SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1114 AM CDT Mon Jun 21 2021 Valid 211630Z - 221200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EARLY EVENING FROM CENTRAL PENNSYLVANIA INTO VERMONT.... ...SUMMARY... Scattered severe thunderstorms are expected from the upper Ohio Valley and Mid-Atlantic into northern New England, capable of damaging gusts, sporadic severe hail, and perhaps a couple of tornadoes. ...Northeast States... Water vapor imagery shows a broad upper trough digging across the Great Lakes region, with the associated cold front sweeping across southeast Ontario and OH. Mostly clear skies and dewpoints in the 60s to lower 70s ahead of the front, coupled with steep midlevel lapse rates shown on 12z raobs and model forecast soundings will yield a moderately unstable air mass by early afternoon (MLCAPE over 2000 J/kg). It appears thunderstorms will develop by early afternoon along the front - and in the free warm sector to the east. Vertical shear will be sufficient for a mix of multicell and occasional supercell structures, capable of damaging winds and large hail. Low level shear is strongest over Quebec, but may be sufficient over parts of VT/NY for an isolated tornado or two as well. Activity will sweep eastward across the ENH risk area through the early evening, before weakening as it approaches cooler marine-influenced air mass over eastern New England and NJ. ...TN/KY/WV... Thunderstorms are likely to develop southwestward along the front from eastern OH into KY/TN this afternoon. Vertical shear weakens with southward extent, but given the degree of instability and midlevel winds of 30-40 knots, will be sufficient for at least occasionally intense storms capable of damaging winds and hail. Therefore, have extended the SLGT farther southwest into these regions. ...TX/OK/AR/LA... Several clusters of thunderstorms are expected to develop today across a relatively large area of TX and the mid/lower MS Valley. CAPE will be sufficient for robust updrafts/downdrafts, but weak vertical shear will limit the convective organization. Nevertheless, the strongest cells will pose a risk of locally gusty/damaging winds and hail. ...Northern CA/OR... There continues to be a good signal in the 12z model guidance for a small area of strong thunderstorms this afternoon and evening over portions of northern CA into central OR. A deeply mixed boundary layer and inverted-v profiles suggest that locally damaging wind gusts are the main threat. ..Hart/Bentley.. 06/21/2021
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