It looks like Monday December 22nd and Tuesday December 23rd will be relatively active across the southeast.
Scenario
A large area of low pressure across the upper-Midwest will push a cold front through the the southeast. The change in airmass will promote the development of showers and thunderstorms for parts of Louisiana, Arkansas, Tennessee, Mississippi, Alabama and Georgia.
The latest model guidance shows sufficient ingredients for the development of severe weather ahead of and along the cold front. Ahead of the cold front storms may develop as a lingering boundary layer lifts north from the Gulf of Mexico.
Monday’s forecast from the SPC:
The boundary layer over the gulf will continue to modify with a broad fetch of sly near-sfc winds supporting dewpoints in the upper 60s to near 70 offshore and low-mid 60s advecting inland monday night as warm front lifts nwd. Steeper mid-level lapse rates will spread ewd and eventually intercept wrn fringe of richer low-level moisture from sern tx into the lower ms valley where mucape could approach 1500 j/kg monday night. Cape will remain marginal farther east into the gulf coast states. Sly llj will strengthen overnight as the upper trough amplifies…Resulting in an increase in forcing for ascent. Showers and a few thunderstorms should develop later monday night…Most likely on the ern fringe of the eml where the cap will be weaker from a portion of the lower ms valley into the gulf coast states. Strong effective bulk shear in presence of at least modest cape raises concern for at least a marginal severe risk. However…Time of day and likelihood that richer moisture will remain offshore suggest convection will probably be elevated above a stable sfc layer. Nevertheless…A few storms could pose a threat for marginally severe hail.
This seems reasonable, but I’m also concerned about the opportunity for a few brief and weak tornadoes to be spun up as the boundary layer lifts north and interacts with a strengthening jet and sufficient turning with height. In recent weeks during what the SPC would deem “non-events” sections of Louisiana, Mississippi and Alabama have been hit with (weak) tornadic storms.
As the cold front moves through there will a better chance for severe weather, though the threat for tornadoes may be limited by the lack of sufficient wind turning with height.
Tuesday’s forecast from the SPC:
Models remain in good agreement regarding evolution of a high-amplitude upper trough that is forecast to advance through the lower ms valley into the sern states tuesday. Though some uncertainty remains regarding overall severe threat on day 4 /primarily due to early onset of precipitation/ feel at least a 15% area appears warranted from the lower ms valley into the gulf coastal region into a portion of the fl peninsula. Richer low-level moisture with low-mid 60s dewpoints will advect inland contributing to moderate instability over the lower ms valley where steeper lapse rates will exist. Cape will remain limited farther east along the gulf coastal states due to early onset of precipitation. Strong shear accompanying the upper trough will be sufficient for severe storms. Storms should increase along and ahead of the front as well as along the gulf coastal region…A few of which could be strong to severe during the day. Overnight…The severe threat may increase farther east over the fl peninsula as mcs over the gulf moves inland.
