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Feb 25-26 Discussion/pbp


Wow

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This is crazy. Looks like we could get more snow today than we thought yesterday, and who knows what will happen Wednesday. NAM sticks to its guns, GFS and Euro go a little south, but their ensembles look better for here. WPC calling for a Euro and UK blend and a good hit here. Just seems like it is still up in the air. Good thing is there are still two storms on the table.

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Latest discussion from RNK ....

 

 

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 430 AM EST TUESDAY...

AN INVERTED TROUGH ON WEDNESDAY WILL ADVECT MOISTURE INTO OUR REGION
FROM A DISTURBANCE TRACKING ACROSS THE GULF COAST. THE SURFACE LOW
WILL TRACK ACROSS THE SOUTHEAST UNITED STATES WEDNESDAY NIGHT...THEN
OFF THE COAST THURSDAY. SHORT WAVES/DEFORMATION ZONE ON THE NORTHERN
PERIPHERY OF THIS DISTURBANCE WILL TRACK OVER THE SOUTHERN
APPALACHIANS WEDNESDAY EVENING INTO THURSDAY MORNING. THE NAM...GFS
AND ECMWF KEEP QPF TO THE SOUTH OF OUR CWA THROUGH 00Z THURSDAY.
AFTER 00Z THURSDAY...DIFFERENCES IN THE AMOUNTS AND NORTHERN EXTENT
OF QPF ARE NOTED ON THE MODEL SOLUTIONS. USED A BLEND OF GFS AND
ECMWF FOR POPS AND FEEL THAT SIGNIFICANT SNOW ACCUMULATIONS WILL BE
AFTER 06Z. THE HEAVIEST SNOW WILL OCCUR TO OUR SOUTH ACROSS NORTH
CAROLINA. ANOTHER TIGHT GRADIENT SNOWFALL EXPECT...BEING ON THE
NORTHERN EDGE OF SNOW...TOTALS FROM ZERO IN THE NORTH TO AROUND 4
INCH POSSIBLE IN HIGHEST ELEVATIONS OF WATAGUA COUNTY. WITH IT BEING
4TH PERIOD WILL HOLD OFF ON ANY HEADLINES TO WORK OUT DETAILS ON
SNOW ACCUMULATIONS. WILL ADD MENTION TO THE HWO ON SNOW POTENTIAL.

THIS DISTURBANCE TRACKS EAST OF THE AREA BY THURSDAY MORNING...THEN
ANOTHER COLD FRONT DROPS SOUTHEAST INTO THE AREA LATE THURSDAY
AFTERNOON INTO THURSDAY NIGHT. SHORTWAVE AND MOISTURE ALONG THIS
FRONTAL BOUNDARY WILL BRING LIGHT SNOW TO MAINLY MOUNTAIN COUNTIES
THURSDAY AFTERNOON INTO THURSDAY NIGHT. WILL CONTINUE LIGHT POPS FOR
EAST OF THE BLUE RIDGE THURSDAY NIGHT AS THE FRONT ROLLS THROUGH.
SNOW ACCUMULATIONS OF 1 TO 2 INCHES POSSIBLE IN THE WEST WITH HIGHER
AMOUNTS ALONG THE RIDGES TO LESS THAN HALF OF AN INCH EAST.

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Wow Chris Justus from WYFF in Greenville SC just showed the NAM snow output on air. He did preface it with it's not what he is expecting but what is on the high end based on the weather model. He did say a good possibility of a widespread 4-6"

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LOL, well, thats Atlanta's 2nd biggest snow on record if correct...7-10 inches if you assume 9-10:1 ratios and the  RGEM being right.

 

Hey, the RGEM and the NAM were all alone showing accumulating snow in the event here this morning and they nailed it. The RGEM has been money here this winter I wouldn't feel bad about riding it at all.

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Hey, the RGEM and the NAM were all alone showing accumulating snow in the event here this morning and they nailed it. The RGEM has been money here this winter I wouldn't feel bad about riding it at all.

 

It was not as aggressive though on the FZRA as far south, a big reason I think frozen precip got as far south there this AM as it has was that little period of rain around sunset last night, it wet bulbed everything down early and gave a good 3-4 degree push on temps.

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Still a lot of variation on the outcome of the Wednesday Night event when looking only at the models.

 

We should see things start to come together by the 0z this evening.

 

Images courtesy of Weatherbell

 

4CbgqGv.png

 

HXBkwds.png

 

Note: For some reason, the Weatherbell 6z Total Snow Depth is displaying totally different from the 3 hour snow accumulation.   At first glance, I am not sure what the difference in the algorithm is that is causing the difference.  I will check with Dr. Ryan Maue.   It appears to be related to the Hires Nam is seeing temperatures at the surface in the heavier snow areas staying above freezing during the precipitation.    

 

Brad Panovich also had input last night that he thought that what fell would rapidly melt on the ground.   It's all up to the amount of cold air that can get in at the lower levels and at the surface.

 

 

jGU2EQa.png

 

Note the NAM shows the heavier precipitation streaks in the Southern Piedmont above 32 degrees 

 

RctLCdL.png

 

 

148
FXUS62 KGSP 241140
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
640 AM EST TUE FEB 24 2015

 

 

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 330 AM TUESDAY...WE MIGHT HAVE AN EVEN MORE INTERESTING STORM
TO DEAL WITH AFTER WE ARE FINISHED WITH THIS MORNINGS EVENT. OUR
FOCUS SHIFTS TO THE NEXT SURFACE WAVE THAT DEVELOPS OVER THE NW GULF
OF MEXICO EARLY WEDNESDAY IN RESPONSE TO A STRONG WAVE MOVING EAST
ACROSS THE SRN PLAINS. CONFIDENCE CONTINUES TO SLOWLY INCREASE AS TO
THE EXPECTED EVOLUTION OF THIS SYSTEM AS AT CROSSES THE DEEP SOUTH
THROUGH WEDNESDAY NIGHT AND MOVES OFFSHORE THURSDAY MORNING...AND IS
NOW ABOVE AVERAGE FOR WHAT IT HAS BEEN SO FAR THIS SEASON. THE
MODELS ARE IN GOOD AGREEMENT WITH BRINGING A RAPID INCREASE IN
FORCING ACROSS NE GEORGIA LATE WEDNESDAY AND THEN ACROSS THE WRN
CAROLINAS MAINLY ON WEDNESDAY EVENING. A COUPLED JET INTERACTION
SHOULD BRING EXCELLENT UPPER DIVERGENCE AS THE DAMPENING SHORT WAVE
MOVES OVERHEAD. LOW LEVEL ISENTROPIC UPGLIDE SHOULD ALSO KICK IN BY
AROUND 00Z THURSDAY. A CONSENSUS OF THE GUIDANCE BRINGS PRECIP NEWD
STEADILY LATE IN THE DAY. WILL FINE TUNE THE PRECIP PROBABILITY TO
GO WITH A CATEGORICAL TO LIKELY POP WITH A NW TO SE GRADIENT FOR
WEDNESDAY NIGHT...WITH PRECIP CHANCES DROPPING OFF EARLY THURSDAY
MORNING WITH THE PASSAGE OF THE LOW TO THE SOUTH AND THE EXIT OF THE
STRONGER FORCING AFTER 06Z. PARTIAL THICKNESS AND FCST SOUNDINGS
ONCE AGAIN SUGGEST PRECIP TYPES LOOK TO BE A RAIN VERSUS SNOW
SCENARIO...WITH SFC WET BULB TEMPS PLAYING A BIG PART. THINK THE
STRONG FORCING WILL RESULT IN SOME DYNAMIC COOLING THAT WILL HELP
KEEP PROFILES BELOW FREEZING SUCH THAT THE HEAVIER PRECIP WILL FALL
AS SNOW ACROSS ALL BUT MAYBE THE LOWER PIEDMONT AND LAKELANDS OF SC
.
THE FCST LEANS MORE ON THE ENSEMBLE GUIDANCE IN ORDER TO DAMPEN SOME
OF THE RUN-TO-RUN VARIABILITY OF THE LOW TRACK AND NRN EXTENT OF THE
PRECIP SHIELD. THE FCST ALSO BORROWS HEAVILY FROM THE QPF GUIDANCE
ISSUED BY WPC...AND ONCE THAT IS CONVERTED TO SNOWFALL...WE HAVE A
FCST THAT SUGGESTS WE WILL REACH 12HR WARNING CRITERIA SNOWFALL
ACROSS ALMOST ALL THE FCST AREA
. THE PLUME DIAGRAMS FROM THE 03Z
SREF ARE COMPELLING. ONCE AGAIN...THE MAJORITY OF THE SREF MEMBERS
HAVE WARNING CRITERIA SNOWFALL AT MOST SITES BY 06Z THURSDAY. THERE
ARE A FEW CAVEATS...WHICH IS TO BE EXPECTED GIVEN MOST EVENTS DO NOT
ALWAYS GO ACCORDING TO PLAN. THE FCST STILL ASSUMES THAT COLD AIR
WILL ARRIVE FROM THE N/NW AS THE PRECIP SPREADS UP FROM THE SW AS
THE BOUNDARY LAYER ALSO COOLS WEDNESDAY EVENING. IF THE COLD AIR IS
DELAYED...MORE OF THE PRECIP WILL FALL AS RAIN ALONG/S OF I-85. IF
THE TRACK OF THE LOW REMAINS TOO FAR S...THE MTNS AND I-40 CORRIDOR
WILL NOT GET SUFFICIENT PRECIP TO REACH WARNING CRITERIA. THERE WILL
PROBABLY BE A 50 MILE WIDE BAND WHERE SNOWFALL IS MAXIMIZED...
RUNNING WSW TO ENE ACROSS THE WESTERN CAROLINAS AND NE GEORGIA. ALL
THAT ASIDE..
. THINK THE BEST COURSE OF ACTION IS TO ISSUE A WINTER
STORM WATCH WITH THIS FCST PACKAGE...AS CONFIDENCE IS ABOVE 50 PCT
THAT WE WILL SEE SOMETHING IN THE NEIGHBORHOOD OF 3-4 INCHES OF SNOW
MAINLY WEDNESDAY EVENING. WILL OPT TO KEEP THE GOALPOSTS WIDE FOR
NOW...SO THE WATCH WILL BE ISSUED FOR THE ENTIRE FCST AREA FOR
WEDNESDAY NIGHT.

THE REST OF THE FCST IS LESS BUSY. THERE SHOULD BE SOME LINGERING
SNOW POTENTIAL ACROSS THE MTNS ON THURSDAY...BUT MODEL GUIDANCE ALSO
SUGGESTS SOME LINGERING SHOWERY PRECIP MAINLY ACROSS THE NC
FOOTHILLS AND WRN PIEDMONT INTO THURSDAY EVE. ANY NW FLOW POTENTIAL
ON THE TN BORDER SHOULD DIMINISH BY FRIDAY MORNING.

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Nam still looks bogus and too far north. If doc came north last night I would say ok. But It didn't. Not even close to what the nam shows. IMHO is clueless. We will see with the 12z runs today, but if I'm in ATL I'm preparing for a winter storm with up to a half a foot of snow.

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Nam still looks bogus and too far north. If doc came north last night I would say ok. But It didn't. Not even close to what the nam shows. IMHO is clueless. We will see with the 12z runs today, but if I'm in ATL I'm preparing for a winter storm with up to a half a foot of snow.

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Only thing Chris is the Euro was clueless about today. RGEM and nam both nailed it. I would say a split of the RGEM and nam is probably a safe bet.
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Still a lot of variation on the outcome of the Wednesday Night event when looking only at the models.

 

Interesting to note on the 6z 4km Hires NAM that the NAM has now backed off on it's aggressive QPF output from yesterday and has shifted things back to the N and NW.    We should see things start to come together by the 0z this evening.

 

Not true.  Take that snowfall map out further than 4 AM on Thursday, and you'll see the totals ramp up across the entire state.  The 06Z NAM was incredible for the entire state of NC:

 

OJjf8Hi.png

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Nam still looks bogus and too far north. If doc came north last night I would say ok. But It didn't. Not even close to what the nam shows. IMHO is clueless. We will see with the 12z runs today, but if I'm in ATL I'm preparing for a winter storm with up to a half a foot of snow.

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The NAM (both versions) has Atlanta getting hit hard, especially from downtown north. At least on Allan's maps. 

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Only thing Chris is the Euro was clueless about today. RGEM and nam both nailed it. I would say a split of the RGEM and nam is probably a safe bet.

To my knowledge the euro did good with today. It was one of the wettest models around here. But I would say I don't think the nam is correct because it's too strong and north with the H5 look. Not even the southern branch happy doc is.

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