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000 ACUS01 KWNS 030600 SWODY1 SPC AC 030559 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Wed Jun 03 2020 Valid 031200Z - 041200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF PA INTO NJ AND THE NYC METRO... ...SUMMARY... Clusters of strong to severe storms are possible today and tonight from the central Plains through the Midwest and Mid-Atlantic. The most intense storms, capable of damaging winds and hail, are expected from parts of Pennsylvania into New Jersey and the New York City metro area. ...Synopsis... A broad swath of northwesterly flow will stretch from the northern High Plains to the Great Lakes and Northeast/Mid-Atlantic today as several shortwave impulses migrate through northern-stream flow. At the surface, 60s F dewpoints will exist from the southern/central Plains eastward across much of the Midwest to the Mid-Atlantic ahead of a southward sagging cold front. More modest boundary-layer moisture will exist across the northern/central High Plains a more diffuse cold front associated with a surface low over Saskatchewan develops eastward. ...PA into the Mid-Atlantic... Storms are expected to develop in the vicinity of Lake Erie by late morning as a cold front develops east/southeast across the international border. Ahead of the front, low to mid 60s dewpoints will be maintained on southwesterly low level flow. Seasonally warm temperatures in the 70s to low 80s will support MLCAPE values from 1500-2000 J/kg. Fast midlevel flow will be in place across the region with 35-50 kt winds noted in the 850-700 mb layer in most guidance. Deep layer flow will mainly be unidirectional, but increasing winds with height from the surface through 700 mb will result in effective shear greater than 40 kt, supporting organized storm structures amid moderate midlevel lapse rates (7-7.5 C/km). Daytime heating will result in steepening low-level lapse rates, and PW values near 1.75 inches will further support strong downdrafts. Some upscale growth is expected via outflow interactions and possible cold pool generation. Most CAMs guidance support one or more bowing segments tracking east/southeast across portions of northern/eastern PA into NJ and the NYC Metro area from early afternoon into the evening hours, and a corridor of damaging winds is expected. Some severe hail is also possible given the thermodynamic and kinematic parameter space, but may be limited by storm mode. ...Midwest... Thunderstorms are expected to develop in the vicinity of the surface cold front from MO eastward through OH. Strong heating and mid-to-upper 60s F dewpoints beneath modestly steep midlevel lapse rates will support 2000-3000 J/kg MLCAPE. Deep-layer flow will be weaker across the Midwest as strong shortwave impulses are expected to remain to the west across parts of the Plains and to the east across the Mid-Atlantic, and effective shear will be marginal, around 20-30 kt. This will result in briefly intense cells capable of strong downburst winds and hail. ...Portions of the Northern/Central Plains... A shortwave impulse is forecast to eject across WY and shift east/southeast over NE/KS toward northwest MO through the period. Initial high-based convection over the northern High Plains will pose a threat for strong downburst winds via a dry, deeply-mixed sub-cloud layer. As the impulse shifts east toward the central Plains, convection will encounter increasing moisture and a strengthening low level jet during the evening/overnight. Initial cells will be capable of large hail with midlevel lapse rates in excess of 8 C/km and 40+ kt effective shear across the region. By evening, upscale growth is expected as the low level jet increases, and a bowing MCS may track eastward across parts of NE and northern KS, posing a damaging wind threat. ..Leitman/Lyons.. 06/03/2020 $$