SPC AC 011940

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0240 PM CDT Tue Sep 01 2020

   Valid 012000Z - 021200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN PLAINS AND MID-SOUTH...

   ...SUMMARY...
   Severe thunderstorms capable of large hail, damaging winds, and a
   tornado or two are most likely to occur between 4 PM and 12 AM CDT
   in parts of western Oklahoma and northwest Texas from the Panhandle
   to the Big Country. Other severe storms may produce isolated
   damaging winds and perhaps a few tornadoes across parts of the
   Mid-South through this evening.

   ...20Z Update...
   Severe probabilities for damaging winds and isolated tornadoes have
   been increased across parts of central/eastern AR into the MO
   Bootheel and far western TN. Convection that has recently increased
   in intensity across central AR along an outflow boundary has shown
   persistent signs of low-level rotation. Current expectations are for
   ongoing storms to spread northeastward across the Mid-South through
   the remainder of the afternoon into the early evening along/south of
   a strong low-level instability gradient. A small-scale shortwave
   trough moving over this region is supporting 30-35 kt of effective
   bulk shear, which should be sufficient for continued storm
   organization. Low-level winds from recent KLZK VWPs also show a
   strengthening/veering profile, and the potential for a few tornadoes
   with low-topped supercells and cells embedded within the larger line
   remains apparent. For more information on the near-term severe risk
   across this area, see Mesoscale Discussion 1662.

   Severe hail/wind probabilities have also been expanded eastward into
   parts of western OK, where storms may develop along a stalled front
   later this afternoon. The airmass is becoming at least moderately
   unstable across this area, and deep-layer shear will support
   supercells. There is also some potential for strong to severe
   convection to spread eastward from the TX Panhandle into western OK
   later this evening. For more information on the short-term severe
   threat across this region, see Mesoscale Discussion 1663.

   ..Gleason.. 09/01/2020

   .PREV DISCUSSION... /ISSUED 1125 AM CDT Tue Sep 01 2020/

   ...Southern Great Plains...
   In the wake of an ongoing MCS across eastern/southern OK into north
   TX, pockets of stronger boundary-layer heating are underway across
   northwest TX into western OK. A plume of moderate buoyancy is
   expected to develop from the Big Country north into the eastern
   Panhandles by late afternoon. With a shortwave trough approaching
   from northwest NM/southwest CO, low-level convergence should become
   maximized near the I-27 corridor. Scattered thunderstorms are
   expected to develop across the TX Panhandle and farther
   south/southeast along the remnant outflow from the midday MCS near
   the Big Country. A swath of 30-35 kt 500-mb southwesterlies across
   both regions should support a few supercells and multicell clusters
   capable of producing large hail, severe wind gusts, and a tornado or
   two. Clusters should amalgamate into a broader MCS this evening into
   tonight across parts of west-central and north TX. Convective
   outflow will gradually shift south and become increasingly displaced
   from the stronger deep-layer shear, likely limiting the overall
   magnitude of the severe risk overnight.

   ...Mid-South to the Midwest...
   Multiple clusters/MCS are ongoing from IL south into the Mid-South
   and then southwest into eastern OK/western AR/north TX. A belt of
   stronger 700-500 mb flow will probably remain displaced to the west
   of the leading convection. Pockets of moderate buoyancy appear most
   likely to develop across southern Lower MI into northern IN and
   across southern AR into western TN. Morning guidance lacks a signal
   for organized clustering to occur across the region suggesting that
   a broad cat 1/MRGL risk for mainly localized damaging winds appears
   warranted. A conditional risk for a brief tornado or two still
   exists in a portion of the Mid-South to Lower OH Valley with any
   late afternoon thunderstorm redevelopment where 30-35 kt 850-mb
   winds overlap with the northern periphery of moderate buoyancy.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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