Severe Storm Outlook Narrative (AC)
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Issued by NWS
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611 ACUS01 KWNS 271300 SWODY1 SPC AC 271259 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Mon May 27 2024 Valid 271300Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE ATLANTIC SEABOARD AND NORTH/CENTRAL TX... ...SUMMARY... Severe thunderstorms are expected today across parts of the lower Great Lakes, Mid-Atlantic, and Southeast. More isolated severe thunderstorms are possible this afternoon and evening across much of central and east Texas, as well as southwest Oklahoma and the mid/upper Mississippi Valley. ...Synopsis... In mid/upper levels, a messy synoptic-scale trough -- accompanied by several northern- and southern-stream shortwaves and vorticity maxima -- will proceed eastward across ON, the upper Great Lakes, and the Ohio/Tennessee Valleys through the period. A northern- stream perturbation -- initially extending from Lower MI across N -- should pivot over Lake Huron and the upper Ohio Valley/lower Great Lakes today. The southern part should reach central/eastern PA and central NY by 00Z. Meanwhile, a strong upstream perturbation -- now evident in moisture-channel imagery over the Dakotas -- should move southeastward to southern MN and IA by 00Z, then portions of IN/OH around the end of the period. In the southern stream, a positively tiled shortwave trough -- containing a string of vorticity maxima (some convectively induced) -- will move eastward over the southeastern CONUS. At the surface, a well-occluded low was apparent at 11Z over northern Lake Michigan, with occluded/cold front arching across Lower MI, OH, the Ozarks, and north-central to west-central TX. The front was preceded over much of the Appalachians, Southeast and Mid-South by extensive convective outflow. By 00Z, the front should reach western/central NY, the central/southern Appalachians, and central LA, becoming a stationary to slow-moving warm front over north-central/northwest TX into northern NM. A dryline -- now located near a DYS-SJT-SOA line and into northern Coahuila -- should move only slightly eastward today while becoming more sharply defined as moisture returns northward, to the south of the frontal zone. ...Atlantic Seaboard to Southeast... Ongoing complexes of strong-severe thunderstorms over portions of AL and GA may produce continued damaging wind -- along with isolated large hail and/or a tornado -- while moving into a favorably moist and slowly diurnally destabilizing airmass in their path over GA. Meanwhile, initially subsevere northeastern parts of the original MCS that crossed the southern Appalachians also may re-intensify over the remainder of the morning into midday. See SPC Severe Thunderstorm Watches 331-332 and related mesoscale discussions for near-term details. Northern parts of this activity -- or additional thunderstorms developing along the front of the residual pressure and theta-e perturbations from activity that crossed the Appalachians overnight -- may result in widely scattered to scattered thunderstorms in clusters through at least midday over parts of the Carolinas, and perhaps into southern VA. Meanwhile, isolated to scattered strong-severe thunderstorms are expected to develop along/ahead of the front during midday and through the afternoon from the Mid-Atlantic into parts of upstate NY. Overall convective coverage may increase northward into stronger large-scale lift and frontal/prefrontal convergence, though low-level moisture will generally decrease, along with diurnal heating and midlevel lapse rates. Surface dewpoints should range from the low/mid 70s across GA and the Carolinas Piedmont/coastal plain (recovering behind last evening`s MCS) to the 60s over most of the rest of the outlook corridor. Enough veering with height in the boundary layer and related hodograph curvature exist in forecast soundings -- especially from eastern NC northward -- to support effective SRH in the 150-300 J/kg range, with supercell potential and some tornado threat apparent. Effective-shear magnitudes of 35-45 kt should be common, contributing to potential for both supercells and organized multicells in lines or clusters. ...Southern Plains... Isolated to scattered thunderstorms are possible from north west TX southeastward across parts of LA and southern MS. Damaging gusts and large hail are the greatest concerns. Within that corridor, however, a conditional potential exists for isolated supercells offering large to very large/destructive hail, especially over north-central and parts of central TX. Given the large buoyancy forecast, and favorable deep shear, along with weak MLCINH and regionally maximized convergence expected with a surface low near the front/dryline intersection, confidence has increased enough to introduce unconditional significant-hail probabilities, upon which the "slight" area is based. Strong diurnal heating and decreasing EML-related capping with eastward extent will result in progressively greater convective potential and denser coverage along/ahead of the front this afternoon from northwest TX to the central Gulf Coast States. Surface dewpoints commonly in the 70s F and steep midlevel lapse rates will support a field of 4000-5000 J/kg MLCAPE over central/ north TX south of the front, decreasing to a still favorable 2500- 3500 J/kg over southern MS. Veering of winds with height, and a lengthy hodograph structure well-suited for hail production in any sustained supercells -- are expected in north-central TX. Coverage concerns linger, considering that height rises are forecast across this region through the period, behind the synoptic trough. ..Edwards/Goss.. 05/27/2024 $$