Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0300 AM CST Wed Dec 16 2020 Valid 191200Z - 241200Z ...DISCUSSION... Based on the latest model output, low pattern predictability appears an increasing concern through this period. Short wave developments, within branching flow downstream of a strong mid/upper jet across the southern mid-latitude/subtropical Pacific, are becoming more unclear. In general, though, guidance continues to suggest that there will be increasing amplification within the flow, probably including a prominent building mid-level ridge near the Pacific coast by early next week. It appears that this may be followed by downstream large-scale upper trough amplification across the central and eastern U.S., perhaps accompanied by strong surface cyclogenesis east of the middle Missouri Valley through the Great Lakes region by the middle of next week. If this occurs, large-scale forcing for ascent and strengthening deep-layer wind fields and shear within the evolving warm sector probably will become at least conditionally supportive of increasing severe weather potential, somewhere east of the Mississippi Valley into the Appalachians. It does still seem unlikely that there will be opportunity for deep boundary-layer moistening over the Gulf of Mexico, and substantive inland return flow to the warm sector, by this time. While this may tend to minimize severe weather potential with vigorous, deep convective development, it is possible that the environment could still become conducive to damaging surface gust potential enhanced by an evolving pre-cold frontal low-topped convective line.
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