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Tuesday, June 15, 2021

SPC Jun 15, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0240 PM CDT Tue Jun 15 2021 Valid 152000Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON ACROSS PARTS OF THE CAROLINA COASTAL PLAIN... ...SUMMARY... A corridor of scattered damaging winds and large hail is possible through about 7 PM EDT across the coastal plain of the Carolinas. ...20Z Outlook Update... Some adjustments have been made, mostly to the 10 percent probability of thunderstorms line, in an attempt to account for ongoing destabilization trends and progression of synoptic features. Beneath strong mid-level ridging across the Southwest, Rockies and Great Plains, probabilities for thunderstorms appear seasonably low, and largely confined to favorable orographic forcing near the higher terrain. Across much of the Great Plains, very warm elevated mixed-layer air is contributing to strong inhibition. However, guidance remains suggestive of, perhaps, near minimum threshold probabilities of thunderstorms across the middle to lower Missouri Valley, perhaps into portions of the Ozark Plateau, near the eastern periphery of the slowly eastward advecting plume of elevated mixed-layer air. Large-scale forcing for ascent appears rather subtle, but there has been recent isolated thunderstorm development east of Columbus, NE, with attempts at additional deepening convective development ongoing beneath north-northwesterly mid-level flow, both up- and downstream. Please refer to the latest SPC mesoscale discussions for details on ongoing strong to severe storm development across parts of the Southeast and Northwest. ..Kerr.. 06/15/2021 .PREV DISCUSSION... /ISSUED 1125 AM CDT Tue Jun 15 2021/ ...Carolina Coastal Plain... A shortwave impulse over the central OH Valley will approach the Carolinas as it moves through the basal portion of the broader trough in the East. This should enhance convergence along the surface cold front that is sliding southeast across eastern NC through the SC Midlands. Nearly full insolation ahead of this boundary will support steep low-level lapse rates throughout the region. A westerly component to pre-frontal boundary-layer flow and the relatively deep mixing should yield a pronounced gradient in MLCAPE with values in excess of 2000 J/kg likely being confined to the immediate coast. While one mid-level speed max will move further off the Mid-Atlantic Coast, the upstream jet attendant to the OH Valley will provide adequate deep-layer shear for splitting cells with mid-level rotation. These may consolidate into an east-southeast moving cluster before progressing offshore. Scattered damaging wind gusts along with some severe hail appear possible during the mid to late afternoon. ...Gulf Coast... Scattered thunderstorms are expected to form by early-mid afternoon along a slow-moving cold front and sea breeze boundaries from south GA/north FL westward along the Gulf coast to TX. Vertical shear will be weak with a northerly component to midlevel flow, but large buoyancy characterized by MLCAPE of 2500-3500 J/kg may support occasional microbursts with strong outflow winds. ...SD/MT/WY border vicinity... Hot conditions are expected across the region beneath the mid-level ridge emanating from the stout anticyclone near the Four Corners. Surface mixing could be deep enough to remove convective inhibition and allow very isolated storm development along the convergent dryline/lee trough as surface temperatures breach 100 F. This appears most likely across southeast MT into northeast WY. A conditional threat for strong outflow gusts and hail may occur for a couple hours in the early evening. ...Northern Rockies... Ascent tied to a shortwave trough ejecting from OR to the northern Rockies should aid in renewed thunderstorm development later this afternoon into the evening from northeast OR to northwest MT. Buoyancy will be the primary limiting factor, but steep mid-level lapse rates and pronounced effective shear should support a threat for isolated severe hail. Some of this activity might spread/develop atop a residual inverted-v thermodynamic profile for a threat of locally strong gusts towards north-central MT this evening. ...New England... Scattered lower-topped convection is expected through the afternoon downstream of a shortwave trough moving east from NY. Seasonably cold mid-level temperatures and modest boundary-layer heating within cloud breaks (primarily across southern and western New England) should support weak buoyancy with MLCAPE below 1000 J/kg. While the mid-level jet associated with the trough will shift farther offshore, adequate deep-layer shear may persist for a threat of isolated marginally severe hail and damaging winds. Much of the convection will likely remain sub-severe. Read more LIVE: spc.noaa.gov
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