SPC AC 101957

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0257 PM CDT Wed May 10 2017

   Valid 102000Z - 111200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF SOUTHWEST OKLAHOMA AND NORTHWEST TEXAS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS EXTENDING FROM
   PARTS OF INDIANA/ILLINOIS WEST-SOUTHWEST TO SOUTHEAST COLORADO...AND
   SOUTHWARD INTO TEXAS...

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

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

   ...Discussion...
   Forecast reasoning from prior outlooks remains on track, with
   current convective evolution generally in line with expectations. 
   As such, changes with respect to the current outlook are limited to
   line tweaks -- particularly with the ENH risk area which is being
   shifted slightly southward.  With convective outflow currently
   aligned from roughly El Reno, OK southwest through Childress, TX to
   a dryline/outflow intersection point in Motley County TX, the
   centroid of greatest severe risk appears to be focused a tad farther
   south.  Along with risk for large hail -- including with a
   developing storm near the dryline/outflow intersection, greatest
   tornado risk appears likely within this southwest-to-northeast
   corridor in the vicinity of the outflow.

   Otherwise, no major changes to the outlook appear necessary at this
   time.

   ..Goss.. 05/10/2017

   .PREV DISCUSSION... /ISSUED 1135 AM CDT Wed May 10 2017/

   ...Northwest TX/western OK...
   A persistent MCS continues to generally weaken as it spreads
   northeastward across south-central/southeast KS at late morning. A
   trailing outflow boundary extends southwestward and continues to
   exhibit some southward movement across west-central/southwest OK
   into parts of the northwest TX low rolling Plains and Caprock
   vicinity. 

   A closed mid/upper trough over eastern AZ/western NM this morning
   will gradually accelerate east-northeastward, reaching the
   south-central High Plains late tonight. 12Z upper-air analysis
   featured a belt of a strong southwesterly winds (50+ kt at 500mb and
   100 kt 250mb) over northern Mexico into the southern High Plains.
   The strong mid/high-level winds will continue to spread
   east-northeastward through afternoon and evening atop an
   eastward-mixing dryline across much of west/northwest TX.

   An northeast-advecting elevated mixed layer atop middle 60s F
   surface dewpoints will contribute to 2000-2750 J/kg MLCAPE in west
   TX and western OK areas to the east of the dryline and south of the
   remnant outflow boundary. Severe thunderstorm development is most
   likely by mid/late afternoon near the dryline and modifying
   outflow-related triple point across the southern TX Panhandle/TX low
   rolling Plains and western parts of north TX into southwest OK.
   Effective shear in excess of 50 kt will support supercells capable
   of very large hail. While low-level shear will initially be weak,
   the influence of the outflow boundary and an evening-time increase
   in a southerly low-level jet will support the potential for
   tornadoes.

   ...IA/MO/IL/IN...
   A warm front will continue to slowly spread northward across
   southeast IA and north-central portions of IL/IN and southern OH,
   while a weak surface wave develops east-southeastward across the
   region through tonight. Surface dewpoints in the low/middle 60s F
   near and south of the front will contribute to MLCAPE values of
   1000-2000 J/kg with weak inhibition by mid-afternoon. Aided by an
   MCV/weak mid-level disturbance, initial strong to severe
   thunderstorm development should occur this afternoon across southern
   IA and northern MO into IL. Deep-layer shear will be favorable for
   initial supercells, while low-level shear will be adequate for some
   tornado risk, particularly just east of the surface wave. Storms are
   likely to cluster over time and move east-southeastward into IL/IN
   from late afternoon into evening, potentially with an increased risk
   for damaging winds.

   ...TX Edwards Plateau/Big Country late tonight...
   The dryline will likely stall this afternoon and then retreat some
   to the west late this evening. Thunderstorm development will be
   possible along this boundary overnight, when lingering
   moderate-strong buoyancy and substantial deep-layer shear will
   support a risk of storm clusters capable of producing large hail and
   damaging winds.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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