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December 23rd light snow potential


ORH_wxman

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Euro is pretty similar to the GFS with the surface low positioning too. Pretty much exits right off the NJ coast. H85 profiles seem more similar to the GFS than the NAM. Not surprising for the NAM to be too cold -- usually is in these situations. But I've seen it score a coup before. We will see I guess.

Oddly enough the Euro is warmer at H85 yet colder with surface temperatures especially over Central and Eastern MA. Likely owing to the stronger system/better dynamics and heavier precipitation.

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Earthlights flying birds signature always brings hope for snow ... Is there a chance of the rain/snow line slipping down to the NYC/LI area during the 12/23 event ???

It doesn't look promising. The mid levels and BL are just too warm during the event. Maybe if the CAA comes in strong enough you can end as flakes, but I wouldn't count on it.
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Euro is pretty similar to the GFS with the surface low positioning too. Pretty much exits right off the NJ coast. H85 profiles seem more similar to the GFS than the NAM. Not surprising for the NAM to be too cold -- usually is in these situations. But I've seen it score a coup before. We will see I guess.

Oddly enough the Euro is warmer at H85 yet colder with surface temperatures especially over Central and Eastern MA. Likely owing to the stronger system/better dynamics and heavier precipitation.

The ECMWF temperatures look more like the NAM to me.

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The ECMWF temperatures look more like the NAM to me.

Well the Euro has the H85 0c about 50 miles north of the CT/RI/MA South coast at 60 hrs. The NAM at that time has the H85 0c south of New York City and crossing through Central Long Island. It's a small difference but it's worth noting. I found the GFS to be more similar to the Euro in that regard.

Euro left, NAM right. You can see the NAM is definitely farther south with the H85 temperature gradient if you're using the 0c "line" as a reference point.

post-6-0-24316300-1324448682.png

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Well the Euro has the H85 0c about 50 miles north of the CT/RI/MA South coast at 60 hrs. The NAM at that time has the H85 0c south of New York City and crossing through Central Long Island. It's a small difference but it's worth noting. I found the GFS to be more similar to the Euro in that regard.

Euro left, NAM right. You can see the NAM is definitely farther south with the H85 temperature gradient if you're using the 0c "line" as a reference point.

post-6-0-24316300-1324448682.png

The NAM is actually a bit slower than the GFS and ECMWF which is why the differences look more drastic than they really are (66h NAM may be a better match up to the 60 hr ECMWF, esp. in New England). Now, you are right that the NAM is definitely honing in on the ageostrophic / gradient potential and is cooler than most of the guidance; but in terms of the general picture, the GFS is the warmest model (especially in New England).

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The NAM is actually a bit slower than the GFS and ECMWF which is why the differences look more drastic than they really are (66h NAM may be a better match up to the 60 hr ECMWF, esp. in New England). Now, you are right that the NAM is definitely honing in on the ageostrophic / gradient potential and is cooler than most of the guidance; but in terms of the general picture, the GFS is the warmest model (especially in New England).

I'll tell you what..it's amazing how these southwest flow-type events usually play towards the models biases that haven't changed much over the past few years. There have been numerous explanations for them all (GFS resolution is poor, too warm...NAM's dynamics are overdone, too much dynamic cooling...etc etc). But I've found the truth usually lies somewhere in between...and the SREF/ECMWF combination can be a great tool for thermal profiles in that regard. In this case, the SREF mean is still fairly far south on their latest 21z run but the H85 profiles definitely lean towards the NAM.

Also...the GFS is definitely the warmest of the guidance right now in regards to the entire thermal profile. I was inclined to say the ECMWF looked more like the GFS than the colder NAM -- but I guess it's also fair to say it is somewhere between the two NCEP models. The NAM seems slower but at 66 hours is already dry.

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I'll tell you what..it's amazing how these southwest flow-type events usually play towards the models biases that haven't changed much over the past few years. There have been numerous explanations for them all (GFS resolution is poor, too warm...NAM's dynamics are overdone, too much dynamic cooling...etc etc). But I've found the truth usually lies somewhere in between...and the SREF/ECMWF combination can be a great tool for thermal profiles in that regard. In this case, the SREF mean is still fairly far south on their latest 21z run but the H85 profiles definitely lean towards the NAM.

Also...the GFS is definitely the warmest of the guidance right now in regards to the entire thermal profile. I was inclined to say the ECMWF looked more like the GFS than the colder NAM -- but I guess it's also fair to say it is somewhere between the two NCEP models. The NAM seems slower but at 66 hours is already dry.

Great post; I agree. The 3z SREF and 00z ECMWF will be the way I head for tonight's forecasts. This gives the possibility for some accumulating snow as far south as Sussex, NJ to Danbury perhaps?

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Great post; I agree. The 3z SREF and 00z ECMWF will be the way I head for tonight's forecasts. This gives the possibility for some accumulating snow as far south as Sussex, NJ to Danbury perhaps?

Agreed entirely with that line for the farthest-south extent of the accumulation potential. Sussex can pull off some sneaky accumulations with tracks like this. This is not all that typical as the antecedent airmass isn't all that great .. but I would think that if the storm tracks as modeled on guidance they could pull something off. The NW fringes of Uptons CWA can be very sneaky in these events...Orange County can score a light snowfall too.

Will looks to be in a decent spot in Worcester Mass as well. Really anybody from Litchfield Ct through Worcester and on Northeast could pull out an advisory level event if these models have any clue. But I would urge caution at this range considering how badly they have been struggling so far. These cutoff lows and embedded shortwaves are very tough on the guidance.

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I think the SREFs are still playing a little bit of catch up. I think they're a little south with the mid level features.

They tend to do that at this range. With such a wide variety of ensemble members as far as model physics, there's a bit of a lag in their mean.

Slightly off topic, but given the time of year and the conversation about the SREFs... I can't help but remember the SREF's being so far out to sea the night of Dec 24/00z runs last year. There was one (1) member which showed the storm coming up the coast...ETA 5. I'll never forget it..it showed the exact H5 solution over the Central Plains that all the guidance would show 12 hrs later.

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You can use the 15 panel Ewall maps to get a good idea of where the NAM is at beginning around this range (+60hrs). This follows the thoughts layed out by myself and HM pretty nicely as far as the southward extent of the accumulating snow potential. Although I still suspect it may be too cold...you can see the gradient very nicely here.

Also notice the low level and boundary layer issues which are exposed by looking at two maps: H85 and precipitation type/2m temperature. Right near NYC and Northeast NJ the boundary layer is awful while H85 temperatures are (albeit barely) decent. These problems continue along the south shores of SNE.

f60.gif

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Some more graphical tools to utilize if you're trying to get a good handle on things. Here are the high resolution simulated radar and precipitation types from the 00z NAM.

54 hr: http://policlimate.c...ame_cref_42.png

57 hr: http://policlimate.c...ame_cref_43.png

60 hr: http://policlimate.c...ame_cref_44.png

60 hr snow depth: http://policlimate.com/weather/wrf/hires2011122100/nam_snow_ne_45.png

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Well up early looking at the late guidance...it appears the Euro was a compromise between the NAM and GFS...06z NAM was like 00z maybe a shade warmer but not a lot. 06z GFS appears to have cooled a bit from 00z which isn't a shock since it was the warmest model at 00z. Ditto the NAM warming slightly.

The 03z SREF probs have shot up significantly again...they are still on the edge of their useful range for snow, but you normally do not see the probs over 50% unless they really like the idea so it does give a bit more confidence.

f12s60.gif

I still think we will have to watch for another small tick north, but I'm not sure how much more room it has between those two features (SE ridge off the Atlantic coast and s/w diving into the lakes). The timing of the system also appears to have slowed just a bit since 12z yesterday.

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From HPC overnight....I think this makes the point that the loss of the storm could be a temporary thing, perhaps a bit like what we saw last year for the Boxing Day storm...and like we sometimes see at this timeframe on storms that involve interactions of 2 or 3 streams. Storm could be a no-show for sure but storms have tended to not be no-shows this fall.

WHATEVER CONSENSUS WAS EMERGING FROM THE THE MODEL SOLUTIONS ON

THE 00Z/20 CYCLE IS NOW FLEETING...HAVING FALLEN VICTIM TO THE

EVER DICEY INTERACTION BETWEEN SPLIT STREAMS. IN THIS CASE...THE

CLIPPER SYSTEM DIGGING INTO GREAT LAKES AT THE END OF THE SHORT

RANGE APPEARS MORE DOMINANT THAN IT DID...SQUASHING THE WAVE

EMERGING FROM TEXAS. THE FLY IN THE OINTMENT IS THE PERSISTENT

SUBTROPICAL RIDGE OVER THE SOUTHEAST. EVEN WITH A MASSIVE ENOUGH

INFLUX OF CONTINENTAL POLAR AIR...IT WILL BE DIFFICULT TO DAMPEN

THE SOUTHERN RIDGE. HENCE...KEPT AT LEAST HALF OF THE OLDER ECMWF

GUIDANCE IN THE MANUAL BLEND

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I have a feeling this might actually buck the trend and tick south to get folks in southern sections/coastal in on the act. That cold northley drain is going to to be fairly impressive and should be strong enough to bump things south. NAM you would expect to see this and I think is the reason why we've seen the last couple runs trned colder

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Put this in the wrong thread....

From HPC overnight....I think this makes the point that the loss of the storm could be a temporary thing, perhaps a bit like what we saw last year for the Boxing Day storm...and like we sometimes see at this timeframe on storms that involve interactions of 2 or 3 streams. Storm could be a no-show for sure but storms have tended to not be no-shows this fall.

WHATEVER CONSENSUS WAS EMERGING FROM THE THE MODEL SOLUTIONS ON

THE 00Z/20 CYCLE IS NOW FLEETING...HAVING FALLEN VICTIM TO THE

EVER DICEY INTERACTION BETWEEN SPLIT STREAMS. IN THIS CASE...THE

CLIPPER SYSTEM DIGGING INTO GREAT LAKES AT THE END OF THE SHORT

RANGE APPEARS MORE DOMINANT THAN IT DID...SQUASHING THE WAVE

EMERGING FROM TEXAS. THE FLY IN THE OINTMENT IS THE PERSISTENT

SUBTROPICAL RIDGE OVER THE SOUTHEAST. EVEN WITH A MASSIVE ENOUGH

INFLUX OF CONTINENTAL POLAR AIR...IT WILL BE DIFFICULT TO DAMPEN

THE SOUTHERN RIDGE. HENCE...KEPT AT LEAST HALF OF THE OLDER ECMWF

GUIDANCE IN THE MANUAL BLEND

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I have a feeling this might actually buck the trend and tick south to get folks in southern sections/coastal in on the act. That cold northley drain is going to to be fairly impressive and should be strong enough to bump things south. NAM you would expect to see this and I think is the reason why we've seen the last couple runs trned colder

that would certainly buck the trend, will met you know if it happens

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I have a feeling this might actually buck the trend and tick south to get folks in southern sections/coastal in on the act. That cold northley drain is going to to be fairly impressive and should be strong enough to bump things south. NAM you would expect to see this and I think is the reason why we've seen the last couple runs trned colder

Its possible. There's definitely some opposing forces...the confluence gets pretty good to the northwest and that high tries to build in, but at the same time, the ridge just off the SE coast is a monster. The northerly drain really increases toward the end of the event, so places that are marginal early on will have a race with the precip versus the cold air filtering down.

This could make the difference for a place like Boston getting an inch or two or just ending as wet flakes.

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BOX sees it fit to post this in a GC HWO:

MAZ002-003-NHZ011-015-220930-

WESTERN FRANKLIN MA-EASTERN FRANKLIN MA-CHESHIRE NH-

WESTERN AND CENTRAL HILLSBOROUGH NH-

421 AM EST WED DEC 21 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MASSACHUSETTS AND

SOUTHERN NEW HAMPSHIRE.

.DAY ONE...TODAY AND TONIGHT.

THERE IS THE LOW PROBABILITY OF LIGHT FREEZING RAIN THIS MORNING.

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

ADVISORY LEVEL ACCUMULATING SNOWFALL WILL BE POSSIBLE FOR LATE

THURSDAY NIGHT INTO FRIDAY.

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