SPC AC 152000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Sat Jun 15 2019

   Valid 152000Z - 161200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTH CENTRAL PLAINS...

   ...SUMMARY...
   One or two clusters of thunderstorms may be accompanied by hail and
   swaths of strong, potentially damaging wind gusts this evening
   across parts of the Texas Panhandle and northwest Texas into western
   and northern Oklahoma.  Additional strong to severe thunderstorms
   are possible late this afternoon and evening across parts of the
   middle Missouri, middle Mississippi and lower Ohio Valleys.

   Two notable changes have been made for the 20Z outlook:

   1. A small 30% hail area and hatched (10% significant hail) area has
   been added for portions of northern OK. Guidance is in generally
   good agreement that storms will form along a surface boundary by
   early evening as the low-level jet gradually increases and a
   vorticity maximum approaches from the west. While effective shear
   will only be marginally supportive of organized convection, very
   steep midlevel lapse rates and strong to extreme buoyancy will
   support a conditional very large hail risk within 1-2 hours of
   initiation, before consolidating outflows result in a more linear
   storm mode.

   2. Portions of extreme eastern NE and far western IA have been
   removed from the Slight Risk, due to passage of a surface boundary
   and stabilizing effects of midlevel cloudiness. Convection still
   cannot be entirely ruled across this area, and Marginal Risk remains
   in place for now. 

   Otherwise, no significant changes have been made to the outlook. See
   the previous discussion below, and MCDs 1071-1073, for more
   information.

   ..Dean.. 06/15/2019

   .PREV DISCUSSION... /ISSUED 1128 AM CDT Sat Jun 15 2019/

   ...Synopsis...
   Seasonably strong westerlies appear likely to remain confined to
   northern portions of the Great Lakes region into the Northeast
   during this period, on the southern periphery of a fairly deep
   lower/mid tropospheric cyclone migrating across western through
   northern Quebec.  In response to this development, the center of a
   broader scale mid-level low appears likely to gradually shift east
   of James Bay.  

   In the wake of this feature, generally weak, broadly confluent,
   northwesterly to westerly mid/upper level flow will prevail across
   much of the U.S., but a belt of stronger flow appears likely to
   linger across parts of the middle Mississippi into Ohio Valleys,
   associated with an eastward propagating, convectively generated or
   enhanced speed maximum (including 40-50+ kt at 500 mb).

   Due to a prior intrusion of seasonably dry/cool air, seasonably
   moderate to high boundary layer moisture content remains largely
   confined to the interior U.S. to the west/southwest of the more
   strongly confluent regime into the Canadian mid-level low.  But,
   elevated layers of steep lower/mid tropospheric lapse rates,
   emanating from prior days strong daytime heating and mixing across
   the high Plains and Intermountain West/Rockies, are expected to
   contribute to moderate to large potential instability.  This may
   extending over a rather broad area of the central and southern
   Plains through the middle and lower Missouri and Mississippi
   Valleys.  However, largest CAPE and steepest lower/mid tropospheric
   lapse rates will remain focused beneath the residual plume of
   warmest (and still potentially strongest capping) elevated mixed
   layer air across the southern Plains.

   This instability will provide potential for scattered strong to
   severe thunderstorm development today into tonight.  The most
   substantive of this potential may become focused with a remnant
   mesoscale convective vortex migrating into the lower Ohio Valley, a
   developing area of large-scale ascent across parts of southern
   Minnesota into Iowa, and perhaps most prominently with a
   low-amplitude short wave trough approaching the southern Plains.

   ...Southern Plains...
   Models indicate that a relatively focused area of weak to modest
   mid-level height falls will overspread the Texas Panhandle through
   much of western/northern Oklahoma this evening into the overnight
   hours, associated with a low-amplitude short wave trough emerging
   from the Southwest.  While this area still appears likely to be
   under the influence of the warm and capping elevated mixed-layer
   air, associated forcing for ascent is expected to be sufficient to
   maintain and support additional vigorous thunderstorm development.

   Convective evolution remains at least somewhat uncertain, but models
   suggest that thunderstorms may initiate across the Sangre de Cristo
   Mountains and Raton Mesa area this afternoon, and eventually along
   the dryline, near a broad surface low over the Texas South Plains. 
   Aided by the mid-level forcing, this activity is expected to
   eventually consolidate and/or grow upscale, while spreading east of
   the higher Plains.

   Although deep layer mean wind fields and shear likely will be
   initially weak, thermodynamic profiles appear supportive of
   relatively cold convective outflow with potential for producing
   strong surface gusts.  This potential may increase through the
   evening, aided by modest southerly 850 mb jet strengthening, along
   the gust front of consolidating surface cold pools.

   ...Middle Mississippi into lower Ohio Valleys...
   Severe weather potential remains a little unclear, and may
   considerably hinge on the extent of insolation near a remnant
   outflow boundary, generally east/southeast of the St. Louis metro
   through portions of southern Illinois and Indiana, toward the
   Cincinnati area.  Boundary layer moisture is initially modest across
   this region, but moistening appears underway, as the remnant MCV
   (currently just west of St. Louis) progresses eastward.  It is
   possible that strengthening wind fields/shear and destabilization
   near this boundary may contribute to an environment conducive to
   supercells that could pose a risk for tornadoes by late this
   afternoon or evening.

   ...Middle Missouri into middle Mississippi Valley...
   Forcing for ascent near a weak frontal wave (on the southern
   periphery of a low amplitude short wave progressing across the
   Dakotas into Minnesota) may contribute to increasing thunderstorm
   development near/south of the Minnesota/Iowa border by late this
   afternoon.  In the presence of moderately large CAPE, deep layer
   shear near the southern periphery of the mid-level trough may be
   sufficient to contribute to an upscale growing cluster of storms. 
   This activity may pose a risk for severe wind and hail while tending
   to propagate south-southeastward through this evening.

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