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January Pattern and Storm Discussion II


Cold Rain

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There will be lots of "ifs" and "buts" with this system. But if only 18z was little slower and if it tilted a little earlier. 

 

Weakens it really fast. If it stays closed it'll slow down & allow the HP to move over to provide in-situ CAD. The strong PV will provide more than enough cold air to tap into should it occur.

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Weakens it really fast. If it stays closed it'll slow down & allow the HP to move over to provide in-situ CAD. The strong PV will provide more than enough cold air to tap into should it occur.

 

Yep, we literally have to time this perfectly, but if if if if, lots of if's, there is a chance for some snow.

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Weakens it really fast. If it stays closed it'll slow down & allow the HP to move over to provide in-situ CAD. The strong PV will provide more than enough cold air to tap into should it occur.

 

Personally I have a good feeling about it. The fact is it's still on the table and we're four days out. Hopefully all the if's can occur. 

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GSP's afternoon

 

.LONG TERM /FRIDAY THROUGH MONDAY/...
 

-- Changed Discussion --

AS OF 230 PM EST MONDAY...THE MEDIUM RANGE MODEL GUIDANCE HAS SHOWN SOME IMPROVED RUN-TO-RUN CONSISTENCY AND CONSENSUS WITH REGARD TO MOVING A DEAMPLIFYING UPPER LOW EASTWARD ACROSS THE WESTERN CAROLINAS THURSDAY EVENING. THE 00Z ECMWF AND 12Z GFS WERE IN GENERAL AGREEMENT WITH THE BEST FORCING MOVING MAINLY ACROSS THE NE GEORGIA AND UPSTATE SC PART OF THE FCST AREA EARLY THURSDAY EVENING...SO CONFIDENCE IS INCREASING THAT WE WILL SEE SOME PRECIP THURSDAY EVENING. HOWEVER...THAT THOUGHT IS TEMPERED BY A LOOK AT THE 12Z ECMWF WHICH KEEPS THE BETTER PRECIP TO THE SOUTH AND EAST OF UPSTATE SC THURSDAY EVENING. THAT IS A GOOD INDICATOR OF OUR CONFIDENCE PROBLEM GOING FORWARD WITH THIS FCST. EVEN THE FARTHER SOUTH NEW ECMWF WOULD BRING MEASURABLE PRECIP OVER THE SRN HALF...SO PRECIP CHANCES WERE ALLOWED INTO TO THE LIKELY CATEGORY MOST PLACES ALONG AND S OF I-85...WITH CHANCES ELSEWHERE. THE PRECIP WILL BE RELATIVELY SHORT LIVED AS THE FORCING MOVES QUICKLY EAST OF THE FCST AREA BY AROUND DAYBREAK FRIDAY...ASSUMING THIS TIMING HOLDS...WHICH IS A BIG ASSUMPTION. PRECIP TYPE IS THE MAIN CONCERN...BASED ON A CONSIDERATION OF PARTIAL THICKNESS ON BOTH MODELS. THE FCST LARGELY FOLLOWED THE GFS AND ITS THERMAL PROFILES FOR P-TYPE DETERMINATION. THAT SAID...THERE IS NOT MUCH OF A WARM NOSE...SO IT LOOKS MAINLY LIKE A RAIN OR SNOW PROSPECT FOR THURSDAY EVENING. LOW LEVELS AND MIN TEMPS LOOK LIKE THEY WILL REMAIN TOO WARM OVER UPSTATE SC AND NE GEORGIA FOR ANYTHING BUT A COLD RAIN. OVER THE MTNS...SNOW LEVELS SHOULD DROP DOWN TO THE VALLEY FLOORS OVERNIGHT. THE PRECIP AMTS ON THE GFS WOULD SUPPORT A LIGHT ACCUMULATION OF SNOW OVER MAINLY THE CENTRAL AND NRN MTNS...BUT THERE REMAINS MUCH UNCERTAINTY AS TO QPF. MOST OF THE NC PART E OF THE BLUE RIDGE WOULD ALSO SEE MAINLY A COLD RAIN...BUT WITH SOME POTENTIAL FOR BRIEF CHANGEOVER TO SNOW SHOWERS AS THE PRECIP WAS ENDING. SO FOR NOW...WE LEAVE IT AS A CHANCE OF SOME WINTRY PRECIP OVER THE MTNS LATE THURSDAY AND THURSDAY NIGHT... AND WE WATCH MODEL TREND FOR MORE CONSISTENCY.

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more positives than negatives from the last 12 hours of forecast model trends: 1) upper level low staying bundled together a bit longer and is a closed contour or so stronger on a few runs (we need a stronger trend at 500mb to continue) ... & 2) most QPF charts continue to show the ability for this system to produce heavy precip rates (which is THE BEST part of this whole setup)

 

even with the possible in-situ CAD for some... we all know the slightly warmer low-levels (at the boundary layer & 925mb) will be too tough of a situation to overcome n most areas... but, the only way the boundary layer will be overcome in SOME areas is with heavy precipitation rates able to mix down some mid-level cold dynamically using the precip

 

temperature-wise, this system doesn't have a very high ceiling in terms of how much mid-level cold it can produce because of the decaying look of the vorticity (decaying upper low) at 500mb

 

ideally, along with some cold air damming at the surface, I would like to see some -3C at 850mb underneath the upper low - would be really good snow growth, but that doesn't appear to be possible... best case scenario would be some -3C to -6C at 5,000ft (in addition to a weak surface CAD) similar to the the upper low back on March 9th/10th, 2009

 

again, knowing that boundary layer issues will prevent most from snow and bring mostly rain to everyone (w/ some snowflakes mixing in at times) outside of Western NC and north of I-40 in NC (mostly snow), we'll sit back an enjoy some small area lollipopped with snow under heavy sustained precip rates and around -1C to -2C at 5000ft... I like Western NC's chances... I'll also pull for southern and eastern TN, but the precip rates there may not be heavy enough to dynamically cool the column

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Date: 3.5 day AVN valid 6Z FRI 18 JAN 13
Station: 35.31,-81.23
Latitude:   35.31
Longitude: -81.23
-------------------------------------------------------------------------------
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   219                                                                
SFC  996   254   1.0  -1.9  81  2.8  -0.2  21   7 274.5 275.0 273.2 283.6  3.34
  2  950   634   2.4  -6.0  54  8.4  -0.7  30  18 279.6 280.1 275.0 286.9  2.56
  3  900  1069   1.2 -10.6  41 11.8  -2.8  38  21 282.7 283.1 275.7 288.3  1.90
  4  850  1528   0.6 -18.5  22 19.2  -4.8  36  21 286.8 287.0 276.6 290.0  1.04
  5  800  2015   1.5 -27.8   9 29.3  -5.5  32  16 292.7 292.8 278.7 294.3  0.49
  6  750  2534   1.1 -31.6   7 32.7  -6.3  32  11 297.8 297.8 280.9 299.0  0.36
  7  700  3085  -1.1 -33.7   6 32.6  -8.1   9  11 301.3 301.3 282.3 302.3  0.32
  8  650  3673  -3.3 -36.4   6 33.1  -9.9 341  13 305.2 305.3 283.8 306.2  0.26
  9  600  4302  -6.6 -37.9   6 31.2 -12.5 320  16 308.4 308.5 285.1 309.3  0.24
10  550  4976 -10.6 -42.4   5 31.8 -15.6 315  20 311.6 311.6 286.1 312.2  0.17
11  500  5702 -15.2 -47.5   4 32.3 -19.3 311  27 314.5 314.6 287.1 314.9  0.11
12  450  6489 -20.9 -46.5   8 25.6 -23.8 301  34 317.0 317.0 287.9 317.5  0.13
13  400  7348 -27.2 -46.6  14 19.4 -29.1 288  35 319.6 319.7 288.8 320.2  0.15
14  350  8295 -34.5 -53.0  14 18.5 -35.7 275  38 322.2 322.2 289.5 322.5  0.08
15  300  9355 -42.1 -64.4   7 22.2 -42.8 266  47 326.0 326.0 290.6 326.1  0.02
16  250 10564 -50.6 -68.5  10 17.9 -51.0 262  60 330.8 330.8 291.9 330.9  0.02
17  200 11989 -58.9 -69.4  25 10.5 -59.0 255  69 339.5 339.5 294.2 339.6  0.02
18  150 13769 -63.6 -71.0  35  7.5 -63.6 256  75 360.6 360.6 298.8 360.7  0.02
19  100 16239 -65.6 -77.4  18 11.8 -65.7 254  63 401.1 401.1 305.3 401.1  0.01
TRP                                             0                             
WND                                             0                             

 


 

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18Z GFS came and went - and I'm surprised nobody commented on it. It seems to keep the moisture away from the 0C 850 line, so not much luck with that run.

 

 

18z GFS was much quicker with pushing the storm energy east compared to the last several runs

 

& much quicker is a bit of an understatement... seemed to default back to typical GFS breaking the sound barrier-bias of being too fast

 

I don't usually throw out a model run, but that 18z GFS looked strange with the fast evolution of the storm energy at 500mb

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