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March 5 Snow Thread-Model Discussion ONLY


stormtracker

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I agree that its best uvv and fronto that are causing qpf shifts. Those factors line up so it shouldn't be a surprise that what's being shown is evolving in that manner.

The overall setup hasn't really changed at all lately. This is not like situations where it's rapidly evolving up to game time IMO. Of course figuring out exactly where the best banding will set up is tricky though I wouldn't bet against just NW of the cities at this point heh. 

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Nah. Temps aloft are never cold enough for good dendrite formation. Probably standard 9-11:1.

Perhaps the 12 hour average will be close to 10-1, but we've got quite the subtropical connection going this time around (actually meeting the definition of an atmospheric river per the source of origin and PW anomalies). Enough for 12-1 at times, which is good for the daytime in early March. The soundings last night (when I was working) actually showed that -- much deeper moisture above 500 mb this go around compared to events up to this point. The "seeder-feeder" conceptual model should be quite applicable here. Lots of available ice nuclei from way up in the trop.

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I agree that its best uvv and fronto that are causing qpf shifts. Those factors line up so it shouldn't be a surprise that what's being shown is evolving in that manner.

That upper level jet (over 170 kts at 250 mb) is no joke. Someone's going to cash in along that frontogenetic band in the RRQ of the robust northern jet coinciding with the shortwave energy from the southwest phasing in.

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That upper level jet (over 170 kts at 250 mb) is no joke. Someone's going to cash in along that frontogenetic band in the RRQ of the robust northern jet coinciding with the shortwave energy from the southwest phasing in.

I've brought that up on a few occasions in the PA sub forum. That UL jet is not something you see everyday in this setup. Someone will reap the benefits of that for sure.
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Not sure it's really a SE trend just a shift in best frontal lift.

Yeah, there hasn't been any real shift in the primary components from what I can see, just a tightening of the secondary precip gradient as the boundary slides south ahead of the slightly delayed 2nd impulse.

I can already foresee the panic early Thursday morning when we're in a lull between waves and those N/W have racked up 3-4" while DC is just changing over. Then the 2nd impulse rolls through and it's the westerners that are shafted.

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FINAL CALL for DC:

2am - 4am: Steady light rain mixes with and changes to sleet, Temps falling into the mid 30s.
4am - 6am: Light intermittent sleet with temps in the low to mid 30s.
6am - 8am: Light sleet transitions over to light snow. Temps in the low 30s.
8am - 10am: Snow becomes steadier, with temps falling below freezing.
10am - 4pm: Moderate to Heavy snow with temps in the mid to upper 20s.
4pm - 6pm: Snow becomes lighter and tapers off.

Total storm accumulation: 5-8"

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While LWX doesn't seem to have updated their expected snow/ice accumulations map yet,  I just noticed that they have updated their minimums map, happily taking <1" well off the table.  They also updated their high end map.  Minimums (I think this is a 10th percentile) map: 

 

SnowAmt10Prcntl.png

 

ETA: for metro DC.  Sorry Fredricksburg...

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FINAL CALL for DC:

2am - 4am: Steady light rain mixes with and changes to sleet, Temps falling into the mid 30s.

4am - 6am: Light intermittent sleet with temps in the low to mid 30s.

6am - 8am: Light sleet transitions over to light snow. Temps in the low 30s.

8am - 10am: Snow becomes steadier, with temps falling below freezing.

10am - 4pm: Moderate to Heavy snow with temps in the mid to upper 20s.

4pm - 6pm: Snow becomes lighter and tapers off.

Total storm accumulation: 5-8"

 

 

nice forecast... gonna go clear off the measure spots shortly (although the rain is helping with that). 

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While LWX doesn't seem to have updated their expected snow/ice accumulations map yet,  I just noticed that they have updated their minimums map, happily taking <1" well off the table.  They also updated their high end map.  Minimums (I think this is a 10th percentile) map: 

 

SnowAmt10Prcntl.png

 

ETA: for metro DC.  Sorry Fredricksburg...

The min, max, and expected snowfall maps were all updated at the same time.

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Looks like a Parr's ridge jackpot based on the snow map. From das to psuhoffman

There are two very distinct camps right now, amazing considering its 18 hours away.  The euro/ggem/ukmet/sref have a more amped and stronger second wave tomorrow.  The GFS/NAM have a weaker suppressed second wave.  The RGEM is kind of riding the middle fence right now.  For DC and VA its not really that much of a difference but for the northern MD area it makes a huge difference and creates a very difficult forecast as the NAM/GFS imply basically a 2-4" snow up this way while the others imply a 6-10" snowfall.  Despite my pessimism I would lean towards the Euro/GGEM/UKMET idea right now just based on the gut feeling that the other models may be putting too much emphasis on the front runner wave tonight and dampening the second a bit too much.  I've seen it before.  My hunches have been wrong a lot lately in this pattern though so take that for what its worth, not much. 

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Here's the WPC update on model preference:

 

...NORTHERN STREAM TROUGH DIGGING THROUGH THE MIDWEST/NORTHEAST...
...COLD FRONT SETTLING THROUGH THE EAST...
...SURFACE WAVE DEVELOPING ALONG THE FRONT AND IMPACTING THE
MID-ATLANTIC...

PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: AVERAGE

THE MODELS CONTINUE TO FORECAST A COLD FRONT ADVANCING
SOUTHEASTWARD OVER THE NEXT DAY OR SO DOWN THROUGH THE
MID-ATLANTIC AND SOUTHEAST AS ARCTIC HIGH PRESSURE NOSES SOUTH
DOWN THROUGH THE PLAINS AND MIDWEST. THE 12Z UKMET IS SLOWER THAN
THE GLOBAL MODEL CONSENSUS WITH THE FRONTAL PROGRESSION. THE 12Z
NAM AND 12Z GFS ARE GENERALLY A BIT FASTER TO DROP THE FRONT DOWN
TO THE SOUTH...AND BECOME MOST SUPPRESSED WITH THE FRONT. THE 12Z
GEM AND 12Z ECMWF ARE IN BETWEEN THE TWO CAMPS. MEANWHILE...A
SHORTWAVE TROUGH IS FORECAST TO BE DIGGING SOUTHEAST ACROSS THE
MIDWEST THROUGH THE PERIOD AND SHOULD CROSS THE OH VALLEY BY LATE
THURS AND THEN THE NORTHEAST THURS NIGHT. THE 12Z NAM IS THE
WEAKEST SOLUTION WITH THIS ENERGY...WITH THE REMAINING MODELS ALL
SLIGHTLY MORE AMPLIFIED. THE LATEST GEFS MEAN AND ECENS MEAN ARE
STRONGLY SUPPORTIVE OF THEIR RESPECTIVE DETERMINISTIC SOLUTIONS.
SO...BASED ON THIS WILL PREFER TO BLEND THE GFS AND ECMWF.

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Here's the WPC update on model preference:

 

...NORTHERN STREAM TROUGH DIGGING THROUGH THE MIDWEST/NORTHEAST...

...COLD FRONT SETTLING THROUGH THE EAST...

...SURFACE WAVE DEVELOPING ALONG THE FRONT AND IMPACTING THE

MID-ATLANTIC...

PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF

CONFIDENCE: AVERAGE

 

 

ETA - Euro-GFS seems like an odd blend of extremes to me; welcome further thoughts.

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Here's the WPC update on model preference:

 

...NORTHERN STREAM TROUGH DIGGING THROUGH THE MIDWEST/NORTHEAST...

...COLD FRONT SETTLING THROUGH THE EAST...

...SURFACE WAVE DEVELOPING ALONG THE FRONT AND IMPACTING THE

MID-ATLANTIC...

PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF

CONFIDENCE: AVERAGE

THE MODELS CONTINUE TO FORECAST A COLD FRONT ADVANCING

SOUTHEASTWARD OVER THE NEXT DAY OR SO DOWN THROUGH THE

MID-ATLANTIC AND SOUTHEAST AS ARCTIC HIGH PRESSURE NOSES SOUTH

DOWN THROUGH THE PLAINS AND MIDWEST. THE 12Z UKMET IS SLOWER THAN

THE GLOBAL MODEL CONSENSUS WITH THE FRONTAL PROGRESSION. THE 12Z

NAM AND 12Z GFS ARE GENERALLY A BIT FASTER TO DROP THE FRONT DOWN

TO THE SOUTH...AND BECOME MOST SUPPRESSED WITH THE FRONT. THE 12Z

GEM AND 12Z ECMWF ARE IN BETWEEN THE TWO CAMPS. MEANWHILE...A

SHORTWAVE TROUGH IS FORECAST TO BE DIGGING SOUTHEAST ACROSS THE

MIDWEST THROUGH THE PERIOD AND SHOULD CROSS THE OH VALLEY BY LATE

THURS AND THEN THE NORTHEAST THURS NIGHT. THE 12Z NAM IS THE

WEAKEST SOLUTION WITH THIS ENERGY...WITH THE REMAINING MODELS ALL

SLIGHTLY MORE AMPLIFIED. THE LATEST GEFS MEAN AND ECENS MEAN ARE

STRONGLY SUPPORTIVE OF THEIR RESPECTIVE DETERMINISTIC SOLUTIONS.

SO...BASED ON THIS WILL PREFER TO BLEND THE GFS AND ECMWF.

I think they do more than just QPF hug there. 

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they're off...I have 2 different subscription maps which corroborate each other and the 2nd one is weatherbell level...

The high resolution maps i just saw are kind of in between those 2... weird

This is for after 12z

Westminster .65

MRB .55

JYO .7

IAD .8

DCA .8

BWI .75

 

We are splitting hairs here though it was a GREAT run

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