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Feb 25-26 Discussion/pbp


Wow

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Rap forecast sounding for atlanta at 12 hours.. ridiculously close. Pretty much ignore the surface temp/dps because it's highly likely it's too warm since rap has a warm bias at the surface. The rap is actually showing quite a bit of cooling after saturation which implies it's seeing cooling thanks to the heavy precip/dynamics instead of evaporation. What this means is the models might be too warm and as you can see it would take such a tiny bit of cooling aloft for it to go over to mostly snow..assuming these temps are exactly right..which they probably aren't just because of average margin of error.

 

That said, it must be cautioned they could be a touch too cold if the waa is under estimated. But it's hard to see that being the case...especially since the trend has been to show more cooling thanks to strong dynamics/precip rates.


Date: 12 hour  valid 3Z THU 26 FEB 15
Station: 33.65,-84.42
Latitude:   33.65
Longitude: -84.42
-------------------------------------------------------------------------------
LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W
     mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg
-------------------------------------------------------------------------------
  0 1000    56                                                                 
SFC  976   258   2.1   1.6  97  0.5   1.9  50   6 277.2 277.9 276.2 289.2  4.41
  2  950   482   0.7   0.6  99  0.1   0.7  63  16 277.9 278.6 276.4 289.5  4.21
  3  900   916   0.6   0.3  98  0.3   0.5  94  19 282.1 282.9 278.7 294.3  4.36
  4  850  1375   0.7   0.6  99  0.2   0.7 135  13 286.9 287.8 281.4 300.3  4.69
  5  800  1862   0.5   0.4  99  0.1   0.4 205  13 291.6 292.5 283.7 305.9  4.92
  6  750  2380  -0.7  -1.0  98  0.3  -0.8 220  21 295.8 296.7 285.2 309.8  4.75
  7  700  2930  -2.1  -2.3  98  0.2  -2.2 213  34 300.2 301.0 286.8 314.0  4.60
  8  650  3518  -2.6  -2.7  99  0.1  -2.6 209  56 306.1 307.0 289.0 320.9  4.84
  9  600  4152  -4.2  -4.3  99  0.1  -4.3 214  74 311.2 312.1 290.5 325.
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For last weeks event the RGEM was insistent on flipping to freezing rain for RDU, we never did.  The NAM consistently said it would be all sleet and it was.  Will see, it's close.  Usually, atleast for RDU, we almost always mix with bigger events, so I am expecting some sleet, hoping half snow and half sleet.

Thanks Pack...in our good snows here, we don't usually mix to sleet much at all...going to be close

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That has the look of a future dry slot all over it IMO. Jackpots Oxford/ Henderson all the way to Norfolk. We've had this set up before folks.

With the 5h vort max tracking to our west into W NC, I would normally agree that you would see notable dry slotting into W SC and C / E NC.  However, this is going to be a compact, relatively fast moving storm....as opposed to a slower moving, wound up storm that would be more subject to the development of a dry slot.  Essentially, the dry slot doesn't get a good chance to form as all of the good precip is over with before it does....the radar simulations show this well....my opinions on it anyway

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The latest RAP soundings aren't far off from a Wintry event into the Lake Murray area (West of Columbia)  0.1 off at one point.  KCAE basically doesn't know where the gradient will setup either.

I'm between Irmo and Chapin right near the lake and I may see something. Unfortunately it will prob be less wintry than what I saw yesterday morning otw to work.

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With the 5h vort max tracking to our west into W NC, I would normally agree that you would see notable dry slotting into W SC and C / E NC.  However, this is going to be a compact, relatively fast moving storm....as opposed to a slower moving, wound up storm that would be more subject to the development of a dry slot.  Essentially, the dry slot doesn't get a good chance to form as all of the good precip is over with before it does....the radar simulations show this well....my opinions on it anyway

I don't really see much of a dry slot as this is working out.  Dry slots are more associated with miller B's.  The low is coming out of the deep south and up the SE coast.  Yes, there will be less qpf as you head west from the coast, but I don't consider this a dry slot.

TW

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UK is interesting.  It previously had a big south bias with storms, but it got an upgrade in the past year...and I believe it was a little north biased with our last event

I have closely followed the UK for a few different storms this year. It has been just money around 4 days out but inside the last 48 hours it has been somewhat erratic. It wouldn't make my top 5 preferred guidance right now but it's hardly alone in its trends.

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I'm between Irmo and Chapin right near the lake and I may see something. Unfortunately it will prob be less wintry than what I saw yesterday morning otw to work.

 

This is a highly volatile forecast.  I will tell you, that some of the dynamic cooling will throw major kinks into the current forecast at points in the storm.  If the warm air advection is over-done, then expect some big surprises with a tight gradient around the entire area of the Midlands from a line of McCormick over to Lee county.  West Columbia and point's west have a higher change to mix over or even possibly change over to Wintry weather under the heaviest precipitation.

 

Any Southern shift in the Low track can greatly affect the final precipitation-type.  If you remember the freezing rain scare recently, that was forecast to stay well North of the area but the Low made a last adjustment just enough South to get Blytewood involved and ultimately forced a Freezing Rain Advisory all the way down to Southern Lexington county.

 

On the flip side, if the Low tracks stronger and slightly more Northwestward, a lot more areas will end up "just" too warm.  This system is a quick mover and I would assume by 2-3AM, the entire CAE region is seeing the last of the precip exit the region.

 

KCAE currently has a HWO out that reads the following:

 

HAZARDOUS WEATHER OUTLOOK

NATIONAL WEATHER SERVICE COLUMBIA SC

415 AM EST WED FEB 25 2015

GAZ040-SCZ018-025>029-031-260915-

LINCOLN-MCCORMICK-EDGEFIELD-SALUDA-LEXINGTON-RICHLAND-LEE-SUMTER-

415 AM EST WED FEB 25 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL GEORGIA AND

CENTRAL SOUTH CAROLINA.

.DAY ONE...TODAY AND TONIGHT.

DUE TO THE NEARNESS OF THE RAIN/SNOW CHANGEOVER LINE WITH THE

SYSTEM MOVING THROUGH...THERE IS A SLIGHT POSSIBILITY OF SEEING A

RAIN/SNOW MIXTURE ACROSS THESE COUNTIES AT SOME POINT TONIGHT.

MINIMAL ACCUMULATIONS EXPECTED.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

$

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