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Saturday’s Severe Threat – And How Its VERY Slow Movement Could Mean 3-4 Days Of Storms

23 Apr 2014, 11:26 am

One of my favorite things as a meteorologist (and storm chaser) is examining an upcoming severe weather threat.  A lot has been mentioned about this Saturday’s severe threat, so we’ll talk about that before we get to how sluggish this next storm system looks to be – and the overall severe risk as a result.

Here is the basic wind flow forecast (the large “L” indicates the center of low pressure) for Saturday evening:


See all of the reds and pinks there?  That is warmth.  We’re watching humidity also.  I’ve been mentioning a lot about drylines lately (you can read more about them here) on WeatherNation – as severe season has kicked in… and there is another potent one to discuss setting up with our next weekend storm system.

If you just read that Wikipedia link you’ll really get a good feel for things with this dewpoint forecast for Saturday evening… I highlighted in brown the dryline region:



That is your root cause for what looks to be day 1 of at least 3 days of severe storms.  Even the Storm Prediction Center is talking about the extended series of days with severe threats:



Day 4, 5, and 6 on this map correlate to Saturday/Sunday/Monday in real life – if you’re keeping score.

So what gives?  Why are we seeing such a slow moving system?

Well, to start with – the low pressure center wraps itself up to the point we could even add a 4th day to that severe outlook (I’d imagine it’s not there just yet largely because a 4th day of a wrapped up low isn’t usually a sure thing this far out).

Here is a 4 day progression I just mapped out – with the “L” indicating the low pressure center.  Think of that as your northern tip of the severe chances for each of those days.



Look at that progression!  It’s a state or so a day – if that!

So why do storms sometimes wrap up and move slowly east?  That is a very large question/issue, and I’ll explain in basic terms with a link to a longer explanation if you’re curious.  Basically, there are tilts in the jetstream.  When it is tilted a certain way, patterns tend to be more “progressive,” while if they are tilted a different way they will be more stagnant.  That way is often described as “negatively tilted” and that is exactly what we’re dealing with for this upcoming system.

Look at this jet-level wind map for Saturday evening:



So there you go.

You’ll definitely want to stay tuned.

WeatherNation Meteorologist Aaron Shaffer @ashafferWNTV

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