SPC AC 262000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Sun Mar 26 2017

   Valid 262000Z - 271200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL
   OK AND FAR NORTH-CENTRAL TX...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
   CENTRAL/EASTERN OK AND NORTH TX...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE SOUTHERN PLAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TX
   TO THE OZARKS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
   OH VALLEY...

   ...SUMMARY...
   Numerous severe storms with very large hail, tornadoes, and damaging
   winds are expected after 4 pm CDT especially across central and
   eastern Oklahoma and north Texas through evening.

   ...Discussion...
   The overall forecast philosophy remains relatively unchanged, with
   an expectation for severe thunderstorms to rapidly develop late this
   afternoon along a dryline across central Oklahoma southward into
   north Texas. Initial elevated convection that developed over central
   Oklahoma early this afternoon continues to advance east/northeast in
   tandem with a low-level jet. These cells may continue to briefly
   pose a marginally severe hail threat, but are expected to weaken
   with northeastward extent.

   Farther southwest, despite pockets of stronger mixing, dew points in
   the mid/upper 50s to lower 60s have streamed north ahead of the
   dryline, resulting in MLCAPE values around 1000-1500 J/kg across far
   southern Oklahoma and north Texas. As stronger large-scale ascent
   continues to overspread this corridor, storms should expand in
   coverage, with supercell modes capable of all very large hail,
   damaging winds, and a few tornadoes. The most notable change with
   this outlook is the expansion of higher hail and tornado
   probabilities southward across north Texas. Recent visible satellite
   imagery and hi-res guidance suggest a relative maximum in severe
   potential near and perhaps just south of the Red River. Cells
   developing to the west/southwest should mature as they enter this
   corridor of relatively greater low-level moisture. For more
   information on the threat, reference Mesoscale Discussion 335.

   ..Picca.. 03/26/2017

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Mar 26 2017/

   ...Southern Plains...
   Embedded within a moderately strong belt of southern-stream
   westerlies, a relatively compact shortwave trough over the
   south-central High Plains at late morning will continue eastward and
   reach the Ozarks by late tonight. Within the base of this trough,
   12Z upper-air analysis featured a 50 kt belt of mid/high-level (500
   mb and above) southwesterly winds that extend from southern/eastern
   NM into the TX panhandle/far western OK/southwest KS. Given that
   less that 48 hours has passed since the prior system (now over the
   Midwest) at this general latitude/longitude, moisture
   return/availability across the southern Plains remains a point of
   uncertainty, especially regarding the magnitude of the tornado risk
   in an otherwise very favorable early-Spring Southern Plains setup. 

   Beneath an eastward-advecting elevated mixed plume (sampled across
   the south-central High Plains at 12Z), surface observations feature
   around 60F dewpoints into southern parts of DFW Metroplex as of 16Z.
   These near-60F dewpoints should reach parts of south-central OK by
   21Z-00Z. Visible satellite imagery shows a band of higher-level
   cloud cover that will overspread the increasingly moist warm sector
   this afternoon. While not typically a severe-favorable factor, this
   cloud cover should at least partially shield the boundary layer and
   somewhat deter mixing while otherwise supporting a gradual increase
   in near-surface moisture through the afternoon/early evening.
   Current trends/short-term guidance suggest this cirrus should
   overspread/progress east of the dryline toward/after roughly 21Z.

   Ahead of the slow-eastward-mixing dryline, near-60F surface
   dewpoints should generally result in around 1500-2000 J/kg of MLCAPE
   by peak heating from south-central OK into western parts of North
   TX. Weaker near-surface destabilization is expected farther north
   into northwest/north-central OK and extreme southern KS.  

   As forcing for ascent and deep-layer shear (effectively 40+ kt)
   increase,  late-morning thinking is that semi-discrete supercells
   will begin to develop by mid-afternoon (around 21Z/4PM CDT) across
   west-central OK into western north TX, initiating just west of the
   I-35 corridor. Potentially very large hail is likely along with at
   least some tornado risk, which should at least somewhat increase
   through 23Z-01Z toward/east of the I-35 corridor, especially across
   south-central OK and far north TX as low-level moisture continually
   increases and low-level hodographs enlarge. 

   Sustained warm advection should contribute to an eventual clustering
   and bowing of storms by late evening as storms persist generally
   eastward especially across southeast OK and extreme northeast TX.
   Accordingly, damaging wind potential may increase for a time late
   this evening before updraft/downdraft intensities wane overnight as
   storms progress into AR/ArkLaTex vicinity.

   ...Upper Ohio River Valley...
   A shortwave trough centered over northern/central IL late this
   morning per water vapor satellite imagery will continue
   east/northeastward today, with a weakening/opening trend expected
   tonight. Moderately strong winds aloft (12Z upper-air data and more
   contemporary WSR-88D vwp data) just ahead of this trough will
   overspread the upper Ohio River Valley vicinity through the
   afternoon/evening. Modest moisture (lower to middle 50s F surface
   dewpoints aside), prevalent cloud cover and multiple ongoing bands
   of showers suggest that overall destabilization should remain
   limited. Even so, locally damaging winds, marginally severe hail and
   possibly a brief tornado could occur presuming at least modest
   diurnal destabilization. Parts of southern OH, northeast KY into
   western/northern WV currently appear most susceptible to a
   severe-storm risk this afternoon/early evening.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z