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First half of February...another pattern shift?


ORH_wxman

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What winter am I thinking of when BOS only had like 26 inches or something. I had 43 inches..Thought it was 06-07..but you know me and dates

BOS had 17 in 2006-07, probably more than half of it in March. I remember flying out for Israel in early March and it was 5 at BOS.

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MJO going from 6-7-8 ? at amplitude, looks that way to me. Is that what you are talking about, if so, sweeet

Yes, at least we have that trying to agree. But, there is the chance, the ridge amplitude may not be high enough, and overall temps are milder, but so far, I like what I see as far as chances go. I don't have the balls to go colder than normal.

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We do not have a thread for the longer range right now...we've been discussing this in various storm threat threads, so I thought I would start this for the February pattern. What we are seeing is a pretty strong move by ensembles (both GFS and ECMWF) toward a +PNA pattern...with potentially a -EPO as well but it may hang more near neutral. For those not familiar with what it means...here are the loading patterns for the positive phases of both the EPO and PNA....

+EPO pattern:

+PNA

The EPO pattern I posted is positive...but the forecasted pattern is more negative shifted a tad east. It also depends on which set of ensembles you use as to the nuances of the pattern. The ECMWF ensembles are a bit more -EPO while the GEFS are more neutral. Both however are a big +PNA pattern. The nuances in the PNA ridge and if it can produce a more -EPO will determine the temperature departures in the period in question...but I'm going to focus more on the snow potential.

A +PNA means a very large ridge out west usually and that teleconnects well to a trough in the east which is of course how we are going to get storminess more often.

Here is the GFS ensemble mean valid for 00z Feb 7

That is a big +PNA but the EPO is kind of neutral or even slightly negative there...however the Euro ensembles are like the image above except shifting the ridge a bit west and higher into AK which would be a bit of a colder pattern. Another notable difference on the Euro ensembles is they have a more distinct ridging signal into Greenland whereas the GFS ensmebles above clearly do not. Both of these difference would make the Euro ensembles more conductive to cold/snow chances versus the GEFS....but the GEFS isn't bad. It would likely still offer some storm chances with a ridge like that to the west, but the cold wouldn't be as impressive.

There is going to be a shift going on over the next 10 days or so to really get this pattern into place (assuming it happens)...in those next 10 days, we should average out mild and the storm chances will probably be tougher to get. My best estimate for more chances would be in the period after Feb 5th...probably until the 15th or 20th if this winter is any indication on how the favorable PAC patterns break down after 10-14 days....but its possible it could stay longer.

Its also possible that the ridging is being over modeled on the ensembles...however, given that it has become more and more impressive the closer we get, it leads to a bit more confidence that we should experience a period with a significantly positive PNA which in turn will hopefully lead to an active pattern for storm threats.

The NAO and how far north the ridge pushes in the west will be X-factors on the temperature departures...and the NAO of course can always help with the synoptics of a storm threat too.

Nice post, Will. I like all of your ideas moving forward over the next few weeks. My general idea moving forward over the next few weeks is that we are likely in a stale-mate for the next 1 to 2 weeks. A few days ago I mentioned super-bowl weekend as the potential time frame for the possibility of major amplification on the East Coast. These PNA amplification's like to come in with a bang -- and the forecast model guidance is starting to hint at it being more anomalous as we get closer.

That being said...we are playing with fire even with the PNA flux. If, for instance, the Atlantic and the NAO were to not cooperate -- we would fall back a few steps once again. The reality of it is that through the first week of February, the majority of the polar air is located with the PV on the Pacific side of the Arctic Circle. We can see this on the image below...GEFS around +180 hr...which is a moderate lead. Here we have a PNA ridge trying to amplify on the west coast...but the Atlantic is stubborn, still with a trough extending over Baffin Island to Greenland. I think there is the legit possibility of February beginning with 3-6 days of above normal temperatures

post-6-0-50747700-1327532009.png

.

After this things start to get very interesting as you noted above. The hemispheric regimes are changing and there is no denying that. But I urge caution here because the sheer amount of false-starts we have been victim of. It's not all our fault as forecasters -- the medium range ensembles have been rather poor with this pattern. But if the 12z GEFS are correct...we'll see a +PNA ridge building on the west coast and even north into British Columbia. That would be the most anomalous feature we've seen so far this winter. The GEFS and ECMWF Ens are pegging Feb 6-8 right now...so I would at least keep one eye open around that period.

Point is...move forward cautiously. The image below is the GFS AO forecast bias from the past several weeks which I posted in a thread over in the NYC forum from last night. Some pretty poor mid range forecasting here from the GFS and several instances when it forecasted the AO to drop well into negative values when it barely made it to neutral. Obviously we have killed the curse now and are between -1 and -2 ...but it does still seem to be biased in the negative departures.

patternchange3.png

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John, I think the Arctic and the Atl are more crucial to snow chances from your area points south in latitide....they would help up here, but we do not need them...they would just make for more snowPACK weather and increase the odds of a MECS\HECS..

Without a -NAO, or at least a pseudo -NAO blocking type feature, we'd run the risk of storms trying to go west like through the OH valley at times...we could still do well on those as we all know, but certainly the M.A. would be in dire straights...and no guarantee we'd clean up.

For more classical coastal type storms, the +PNA/-NAO combo is a lot more favorable. At the very lest though, this should get us a more active pattern...whether it ends up more SWFEs/clipper-redevelopers or actual coastal storms.

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Without a -NAO, or at least a pseudo -NAO blocking type feature, we'd run the risk of storms trying to go west like through the OH valley at times...we could still do well on those as we all know, but certainly the M.A. would be in dire straights...and no guarantee we'd clean up.

For more classical coastal type storms, the +PNA/-NAO combo is a lot more favorable. At the very lest though, this should get us a more active pattern...whether it ends up more SWFEs/clipper-redevelopers or actual coastal storms.

That's how I view it. Maybe I get screwed, but it should be more active.

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Without a -NAO, or at least a pseudo -NAO blocking type feature, we'd run the risk of storms trying to go west like through the OH valley at times...we could still do well on those as we all know, but certainly the M.A. would be in dire straights...and no guarantee we'd clean up.

For more classical coastal type storms, the +PNA/-NAO combo is a lot more favorable. At the very lest though, this should get us a more active pattern...whether it ends up more SWFEs/clipper-redevelopers or actual coastal storms.

Yea, that's what I mean....we don't NEED it, though it helps...if they do not have it, then it's absolutely game over.

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Nice post, Will. I like all of your ideas moving forward over the next few weeks. My general idea moving forward over the next few weeks is that we are likely in a stale-mate for the next 1 to 2 weeks. A few days ago I mentioned super-bowl weekend as the potential time frame for the possibility of major amplification on the East Coast. These PNA amplification's like to come in with a bang -- and the forecast model guidance is starting to hint at it being more anomalous as we get closer.

That being said...we are playing with fire even with the PNA flux. If, for instance, the Atlantic and the NAO were to not cooperate -- we would fall back a few steps once again. The reality of it is that through the first week of February, the majority of the polar air is located with the PV on the Pacific side of the Arctic Circle. We can see this on the image below...GEFS around +180 hr...which is a moderate lead. Here we have a PNA ridge trying to amplify on the west coast...but the Atlantic is stubborn, still with a trough extending over Baffin Island to Greenland. I think there is the legit possibility of February beginning with 3-6 days of above normal temperatures

post-6-0-50747700-1327532009.png

.

After this things start to get very interesting as you noted above. The hemispheric regimes are changing and there is no denying that. But I urge caution here because the sheer amount of false-starts we have been victim of. It's not all our fault as forecasters -- the medium range ensembles have been rather poor with this pattern. But if the 12z GEFS are correct...we'll see a +PNA ridge building on the west coast and even north into British Columbia. That would be the most anomalous feature we've seen so far this winter. The GEFS and ECMWF Ens are pegging Feb 6-8 right now...so I would at least keep one eye open around that period.

Point is...move forward cautiously. The image below is the GFS AO forecast bias from the past several weeks which I posted in a thread over in the NYC forum from last night. Some pretty poor mid range forecasting here from the GFS and several instances when it forecasted the AO to drop well into negative values when it barely made it to neutral. Obviously we have killed the curse now and are between -1 and -2 ...but it does still seem to be biased in the negative departures.

The Euro ensembles show a lot more of a -NAO, which I hope is right...but I have minimal confidence at the moment on the NAO...I'm pretty confident on the PNA ridging.

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With the pesky low, I think there is a question as to the amplitude of the ridge. It's not Scooter caution..it's for real.Like I said, I do have optimism for chances going forward into February. At least we have the MJO trying to help out.

Though as HM alludes to in his write-up in the main thread, the current state in the octant graph may actually just be the result of BS stagnant forcing, and not the MJO

"We have not seen a true MJO wave since the autumn with a very long-lived wave that started in late September.This wave went around the equatorial regions nearly 3 times before finally dampening to ENSO forcing by December. Ever since, the tropical forcing has been stagnant.

Despite what the octant charts indicate, there are actually two areas where wind/OLR anomalies are juxtaposed for a possible MJO wave. Some of the strongest anomalies, currently, are coming from the Indian Ocean. Roundy also agrees..."

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Roger Smith Ftw? I don't recal his exact forecast but I do believe he called for a warm winter on the east coast right up to middle of Feb then turning sharply colder. Ballsy call considering he made it in the end of Oct early Nov. Seems bang on so far. I guess we'll see how it all plays out. I hope he's right. Would be nice to salvage some form of winter this year.

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