SPC AC 291729

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CST Fri Jan 29 2021

   Valid 301200Z - 311200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY
   AFTERNOON INTO SATURDAY EVENING ACROSS PARTS OF EASTERN OKLAHOMA
   THROUGH NORTHERN ARKANSAS AND SOUTHERN MISSOURI...

   ...SUMMARY...
   An isolated strong thunderstorm or two may impact a narrow corridor
   across parts of eastern Oklahoma through northern Arkansas and
   southern Missouri Saturday afternoon and evening, accompanied by at
   least some risk for severe weather.

   ...Synopsis...
   Ongoing amplification within the westerlies across the central into
   eastern mid-latitude Pacific appears likely to begin translating
   inland across western North America during this period.  This is
   forecast to include the continuing evolution of deep large-scale
   mid-level troughing across the eastern Pacific (generally just west
   of the Pacific coast), and building large-scale ridging across the
   U.S. Intermountain West and Rockies.

   As this occurs, an initially vigorous short wave impulse, to the lee
   of the southern Rockies by 12Z Saturday, is forecast to continue an
   east-northeastward acceleration. However, models indicate at least
   some weakening is possible as it progresses into a broadly confluent
   regime between low amplitude downstream ridging overspreading the
   south Atlantic coast and the western flank of remnant large-scale
   troughing shifting east of the Atlantic Seaboard.

   It does appear that the perturbation will be accompanied by a
   significant surface cyclone emerging from the high plains of
   southeastern Colorado.  And guidance indicates that this may include
   a period with at least some further deepening as it migrates across
   the Kansas/Oklahoma border vicinity into the lower Missouri Valley.

   In the wake of a recent cold intrusion, boundary-layer moistening
   may be underway across much of the southwestern Gulf of Mexico by
   early Saturday, and continue through the period across much of the
   remainder of the Gulf.  However, this may still be fairly modest,
   with deepest inland boundary-layer moistening confined to southeast
   Texas through the lower Mississippi Valley, with surface dew points
   in the mid 50s to around 60F.

   ...Southern Great Plains into Ohio Valley...
   Potential for thunderstorm activity is expected to initially be in
   association with elevated moisture return (of lower latitude eastern
   Pacific origin) and destabilization, supported by strong large-scale
   forcing for ascent downstream of the progressive short wave trough. 
   Lower/mid tropospheric warm advection, beneath divergent high-level
   flow, may be contributing to this early, across Oklahoma and
   adjacent portions of the Great Plains/Ozark Plateau.  It appears
   that this may diminish during the day, with probabilities for
   renewed thunderstorm development becoming focused near the compact
   mid-level cold core (including 500 mb temps of -20 to -25 C).  This
   is expected to spread across parts of the lower Missouri Valley and
   Ozark Plateau by Saturday evening.  It might not be out of the
   question that convection capable of producing lightning could
   continue east-northeastward in a corridor along the Ohio River
   Saturday night, but this potential becomes more unclear due to model
   spread.

   The stronger mid-level cooling, to the  north of an initially
   intense mid-level jet (around 100 kt at 500 mb), appears likely to
   spread to the north of the better warm sector boundary-layer
   moistening, with warm mid-levels to the south of the jet capping
   convective development.  However, early day precipitation will
   contribute to boundary-layer moistening in advance of the cold pool,
   and forecast soundings suggest potential for weak boundary-layer
   destabilization with some insolation beneath a developing dry slot.
   Current model output suggests this is most probable along a corridor
   across east central Oklahoma through north central Arkansas/south
   central Missouri Saturday afternoon into early Saturday evening. 
   However, given spread evident among the model output, this axis
   could be displaced at least somewhat to the north or south.

   Regardless, given the potential for a developing narrow corridor of
   at least weak boundary-layer destabilization, vigorous thunderstorm
   development appears possible in the presence of strong deep-layer
   mean wind fields and vertical shear.  It appears that this will
   include 50-70 kt southwesterly to westerly flow in the 850-700 mb
   layer, which could support a small organized cluster and/or isolated
   supercell structure or two, accompanied by the risk for damaging
   wind gusts and perhaps an isolated tornado.

   ..Kerr.. 01/29/2021

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