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    Day 2 Outlook >
Mar 23, 2017 1300 UTC Day 1 Convective Outlook
Updated: Thu Mar 23 12:54:35 UTC 2017 (Print Version | 20170323 1300Z Day 1 shapefile | 20170323 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 231254

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0754 AM CDT Thu Mar 23 2017

   Valid 231300Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
   CENTRAL PLAINS TO THE SOUTHERN HIGH PLAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   CENTRAL/SOUTHERN FLORIDA...

   ...SUMMARY...
   Strong to severe thunderstorms are expected from parts of the
   central and southern Plains to the mid Missouri Valley late this
   afternoon into tonight, offering hail and damaging gusts. 
   Thunderstorms with a risk for severe wind and hail are also possible
   today across parts of central and southern Florida.

   ...Synopsis...
   A progressive and somewhat highly amplified mid/upper-level pattern
   will cover the contiguous U.S. this period, as a synoptic-scale
   ridge shifts eastward across the Mississippi River Valley to the
   Great Lakes and Southeast.  In the difluent upper pattern southeast
   of that ridge, a weak shortwave trough was evident moving
   southeastward across northern FL and the northeastern Gulf. This
   feature will proceed southeastward across the rest of FL through
   tonight.  Out west, split flow will predominate around an intense
   trough now located from eastern NV to northern/central Baja.  A
   basal vorticity max -- now apparent in moisture-channel imagery over
   northern Baja -- will eject northeastward to eastern/southern NM by
   00z then wind itself into a closed 500-mb low over southeastern CO
   and southwestern KS overnight.  By 12Z, the accompanying, positively
   tilted mid/upper trough should extend from that low south-
   southwestward across the TX Panhandle and Llano Estacado to the
   Trans-Pecos and central/southern Chihuahua.

   At the surface, a diffuse cold frontal zone -- associated with a
   mid/upper trough that has departed the East Coast, will sag
   southward across the southern FL Peninsula, extending as a
   decelerating baroclinic zone over the northeastern/north-central
   Gulf.  The western limb of this frontal zone will shift or
   re-develop rapidly northeastward across the southern/central Plains
   today into a zone of warm frontogenesis over portions of NE and MO,
   as a lee cyclone deepens over eastern CO.  A lee trough was analyzed
   from a low over southeastern CO southward across eastern NM and
   blending with a dryline there.  The dryline will mix eastward across
   the CO/KS and TX/NM borders today, likely prior to severe-level
   growth of any associated convection.  The trough and dryline will be
   overtaken from the west by a Pacific cold front crossing the
   southern Rockies this evening and overnight.  By 12Z, the combined
   boundary should arch from a primary surface low over southwestern KS
   across western OK and west-central TX to the Edwards Plateau, with a
   warm to quasistationary front from the low northeastward across IA
   to WI.

   ...Central Plains, southern High Plains...
   Widely scattered high-based thunderstorms are expected to develop in
   a regime of intense/deep mixing near the dryline and move
   northeastward across the central/southern High Plains from late
   afternoon into early evening.  Activity will cross a narrow corridor
   of relatively maximized MLCINH corresponding to strong heating,
   steep low/middle-level lapse rates, increasing large-scale lift, and
   a proximal surface moist axis characterized by dew points generally
   50s F.  Damaging wind and large hail will be the main concerns,
   amidst vertical wind profiles suitable for both supercells and
   organized multicellular structures.  Some of this activity may
   congeal into a broken band of convection this evening as the
   overtaking Pacific front supplies additional low-level forcing;
   however, weakening near-surface instability with time and eastward
   extent will help to mitigate lingering severe threat therewith.

   Farther north, a mesoscale reservoir of relatively maximized
   low-level moisture -- characterized by dew points mid-upper 50s F on
   11Z-12Z surface charts and 0.8-1.1-inch PW in GPS readings -- was
   evident over northwestern OK and southern KS, and was sampled to
   some extent by the 12Z DDC sounding.  This area of moisture may
   reach the vicinity of the developing frontal zone over
   southern/central NE relatively unperturbed by strong mixing, while
   underlying a regime of cold air aloft with 8.5-9 deg C/km midlevel
   lapse rates this afternoon, amidst weakening MLCINH and
   strengthening lift. That combination may support a pocket of
   2000-2500 J/kg MLCAPE amidst 50-kt effective-shear magnitude,
   suitable for supercell character with any relatively
   sustained/discrete storm(s) that can develop and move into the
   regime.  While coverage of any such convection is in question,
   precluding a greater unconditional probability line at this time,
   isolated very large hail or even a tornado cannot be ruled out.

   ...FL...
   In addition to ongoing convection near the east-central coast,
   widely scattered to scattered thunderstorms are expected to develop
   throughout the day.  Convection will move through a regime of
   broadly confluent/convergent, easterly to northeasterly flow in
   low-middle levels, in and south of the frontal zone, amidst subtle
   large-scale lift related to the northwest-flow perturbation aloft. 
   Activity should translate generally southwestward with the
   low/middle-level currents, into a diurnally destabilizing and at
   least marginally moist air mass, with dew points mostly in the 60s
   F.  A long-trajectory residual version of an elevated mixed layer
   will supply steeper than climatological midlevel lapse rates to the
   region today, atop that increasingly well-mixed preconvective
   boundary layer, with insolation leading to erosion of already weak
   MLCINH.

   All that should lead to pre-storm MLCAPE in the 1000-2000 J/kg
   range, with much of the buoyancy, largest LIs and strong storm-scale
   internal parcel UVV located in icing layers ideally suited for hail
   generation aloft.  With forecast vertical wind profiles yielding
   weak low-level and deep-layer shear, the predominant mode should be
   multicellular, limiting the potential for very large hail; however,
   large volumes of small to marginally severe hail may be generated in
   the most intense cores.  For midday to afternoon convection, the
   projected well-mixed/inverted-v character to the subcloud
   thermodynamic profile supports evaporative downdraft-parcel
   accelerations and strong to locally severe winds as well.

   ..Edwards/Broyles.. 03/23/2017

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z

        
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