Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0350 AM CDT Sat Sep 11 2021 Valid 141200Z - 191200Z ...DISCUSSION... An upper trough should move eastward across central/eastern Canada and the north-central CONUS on Day 4/Tuesday, while at the surface a cold front advances southeastward across the central Plains to Midwest. Low-level moisture should increase in a narrow corridor ahead of the front, but both instability and deep-layer shear appear a bit too weak to support more than a marginal/isolated severe threat. Some severe threat may exist on Day 5/Wednesday across parts of the Northeast ahead of the cold front, as the upper trough continues eastward over this region. At this point, there is still a fair amount of uncertainty regarding how much instability will develop across the Northeast ahead of the front Wednesday afternoon, and confidence is not high enough to include a 15% severe area. However, parts of NY into New England will be monitored for possible inclusion of severe probabilities in a later outlook, if current model trends continue. Medium-range guidance has started to come into better agreement with the evolution of another upper trough moving eastward across central Canada and the north-central CONUS on Day 6/Thursday. Low-level moisture return and related instability across parts of the northern/central Plains and Upper Midwest may be sufficient to support surface-based storms and an organized severe threat ahead of a cold front. Regardless, there is considerable uncertainty in the evolution of the upper trough and the placement of the front at this extended time frame. This suggests confidence is too low to include any severe probabilities for Thursday at this time. The synoptic-scale upper pattern across the CONUS becomes quite uncertain by Day 7/Friday, with limited predictability regarding any severe potential. Read more LIVE: spc.noaa.gov
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