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Feb 25-26 Discussion/pbp


Wow

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i've been thinking for a while that there could be a very narrow area of sleet since soundings have suggested it's possible but it's impossible to tell where that will be since a lot of that will depend on meso effects that simply are impossible to narrow down this far in advance imo

 

That said, the rap is throwing a big monkey wrench into things as it's showing major dynamical cooling on it's latest run with 850s dropping to 0 or below all the way into central ga. As a whole it's been colder than the nam/gfs anyway at 850s but  this would spell the possibility of snow accumulations south of where the transition is expected to be.  I'm not sure if it will be as far south as it's 850s would say since the low levels are probably not cold enough in central ga but  what is important is it's showing that cooling  its possible.

 

btw other panel is to show that the rap is quite a bit further south with the 0c 850 on some runs

I just had to triple take on that ..hahah  I see that 0c line very close.  I have said all along this is a "rates driven" storm...I would agree, that its very possible that portions of Mid GA could see 850's at or slightly below.  our 2m temps will likely be too warm, prolly near 40, but something to watch for sure.  I guess same thing the NAM was showing last night?

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This is the Euro's 850 temps right at the height of the precip for central NC, verbatim, the Euro is no mixing for Wake.   I think I-95 will be the rain/snow line, maybe a little east of that.  The Euro was about 0.75" QPF for all of Wake Co with 0.5" reaching the triad.  That probably is the best QPF expectation, not buying the insane 1.5" QPF of the NAM's.  The RGEM/GFS are roughly around the Euro QPF wise.

Thanks for the update on the RGEM and euro. Do you mind posting the euro total precip map? Those are some cold 850's! It would match up with NWS discussion of 12:1-14:1 ratios for the western areas.

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Thanks for the update on the RGEM and euro. Do you mind posting the euro total precip map? Those are some cold 850's! It would match up with NWS discussion of 12:1-14:1 ratios for the western areas.

 

Here you go...

 

Edit:  EuroWx has GSO with 11:1 to ratios, RDU with 10:1.

post-2311-0-81898300-1424869022_thumb.pn

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From about 10pm tonight till about 4am tomorrow the 6z NAM is an absolute paste bomb here, I have no confidence in the SN maps painting that transition zone correctly.  Baginess in both the 1300 /1550 thick lines is pretty telling at 27hrs, soundings also show a deep isothermal layer.  Transition zone will likely fall along a Sanford to Washington line, it will wobble and move a little as the disorganized 850 passes just to the south, but that would be my rough guess in this late stage.  I do think Greenville does well, more to the north and west but that is always the case.  

 

Credit Model Center http://www.americanwx.com/models

post-382-0-08756900-1424868989_thumb.png

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This is the Euro's 850 temps right at the height of the precip for central NC, verbatim, the Euro is no mixing for Wake.   I think I-95 will be the rain/snow line, maybe a little east of that.  The Euro was about 0.75" QPF for all of Wake Co with 0.5" reaching the triad.  That probably is the best QPF expectation, not buying the insane 1.5" QPF of the NAM's.  The RGEM/GFS are roughly around the Euro QPF wise.

 

Precip is pretty much out of here at 36hrs per the EC graphics on WunderMap, 27, 30, and 33hrs look to be the money shot.

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I think it's pretty clear that 1 inch qpf is not going to be a rare event for this system lol. The EURO/GFS are likely underdone. I am just hoping that beefed up totals today do not bring in more mixing. The NAM has raleigh pretty much right on the line for all snow vs sn/ip/sn. Just NW of that line will have some impressive totals this time tomorrow.

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It dropped a little while ago to 28.6 in Dunwoody with heavy frost (now 28.9). It looks like there may be an hour or so of partial sunshine per current skies here and satellite.

Scratch that about chance for some sun. Satellite pic was couple of hours old. Never got sun.

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Birmingham 

 

MESOSCALE DISCUSSION...CORRECTED TIME STAMP...

TAKING A LOOK AT THE MORNING SOUNDING...WE CAME IN A BIT WARMER
ALOFT THAN EXPECTED.  HOWEVER...WE WERE DRIER AS WELL...SUGGESTING
THAT THE WET BULBING EFFECTS WILL BE CRITICAL TO THE FORECAST.  THIS
IS NOTHING NEW...BUT MOST PROJECTIONS ALOFT STARTED AT ABOUT
+4...WHERE OUR SOUNDING CAME IN AT +8 AT 800MB.  SINCE THERE IS
LITTLE TO NO COLD AIR ADVECTION PROCESSES TO HELP OUT THE FROZEN
PRECIP...WE WILL HAVE TO RELY COMPLETELY ON DYNAMICAL OR MECHANICAL
COOLING...THAT IS FORCING COLDER AIR ALOFT DOWNWARD THROUGH HEAVY
PRECIP PROCESSES.

OTHERWISE...THE START TIME TO THE MOISTENING IS LOOKING QUICKER THAN
EXPECTED WHICH WILL POSSIBLY NOT ALLOW ALL THAT MUCH IN THE WAY OF
SURFACE WARMING.  BIG DIFFERENCE BETWEEN EET AT 35/23 AND BHM
32/22...AS BHM WOULD WET BULB SEVERAL DEGREES BELOW FREEZING AS LONG
AS ANY PRE-PRECIP WARMING IS NOT TOO DRAMATIC.

WE ARE MOVING FROM THE MODELS TO OBSERVATIONS.  WE WILL LAUNCH 1 OR
2 SPECIAL BALLOON RUNS TO TRY AND ASSESS MOVING FORWARD.  FORECAST
WILL REMAIN THE SAME...BUT WITH WARMER TEMPS ALOFT AND COOLER
SURFACE WET BULBING...BE EXTREMELY WEARY OF SLEET AT THE ONSET AND
POSSIBLY SLEET FOR THE DURATION IN SOME LOCATIONS ALONG THE SOUTHERN
END OF THE WARNING.  MY TWO RULES FROM HERE GOING FORWARD WILL BE TO
WATCH SURFACE AND 850MB TEMPS AND DEWPOINTS...WHICH ARE BEST
ASSESSED THROUGH OBSERVATIONAL DATA.

LAST POINT...THE PRECIPITATION IS EXTREMELY HEAVY...CONVECTIVE IN
SOME CASES...SO THE DYNAMICAL PROCESSES WILL BE AMPED SIGNIFICANTLY
COMPARED TO OUR TYPICAL WINTER EVENTS.  KEEP THIS IN MIND...THAT
COOLING THE COLUMN WILL OCCUR QUICKLY AND IT WILL LIKELY MODIFY ANY
FORECAST SOUNDINGS PROJECTED.  USING FORECAST SOUNDINGS WILL BE A
VERY DANGEROUS PROPOSITION FROM HERE FORWARD.

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