SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1216 PM CDT Tue Sep 14 2021 Valid 151200Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE UPPER OHIO VALLEY INTO NEW ENGLAND... ...SUMMARY... Isolated strong to severe storms are possible across the Ohio Valley with scattered severe storms possible into the Northeast Wednesday afternoon and evening. Damaging winds, large hail, and a few tornadoes will be possible. ...Northeast into the Upper Ohio Valley... Latest water-vapor imagery depicts a mid-level short-wave trough over SD. This feature is forecast to advance to a position from lower MI into eastern IL by mid day Wednesday. Subsequently, this feature will move into the lower Great Lakes/OH Valley by 16/00z as strongest 500mb flow translates across northern New England into southeast Canada. Associated surface front will progress into upstate NY early in the period, trailing across the northern Hudson Valley-western PA by 18z. Strongest mid-level height falls will remain north of the international border, thus frontal convergence/boundary-layer heating will prove instrumental in convective development through the period. Latest guidance suggests the strongest heating will be noted across the central Appalachians into eastern PA where surface-3km lapse rates could approach 7.5 C/km by early afternoon. Northeast extent of this more buoyant air mass will stretch into the Hudson Valley prior to frontal passage. NAM forecast sounding at 17z for ALB depicts an uncapped surface parcel with 2700 J/kg MLCAPE and 45kt of surface-6km bulk shear. Scattered thunderstorms should easily develop within this environment and organized robust updrafts are expected given these conditions. Supercells are certainly possible prior to storm mergers and possible line segment development. Greatest tornado potential should extend along a corridor from the Hudson Valley across southern VT/NH into extreme southern ME. Otherwise, more isolated, less sheared, convection should extend southwest along the front across PA into WV. More unstable thermodynamic environment across this region will however support at least a threat for damaging winds and some hail. ...Central Gulf Coast... Remnants of Tropical Cyclone Nicholas will drift east across the upper TX Coast into southern LA during the day2 period. Poor lapse rates, due to extensive cloud cover, will greatly reduce buoyancy where low-level shear is maximized. Forecast soundings suggest southern MS into the western part of the FL Panhandle may experience the greatest combination of low-level shear with at least marginal surface heating. For these reasons, have adjusted the eastern edge of the MRGL Risk a bit east across the FL Panhandle. ..Darrow.. 09/14/2021
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