Late Morning Notes

Here are a few notes or random thoughts about the upcoming weather situation. This is not an organized post but rather some thoughts swirling through my head.

Now: Most of the rain has cleared the Interstate 85 corridor, so little additional rain is expected across Central Alabama. Some spots especially across the western half of the state are seeing some sun, a bit earlier than I thought we would. But there is also another mass of clouds back across northwestern Mississippi that may curtail some of the sunshine. Temperatures are mild with readings ranging from the mid 50s in the eastern areas to the lower 60s in the west central counties.

Models: The various computer models continue to be in good agreement on the track and development of the low pressure storm system that will affect us Christmas afternoon through early Wednesday. I have some concerns that the latest models, those that work in the shorter terms, are coming in somewhat stronger with the strength of the surface low. If the surface low is stronger, then conditions are likely to become even more favorable for severe weather and they are already favorable.

One model concern I have is that the GFS may not be initializing well. I was looking over the MOS numbers and dew points are not projected to get above about 53 degrees in Birmingham. But the current dew points are already higher by about 5 degrees than the MOS numbers for noon today! It also appears that the GFS MOS numbers are too low on the strength of the wind flow especially if the surface low is stronger. One of the short range models, I think from SPC, was showing a 994 millibar low. That kind of strength could mean severe weather conditions push into the Tennessee River Valley.

Severe weather parameters: Looking across the severe weather parameters, it appears that we have a low CAPE and high shear environment. While CAPE which provides information on instability is low with values at or below 700, those values are sufficient for severe weather. The high shear means that storms will be rotating. We should see high low level moisture values with dew points reaching near 60 or perhaps edging into the lower 60s. And it also appears that the storms will be rooted into the boundary layer with LCL (lifting condensation level) values low.

Serious: There is no doubt in my mind that this is a serious situation. Everyone needs to take it seriously. People are going to be distracted due to the holiday as we should, so it is imperative that everyone be aware of the severe weather threat and have a way to receive weather warnings tomorrow. And whatever that method is, do not be turning it off for Christmas dinner or other activities. And remember, don’t rely on outdoor weather sirens.

Be safe.

-Brian-

Category: Alabama's Weather