New Severe Weather Thoughts

The first storm system this week is moving well to our north and west. A weakening line of showers associated with the cold front remains over Central Arkansas and some of these may hold together to impact Northwest Mississippi later tonight. The cold front will dissipate before it reaches our area, but some showers are possible tomorrow in association with this dying front. Tomorrow will be another warm day with highs in the 70s area wide. Gusty southerly winds will continue to pump more Gulf moisture into the region and this should win the battle against mixing. Therefore, dew points should rise into the 50s tomorrow and will set the stage for a chance of storms with the second cold front due in here on Wednesday.

Our main system of interest has moved into Southern California this evening and caused some showers north of the Los Angeles area. This system will quickly eject out into the Southern Plains tomorrow and potentially cause a severe weather outbreak for Northern Texas and Southern Oklahoma.

TIMING
The Canadian was the outlier a few days ago, but seemingly every model has trended toward its solution of a faster moving system. Almost every available model run suggests the cold front will exit the area by early Wednesday afternoon.

TRACK
There is reasonable agreement in the models up to 24 hours, but considerable uncertainty exists at 48 hours. Some models place the surface low in Southern Missouri while others are further north and east. Both the GFS and Canadian ensembles suggest the surface low is located in Illinois by Wednesday morning, but uncertainty even exists in all of the members. If this does play out, it will significantly lessen the chance of severe weather for our area. However, if the operational run of the GFS, ECMWF, NAM, WRF, and UKMET are correct, there will be a chance of severe weather in our area since they all show the low pressure over Southern Missouri by Wednesday morning. I've always preferred the deeper solution, and I still am leaning this way, especially given the consistency of the very reliable ECMWF.

Putting these two factors together suggests that severe weather is a possibility late Wednesday morning. With the timing of the front coming through in the late morning, this will likely decrease the amount of destabilization that can occur. In fact, MLCAPE values of only 200-400 J kg-1 are forecast by the NAM as the front moves through. However, recent cool season severe weather events have shown it doesn't take a lot of instability to cause some problems.

THREATS
Strong dynamic forcing will result in the development of a squall line late tomorrow night in Oklahoma and Texas that will begin to accelerate eastward. This line of storms should be located just west of the Mississippi River by sunrise Wednesday. As the dynamics lift to the north and east and the instability wanes Wednesday morning, look for the line to weak as it approaches the I-55 corridor and the Oktibbeha County area. Still, given a highly sheared environment and some lingering instability, a chance of severe weather certainly exists for our area. Making the forecast slight more interesting is the presence of very dry air and strong winds just above the surface. If downdrafts associated with the squall line can tap the dry air, it should be relatively easy to transport the stronger winds to the surface. I feel that a low end threat for damaging winds is the main threat with this system, but an isolated tornado can't be completely ruled out late Wednesday morning. With most of the CAPE confined to the lower levels, this could combine with moderate 0-1 km SRH (>150 m^2 s^-2) to produce low level rotation in the strongest storms. It was a little over a month ago that a similar setup produced a couple of tornadoes in Southeast Mississippi and Southwest Alabama.

The limiting factor with this system appears to be the moisture return. If dew points were several degrees higher, we could be dealing with a much more dangerous situation. Fortunately, the arctic air intrusions over the last month will likely prevent a major outbreak for our region this time.

To recap, look for a line of thunderstorms to impact our area late Wednesday morning. Severe weather is a possibility, but the best chances for severe weather will likely be to our north and west. Damaging winds are the main threat, but an isolated tornado is not out of the question. Rain should exit the area by early Wednesday afternoon and temperatures won't cool much behind the front given the Pacific origin of the incoming air mass.