Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0329 AM CST Thu Dec 02 2021 Valid 051200Z - 101200Z ...DISCUSSION... A highly amplified regime, particularly in the southern mid- and subtropical latitudes of the eastern Pacific, appears likely to persist late this coming weekend through early next week. This may include the evolution of a prominent mid/upper high over the subtropics, before it becomes suppressed as a significant short wave impulse progresses through a consolidating belt of mid-latitude westerlies to its north, during the middle to later portions of next week. However, models continue to exhibit considerable spread concerning short wave developments within and downstream of this regime, across North America, through this period. It does appear that there may be several significant waves progress through the belt of stronger flow downstream of the Pacific, initially near or just south of the Canadian/U.S. border vicinity, but forecast to gradually shift south of much of the northern tier states by late week. Guidance suggests that each may have the potential to support strong surface cyclogenesis to the lee of the Rockies, but the predictability of these features appears low. For example, latest model output now appears substantially stronger with cyclogenesis accompanying a lead short wave, from the northern Great Plains through the Great Lakes and eastern Canadian provinces on Sunday and Monday. Although not optimally timed with regard to potential for a substantive return flow of moisture from the Gulf of Mexico, current depictions of the cyclogenesis suggest that the risk for severe weather may not be completely negligible ahead of an east-southeastward advancing cold front. This could include portions of the Ohio Valley into the Northeast, where a line of low-topped boundary-layer based convection aiding the downward transfer of potentially damaging winds might not be entirely out of the question. Severe thunderstorm potential across parts of the lower Mississippi Valley through Mid South for next Tuesday and Wednesday is now more unclear, as the last couple runs of the ECMWF have been considerably less amplified with surface frontal wave development emerging from the southern Great Plains. Read more LIVE: spc.noaa.gov
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