Storms Expected Christmas Afternoon & Night

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Merry Christmas Everyone!  We are waking up to cold, foggy and dry conditions across the Tennessee Valley this morning.  A large swath of showers and embedded storms north of a warm front that is currently along the coast, is lifting northeast across central and southern Mississippi and southwest Alabama.  Expect these showers and storms to start moving into Northwest Alabama this afternoon. A few wind gusts could accompany the stronger storms but severe weather is not expected with this batch and will remain limited with the entire system for the Tennessee Valley.  Below is a current check of the radar as of 10:45 am.

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A potent low pressure system will track northeast from Texas, across Louisiana and Mississippi before making it’s way across Northwest Alabama and southern middle Tennessee late tonight and early Wednesday.  The latest from the Storm Prediction Center still has the entire state of Alabama and all of the Tennessee Valley in a ‘Slight Risk’ for severe storms, with the greatest threat for severe weather in southwestern Alabama, central and southern Mississippi and much of Louisiana as outlined by the ‘Moderate Risk’ area.

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Below outlines the tornado threat, which is highest to the south and west of the Tennessee Valley.

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Below is an outline of the wind threat, which is the greatest threat of any storm that develops.

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Below is the hail threat, which remains extremely low for all of Alabama and the Tennessee Valley.

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This is a powerful storm system and if you are traveling south today towards Birmingham, Tuscaloosa, Montgomery, west into Mississippi or Louisiana, make sure to have a way to get the latest weather information and warnings because severe weather is possible, with all modes of severe weather possible (damaging wind, tornadoes and hail).

For the Tennessee Valley, the threat for any severe storms remains marginal.  A “marginal” threat means we are not expecting significant severe weather; though it only takes ONE storm to have a big impact. This system is very dynamic and is a classic winter system, with low instability and high shear. The potential for severe storms depends on the track of the low, how far north the warm front lifts and how unstable the atmosphere will be.  As of right now, most models are tracking the low over Northwest Alabama and northeast into Tennessee, which will limit how far north the warm front lifts and therefore the most unstable air. The highest instability will remain to the south of the Tennessee Valley.

High temperatures are only forecast to reach mostly into the low to mid 50s, with dewpoints only in the 50s. In fact a few models keep some dewpoints in Northeast Alabama and adjacent southern middle Tennessee in the 40s tonight.  For severe storms to develop and to sustain severe storms the magic number for sufficient moisture is a dewpoint at, or above 60 degrees. You can get severe storms with dewpoints in the upper 50s, but 60 and above is what you are mainly looking at for a severe threat.  Below is a look at forecast dewpoints at 10:00 pm tonight as the cold front and storms push through. The 60 degree dewpoint line is south and west of Birmingham.

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With the lack of substantial moisture return to the area, there is not much fuel to support severe storms.  You can have all the shear in the world, but if you do not have enough instability/moisture, you will not get storms to develop. The combination of the track of the low and limited moisture, means that there could be a few stronger storms with high wind and heavy rain, but the severe weather threat remains low.  The time frame for the strong storms to move through is after 6:00 pm and overnight into early Wednesday.  Locations east of I-65, and along and southeast of I-59 will have the highest potential for a stronger storm, but even that threat is low.  On the back side of the system, a few snowflakes may mix in with the rain as it exits the area, especially in southern middle Tennessee, but no accumulations are expected, though the Cumberland Plateau could pick up a light dusting.

Beside showers and storms this powerful storm system has a wintry side, which will make for rough travel across the southern Plains, through the Ohio River Valley and into the Northeast. There are even Blizzard Warnings in extreme northwest Tennessee (indicated by the orange/red color in the Mid Mississippi River Valley).

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Please travel safely if you are heading north or south today or returning from those areas to the Tennessee Valley. Enjoy today with family and friends, rest easy and just make sure that your NOAA weather radio is working properly and you have someone designated to pay attention to the weather and that you have a way to get any warnings if they are issued.

Stay up-to-date here on the blog, WHNT News 19, and our mobile offerings:

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Have a safe and Merry Christmas everyone!

- Jennifer Watson

Twitter: @JWatson_Wx

Facebook: Jennifer Watson WHNT

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