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Feb 25-26 Discussion/pbp


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Burger, are you talking about the January 2013 ULL?

 

 

 

The majority of NC and probably upstate SC were under WSWs for that one, IIRC, but most places never changed over from rain until the very end, aside from the Triad area (where we got a heavy wet snowfall at 33-34 degrees that evening with like 5:1 ratios).

 

Yea it must of been that one. Totally different scenario though so it's probably just confusing anyone reading this thread who is ready to jump the cliff. 

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Yea it must of been that one. Totally different scenario though so it's probably just confusing anyone reading this thread who is ready to jump the cliff. 

 

I think we have a colder airmass to work with here.  I recall it getting up to about 50 the next day and zapping most of the snow away.  I don't think temps ever fell below freezing and possibly rose into the mid or upper 30s overnight after the snow ended around midnight.

 

I remember having basically flooding rains for the entire day beforehand, too.  Pretty sure soil temps were awful and all that jazz, too.

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The trends at 850 have been not the greatest today.  Its a close call for atl proper.  The north side and north look fine, but that 0c line has been trending north on EVERY model today.  

 

 

The trends at 850 have been not the greatest today.  Its a close call for atl proper.  The north side and north look fine, but that 0c line has been trending north on EVERY model today.  

 

With the exception of the NAM the 850 low appears weak or open enough to me that strong precip rates can overcome its track, the 0C line is close but the other thing I noticed is there is massive room for evaporative cooling in the 800-900-mb layer...the big difference between the NAM and GFS is the NAM has screaming SW flow and WAA from 800-850mb over Ga, the GFS and most other guidance does not, its all 700-780mb where its easily cold enough to stay below 0C.  If the NAM is wrong on that 800-850 idea there will be massive busts in south Atlanta.  The new GFS cannot be trusted thermally in the 1000-850 layer, its got serious issues being too warm.

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WSW from GSP

Interesting... they changed accumulations from 3-5" (from this morning) to 3-7".

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...

AS OF 230 PM TUESDAY...THE MAIN FOCUS OF COURSE FOR THE SHORT TERM

IS THE IMPENDING WINTER EVENT WHICH BEGINS WED. AFTERNOON AND THEN

UNFOLDS ACROSS THE ENTIRE AREA WED NIGHT. THERE IS GOOD MODEL

CONSENSUS THAT THE SOUTHERN STREAM UPPER WAVE OVER THE 4 CORNERS

THIS MORNING WILL MOVE RAPIDLY EASTWARD AND INDUCE CYCLOGENESIS OVER

THE GOM EARLY WED. THE GULF LOW IS THEN FORECAST TO MOVE QUICKLY

EASTWARD ACROSS THE DEEP SOUTH WED NIGHT. THE MAIN CONCERN FOR THIS

FORECAST IS WHERE THE BEST BANDING WILL SET UP AND THE SUBSEQUENT

QPF RESPONSE. ALSO FOR THE PIEDMONT AREA...THE QUESTION OF QUICKLY

THE BOUNDARY LAYER COOLS IS A BIG PLAYER IN SNOW ACCUMS. BASED ON

SURFACE WET BULBS...IT LOOKS INITIALLY ALONG AND SOUTH OF I-85

PRECIP WILL BEGIN AS RAIN WHICH WILL USE UP SOME QPF.

HENCE...SNOWFALL ACCUMS WILL FALL OFF TO THE SOUTH WITH THE

RAIN/SNOW LINE MOST LIKELY SETTING UP SOMEWHERE ACROSS THE SOUTHERN

FRINGS OF NE GA AND THE SOUTHERN UPSTATE...FROM ELBERT COUNTY GA

EAST THROUGH ABBEVILLE AND GREENWOOD COUNTIES. THE SREF PLUMES CATCH

THIS SCENARIO WITH THE HIGHEST TOTALS OUTSIDE THE MOUTAINS ALONG AND

NORTH OF I-85 WHERE 4-6 INCHES OF SNOW IS THE MEAN FORECAST. THE

PLUMES INDICATE THAT ACTUALLY THE SW MOUNTAINS MAY ACHIEVE THE MOST

SNOW OF 6-8 INCHES WHICH IS PLAUSIBLE BASED ON UPSLOPE. THE WPC WWD

PAINTS A SWATH OF 4-6 INCH SNOW FROM THE GA MOUNTAINS EASTWARD

THROUGH CLT. HAVE FOLLOWED THIS GENERAL IDEA WITH SNOW GRIDS...

EXCEPT WENT HIGHER IN THE SW MOUNTAINS (6-8 INCHES SOME AREAS). 12Z

MODEL QPF HAS A LITTLE BETTER AGREEMENT WITH THE GFS NOW WETTER BUT

STILL NOT QUITE AS WET AS THE NAM. THE UPSHOT IS THAT CONFIDENCE IS

HIGHEST TO GO AHEAD AND PULL THE TRIGGER ON A WINTER STORM WARNING

FOR MOST OF THE AREA BEGINNING WED LATE AFTERNOON. THE EXCEPTION IS

THE SOUTHERN TIER OF COUNTIES OF ELBERT...ABBEVILLE...GREENWOOD

WHERE WILL A WINTER STORM WATCH WILL BE MAINTAINED AS RAIN/SNOW LINE

WILL BE IN VICINITY.

where do you see 3-7"? In the Winter storm warning it clearly says 3-6" north of 85 and 8+ in the SW mountains of NC.
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the 540 lthickness line is

 

 

The 540 thickness line is not as valuable in this part of the country as is 1000-850mb and 850-700mb thickness values

Looking at the cross section temp profile of the NAM below for KCLT, this goes from rain to snow to maybe rain to snow. 540 is not valuable at all here? Never heard that one before. 

temp.png

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Based on the visible sat image this afternoon, it would be huge if we could get some clearing overnight to get some radiational cooling......if that allowed us to drop 2 or 3 more degrees than forecast.  Then have the clouds roll in before the sun comes up.  That would probably be a best case scenario for us in Georgia.  If we can hold to about 34 to 36 tomorrow before the precip, that would be a good sign.  Any temps 38 to 40 would be somewhat alarming.

 

- Buck

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Based on the visible sat image this afternoon, it would be huge if we could get some clearing overnight to get some radiational cooling......if that allowed us to drop 2 or 3 more degrees than forecast.  Then have the clouds roll in before the sun comes up.  That would probably be a best case scenario for us in Georgia.  If we can hold to about 34 to 36 tomorrow before the precip, that would be a good sign.  Any temps 38 to 40 would be somewhat alarming.

 

- Buck

 

I think your bigger problem there is the mid-levels, surface I think you're fine, this is a strong enough storm it will cool down to 32 or 33 and the guidance tomorrow is most definitely too warm. It really is all about the 800-880mb layer with this storm, the models think the BL is going to be warm but they're wrong IMO.

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Looking at the cross section temp profile of the NAM below for KCLT, this goes from rain to snow to maybe rain to snow. 540 is not valuable at all here? Never heard that one before. 

temp.png

I've seen a lot of snow here with thicknesses around 546 and even close to 550. The 540 rule is at best an absolute first guess of where the rain/snow line is. Way better to use partial thicknesses; and even then they may miss subtle warm layers.

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Unless there's more of a jump North in the evening modeling the blend of guidance still is a crapshoot for ATL. Depending on your back yard the model solutions are being bandied about, even with their known biases. Been here for 20+ yrs, as has been stated the line is usually N or S of ATL proper. Glad I don't have folks relying on my forecast, at this time will go with GFS/EURO blend only slightly cooler due to warm biases. Tomorrow is the big show, boom or bust for this area. Given last two events and being colder than modeled will stick with that, boom for somewhere in this area.

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Based on the visible sat image this afternoon, it would be huge if we could get some clearing overnight to get some radiational cooling......if that allowed us to drop 2 or 3 more degrees than forecast.  Then have the clouds roll in before the sun comes up.  That would probably be a best case scenario for us in Georgia.  If we can hold to about 34 to 36 tomorrow before the precip, that would be a good sign.  Any temps 38 to 40 would be somewhat alarming.

 

- Buck

 

Good point. I was worried when I saw the temp climb to 40F with an overcast but now it has already dropped to 39F and I see blue sky between the clouds for the 1st time today. Excellent timing for radiational cooling!

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Still think all of Metro ATL gets all rain, only far northern burbs have any shot at accumulations. WSI RPM ("futurecast" on TV stations), SREF, NAM, GFS all screw us- and we are now less than 24 hours away. The fat lady has sung. Congrats far north GA, you will get nailed, down here another hose job.

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Interesting...wonder if GFS is picking up the snow cover...RDU has 2" of snow on the ground with a  hard freeze tonight.

 

Could be.  Looks overdone, though.  In any case, temperatures are easily into the mid-30s by the time precip arrives here, so no worry.  Looks like precip won't arrive until a few hours after dark, so that will help.  I really don't think we start out as rain here.

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I've seen a lot of snow here with thicknesses around 546 and even close to 550. The 540 rule is at best an absolute first guess of where the rain/snow line is. Way better to use partial thicknesses; and even then they may miss subtle warm layers.

I see your point, i go to 500-1000mb first then look deeper. 546 means somewhere the column is above freezing and that appears to be at the surface. Maybe snow rates overcome melting? maybe. that warm pocket is also concerning, but seems like a outlier maybe....hopefully for CLT's sake.  

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I think your bigger problem there is the mid-levels, surface I think you're fine, this is a strong enough storm it will cool down to 32 or 33 and the guidance tomorrow is most definitely too warm. It really is all about the 800-880mb layer with this storm, the models think the BL is going to be warm but they're wrong IMO.

 

I hope you're right regarding the model guidance......I'm about 45 miles NE of downtown and even further away from Hartsfield, where all the "official" KATL forecasts for Atlanta are for.  There's several of us on here that are roughly 15 miles south of Gainesville, so hopefully when all is said and done we'll be in the sweet spot.  It's crazy that a lot of the model snowfall maps show the southern end of our county with zilch while we're close to the 6 to 10 inch.  It's gonna be really interesting to see just how the gradient sets up.

 

- Buck

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Still think all of Metro ATL gets all rain, only far northern burbs have any shot at accumulations. WSI RPM ("futurecast" on TV stations), SREF, NAM, GFS all screw us- and we are now less than 24 hours away. The fat lady has sung. Congrats far north GA, you will get nailed, down here another hose job.

Maybe we will have a better shot in March. There's no way we go all winter without any snow or ice. Not a winter with so much cold and moisture around. For that to happen, we would have to have horrible luck.

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Still think all of Metro ATL gets all rain, only far northern burbs have any shot at accumulations. WSI RPM ("futurecast" on TV stations), SREF, NAM, GFS all screw us- and we are now less than 24 hours away. The fat lady has sung. Congrats far north GA, you will get nailed, down here another hose job.

 

We seriously cannot get a break this winter. So frustrating storm after storm...same exact thing, same exact story every time.

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Burger, are you talking about the January 2013 ULL?

accum.20130117.gif

The majority of NC and probably upstate SC were under WSWs for that one, IIRC, but most places never changed over from rain until the very end, aside from the Triad area (where we got a heavy wet snowfall at 33-34 degrees that evening with like 5:1 ratios... knocked out power here, too.).

Question? These images that are posted and say gif, are they really gifs? They are just overzoomed images when i ooen them. I have a new android phone and trying to relearn how to use a phone after being on iPhone for years. Any help?
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