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December 23-27th Storm System's/Severe Weather Potential


HillsdaleMIWeather

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Hey forumers :santa:

 

I live in northwest Alabama and I see Dr Forbes has us with a Torcon of 7 for Wednesday (what is it about Wednesdays?!). Every time really severe weather hits, I lose electricity and cable for days. As with the 4/27/2011 outbreak, I was in the dark about what happened until May 1st when I was able to access this board and catch up. You guys were amazing! If we get it again, I hope I can depend on your intelligence and diligence once again. Have a good day!

BMX just updated their AFD... they mention your area is the best area to see tornadic supercells. They sound very worried; they even mentioned the possibility of an EF4+ tomorrow. Good luck and stay safe!

 

NATIONAL WEATHER SERVICE BIRMINGHAM AL

318 PM CST TUE DEC 22 2015

...SEVERE WEATHER OUTBREAK MAY AFFECT PARTS OF CENTRAL ALABAMA ON

WEDNESDAY AFTERNOON INTO EARLY THURSDAY...

.DISCUSSION...

WITH DISRUPTIVE GULF CONVECTION OUR OF THE PICTURE...THE MAIN

QUESTION AT THIS POINT IS RELATED TO STORM COVERAGE ON WEDNESDAY.

FORTUNATELY STORMS WILL PROBABLY BE VERY ISOLATED AS THE STRONGEST

FORCING BRUSHES BY TO THE NORTH.

MODELS HAVE TRENDED MORE AGGRESSIVE WITH THE RAPID NORTHWARD

SURGE OF A WARM SECTOR WEDNESDAY MORNING BEHIND A WAVE OF EARLY

MORNING SHOWERS AND STORMS. AT LEAST A FEW MODELS INDICATE THE

POSSIBILITY OF NEAR 70 DEGREE DEWPOINTS AS FAR NORTH AS

BIRMINGHAM BY EARLY TOMORROW AFTERNOON. SEVERAL LOW-LEVEL

CONFLUENCE BANDS ARE EXPECTED TO BE PRESENT IN THE WAKE OF THE

MORNING CONVECTION AS IT MOVES RAPIDLY TO THE NORTHEAST. AN

ISOLATED TORNADIC SUPERCELL CANNOT TOTALLY BE RULED OUT ANYWHERE

ACROSS THE AREA THROUGH THE EARLY AFTERNOON...BUT THE HIGHEST

CHANCE FOR TORNADIC SUPERCELLS WILL OCCUR DURING THE EVENING AND

INTO THE NIGHT GENERALLY NORTHWEST OF INTERSTATE 59 AS A STRONG

LOW-LEVEL JET AXIS SHIFTS EASTWARD INTO ALABAMA.

THE LIMITING FACTORS TO THIS SETUP ARE TIED TO A TENDENCY FOR

500 MB HEIGHT RISES AND A LACK OF LIFT. 200 MB DIVERGENCE AND

LOW-LEVEL CONVERGENCE SHOULD BE SUFFICIENT FOR AT LEAST A FEW

SUPERCELLS FOCUSED IN THE NORTHWEST PART OF THE FORECAST AREA. THE

ISOLATED NATURE OF THESE STORMS MAY ALLOW THEM TO BECOME INTENSE

NEAR THE BEST CAPE/SHEAR OVERLAP...WITH THE POSSIBILITY OF STRONG

AND LONG-TRACK TORNADOES. A VIOLENT TORNADO CANNOT BE RULED OUT IF

ALL OF THE RIGHT SEVERE WEATHER INGREDIENTS COME TOGETHER.

 

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A couple things to note, most places today were warmer than forecast in the region. Detroit for example was +5 off of the forecast and furthermore the dew points haven't dropped off as quickly as originally thought. If we are starting ahead of the forecast. With more cloud cover moving in tonight with the moisture advection expecting to begin overnight, we shouldn't drop off much tonight as well. These higher values the NAM is pumping out, might not be as unrealistic as we originally thought.

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How good is the 4km NAM at predicting instability?

It tends to be a bit high, but in strong moisture advection regimes it tends to not be too far off of the truth.

It is usually more overzealous in the summer though, in cold season events it isn't too far off from reality.

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This 18z 4 km NAM image valid 3z Thursday is scary, for lack of a better word, note the supercells over S IN. To see this popping 60 dBZ cores with those things in TN and KY is unreal for December.

 

 

I don't even...

 

How good is the 4km NAM at predicting instability?

Probably not so good overall... I doubt it's an outlier at this point. Even Euro has 1000+ CAPE crossing the Michigan border. 

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Locally, the morning into afternoon activity does have me mildly concerned as far as how much instability will build in its wake (whether we can reach the higher end of progs), but most models agree on sufficient recovery.  It may be tempting to write things off around midday tomorrow but an important factor in this setup is the steepening mid level lapse rates with time, which should allow surface based instability to continue to build even after sunset as nocturnal cooling is offset by the strong southerly flow.

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BMX just updated their AFD... they mention your area is the best area to see tornadic supercells. They sound very worried; they even mentioned the possibility of an EF4+ tomorrow. Good luck and stay safe!

 

I live about 25 north of Phil Campbell. When I was told to drive down there to see if I could help, I had no idea what I was going to see since I had lost my electricity and cable that morning. I feel sick thinking it could happen again.

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I mean there's no forum about this in the Southeast subforum. I personally think it should be on the main forum though.

Yeah, I'm surprised w the lack of discussion in the se forum. Psbl major tornado event less than a day away and they're talking mundanely about winter.... I am interested to see what the Day 1 outlook from the SPC will look like..

Sent from my XT1563 using Tapatalk

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We have to see if the 00z follows the 18z in showing a slightly slower and slightly deeper solution like some of the offices suggested yesterday. This would obliviously give a chance for whatever junk convection there is to clear out and for another round of destabilization to occur. Like others have said, while the 4km NAM usually overdoes CAPE in the warm season, I don't think its playing things up all that much in this event. Even if we cut the instability by a quarter or so, we still have more than enough given the extreme shear and good upper level support. 

 

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4k NAM has a pretty intense squall line from Chicago down to central Arkansas at 15z. It moves about 250 miles or so northeast in six hours and is over central Indiana and western Lower Michigan at 21z. 4k NAM fires up discrete supercells to the southwest of this across western Tennessee and northern Mississippi. Am wondering if the supercell threat has shifted east a bit into Indiana and Ohio for wed evening. Will we see supercells behind this squall line in Illinois?

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