I had fully intended to post about the snow threat in New Mexico today, however, the Moderate Risk for severe weather across the Gulf Coast states takes precedence.
The Storm Prediction Center (SPC) has issued a Moderate Risk for parts of Louisiana, Mississippi and Alabama through this evening.
Associated with the Moderate Risk is a 15% Tornado Threat Ring, and a hatched area of 10% or greater EF2-EF5 Tornado Threat.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows some diffluence aloft, as the nose of the jetstreak spreads out over the area. The added energy from the jetstreak, and the kink in the jetstream on the eastern side of the trough are interesting features to note.
The 500 mb NAM chart shows extremely strong Positive Vorticity Advection (PVA) from the Mississippi River Delta area northwest. This is just ahead of the jetstreak. The PVA will increase convection through this area.
The 700 mb NAM chart shows some extremely fast, rapidly-rising air over central Louisiana. This is in response to the PVA, and will cause some storms to erupt explosively, with strong updraft speeds.
To add insult to injury, the 850 mb NAM chart shows strong Warm Air Advection (WAA) into the same region as the PVA. Anytime you have overlapping strong PVA and strong WAA, there is a threat for severe weather. Also notice that there is a closed low pressure system forecasted over central Louisiana at this layer. This shows a maturing mid-latitude cyclone at its finest.
Currently, the 12Z upper air sounding from Birmingham, AL, is not impressive. There is no Convective Available Potential Energy (CAPE), and the damp atmosphere (1.12 inches of precipitable water) has the lapse rate just above (5.3 C/km) the Moist Adiabatic Lapse Rate (MALR – 5.0 C/km). This sounding is representative of those in the area. However, the low-level shear of 15 kts is enough to support tornadoes, and the deep-layer shear of 37 kts is almost enough to support rotating storms. This station is out ahead of the jetstreak, so the deep-layer shear will increase throughout the day.
To get an idea of what is coming, the 12Z upper air sounding from Lake Charles, LA, shows 57 kts deep-layer shear (mostly due to speed changes), and 20 kts low-level shear (mostly due to direction changes). This is potent shear for long-tracked supercells and tornadoes.
The visible satellite imagery over the area shows heavy cloud cover. This may limit some convective development, but because the synoptics are working so strongly, I expect that the limited daytime heating will not hinder storm development. As is, the WAA is moving in from the Gulf, which has clear skies. The strong onshore breeze may even erode the clouds and allow for more daytime heating.
The surface observations (from the SPC Mesoscale Analysis Map) show the high dewpoints along the Gulf Coast- upper 50’s and low 60’s. The winds point to a center of circulation (low pressure system) over Northern Louisiana.
The HRRR shows that there could be some overlap between shear parameters:
…and thermo parameters over southwestern Mississippi.
…and just for fun, here is the HRRR’s composite radar image two hours after the other two. Notice the storms that moved through Columbus, MS.
*THESE ARE ONLY PREDICTIONS based on model data* Stay tuned to your local news source for real-time information!
Overall, I expect severe weather in this region today. On a half-cocked prediction this morning, I would target Columbia, MS, as good starting point today. No doubt it will be a busy day for my meteorology classmates in Mississippi!
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC