SPC AC 100548

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1248 AM CDT Wed May 10 2017

   Valid 101200Z - 111200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF NORTHWEST TX AND SOUTHWEST OK...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
   PLAINS TO THE MID MS VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   SOUTHWEST TX TO THE OH VALLEY...

   ...SUMMARY...
   Scattered severe thunderstorms are expected to concentrate along a
   corridor from the southern Plains to the mid Mississippi Valley. 
   Strongest activity should focus across parts of northwest Texas into
   southwest Oklahoma where very large hail and a few tornadoes are
   possible.

   ...Southern/Central Plains...

   High-level flow appears to have translated into the southeast
   quadrant of an upper low positioned over southern AZ early this
   morning.  This evolution suggests the low will soon eject into the
   southern Rockies and late evening model guidance supports this with
   the center of the upper low expected into east-central NM by 11/00z.
   Prior to this ejection, a cluster of strong thunderstorms has
   developed across the high Plains from southeast NM into the southern
   TX Panhandle.  Large-scale pattern would suggest this complex of
   storms will propagate across the TX Panhandle into south-central KS
   during the day aided by strong southwesterly mid-high level flow. 
   In its wake, strong boundary-layer heating is expected across the TX
   South Plains and a well-defined dryline should advect/mix to just
   east of the Cap Rock by peak heating.  It appears immediate
   pre-dryline warm sector will become fairly unstable by mid afternoon
   as western edge of maritime tropical air mass is drawn northwest
   into southwest OK/northwest TX.  10/00z sounding at FWD exhibited PW
   on the order of 1.5 inches with a mean mixing ratio of 12.3 g/kg. 
   Given an undisturbed reservoir of moisture across much of TX it
   appears the dryline will become quite unstable by afternoon and CINH
   should be negligible by 21z.  If aforementioned early-day cluster of
   storms ejects across the Panhandle as expected, a
   southwest-northeast oriented outflow boundary could be draped across
   northwest OK into the TX Panhandle.  This boundary could also serve
   to focus thunderstorm development, especially across the southern
   Panhandle where surface heating will be maximized.  For these
   reasons have introduced an ENH risk of severe for the potential for
   supercells during the afternoon/evening hours.  Very large hail may
   accompany this activity and a few tornadoes should be noted as well.

   Scattered severe thunderstorms may also develop across the upslope
   region of southern CO by early evening.  These storms will be
   strongly sheared but boundary layer may not be especially warm. 
   Even so, supercells are possible with convection that evolves off
   the high terrain.

   ...Mid MS Valley...

   Upper ridge is expected to flatten across the mid MS Valley today as
   flow increases within the base of SK/MB upper trough.  This feature
   will force a cold front to a position from southeast IA into
   northeast KS by mid afternoon.  Richer moisture is expected to
   advance northward into this region as LLJ strengthens from the
   southern Plains into eastern IA.  Latest model guidance suggest
   modest instability will develop immediately south of the front and
   boundary layer temperatures should warm enough for a convectively
   active front.  Deep-layer shear will be more than adequate for
   sustaining organized updrafts capable of evolving into thunderstorm
   clusters, though a few supercells can not be ruled out.  Large hail
   and damaging winds are the primary threats.

   ..Darrow/Gleason.. 05/10/2017

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