Severe Weather Winter 2012

[beneficii]

We may have something on Friday, per MEG:

DUE TO THE HIGH DEGREE OF DISAGREEMENT AMONG MODELS...MAINLY IN
TIMING...AFTER MIDWEEK...DECIDED TO HOLD ONTO SLIGHT CHANCE POPS
ON THURSDAY. HOWEVER...THERE IS A GOOD CHANCE THURSDAY WILL BE DRY
AS THE FIRST STORM SYSTEM SHIFTS EAST OF THE MIDSOUTH AND THE NEXT
GETS ORGANIZED TO OUR WEST. THE SECOND ROUND OF WEATHER LOOKS LIKE
IT WILL HAVE BETTER DYNAMICS TO WORK WITH FRIDAY INTO FRIDAY
NIGHT. A LONGWAVE TROUGH WILL SHIFT OUT OF THE PLAINS...WITH A
SHORTWAVE SWINGING ACROSS THE MISSISSIPPI RIVER VALLEY MIDDAY
FRIDAY. FOR NOW THE GFS KEEPS THIS FEATURE POSITIVELY TILTED WITH
A SURFACE LOW TRACKING NEAR MEMPHIS. SURFACE DEW POINTS ARE
EXPECTED CREEP UP INTO THE 60S ACROSS NORTH MISSISSIPPI FRIDAY
AFTERNOON. THIS SCENARIO WOULD LIKELY RESULT IN A FEW
THUNDERSTORMS IN NORTH MISSISSIPPI AND WEST TENNESSEE. NOT
PREPARED TO INTRODUCE ANY STRONG OR SEVERE THREAT IN THE HWO
YET...BUT WILL PAY CLOSE ATTENTION TO THE ORIENTATION OF THE
SHORTWAVE AND TRACK OF THE SURFACE LOW OVER THE NEXT FEW MODEL
RUNS.

Right now, though, the surface low is progged to track near Memphis, and the setup is questionable, but in what has been a fairly slow season, it is something to keep an eye on.

[harlequin]

We may have something on Friday, per MEG:

Right now, though, the surface low is progged to track near Memphis, and the setup is questionable, but in what has been a fairly slow season, it is something to keep an eye on.

Just wondering, why do you think this has been a fairly slow season thus far?

[Kevin]

We may have something on Friday, per MEG:

Right now, though, the surface low is progged to track near Memphis, and the setup is questionable, but in what has been a fairly slow season, it is something to keep an eye on.

I have to echo harlequin in saying this has not been a slow winter season thus far. Sure we haven't had tornadoes right through the heart of Memphis...but there's been two rather robust events so far in Dixie Alley. Its not 2008 at this point but certainly comparing to last year that's active.

[andyhb]

70 preliminary tornado reports thus far in January...I wouldn't say it has been a quiet month...We've already had one significant outbreak.

[Kevin]

By the way...I also hold to my opinion that we were incredibly lucky this past Sunday. Things were more in place last week than any event last year locally...and probably since 2008.

Some of last year's events had supercells but lacked some environmental characteristics due to the timing mostly. Earlier events turned linear but also lacked some parameters that helped favor that mode strongly.

Sunday all the environmental parameters were in play for tornadic supercells capable of strong to even violent tornadoes. The mode shouldn't have changed as early as it did. If it didn't...well again we were as lucky as we'll probably ever get.

[andyhb]

12z ensembles and OP models show the NAO likely turning positive following this brief flirt with negativity, which could enhance the potential for more severe weather as we get later into February and eventually March.

[Bigm33]

70 preliminary tornado reports thus far in January...I wouldn't say it has been a quiet month...We've already had one significant outbreak.

No this has been pretty dicey as far as Januarys go...just not in the MEG CWA. Ever since Super Tuesday '08 they have had the storm shields at full power here  and I'm sure I'm not the only person on the site who thinks it's a tad strange we are discussing severe wx in January and not winter wx. Unless a huge flip comes about soon it may as well be a winter cancel here (and to think just the other day my kids were asking when they would get a snow day home from school...)

[beneficii]

Sorry everybody.  I did have just Memphis in mind when I said that.  I am guilty of IMBYism.

Anyway, with the latest discussion from MEG, it looks like chances, at least for Tennessee, aren't going to be very strong this Friday or weekend, and we may even get some snow on the backside of the system. 

WHILE MODELS ARE IN RELATIVELY GOOD AGREEMENT EARLY IN THE LONG
TERM WITH HIGH PRESSURE BUILDING OVERHEAD THURSDAY...CONSISTENCY
AND PERSISTENCE TAKES A NOSEDIVE LATE IN THE WEEK AND ESPECIALLY
NEXT WEEKEND. LARGE SWINGS IN MODEL SOLUTIONS CONTINUED TODAY WITH
THE GFS DRY FOR THE EXTENDED AND A SPLIT FLOW PATTERN SETTING UP.
THE EURO AND CANADIAN DEVELOP A FAIRLY POTENT LOW PRESSURE SYSTEM
OVER THE LOWER MISSISSIPPI VALLEY NEXT WEEKEND WITH PLENTY OF COLD
AIR TO WORK WITH GIVEN A MORE PHASED SOLUTION. THIS IS IN STARK
CONTRAST TO YESTERDAY WHERE MODELS HAD THEIR OPPONENT/S SOLUTION.
NEEDLESS TO SAY...CONFIDENCE IS QUITE LOW AND WILL CONTINUE WITH
THE LOW CHC POPS FOR FRIDAY AND SATURDAY. IF THE EURO AND CANADIAN
SOLUTIONS PAN OUT...THERE MAY BE A BIT OF SNOW ON THE BACKSIDE OF
THE SYSTEM.

[beneficii]

18z GFS has the surface low going over Dyersburg, with quite a bit of precip on Friday evening.

EDIT: Bulk shear is strong, but instability is marginal except near the Gulf Coast.

[andyhb]

I'd watch that system at 120+ hrs on the 18z GFS for any strengthening trends in future model runs, wind profiles are very strong with excellent directional shear across the Lower MS Valley/Mid-South. It wouldn't take much of a deepening of the surface low/a bit of a westward trend/slightly alteration of the geometry of the trough to get a solid warm sector pulled northward out of the Gulf and provide fuel for svr wx...

NAM at the end of the run has something brewing as well across the Rockies/Inter-Mountain area.

[jmundie]

I'd watch that system at 120+ hrs on the 18z GFS for any strengthening trends in future model runs, wind profiles are very strong with excellent directional shear across the Lower MS Valley/Mid-South. It wouldn't take much of a deepening of the surface low/a bit of a westward trend/slightly alteration of the geometry of the trough to get a solid warm sector pulled northward out of the Gulf and provide fuel for svr wx...

I'd be surprised if it went much further west than its currently showing. The -nao seems to be trending negative faster than the models are picking up on. It won't take much blocking, along with the ridge out west, to suppress the track of this storm pretty significantly.

[beneficii]

Well, it looks like we're getting back into the watching situation.

[beneficii]

I'd be surprised if it went much further west than its currently showing. The -nao seems to be trending negative faster than the models are picking up on. It won't take much blocking, along with the ridge out west, to suppress the track of this storm pretty significantly.

This is an interesting post, but the forecasts seem to be showing the NAO hanging around neutral for the forseeable future, going possibly slightly negative.  Do you think the drop in the NAO will be deeper than what is correctly being modeled?

[jmundie]

This is an interesting post, but the forecasts seem to be showing the NAO hanging around neutral for the forseeable future, going possibly slightly negative.  Do you think the drop in the NAO will be deeper than what is correctly being modeled?

Unless I'm reading it incorrectly, the models have been initializing the nao/ao too high, its decently negative right now (the ao impressively negative) and the gfs, most notably, has been initializing them neutral to positive. The 12z euro run slowly trends negative, and then goes very negative at the end of its 10 day timeframe.

Here's the euro and its forecast spread of late for the NAO



and here's the gfs forecasts

[beneficii]

Looking at those charts, the Euro may have initialized it a little too high, but the difference doesn't seem significant.  You can definitely see the disagreement on the two models, however.

Were you referring to that, or were you refer to another chart when you said a model/models have been initializing it too high?