As of 1:30 pm, we have a few scattered showers that have formed over the central and south-central parts of Central Alabama, but the good news is that these are staying well-behaved at the moment.
Temperatures as of the 1:00 pm roundup were in the lower 70s to the lower 80s across the area. Haleyville was the cool spot at 73 degrees with cloudy skies. Montgomery was at 82 with fair skies. Birmingham was sitting at 78 degrees with cloudy skies.
We continue to have a Slight Risk up for all of Central Alabama and up into the southern half of North Alabama, while an Enhanced Risk continues for the northern half of North Alabama.
Threats with the first round of potentially severe storms will be large hail (up to golf ball size) and damaging wind gusts up to 60 MPH. This threat will be from now through the afternoon and evening hours until 9:00 pm tonight.
Instability values are currently in the 2000-3000 J/kg range, which is more like what we would see during the summer months in Central Alabama. According to the latest SPC Mesoscale Analysis, those values will increase to 3000-4000 J/kg later in the afternoon. Bulk shear values will stay in the 50-60 knot range. Mid-level lapse rates will be in the 6.0-6.5 C/km range. All of these values verify the threat of large hail and damaging winds.
The good news is that storm-relative helicity values will only be around 100 m2/s2, which is less than what is needed to be supportive of rotating updrafts and the potential for tornadoes. Therefore, while the risk is not an absolute zero for a brief tornado, the chances are very, very low.
Not much will change with the unstable airmass over the area during the overnight and into the morning hours on Thursday when the cold front is expected to move across the area from north-northwest to south-southeast, bringing with it a line of potentially strong to severe storms.
Once again, damaging winds up to 60 MPH and hail up to quarter size will be possible. The higher risk for stronger to severe storms will be along and north of the I-20 corridor, but the line will be in the process of weakening as it moves south. There will be a small threat of strong to severe storms south of I-20 down to the US-80 and I-85 corridors.
Timing at this point for this second round of potentially severe storms will be on Thursday from 2:00 am to 9:00 am at this point, but if this system gains a little momentum this afternoon and evening, we may have to go with an earlier time (most likely 12:00 am to 7:00 am).
Instability, bulk shear, and lapse rates will continue to be favorable for damaging winds and hail during this second round. We may have to watch for a brief tornado or two with this round as helicity values in the latest HRRR run have increased and topping out in the 300-400 m2/s2 range in portions of the area. Significant Tornado Parameters are in the 1.0-2.0 range for much of the area with the exception of the extreme western parts of the area and much of the southern parts of the area, where STP values are maxing out in the 4.0-6.0 range.
The majority of significant tornadoes occur with STP values greater than two, even though a few have occurred with values as low as 1.0. Nearly all storms will not produce a tornado with STP values less than 1.0.
Stick with us throughout the rest of the day and through the overnight hours as we’ll have updates and immediate posts when warnings are issued. Be prepared and stay weather aware.