SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1234 AM CDT Mon Sep 06 2021 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE NORTHEAST...UPPER MIDWEST...AND SOUTHERN ARIZONA... ...SUMMARY... Isolated severe thunderstorms are possible today for portions of the Northeast, southern Arizona, and parts of the Upper Midwest late today into tonight. ...Northeast... A potent mid-level shortwave trough will quickly move from the lower Great Lakes and through the Northeast by mid evening. In the low levels, a surface cold front will extend south from a low over Quebec and sweep across the region during the day before exiting the Maine coast near sunset. Model guidance indicates mainly 50s dewpoints, perhaps near 60 deg F over Maine, will contribute to weak buoyancy (200-800 J/kg MLCAPE) as heating occurs during the day. Thunderstorm development will likely begin during the late morning into the early afternoon with a forced convective line potentially evolving across portions of Maine. Isolated damaging gusts with the stronger downdrafts will be the primary risk with this activity. ...Northern Great Plains into the Upper Great Lakes... A strong mid/upper-level trough will move across the Canadian Prairies during the day and subsequently into the Upper Midwest tonight. A surface low will move eastward near the U.S./Canadian border during the day/evening, as a trailing cold front moves through the northern Plains and to Lake Superior by daybreak Tuesday. Low-level moisture will initially be limited across the warm sector with only a narrow plume of 50s dewpoints forecast over the Red River Valley by the late afternoon/early evening. As forcing for ascent increases through the afternoon into the evening, isolated storms are forecast to develop over ND and subsequently spread downstream into MN primarily after dark. Ample deep-layer shear and sufficient MUCAPE will conditionally support a risk for hail/wind with the stronger storms. ...Southern AZ... A mid-level anticyclone will be centered over NV with a belt of modest east-northeasterly mid-level flow forecast across southern AZ. Marginal low-level moisture amidst steep lapse rates will support isolated storms preferentially developing over the higher terrain of southeast AZ. As these storms mature, isolated severe gusts are possible with the stronger high-based storms before the storms weaken during the evening. ..Smith/Squitieri.. 09/06/2021 Read more LIVE: spc.noaa.gov
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