Significant "All Hazards" Winter Storm January 8th-10th

 Ensemble and deterministic model guidance is maintaining a consistent significant "all hazards" winter storm signal that migrates eastward across the central and eastern United States during the January 8th-10th period. By 12Z on the 9th, a vertically stacked deep-layer low is forecast by most guidance to be centered in the vicinity of southwestern Missouri. This will aid in the development of a pronounced surface cyclone and frontal wave advancing from Texas east across the Gulf Coast states. In addition, wind fields will be strong at all levels and upward vertical motion will be substantial. The operational GFS shows relatively high values of boundary-layer theta-e spreading north across the warm sector of the previously mentioned surface wave, and mid-level lapse rates will be fairly steep (>7 C/km), thus there is the potential for MLCAPE values to range from 1000-2000 J/kg, which is large for January. However, it's uncertain whether the warm sector will experience daytime surface insolation due to widespread low-level cloudiness, and that will likely impact convective mode evolution and possible tornado intensity. Nevertheless, current forecast wind fields are exceptionally favorable for long-track violent tornadoes within the previously mentioned surface warm sector (particularly far eastern Texas, southern Louisiana, southern Mississippi, and southern Alabama and adjacent Georgia and Florida panhandle), with mean 0-1 km streamwise vorticity >0.02 s-1.

Farther north, a mainly sub-zero deep-layer airmass will be in place from roughly the mid-Mississippi Valley northeast across the Great Lakes. In addition, very strong upward vertical motion is forecast to occur in the vicinity of a northeastward migrating 700 mb low. Thus, ingredients will likely be favorable for a band of heavy snowfall, the exact location obviously being a function of the near-surface freezing line and mesoscale ascent focused near the previously mentioned 700 mb low. Elsewhere in between the band of heavy snow to the north and severe weather to the south, heavy rain, gusty gradient winds, and perhaps embedded elevated thunderstorm activity will be probable.

Four-panel plot of 500 mb wind/heights valid 12Z 1/9/2024.

Four-panel plot of 850 mb wind/heights/temperature valid 12Z 1/9/2024.

GFS surface theta-e valid 09Z 1/9/2024. Note the northward flux of higher theta-e across southeast Mississippi and immediate surrounding region which is the approximate location of the surface warm sector.

GFS model forecast sounding representing the severe storm/tornado environment valid 09Z 1/9/2024 in southeast Mississippi.

GFS 6-hour snowfall accumulation valid 00Z 1/10/2024.

GFS model forecast sounding representing the heavy snow environment located across Michigan valid 21Z 1/9/2024.