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Potential Coastal Storm This Weekend


IsentropicLift

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This reminds me a little of February 2013; it was a major thread the needle storm in a not so great pattern. Will the results be the same though is the question. I received about 8" from that storm.

Ding Ding Ding! I recieved about 41". Different synoptically though.

United States Coast Guard Rescue Swimmer

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You can still get rapid pressure drops in a progressive pattern provided you have the strong jet streaks and strong PVA. That's what the Euro is doing. 

 

It's going to be hard to avoid some tainting, however, with that low north of the Lakes. I still think there are plenty of dynamics that can help change back over to a nice period of heavy snow. But we do have to remember that it's only Tuesday and the storm is on Saturday. 

 

We're also not far off from closing off at H5 earlier and allowing fewer tainting issues and much more of a CCB afterward.

 

Either way, the coast should be wary of tainting, but that doesn't mean a 4"+ snow event can't happen. 

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The euro ensemble mean is a little warmer than the OP at 96 hrs as the mean track is a few miles 

west of the OP over Eastern NC.

 

http://www.ecmwf.int/en/forecasts/charts/medium/ensemble-mean-and-spread-four-standard-parameters?area=North%20America&step=96&relative_archive_date=2015012012&parameter=Temperature%20at%20850hPa

 

Some of the members are up to sub-975mb over NJ, so I would not use the EPS mean as a temp/snow forecast for this weekend as of now. Obviously things will wind up much less amplified, but all we can take away from the ensembles is that there really isn't an overwhelming chance that this will escape out to sea like yesterdays runs suggested 

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A quick note on the forecast teleconnections:

 

The potential storm is forecast to occur when the AO is positive and the PNA is positive (according to the GFS ensembles). Such a set up has seen numerous 4"-8" snowstorms in the NYC area during the second half of January. In fact, an AO+/PNA+ accounts for 46% of such storms since 1950.

 

If one is looking for a bigger storm, all snowstorms that brought more than 8" to NYC during the second half of January commenced during an AO-/PNA+ set up.

 

 

The AO will not be negative long enough to negate the SE Ridge playing a role for coastal sections. Interior

sections always have more leeway in marginal set ups like this one. 

 

 

 

While I'm not arguing against statistics, I think there's a little too much focus on the index calculation here, and not enough examination of 500mb heights. The latter is far more important in terms of the resultant weather pattern. Over the next 48 hours, the AO value will be negative as per the official calculation: approximately -1 standard deviation according to the ECMWF ensemble mean. At the time of the potential event, 1/24, Saturday, the AO is forecasted to be +0.8 standard deviation. Below are the following images:

 

[1] 500mb anomalies for the time of likely AO minimum value, tomorrow (around -1 SD)

 

[2] 500mb anomalies for 12z 1/24, when the AO is forecasted to be close to +1 SD

 

 

Given this: how is the first image structurally and synoptically superior to the second image, at which time the AO will probably be at least 1.6 standard deviations higher? I would argue that the time at which the AO is technically positive (Saturday) will be more conducive synoptically than the period in which the AO is technically negative (tomorrow), due to the expansion of higher 500mb heights southwestward into northern Greenland, and bridging across the Arctic toward the NW territories. This east based blocking feature, again while not accurately represented by the index calculations of the NAO or AO, has historically been an important feature in antecedent patterns for Northeast US snow events.

 

Thus, it is my opinion, that while the index calculation of the AO is negative now, and positive at the time of the storm, the index calculation does not accurately represent the 500mb progression (as is often the case). Furthermore, the time frame of the storm seems to have more favorable height pattern downstream when the AO is slightly positive. The height rises in the aforementioned region prevent a rapid exit of the 50/50 feature, and that feature limits height rises out ahead of the short wave in question.

 

 

[1]

 

28s9735.png

 

 

 

[2]

 

 

28cpyip.png

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Upton  

 

 

 

LONG TERM /THURSDAY THROUGH TUESDAY/...
HIGH PRESSURE BUILDS FURTHER EAST THURSDAY INTO FRIDAY. THIS SHOULD
PROMOTE GOOD RADIATIONAL COOLING CONDITIONS...WITH LOW TEMPERATURES IN
THE TEENS INLAND AND 20S ALONG THE COAST. HIGH PRESSURE THEN MOVES
OFFSHORE BY FRIDAY NIGHT. BOTH 12Z ECMWF/GFS CONTINUE TO SHOW A
COASTAL STORM THAT COULD IMPACT THE AREA SATURDAY INTO SATURDAY
NIGHT. THERE IS STILL PLENTY OF UNCERTAINTY REGARDING THE TRACK OF
THIS COASTAL LOW AND THE TEMPERATURE PROFILES. AT THIS TIME...WILL
CONTINUE WITH CHANCE POPS.
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The 975 mb members over NJ aren't likely to happen, but that doesn't mean that the OP can't come 20 or 30 miles

closer to the coast than todays run later on. Sometimes when the mean is left of the OP, the OP shifts a hair

west in the next run. But it's hard to tell if that is going to be the case or not until we see the 0z run.

 

The Euro has had tendencies to be too amped the last few years in patterns not favorable for big storms...I think it may be the case again.  It has done well though the last 2 weeks, it definitely came out of its cold streak.

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The important part is that the AO rebound allows the more amplified Euro run to have a stronger SE Ridge ahead of the

low introducing P-Type issues for the coast instead of a 100% snow solution. I don't really have a guess at specific

snow amounts so early in the game, just that we are going to lose a percentage to liquid instead of being all frozen.

A more -AO ahead of the storm would have raised the prospects for all snow or a suppressed storm if the AO was

too strong.

 

The AO rebounds after the storm hits has past us on the Euro Ensemble mean

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