SPC AC 290559

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Sat May 29 2021

   Valid 291200Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   CENTRAL/SOUTHERN HIGH PLAINS...

   ...SUMMARY...
   Widely scattered severe thunderstorms capable of large hail and
   severe wind gusts are possible this afternoon and evening for parts
   of southeast Colorado, eastern New Mexico, and the Texas and
   Oklahoma Panhandles.

   ...Synopsis...
   Stronger westerlies aloft will be relegated to the northern Plains
   and the Eastern Seaboard. An upper trough will progress eastward
   over the Canadian prairies today and tonight, with strengthening
   westerlies and height falls occurring over the Upper Midwest. A
   positive tilt upper trough over the Great Lakes/Midwest will
   gradually take on a more neutral tilt as it slowly progresses
   eastward over the Ohio Valley toward the Appalachians. A
   southward-progressive cold front will relegate richer low-level
   moisture to the Carolinas and Southeast coastal areas as well as
   South Texas and the southern High Plains.

   ...Central and Southern High Plains...
   Although upper-level ridging and only modest-strength westerlies
   will generally be prevalent across the High Plains, a subtle
   mid-level disturbance noted in water vapor imagery over the southern
   Great Basin late Friday night will likely reach the south-central
   High Plains by around peak heating. In response, lee cyclogenesis
   will be focused across southeast Colorado, and to some extent across
   east-central/northeast New Mexico. Air mass modification/recovery in
   the wake of Friday night storms will gradually occur, with
   middle/some upper 50s F surface dewpoints likely to become
   reestablished west/northwestward toward the New Mexico/Texas border
   vicinity into southwest Kansas/southeast Colorado by late today.

   Effective shear will generally be between 30-40 kt, although
   slighter stronger and more supercell-supportive values of 35-45 kt
   are plausible across southeast/east-central Colorado and far
   northeast New Mexico/western Oklahoma Panhandle vicinity. Initial
   storm development and intensification should occur by around 20-21Z,
   potentially including the Palmer Divide vicinity, southeast
   Colorado/Raton Mesa area, and possibly near/east of the Sacramento
   Mountains in southeast New Mexico. Large hail will be the most
   prevalent hazard during the first few hours of storm
   development/maturation, although a brief tornado or two could also
   occur, perhaps especially in vicinity of the Palmer Divide and
   east-central toward southeast Colorado.

   A nocturnally increasing southerly low-level jet coincident with the
   instability axis may be favorable for upscale quasi-linear growth
   and forward propagation (east-southeastward) by evening,
   particularly from southeast Colorado/northeast New Mexico into the
   Oklahoma/Texas Panhandles. A somewhat more organized/sustained
   severe wind risk may evolve for a few hours within this corridor
   before storm intensity wanes overnight.

   ...Carolinas and far southeast Virginia...
   Thunderstorm development and intensification will likely be focused
   across the Carolinas into far southeast Virginia in vicinity of a
   southeastward-spreading front and near/east of a surface wave that
   will likely be focused near the North Carolina/South Carolina border
   vicinity. Low to mid 60s F surface dewpoints within the warm sector
   will contribute to as much as 1000-1500 J/kg MLCAPE. While a few
   transient supercells could occur immediately near the
   southwest/northeast-oriented frontal, multicells capable of isolated
   wind damage should be the most common mode/risk this afternoon
   through early evening.

   ...South Texas/Rio Grande River vicinity...
   Although forecast confidence is limited, there is some potential
   that storms occurring late Friday night across the Permian Basin
   toward the Hill Country may persist southeastward in a
   semi-organized/strong fashion into a residually moist/unstable air
   mass, which could include some early day severe hail/wind risk. Have
   opted to include low severe probabilities across the region to
   account for this potential.

   ..Guyer/Squitieri.. 05/29/2021

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