*This is for central Alabama...the overall severe threat in Mississippi (except potentially areas in southeast Mississippi) looks relatively low.*
A very murky weather situation unfolding across the area this morning. Radar imagery shows an expansive area of showers and embedded thunderstorms along the Mississippi River. Most of this activity is actually occurring behind the front, while isolated activity is occurring ahead of the front across central and southern Mississippi.
Ahead of this front, the air is already warm and muggy, characterized by surface temperatures in the low 70s and dewpoints in the low and mid 60s. Continued moisture advection today will only enhance moisture content across the area. Behind this front, temperatures are dropping off rapidly; for example, Jackson, MS has a temperature of 73 and Monroe, Louisiana has a temp of 48!
Currently, mesoanalysis shows the most unstable air located over central and southeastern pats of central MS back into southern LA. Consequently, the SPC has a tornado watch in effect for these areas until 3 PM this afternoon. However, that axis of instability will begin to shift northeast into Alabama throughout the day today as the cold front moves only very slowly to the east. Surface winds also are backed around to the south-southeast across much of the state, creating some directional shear needed for potential tornadogensis if any storm can mature (more on this later).
By 1 PM, the front should be near the MS/AL state border, with showers and thunderstorms along and behind this feature. The heaviest activity should be right along the front. Since instability values should have increased by this timeframe, some severe storms with damaging winds and perhaps a tornado are possible with these storms over west Alabama (mainly west of US highway 43).
After this timeframe is when the details get blurred with regard to this storm system. The HRRR model (rapid refresh) actually shows a low-level jet max/core moving into central Alabama, centered from Demopolis to Pell City, early this afternoon just ahead of the aforementioned line of storms. This will create the necessary low-level shear (coupled with backed sfc winds) to create 1km helicities of upwards of 300 m^2/s^2. Also, an enhanced area of 250mb diffluence will overspread the area, which will greatly enhance surface uplift. What this means is this: IF surface-based CAPE values can achieve 2000 J/KG as the latest HRRR shows, then some isolated supercell storms could develop across central Alabama, mainly anywhere east of US 43 and southeast of I-20. If these CAPE values remain AOB 1000 J/kg, then a supercell or two is still possible, but this threat would be reduced. Regardless, if any supercell forms, it would have the best potential to produce a tornado.
Otherwise, expect some severe storms area-wide in association with a slow-moving line of thunderstorms. Damaging wind gusts will be the primary threat with this feature, but a spinup tornado or two is possible. If a cold-pool becomes well established and this line can accelerate any, a more enhanced wind damage threat could evolve across eastern sections of Alabama (and the SPC has a 30% wind probability to at least loosely account for this possibility). Any supercells that form will have the best potential at producing tornadoes.
One last note: given the slow movement of this overall system, some areas of flash flooding could develop with training showers and storms, both along and behind this frontal boundary.
Stay close to a source of weather information today, and God Bless!
IW
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