Weekend Storm Discussion 2/18-2/19

[yoda]

EURO out to 24

[phil882]

I'm not surprised by the extreme run to run discontinuity from the GFS. The biggest player finally is coming on the table. The big feature in question? Its a arctic shortwave that is breaking apart over Alaska. I want to highlight how difficult it is going to be to resolve this small feature. But it also means some very interesting things, including a legitimate chance we could see a tripple phaser. In the following images I am going to compare the 18z run with the 00z run and show how small changes in the initialization have caused major changes in the storm evolution.

So where are the changes coming from at the initialization. Well first we can tell the pacific ridge slightly less amplified than the 18z run. This does little to change the position of the primary shortwave, but two most northernmost shortwaves, both are shifted slightly south. This is going to make all the difference as we advance forward in time.

Fast forward to +24 hours (00z Feb 16th)... The Pacific ridge is now a bit more amplified than before, but look how its evolved the two most northernmost shortwaves. The arctic shortwave is actually slower and slightly less amplified than before, while the shortwave located over western Canada has actually sped up slightly. The primary shortwave over the Western US is in nearly the same place at the same intensity, so its likely not a huge source of why we saw a large change between 18z and 00z.

Now we are +48 hours (00z Feb 17th)... The first obvious thing to not is how quickly the northernmost shortwave has really sped up... to the point that its now further east than the 18z run. This is the missing piece that allows the shortwave over Canada to dig down more as both of these pieces of shortwave energy interact. Meanwhile the southernmost shortwave now over the southwest has moved slightly further east of the 18z run, but the change is negligible compared to the other two shortwave features.

Finally at +72 hours (00z Feb 18th)... Major changes are now taking shape. The two northernmost shortwaves are now starting to phase together, but the southern stream shortwave is not far behind. All of the features at 72 hours are much closer together than 18z, and its off to the races beyond that. However, its important to note how important that northernmost shortwave is to getting all the pieces to fall into place. Any slight changes like we saw between the 18z and the 00z cycle are going to completely change the outcome.

So the 00z solution was an interesting phase between the polar and subtropical shortwave, but if the phase occurs earlier between the subtropical/polar shortwave as the arctic interaction occurs, this solution could get very interesting in a hurry. As is, the solution is rather extreme, but plausible given how sensitive these shortwave features are as the subtropical ridge over the northwest pacific amplifies.

[Midlo Snow Maker]

^{well atleast at 500 mb it looks nothing like the gfs a}

[Midlo Snow Maker]

hr 96 1004 low just south of alabama coast

[Midlo Snow Maker]

North/Northwest extent of the precip is a line from Rehoboth Beach to RIC

safe place to be now after the gfs inland torch

[phil882]

Honestly... either the ECMWF or GFS solution is plausible at this time. The shortwave features being handled right now are simply too small to be resolved properly, especially at this time range. One plus is that all of the features are inland now, but the northernmost shortwave will be stretched so much in the next 24 hours that even slight variations in height and vorticity will have large ramifications down the road.

The bottom line... we probably will have one or two major shortwave interactions over the next 5 days between the three features I outlined on the previous page. However, as always, timing is everything. The biggest thing is timing these features and thats pretty much impossible at this time range with features of this size scale. For those hoping for a solution that phases earlier... you want the southern stream to speed up, while the northern stream features need to slow down... of course for a later phase you want the opposite, although if the two features completely miss each other, there might not be much of a system to follow.

[Bob Chill]

Worth staying up for. Euro is holding the se solution and gfs is still figuring it out. Something inbetween isn't unlikely at all. Threat still firmly on the radar.

[HM]

All year these southern s/w lag and I hope this upcoming one doesn't or it's a wide right.

[HM]

I"m hoping the euro "bias" is in play here.....I'm not really that concerned about that sweet phase the GFS is showing given my latitude...If Euro is a bit quicker with ejecting that baja low, the storm will take a better track for me....I don't really care if New England gets a bomb

The next wave on the ECMWF seems pretty progressive too which prevents any meaningful chance they phase. I feel like I am staring at a 500 chart from not too long ago (January?) where this sort of thing happened. It was a "what could have been" scenario where 3 distinct s/w missed each other. Do you remember when?

[HM]

You know, at second thought, the ECMWF is not really lagging the southern stream. The issues are entirely in the northern stream. The GGEM is more lagged than the ECMWF tonight!

[phil882]

The differences between the ECMWF and the GFS are staggering... only 72 hours out... there is a shortwave pretty much right in place of where the GFS has a ridge. This is a pretty stunning difference only three days out.

[phil882]

You know, at second thought, the ECMWF is not really lagging the southern stream. The issues are entirely in the northern stream. The GGEM is more lagged than the ECMWF tonight!

Bingo... I think the northern stream features are what we are going to have to watch over the next few days, especially the northernmost feature since it pretty much has to stretch across the ridge before digging back into western Canada. With so much vorticity elongation, its going to be very difficult for the models to resolve a wave with only tiny spatial details as it scales the ridge.

[HM]

Bingo... I think the northern stream features are what we are going to have to watch over the next few days, especially the northernmost feature since it pretty much has to stretch across the ridge before digging back into western Canada. With so much vorticity elongation, its going to be very difficult for the models to resolve a wave with only tiny spacial details as it scales the ridge.

Yeah I mentioned that wave too a while back about possibly being a wild card. As Adam said in another thread, this is not going to be pretty for people responsible for forecasts in the Mid Atlantic / New England.

[phil882]

Yeah I mentioned that wave too a while back about possibly being a wild card. As Adam said in another thread, this is not going to be pretty for people responsible for forecasts in the Mid Atlantic / New England.

Yep... its going to be a nightmare, especially when you have an extreme solution on the table as well. Some of the GFS ensembles are off the wall insane in both directions.

We could end up with a solution like this:

Vise versa... we might also end up with this:

[HM]

I'll be sure to elaborate that nicely to clients, lol.

[PDIII]

^{The 006Z GFS had thje northern extent of the .25-.5 precip up to Baltimore/ DC. The run seemed pretty warm.}

[winterymix]

For the Mid-Atlantic, snow to rain and back to snow at the end seems

to be a possibility. None of the models have a 500 mb chart that Wes

always posts...the magic chart that has signaled classic good snows in the DC area.

In this blah winter, snow to rain and back to snow will feed the savage snow-weenie beast.

[WinterWxLuvr]

We may not know until Saturday at this rate. The post earlier by one of the mets showing all the players in this thing really does give you an indication of just how hard this will be to nail down. We're still in the game, as is everyone from about Fla to Maine it would seem.

[Midlo Snow Maker]

0z euro ens paint 0.50" mean from ezf to roa----- 0.25" mean near philly to charleston. wva 0c 850 mean ric to roa fwiw

[Herb@MAWS]

I didn't read all the overnite posts, so hope this isn't a repeat:

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

220 AM EST WED FEB 15 2012

VALID 12Z SUN FEB 19 2012 - 12Z WED FEB 22 2012

USED AN EVEN BLEND OF THE 12Z/14 ECMWF AND ECENS MEAN FOR THE

PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7. THIS

MANUAL BLEND FITS MULTI-DAY MEANS FROM THE VARIOUS GLOBAL MODELS

BEST...PARTICULARLY WITH REGARD TO THE SIGNIFICANT SYNOPTIC WAVE

LIFTING FROM THE NORTHERN GULF COAST DAY 4. THE 00Z/15 GFS IS THE

FARTHEST NORTH OF THE MODELS WITH THIS SYSTEM...INDICATING A

SIGNIFICANT DEGREE OF INTERACTION WITH A WAVE IN THE NORTHERN

STREAM. THE UKMET TAKES UP THE FLAT END OF THE GUIDANCE. OVER

THE WEST...THE PACIFIC JET SEEMS DESTINED TO KEEP SPLITTING UPON

REACHING THE CONTINENT...THOUGH THE SYSTEM COMING INTO THE

NORTHWEST DAY 7 MAY HAVE ENOUGH LARGE SCALE SUPPORT TO STAY MOSTLY

INTACT...WITH HIGH SENSIBLE WEATHER IMPACT FOR THE INTERMOUNTAIN

REGION.

[yoda]

0z euro ens paint 0.50" mean from ezf to roa----- 0.25" mean near philly to charleston. wva 0c 850 mean ric to roa fwiw

Sort of same from the 12z EURO ensemble mean

[CAPE]

0z GFS was off its rocker nuts insane. 6z is back in line with the other models....GFS really is a POS model for east coast storms in the medium-long range.

[yoda]

Kinda surprising to see LWX already say that ingredients for a sig snowfall are there in its morning AFD

[usedtobe]

The next wave on the ECMWF seems pretty progressive too which prevents any meaningful chance they phase. I feel like I am staring at a 500 chart from not too long ago (January?) where this sort of thing happened. It was a "what could have been" scenario where 3 distinct s/w missed each other. Do you remember when?

I think a phase is not very likely and posted something like that yesterday as there are just too many players which makes it hard to get things right, not impossible but not very likely. The Euro ensemble mean has backed off to a more southern solution. TThe 06Z GFS still has something but is flatter than the 00Z but still looks like it might be mostly rain.

[ohleary]

The 06Z op GFS is an eastern outlier when compared to the 06Z GFS ensemble members. A trend north/westward with the coastal low at 12Z would not surprise me.

[PrinceFrederickWx]

EDIT: posted this in wrong thread... but I'll leave the relevant part.

http://forecast.weat...0&highlight=off

"INGREDIENTS FOR SIGNIFICANT SNOWFALL ARE THERE...IT IS SIMPLY A

WAITING GAME FOR THE MODELS TO DELIVER CONSISTENCY AND THUS

CONFIDENCE."

[TowsonWeather]

It's probably just my weenie eyes kidding me, but the NAM looks pretty good to me through 78 84. Correct me if I'm wrong, but (in theory) wouldn't this be a good look for us at that stage of the game?

[BaltimoreWxGuy]

It's probably just my weenie eyes kidding me, but the NAM looks pretty good to me through 78 84. Correct me if I'm wrong, but (in theory) wouldn't this be a good look for us at that stage of the game?

I was thinking the same thing, but then again its just the 84 hr NAM...something to look at is all it is.

[Ellinwood]

It's probably just my weenie eyes kidding me, but the NAM looks pretty good to me through 78 84. Correct me if I'm wrong, but (in theory) wouldn't this be a good look for us at that stage of the game?

I wouldn't worry about anything the NAM has to say for another day or so.

[Ji]

I wouldn't worry about anything the NAM has to say until 30 minutes before the event starts

agreed!