Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0320 AM CST Fri Feb 19 2021 Valid 221200Z - 271200Z ...DISCUSSION... Medium-range guidance indicates that initially suppressed mid-level ridging, across the eastern mid-latitude Pacific into the U.S. Pacific coast, may undergo considerable amplification next week, roughly between 130-160 W longitude. It appears that this may build toward the Alaskan Arctic Circle vicinity, as a deep mid-level low (initially centered to the north of Alaska, Yukon and the Canadian Northwest Territories) shifts a bit southward and eastward across north central Canada. As this occurs, a mean west-northwesterly mid-level flow regime, from the northeastern Pacific through the U.S., may take on a much more substantive northerly component near the Canadian/U.S. Pacific coast vicinity, into deepening troughing across the Southwest by late next week. Arctic surface air is expected to begin to surge southward to the lee of the Canadian Rockies, but it may remain to the north of the U.S. international border through at least this period. However, models suggest that it will be preceded by a southward surge of more modestly cold air across much of the central and eastern U.S. by mid to late next week. With guidance indicating little potential for significant surface cyclogenesis to the lee of the southern Rockies, and boundary-layer moistening over the Gulf of Mexico slowed by reinforcing subsidence and drying early next week, the risk for severe thunderstorms appears low (i.e., less than 10 percent probabilities) through at least next Friday.
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