Thematic of the 12Z GFS is maintain warmth in the West days 6-10 beneath a titanic upper-level high pressure ridge which extends north and northeastward in the 11-15-day period causing the Canadian polar vortex to dive southeastward toward the Northeast U.S. The 12Z GFS is loaded with arctic sir and the shifting polar vortex forces the big chill into the Northeast Corridor in the 11-15-day period.

A low latitude cutoff low-pressure system west-northwest of Hawaii entrained tropical moisture during the past week causing heavy thunderstorms across Hawaii and the attendant latent heat release amplified the downstream upper ridge pattern which is bringing record warmth to the West U.S. To compensate for the upper ridge, a deep trough formed in the East-central U.S. early this week causing a widespread severe weather outbreak.

A squall line has (temporarily) lost severe weather qualifiers moving east across the east/southeast Ohio Valley this morning while the southern end of the squall line maintains tornado risk for Mississippi and Alabama. Later today, the squall line re-energizes and brings severe storms including a large tornado risk area to the East.

Major severe weather outbreaks are forecast for today and tomorrow across the eastern third of the U.S. Today’s outbreak includes the East-central and Southeast U.S. Tornado risk is widespread and most focused on the Central Mississippi River Valley. On Monday, the severe weather event regenerates on the U.S. East Coast and features widespread high wind damage risk including tornado threat from South Carolina to Pennsylvania.