3PM Day 1 Convective Outlook for Thursday, June 26. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON FROM NORTHWEST MISSOURI INTO SOUTHERN MINNESOTA/WISCONSIN AND FROM THE MID-ATLANTIC TO THE SOUTHERN APPALACHIANS
SUMMARY
Isolated wind damage and a few tornadoes will be possible this afternoon from northwest Missouri into Iowa, southeast Minnesota, and southern Wisconsin. Scattered wind damage will be possible from the Mid-Atlantic into the southern Appalachians.
20Z Update
The forecast remains on track, and only minor adjustments were made with this update. In particular, the Slight risk was expanded eastward in IA and northern MO -- where warm/moist boundary-layer conditions should support the maintenance of an eastward-moving line of storms (with an associated severe-wind risk) into this evening. Reference Severe Thunderstorm Watch 465 for more information on the severe risk here. Farther north, the potential for tornadoes will continue with both pre-frontal cells within the baroclinic zone in southern WI and with the primary confluence band advancing eastward out of southeastern MN. An upgrade to 10-percent tornado probabilities was considered, but overall confidence in this scenario was too low for the upgrade at this time. For more details, see Tornado Watch 463 and MCD 1458. Finally, the damaging wind gusts will remain possible with evolving storms in the Mid-Atlantic (within Severe Thunderstorm Watch 464).
Upper Midwest
A shortwave trough is evident this morning over NE/SD moving eastward. Lift ahead of this feature will encourage scattered thunderstorm development by early afternoon near the surface low and along a weak cold front over western IA. These storms will track southeastward into a warm and very moist air mass, where MLCAPE values will be 2000-3000 J/kg. Steep low-level lapse rates will promote a risk of damaging winds as the storms spread southeastward through early evening.
From the surface low eastward into southern WI, a corridor of backed low-level winds and enhanced shear along the warm front will be favorable for a few discrete supercells. Similar to yesterday (although perhaps not quite as favorable), there is a risk of a few tornadoes through the afternoon and early evening.
Mid-Atlantic to Southern Appalachians
Full sunshine is occurring again today from southeast PA to the western Carolinas and north GA. This corridor will be hot/humid again today, leading to scattered thunderstorms. Winds aloft are weak, suggesting disorganized/pulse convective modes. However, steep low-level lapse rates and moderate CAPE values will once again result in a risk of locally damaging wind gusts through the afternoon and early evening. Despite the expected weak winds aloft, will introduce a SLGT risk for this corridor given the consensus of model guidance supporting the threat.