SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0239 PM CDT Fri Sep 13 2019 Valid 132000Z - 141200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTHEAST LOWER MI AND NORTHERN OH... ...SUMMARY... Scattered damaging winds, a couple tornadoes, and isolated severe hail are possible across southeast Lower Michigan into northern Ohio through about 9 PM EDT. ...20Z Update... ...MI/OH/IN... Severe Thunderstorm Watch 652 was recently issued across far northeast IN, northwest OH, and southeast Lower MI to cover the risk for scattered damaging wind gusts and isolated large hail with the thunderstorms developing along the pre-frontal trough. A tornado or two is also possible. Isolated thunderstorms are still possible across southeast IN and southwest OH but weaker deep-layer vertical shear should keep any severe risk more isolated. ...Western NC...Western/Central SC... Thunderstorm cluster along the central SC/NC border has recently shown southwestward forward-propagation into central SC. The downstream air mass is warm and moist and the discrete propagation of this thunderstorm cluster is anticipated. Vertical shear is weak, leading to predominantly disorganized storms. Even so, strong updrafts support water loading and the potential for wet downbursts capable of damaging wind gusts. ...North-Central MT... Isolated thunderstorms are still anticipated later this afternoon/evening as the shortwave trough currently moving through southern Alberta/far northwest MT continues eastward. Low-level moisture will be limited but modest buoyancy will still develop amidst a deeply mixed boundary layer and increasing mid-level moisture. A strong wind gust or two is possible, although overall severe coverage is expected to be too low to introduce any risk areas. ..Mosier.. 09/13/2019 .PREV DISCUSSION... /ISSUED 1127 AM CDT Fri Sep 13 2019/ ...MI/OH/IN... An upper low over northwest ON will evolve into an open wave while moving northeastward towards James Bay, as embedded speed maxima rotate around the southeastern periphery of the low. At the surface, a cold front arcing into far southwest Lower MI to the Wabash Valley will progress east across the rest of IN/Lower MI. Thick overcast and residual stratiform rain have tempered destabilization ahead of the front across most of Lower MI, except across the southeast portion with nearly cloud-free insolation occurring from there southward across much of OH and eastern IN. Surface temperatures were already warming through the 80s and will reach the low 90s across most of OH where surface dew points should mix down into the low 60s. A confined corridor of upper 60s dew points should remain near the front and where boundary-layer mixing is not quite as pronounced across southeast Lower MI. Scattered storms are expected to develop in the next couple hours near the front, and then continue eastward across Lake Erie and parts of northern OH into this evening. Despite being on the southeast periphery of the Upper Great Lakes mid-level jet, largely unidirectional/veered wind profiles should hold effective shear to between 25-40 kts. The greatest potential for supercells will exist across southeast Lower MI where the low-level hodograph should be adequately enlarged, yielding a short-duration risk for a couple tornadoes before surface winds veer. Modest mid-level lapse rates will probably limit hail magnitudes. Scattered damaging winds should be the primary hazard with this threat likely diminishing shortly after dusk. ...Western NC into SC... Strong surface heating and lingering low-level moisture along and southwest of a reinforcing frontal surge could provide some focus for thunderstorm development this afternoon. Thermodynamic profiles will favor some risk for damaging downbursts given DCAPE values near 1000 J/kg. Minimal deep-layer shear will temper the potential for organized clustering.
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