December 20 - 21 Coastal Storm Threat

[jm1220]

Winds up east/weaker 

 

East/weaker=less cold at the surface, lighter precip and lighter rain coast/snow inland. West means a coastal hugger and warm air dragged in but more cold manufactured from a stronger upper air low. So it's heavy rain coast/heavy snow inland, or we have to hope it's a "front end thump" storm, which pans out less frequently than modeled. As long as the 50-50 feature gets kicked east when our storm is developing, odds favor it being a bad outcome for many of us. And the 50-50 low will always be transient as long as there's no blocking. So it really comes down to perfect timing or a well placed kicker over the Plains.

[bluewave]

ok so was the 00z euro outcome a better solution for the coast? because people in the new england and mid atlantic forums seem to think so

 

There really isn't a great solution for the coast in a +EPO/+AO/+NAO pattern. We would need to see Canada

cool off with a more -EPO and a drop in the AO/NAO would be a big help. But it's possible to see some light

snow if we get lucky. There was more front end warmth this run on the Euro.

 

 

But the better news is that that long advertised EPO shift is finally showing up

on the 10 day Euro Ensemble means for the last week of the month. 

 

 

 

 

 

[Weathergun]

There really isn't a great solution for the coast in a +EPO/+AO/+NAO pattern. We would need to see Canada

cool off with a more -EPO and a drop in the AO/NAO would be a big help. But it's possible to see some light

snow if we get lucky. There was more front end warmth this run on the Euro.

 

ecmwf_T850_neus_7.pngIt

 

It has little to do with the indices. It's because the storm is 12 hours slower arriving here. We don't get a chance go isothermal before the warmth with easterly flow dominates. The 0z Euro ensemble mean was faster with precip on Saturday afternoon. So it's gets colder throughout the storm:

 

 

[bluewave]

It has little to do with the indices. It's because the storm is 12 hours slower arriving here. We don't get a chance go isothermal before the warmth with easterly flow dominates. The 0z Euro ensemble mean was faster with precip on Saturday afternoon. So it's gets colder throughout the storm:

 

 

 

 

 

It has everything to do with the indices since it much harder to get a heavy snowstorm for the coast under the

pattern that I described. The reason that the last two storms warmed as we got closer in was all about the pattern.

Models tend to show unrealistically cold or snowy solutions long range in poor patterns that get warmer short term.

Don't you remember the Monday 12z Euro run back in late November that was showing the fantasy day 8-10

snowstorm at the coast that never happened? The details that you are mentioning from run to run are just

noise in an unfavorable pattern for the coast. And how about the snowy solutions for the storm last week

that vanished. See JM's great post for the options on the table.

[Weathergun]

It has everything to do with the indices since it much harder to get a heavy snowstorm for the coast under the

pattern that I described. The reason that the last two storms warmed as we got closer in was all about the pattern.

Models tend to show unrealistically cold or snowy solutions long range in poor patterns that get warmer short term.

Don't you remember the Monday 12z Euro run back in late November that wa showing the fantasy day 8-10

snowstorm at the coast that never happened? The details that you are mentioning from run to run are just

noise in an unfavorable pattern for the coast.

 

The 500mb patterns were less favorable. Not just the indices. We didn't have a block and 50/50 low for those past storms.

[bluewave]

The 500mb patterns were less favorable. Not just the indices. We didn't have a block and 50/50 low for those past storms.

 

By indices I specifically mean 500 mb patterns or composites  that the teleconnections are derived from.

[Mikehobbyst]

Now, we try to turn the NYC and LI folks into snowshovelers this next weekend.  Maybe we get the serious snowfall e.g. winter storm warnings flying on Christmas week for the entire weekend .... The grass to not be seen until the bunny comes...........

[REDMK6GLI]

^^^ HE'S BACK!!

[IsentropicLift]

Really sharp cutoff on the 00z ECMWF.

 

Northern Orange County NY is only 0.10". West Milford is 0.40". KNYC is around 0.60" while Staten Island is over an inch. All of Monmouth County is 1.2"+.

 

WxBell snow maps have about a foot in Trenton and 4" in Morristown.

[Dsnowx53]

The 500mb patterns were less favorable. Not just the indices. We didn't have a block and 50/50 low for those past storms.

 

 

First of all, I moved some of the posts from the other thread to in here in order to facilitate more good discussion.

 

But anyway, I'm very much with Weathergun here. While yes, an indice is derived from a 500mb pattern, it's still always much better to look at the 500mb pattern itself since the numbers can be misleading. The numbers say we have a +EPO/+NAO/+AO, but the actual pattern says we have a Rex Block, a strong 50/50 low, a Rockies ridge, and a split flow. None of the other threats had those features in tandem. Yeah, we don't have a block in Greenland to slow the 50/50 low down, but we have a Rex Block that definitely helps to reinforce the 50/50, and that somewhat links with a North Atlantic ridge to help slow down the 50/50 low. With all the past events, the flow in the Atlantic was very, very fast since there was no Rex Block.

 

Not to say that this storm has to end in a very snowy outcome, but it has a better chance than all the other threats did. It also has being later in the calendar on its side. The only thing I hate about this setup is the airmass.

 

Plus, the Euro guidance has been very consistent in having the confluent flow sliding from the northeast into the 50/50 region right as the shortwave ejects from the SW US towards our area -- that is a great look. As I've said before, though, too bad the airmass is pretty bad. 

 

The poor airmass means we're going to need a strong system with a well-defined ageostrophic component. Otherwise any initial light easterly flow will warm us up too much. 

[Zelocita Weather]

This threat has looked pretty good for a while now...almost all the classic players are in place. Broad sprawling high pressure to the north, 50/50, and a low coming underneath. Of course things can still screw up (low placement, not quite cold enough, etc.) but by far our best shot so far at significant snow across the region...

[IsentropicLift]

The 12z GFS is a lot flatter than 06z through 96 hours.

[IsentropicLift]

Major changes on the GFS, looks nothing like the Euro.

[IsentropicLift]

What a mess, nothing makes it north of the Mason-Dixon line. I've lost all faith in this model. It's been awful on just about every event I can remember so far this year.

[rossi]

Major changes on the GFS, looks nothing like the Euro.

Why are you surprised - it sucks and wont be correct until a day before the event.

 

Rossi

[MJO812]

12z GFS takes the storm through a shredder

[IsentropicLift]

The 12z PGFS looks nothing like the OP. They can't put that OP into the moth balls fast enough.

[MJO812]

The 12z PGFS looks nothing like the OP. They can't put that OP into the moth balls fast enough.

Southern stream looks more potent at 114 hours

[IsentropicLift]

The differences are comical. PGFS keeps the lead shortwave over Central TX at 108 hrs while the OP is over the Carolinas and TN Valley.

[IsentropicLift]

1016mb on the MS/AL border. Miller A.

[IsentropicLift]

1010mb over the AL/GA border. Moisture almost up to DCA at hour 135.

[IsentropicLift]

Trough goes negative tilt over the TN Valley. Big 500mb closed low just West of the lakes from hour 114 on.

[IsentropicLift]

Light stuff moving in hour 141-144, probably just virga. Low up to the Carolina coast.

[IsentropicLift]

NYC is completely above freezing at all levels by hour 150.

[IsentropicLift]

1008mb about 75 miles East of Ocean City, MD.

[Allsnow]

Para finally has the storm but warm for most of this sub-forum

[MJO812]

Strong low just south of LI at 156. Warm for coastal areas.

[IsentropicLift]

1004mb 50 miles East of  ACY, dynamic cooling occuring N&W.

[IsentropicLift]

Strong low just south of LI at 156. Warm for coastal areas.

1004mb isn't strong.

[Animal]

1004mb 50 miles East of  ACY, dynamic cooling occuring N&W.

 

Sounds like a great run for the interior.....5 + days out