Severe Weather Threat Wednesday

Well after a week of cold temperatures and 2 winter storms we now are looking at a Spring like storm set-up for Wednesday. Temperatures on Tuesday and early Wednesday will be very warm.Highs might approach 70° both days, but clouds will likely keeps us in the upper 60s. Either way warm and moist air for late January will be flooding into the region.

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The amount of shear ahead of the cold front Wednesday is very impressive. The helicity and shear values are plenty high enough for rotating thunderstorm if they should form as individual cells. My thinking is we will get some kind of LEWP(Line Echo Wave Pattern) which could have some embedded rotation in the book end vortices.

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The biggest question as always with these set-ups will be the amount of instability or CAPE. Something we refer to as thunderstorm fuel. During the cool season you always have loads of shear but not much CAPE. CAPE or instability is just warm and moist surface air. To tap into the incredible amount of shear you need enough CAPE for thunderstorms to become surface based and get high enough to tap into the shear. You don’t need really big storms since the shear is much easier to reach in the winter time. Looking at the NAM 4 model it appears 2 lines of storms try to form. Looks likes a pre-frontal trough and the cold front itself. If clouds and light rain moves in ahead of these it might deter our severe weather threat. If we get a few hours of sunshine or a nice low-level jet of warm moist air ahead of either of these two lines then tornadoes become a bigger threat. Here’s a look at the NAM 4 future radar and CAPE Wednesday:


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CAPE: The model only goes out 60 hours but it looks like a reload of the CAPE is possible.

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The real concern might be the second line along the cold front if the atmosphere can recover then a serious tornado threat could occur. Either way there will be a straight line wind threat with the squall line. Below is the significant tornado parameter for Wednesday at about 3pm from the NAM model. Based on this and the shear from the NAM I would suspect the second line would be the one to watch. Though the first line of storms could stabilize the air mass before it arrives. Either way there is going to be severe weather to our west Tuesday and we need to stay alert for a possible severe weather outbreak here in the Carolinas.

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