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Tuesday, June 1, 2021

SPC Jun 1, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0736 AM CDT Tue Jun 01 2021 Valid 011300Z - 021200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL HIGH PLAINS TO PORTIONS OF NEW MEXICO AND WEST TEXAS...AND FROM EAST TEXAS AND NORTHERN LOUISIANA INTO ARKANSAS... ...SUMMARY... Isolated severe thunderstorms capable of hail and damaging gusts are possible from the central High Plains to portions of New Mexico and west Texas. Isolated damaging gusts may also occur from east Texas and northern Louisiana into Arkansas. ...Synopsis... A slowly progressive upper-air pattern will feature synoptic ridging moving over the West Coast States and Great Basin, while a trough gradually crosses the Upper Midwest, central Plains and west TX. A series of mostly low-amplitude shortwave troughs and vorticity maxima will pivot through the most sharply cyclonic part of the flow field across the lower/mid Missouri Valley, KS, and west TX. Meanwhile, a slow-moving, southern-stream low over northern Baja and adjacent waters will stall near the Baja spur through day-2, and a broad/weak cyclone will meander erratically around the northern Bahamas and Straits of FL. At the surface, 11Z analysis showed a wavy, quasistationary frontal zone from offshore of the Carolinas across central/southern FL, the northeastern Gulf, the Arklatex region, then arching across central/southwest TX and northern Chihuahua. Equatorward from the front, a convective/outflow boundary was drawn across southeast TX, the TX coastal bend, and along the leading edge of a weakening MCS over deep south TX. This boundary will serve as effective frontal zone for later development in the eastern "marginal risk" area discussed below. ...Central High Plains to portions of NM/west TX... Isolated to widely scattered thunderstorms are expected to develop primarily this afternoon and evening, within a southward-broadening swath from central/eastern CO to west TX and southern NM. Isolated severe gusts/hail may occur, especially from any well-organized multicells, transient supercells or upscale-evolving clusters that can mature for long enough. Potential currently appears too widely spaced and/or marginal in magnitude to assign any areas of more-concentrated probabilities. MLCINH largely will be weak across this area, but so will deep-layer forcing. Outside orographic initiation fixtures such as the Front Range, Sangre de Cristos and Sacramento Mountains, foci for convection will be poorly focused and/or mesoscale in nature, and relative local concentrations of strong-severe potential may develop around boundaries yet to be defined. Relatively cool midlevel temperatures -- atop largely "recycled" moisture processed by convection over the past few days -- will combine with diurnal heating to contribute to peak/preconvective afternoon MLCAPE around 500-1500 J/kg over most of this region. Values around 2000 J/kg may occur in the TX Big Bend vicinity, around northern fringes of a leftover EML layer overlapping favorable low-level moisture at higher elevations. Cloud-layer shear should be strongest over the CO and southeastern NM/southwest TX portions of the area, beneath a northerly rear-trough jet and the subtropical jet, respectively. ...East TX, LA/AR... Precip and cloud cover -- initially from deep south TX to east TX -- will both inhibit diurnal destabilization for several hours, and over southeast/east TX into northwestern LA -- will set up differential-heating/outflow boundaries for later activity to use. Widely scattered to scattered thunderstorms should form this afternoon near and east of the aggregate boundary. Damaging to marginally severe gusts will be the main concern. Rich low-level moisture -- with surface dewpoints generally upper 60s to mid 70s F -- will offset modest midlevel lapse rates enough to support afternoon MLCAPE generally in the 1000-2000 J/kg range -- greatest near the coast. Weak low-level winds and effective-shear magnitudes only in the 20-30-kt range over most of the area will foster a predominantly multicellular storm mode. ..Edwards/Gleason.. 06/01/2021 Read more LIVE: spc.noaa.gov