel imagery from the
   lower Ohio Valley southwestward across western TN to eastern LA. 
   This perturbation should move eastward across the Tennessee Valley
   region through midday, then over parts of GA and the Carolinas
   through this evening.

   The 11Z surface map showed a weak, quasistationary frontal zone from
   southern VA across eastern TN, western MS, central LA, and
   south-central TX.  Except where locally reconfigured by convection,
   this frontal zone should remain quasistationary, while gradually
   losing definition.  A lee trough -- drawn from western MT to western
   SD and western KS, should remain nearly in place through the day,
   with slight shifts possible in late afternoon toward strongly heated

   Widely scattered to scattered thunderstorms should form and move
   northeastward over the area this afternoon, as large-scale lift
   ahead of the approaching trough spreads atop a richly moist,
   strongly heated, weakly capped boundary layer.  Damaging to isolated
   severe gusts are possible.  Some of the activity may aggregate into
   loosely organized clusters that maximize damage potential locally. 
   Somewhat enhanced mid/upper flow will contribute to spotty
   effective-shear magnitudes of 30-35 kt, aiding in organization of
   some of this activity.  The inflow layer will be characterized by
   surface dewpoints commonly in the low-mid 70s F and favorable lapse
   rates from surface heating beneath a deep troposphere.  As such, and
   despite the lack of large mid/upper-level lapse rates, a deeply
   buoyant preconvective profile should take shape, with peak MLCAPE in
   the 2000-3000 J/kg range over the Low Country/coastal plain, and
   1500-2500 J/kg across the Piedmont.

   ...Central/southern High Plains...
   Isolated to scattered thunderstorms are expected to develop this
   afternoon along the Front Range/Sangre de Cristo corridor from
   southeastern WY to NM, as well as over the Raton Mesa, near the lee
   trough, and along leftover outflow/differential-heating boundaries
   from prior overnight/morning convection.  Isolated severe gusts and
   hail are possible.

   This activity will be moving into a generally less-buoyant airmass
   than the previous day, thanks to extensive prior convection and
   outflow over much of the region.  Nevertheless, sufficient diurnal
   heating and residual boundary-layer moisture are expected to support
   both well-mixed subcloud layers and enough CAPE for deep convection.
   Though outflow-driven forward propagation may contribute to erratic
   storm motions locally, a general southeastward to southward
   translation is forecast, given the ambient midlevel winds. Although
   strong directional shear is expected, forecast soundings indicate
   much of this will be in the form of backing with height instead of
   veering, and with weak low/middle-level winds limiting vertical bulk
   shear.  Peak afternoon MLCAPE of 1000-1500 J/kg is possible near an
   irregularly defined moist axis extending from the eastern Panhandles
   and southwestern KS northeastward, and over eastern CO.  Buoyancy
   will diminish atop a drier, more deeply mixed layer westward toward
   the mountains.  Overall, convection should diminish in coverage and
   intensity throughout the evening.

   ..Edwards/Broyles.. 07/20/2024



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