Medium Range Discussion Winter 2011-12

[SnowGoose69]

The 00Z Euro held sevre and does suggest the west and the plains will see the best shot for some very cold air to head S into the Great Basin. The GFS is not as amplified with the +PNA ridge. The euro would dump that cold air into Western Canada and points S that has been building for the last several weeks in Alaska during the first week of December. As you and others have stated, the models have struggled beyond the medium range.

The Euro I believe is suffering from its SW U.S. bias through the long range, its been trying to dig systems too hard in that region and as a result has had more of a ridge in the East at times...this is one area in the medium to longer range the GFS often outperforms the Euro.

[Weathergun]

The Euro I believe is suffering from its SW U.S. bias through the long range, its been trying to dig systems too hard in that region and as a result has had more of a ridge in the East at times...this is one area in the medium to longer range the GFS often outperforms the Euro.

Even if so, both models show the PNA ridge tilted somewhat NE to SW, and mostly over the Pacific, during this time frame. I don't think it would support a trough locking in over the East Coast,. Especially with no -NAO block.

[Srain]

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

303 AM EST SAT NOV 26 2011

VALID 12Z WED NOV 30 2011 - 12Z SAT DEC 03 2011

...WINTRY PATTERN FOR MUCH OF THE LOWER 48 THIS PERIOD...

AS WE HEAD INTO DECEMBER...TROUGHING ACROSS CENTRAL CANADA TEAMS

UP WITH RIDGING BUILDING ACROSS THE EASTERN PACIFIC JUST OFFSHORE

THE WEST COAST OF NORTH AMERICA SHOULD LEAD TO A POSITIVELY TILTED

TROUGH SPANNING THE CONTINENT FROM CENTRAL CANADA INTO THE WESTERN

UNITED STATES WITH HEIGHTS REBOUNDING ACROSS THE EAST. THE

GUIDANCE SHARES THESE IDEAS. DETAIL ISSUES CONTINUE TO ABOUND OUT

EAST...WHERE A COMPROMISE OF THE 00Z ECMWF/00Z UKMET MADE THE MOST

SENSE PER THE MODEL DIAGNOSTIC DISCUSSION /PMDHMD/. THIS

PREFERENCE WAS KEPT THROUGH LATE THURSDAY...THE END OF THE UKMET

RUN. THEREAFTER...THE 00Z GFS/00Z ECMWF WERE IN REASONABLE

AGREEMENT SO USED A COMPROMISE OF THOSE PIECES OF GUIDANCE LATE

THIS WEEK. THIS SET OF MODEL PREFERENCES MAINTAINED REASONABLE

CONTINUITY.

SNOW REMAINS POSSIBLE ACROSS THE EASTERN GREAT LAKES/UPPER OHIO

VALLEY EARLY ON WITHIN THE EASTERN CYCLONE COMMA HEAD UNTIL THE

SYSTEM EXITS INTO CANADA DURING THE DAY WEDNESDAY. IN ITS

WAKE...STRONG HIGH PRESSURE WEDGES INTO THE PLAINS WEDNESDAY

THROUGH FRIDAY WHICH SHOULD LEAD TO UPSLOPE SNOWS ACROSS MONTANA

AND WYOMING LATE WEDNESDAY INTO THURSDAY BEFORE THE HIGH MOVES OFF

TO THE SOUTHEAST AND WEAKENS. INCREASING HIGH PRESSURE ACROSS THE

INTERIOR WEST SHOULD LEAD TO OFFSHORE FLOW NEAR THE WEST COAST

BEGINNING THURSDAY AND CONTINUING INTO NEXT SATURDAY.

HOWEVER...NEAR THE CORE OF THE CLOSED LOW DROPPING THROUGH THE

WEST... MODERATE SNOWS ARE EXPECTED ACROSS THE GREAT

BASIN/SOUTHWEST/POSSIBLY THE SIERRA NEVADA LATE NEXT WEEK.

DEPENDING UPON HOW FAR EAST THE DEEP CYCLONE ACROSS THE WEST

TRACKS...SNOW IS ALSO A POSSIBILITY FROM THE BIG COUNTRY OF TEXAS

NORTHWARD TOWARDS THE OKLAHOMA PANHANDLE NEXT FRIDAY AND SATURDAY.

A FRONTAL SYSTEM CROSSING THE NORTHERN PLAINS/GREAT

LAKES/NORTHEAST SHOULD ALSO DROP SOME SNOW FROM THURSDAY INTO

SATURDAY.

[Srain]

While folks along the EC may not be too thrilled, there does appear to be some very chilly air heading S into the West and the Plains. A very deep H5 Low sinks S into Great Basin/N MX setting the stage for the first significant Winter Storm of the season, if the guidance is correct. We will see...

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

843 AM EST MON NOV 28 2011

VALID 12Z FRI DEC 02 2011 - 12Z MON DEC 05 2011

CURRENT GUIDANCE SHOWS REASONABLY GOOD AGREEMENT IN MAINTAINING A

POSITIVELY-TILTED LONGWAVE TROUGH FROM HUDSON BAY TOWARD THE FOUR

CORNERS REGION THROUGH THE MEDIUM RANGE PERIOD...WITH A

CORRESPONDING HIGH AMPLITUDE LONGWAVE RIDGE OVER THE NORTHEAST

PACIFIC...AND A SMALLER BUT STILL SIGNIFICANT RIDGE OVER THE

SOUTHEAST. TELECONNECTIONS WITH THE RIDGE OVER THE PACIFIC WHERE

ANOMALIES APPROACH 3 STANDARD DEVIATIONS ABOVE NORMAL AGREES WITH

THE PROJECTED TROUGH EXTENDING ACROSS THE FOUR CORNERS REGION AND

GENERALLY FAVORS BELOW NORMAL TEMPERATURES FOR MUCH OF THE ROCKIES

AND PLAINS.

CONCERNING THE DAY-TO-DAY DETAILS...THE STRONG FLOW CONSTITUTING

THE POLAR OR ARCTIC STREAM CROSSING THE NORTHERN CONUS...DUE IN

PART TO POTENTIAL INITIALIZATION ERRORS ORIGINATING FROM THE

HIGHER LATITUDES...CONTAINS AVERAGE TO BELOW AVERAGE

PREDICTABILITY AND IS SUPPORTED BY THE INCREASING SPREAD IN THE

GLOBAL ENSEMBLE MEMBERS. IN ADDITION....THIS NORTHERN STREAM FLOW

WILL DETERMINE THE TIMING AND TRAJECTORY OF THE UPPER LOW LEAVING

THE SOUTHWEST AROUND DAYS 4-5/FRI-SAT.

DETERMINISTIC AGREEMENT IS AVERAGE THROUGH DAY 4...WITH THE 00Z

GFS THEN ACCELERATING THE NORTHERN STREAM TROUGH OVER THE PLAINS

AHEAD OF THE MAJORITY OF GUIDANCE...GREATLY ALTERING THE SHORTWAVE

PATTERN EAST OF THE MISSISSIPPI RIVER. GIVEN THAT THE GFS IS ONLY

SUPPORTED BY ITS ENSEMBLE MEAN ALONG WITH THE GFS POSSIBLY

DISPLAYING A FAST BIAS AT LONGER RANGES...THIS SCENARIO IS

DISCOUNTED IN FAVOR OF THE ECMWF/UKMET/CANADIAN WHICH STRONGLY

AGREE ON A SLOWER AND GENERALLY DIFFERENT CONFIGURATION.

BEYOND DAY 5...THE MAIN ISSUE IS RESOLVING THE EVOLVING PATTERN

DOWNSTREAM OF THE AMPLIFYING RIDGE OVER THE NORTHERN PACIFIC.

GENERALLY SPEAKING...AN AMPLIFYING RIDGE IN THIS PROXIMITY FAVORS

THE POTENTIAL FOR CONSIDERABLE DIGGING OF DOWNSTREAM PERTURBATIONS

INTO TROUGHS OR POSSIBLY CLOSED LOWS ALONG WITH INTRUSIONS OF

POLAR OR ARCTIC AIRMASSES. TOTAL SOLUTION SPREAD IS QUITE LARGE

BEYOND DAY 5...BUT GIVEN THE ANTICIPATED LARGE-SCALE RIDGE A

SOLUTION SIMILAR TO THE 00Z ECMWF IS EXPECTED ALBEIT WITH

UNCERTAIN DETAILS. THUS...THE ECMWF WILL REMAIN THE FOUNDATION OF

THE UPDATED PRESSURES/FRONTS FOR ALL DAYS BUT WITH SLIGHTLY

GREATER BLENDING WITH ITS OWN ENSEMBLE MEAN BY THE END OF THE

PERIOD TO ADDRESS THE GROWING SPREAD AND UNCERTAINTY.

IN ADDITION TO BELOW NORMAL TEMPERATURES FOR MUCH OF THE

ROCKIES/PLAINS THROUGH THE PERIOD... CORRESPONDINGLY WARM AREAS

ARE ANTICIPATED OVER PARTS OF THE PACIFIC NORTHWEST BENEATH THE

EASTERN EDGE OF THE LONGWAVE RIDGE...AND ACROSS MUCH OF THE

EAST/SOUTHEAST WHICH WILL REMAIN BENEATH A BROAD BUT WEAKER RIDGE

THAN OVER THE PACIFIC. FINALLY...SIGNIFICANT SNOWS ARE EXPECTED

ACROSS THE CENTRAL/SOUTHERN ROCKIES DAYS 3/4 DUE TO THE UPPER

LOW...WITH A LARGER SHIELD OF PRECIPITATION DEVELOPING ACROSS

PARTS OF THE PLAINS/MISSISSIPPI VALLEY DAY 5 BEYOND AS MORE

ABUNDANT MOISTURE INTERACTS WITH THE EJECTING LOW.

[#NoPoles]

we are moving from bendy tree season, to bendy jet stream season...imagine the Jet stream as a rollercoaster track...i'd probably pee my pants dropping out of the rockies and rounding the bend in NX/TX

[am19psu]

If we can get a phase between the ejecting cutoff low in the SW and the northern stream shortwave, there is going to be a significant system in the Plains/MW next week. Lots of baroclinic energy available for a rapid cyclogenesis.

[Thundersnow12]

If we can get a phase between the ejecting cutoff low in the SW and the northern stream shortwave, there is going to be a significant system in the Plains/MW next week. Lots of baroclinic energy available for a rapid cyclogenesis.

Gotta love the differences between the 12z runs of the NAM and GFS...NAM doesn't cut off the southern wave but ejects it into the plains with a decent snow event where the GFS cuts it off and there is an attempt at a better phase on this run but not major.

[am19psu]

Gotta love the differences between the 12z runs of the NAM and GFS...NAM doesn't cut off the southern wave but ejects it into the plains with a decent snow event where the GFS cuts it off and there is an attempt at a better phase on this run but not major.

I get in trouble with this sometimes, but I feel pretty confident if the phase shows up in the mid-levels as depicted in the GFS, you're going to get a lot stronger surface deepening than what the GFS is showing. Non-hydrostatic pressure falls would be through the roof in that scenario.

[tacoman25]

Looks like the first true Arctic blast of the season coming to the CONUS this weekend/early next week. -18C into MN by hour 150 on latest GFS.

[Thundersnow12]

I get in trouble with this sometimes, but I feel pretty confident if the phase shows up in the mid-levels as depicted in the GFS, you're going to get a lot stronger surface deepening than what the GFS is showing. Non-hydrostatic pressure falls would be through the roof in that scenario.

0z GFS with a better phase and overall better snow event

[am19psu]

0z GFS with a better phase and overall better snow event

Yeah, but it's still not all the way there, with mid-level trough remaining positively tilted and open. The Euro really holds back the southern stream, which will limit the potential, too, if that solution verifies. There is still a chance for a big event if everything comes together, but I'm not holding my breath right now.

[Srain]

Yeah, but it's still not all the way there, with mid-level trough remaining positively tilted and open. The Euro really holds back the southern stream, which will limit the potential, too, if that solution verifies. There is still a chance for a big event if everything comes together, but I'm not holding my breath right now.

These pesky cut off upper lows are a headache to forecast. It is interesting that this pattern has been around for a while now with troughing to the W and ridging to the E. Sort of an IMBY post, but we're going to end November with 4.70 inches of rain at IAH with near normal temps (or slightly below) and who would have thought that in a La Nina Pattern, albeit weak.

HPC Morning Update:

A STRONG POSITIVE MID-LEVEL HEIGHT ANOMALY ACROSS THE NORTHEASTERN

PACIFIC WILL WORK IN CONJUNCTION WITH A WEAKER NEGATIVE MID-LEVEL

HEIGHT ANOMALY ACROSS HUDSON BAY TO HELP MAINTAIN A

POSITIVELY-TILTED LONGWAVE WAVE TROUGH EXTENDING FROM HUDSON BAY

TOWARD THE FOUR CORNERS REGION THROUGH THE MEDIUM RANGE PERIOD.

MODEL TRENDS...WHICH HAVE BEEN TOWARD GREATER REINFORCEMENT OF THE

BASE OF THE TROUGH...AND CLUSTERING OF 00Z GUIDANCE FAVOR

DISCOUNTING THE MORE PROGRESSIVE 00Z GFS. 0OTHERWISE...THE 00Z

UKMET/CANADIAN/ECMWF WERE IN REASONABLY GOOD AGREEMENT THROUGH DAY

5 BEFORE MORE TYPICAL TIMING/STRENGTH DIFFERENCES BECOME MORE

APPARENT. THUS...THE UPDATED PRESSURES/FRONTS WILL BE CONSTRUCTED

USING NON-NCEP GUIDANCE FOR THIS CYCLE...WITH GREATER EMPHASIS

TOWARD DETERMINISTIC SOLUTIONS THROUGH DAY 4 BEFORE TRANSITIONING

TOWARD ENSEMBLE MEAN GUIDANCE FOR DAYS 5-7.

GIVEN ANTICIPATION FOR REINFORCING THE TROUGH EARLY IN THE PERIOD

ALONG WITH MUCH LARGER SOLUTION SPREAD DEPICTED BY 00Z ENSEMBLE

MEMBER SPAGHETTI DIAGRAMS...CONFIDENCE IS MUCH LESS THAN WOULD

OTHERWISE BE SUGGESTED BY JUST CONSIDERING DETERMINISTIC GUIDANCE.

DAYS 3/4 ARE AVERAGE...DAYS 5-7 BELOW AVERAGE. REGARDING SENSIBLE

WEATHER...BELOW NORMAL TEMPERATURES AND WINTER PRECIPITATION ARE

EXPECTED FROM THE SOUTHERN/CENTRAL ROCKIES TOWARD THE GREAT

LAKES...WHILE A WARMING TREND SHOULD COMMENCE ALONG THE EAST COAST

DAYS 5-7. A NARROW REGION OF NEAR TO SLIGHTLY ABOVE NORMAL

TEMPERATURES SHOULD ALSO PERSIST ACROSS THE PACIFIC NORTHWEST.

[CoastalWx]

The 11-15 day euro ensembles try to get a little more NATL ridging going. Heights lowered a bit near and just south of AK, but heights also increased in the west. It means areas in the Mid Atlantic cooled off a bit after the 10th.

Overall the ridge in the GOA does retrograde a good amount, but the difference seemed to be the Atlantic. Not sure how stable this change is so we'll have to see what future models do...but it is possible to have these NATL ridges. It's not a -NAO by any means, but it helps to push down the se ridge just a bit.

[Damage In Tolland]

Pattern change is on it's way..for some at least. Noyes all over it.

http://t.co/D3PWcrlY

[wxmx]

Pattern change is on it's way..for some at least. Noyes all over it.

http://t.co/D3PWcrlY

Not sure what he describes qualifies as a pattern change...regionally probably, and even then, it will be from Above Normal to just near Normal for the Northeast... The big picture, ie. main synoptic features, will remain there with small changes, AO/NAO will remain mostly positive for at least 10-15 days, the Pacific ridge will probably retrograde a bit, and the PV will remain near the Hudson Bay or just N, not a very cold setup for most of the CONUS. The big story, cold wise, next 5-7 days will be in the C/S Rockies and C/S Plains, then the MW and part of the Northeast maybe.

[usedtobe]

Not sure what he describes qualifies as a pattern change...regionally probably, and even then, it will be from Above Normal to just near Normal for the Northeast... The big picture, ie. main synoptic features, will remain there with small changes, AO/NAO will remain mostly positive for at least 10-15 days, the Pacific ridge will probably retrograde a bit, and the PV will remain near the Hudson Bay or just N, not a very cold setup for most of the CONUS. The big story, cold wise, next 5-7 days will be in the C/S Rockies and C/S Plains, then the MW and part of the Northeast maybe.

That's how I see it though I must admit, I'm only working off the 12Z GEFS ensemble mean.

[wxmx]

That's how I see it though I must admit, I'm only working off the 12Z GEFS ensemble mean.

MJO going thru phases 3-5, -OLR anomalies suggesting tropical forcing will progress from the IO to near Indonesia, the current +SOI peak all teleconnect to an Aleutian Ridge and SE ridge... if the Atlantic/Artic don´t make their move soonish, December will end well above normal for most of the CONUS E of the Rockies.

*Cue for Adam to insert blowtorch image*

[wxmx]

As long as the stratospheric PV stays put close to the North Pole and with a roundish look, I would bet against any significant and sustained high latitude ridging. But FWIW, I think Jan will bring significant changes in this respect.

[Srain]

Heh...

[wxmx]

Heh...

just trying to discredit me, huh? ... Not a perfect NAO setup, but works since the Pacific ridge hasn't retrograded that much... I would bet against this solution, and if something similar pans out, I would bet it would be temporary looking at current data...but I have been way wrong before, and I will be wrong again sometime, so I will give it the benefit of the doubt.

[usedtobe]

just trying to discredit me, huh? ... Not a perfect NAO setup, but works since the Pacific ridge hasn't retrograded that much... I would bet against this solution, and if something similar pans out, I would bet it would be temporary looking at current data...but I have been way wrong before, and I will be wrong again sometime, so I will give it the benefit of the doubt.

It will be interesting to see what the euro ensemble mean looks like. Like you, I have my doubts about the solution but that means little, the pattern will do what it wants to do.

[am19psu]

Look what I missed this afternoon...

I agree with Jorge and Wes, FWIW

[NJwinter23]

just trying to discredit me, huh? ... Not a perfect NAO setup, but works since the Pacific ridge hasn't retrograded that much... I would bet against this solution, and if something similar pans out, I would bet it would be temporary looking at current data...but I have been way wrong before, and I will be wrong again sometime, so I will give it the benefit of the doubt.

Yeah I mean it is only one solution, but this second cold shot portrayed on the 12z euro around day 10 (12/9) is still well within the early December time frame where were going to finally see some cold shots in the lower 48. This wouldnt discredit the idea of a a big warm period ensuing by mid-month in my opinion. (I know several people like that idea).

I would also say that the pattern on this 12z euro is still largely driven by the Pacific which remains in -EPO/+PNA through the end of the run, and that North Atl ridging is probably building downstream as a result. In essence, the EPO/PNA ridge doesnt retrograde YET by day 10 on the op euro. Plausible?

[HM]

FWIW, we are seeing some warming at 10mb due to a wave 1 response from an East Asian MT. However, that timed "perfectly" with the recent proton flux from the sun, so I doubt this wave will be able to do anything noteworthy down the road. Meanwhile, the lower stratospheric levels are quite cold (historic cold actually at some levels).

The GWO sequence into early December and long range ensembles do develop a growing positive height anomaly across Siberia in the media range. That is certainly something to take note of for down the road, in terms of the state of the AO.

[wxmx]

FWIW, we are seeing some warming at 10mb due to a wave 1 response from an East Asian MT. However, that timed "perfectly" with the recent proton flux from the sun, so I doubt this wave will be able to do anything noteworthy down the road. Meanwhile, the lower stratospheric levels are quite cold (historic cold actually at some levels).

The GWO sequence into early December and long range ensembles do develop a growing positive height anomaly across Siberia in the media range. That is certainly something to take note of for down the road, in terms of the state of the AO.

Also, E-P flux has had more of an equatorward vector lately, so I also think the wave won't be able to disturb the polar night jet much.

[donsutherland1]

FWIW, the GFS ensembles are generally forecasting that the AO will remain somewhere in the vicinity of +1.5 to +3.0 through the first 10 days of December. A composite of the 500 mb anomalies for all such cases (1950-2010) is below:

The GFS ensemble 500 mb anomalies forecast for 12/5 0z has some similarities albeit they appear to be somewhat farther to the east than the composite idea:

During this time, the EPO- is likely to thwart an all-out blowtorch, but the pattern won't be very wintry in the East. The temperature anomaly for the period as a whole should fall on the warm side of normal during the first 10 days of December. Afterward, there could be brief window of opportunity (December 10-15 +/- a few days timeframe?) for cold and, if timing is good, some snow in parts of the East. Then, barring a development of blocking, ridging could return (just in time to spoil the Hanukkah-Christmas timeframe?).

Anyway, those are my thoughts for the medium range and beyond.

[usedtobe]

Don, Sounds reasonable to me. The negative epo will keep us from torching but that about it down here unless something really freaky happens.

[ORH_wxman]

Don, Sounds reasonable to me. The negative epo will keep us from torching but that about it down here unless something really freaky happens.

It looks like the pattern and tropical forcing really stinks for trying to get a -NAO anytime soon...not counting a transient north Atlantic ridge that may briefly drop the index number to negative. The PV seems to want to set up over Baffin Island and just W of the Davis Straight in the medium to long range on the Euro ensembles...and GEFS too for that matter.

[toronto blizzard]

It looks like the pattern and tropical forcing really stinks for trying to get a -NAO anytime soon...not counting a transient north Atlantic ridge that may briefly drop the index number to negative. The PV seems to want to set up over Baffin Island and just W of the Davis Straight in the medium to long range on the Euro ensembles...and GEFS too for that matter.

Just a question regarding the PV setting up over Baffin Island and the Davis staraight, if it develops there would that lead to lower heights over the GL/NE?

[brad1551]

FWIW, we are seeing some warming at 10mb due to a wave 1 response from an East Asian MT. However, that timed "perfectly" with the recent proton flux from the sun, so I doubt this wave will be able to do anything noteworthy down the road. Meanwhile, the lower stratospheric levels are quite cold (historic cold actually at some levels).

Amen to that .......

The GWO sequence into early December and long range ensembles do develop a growing positive height anomaly across Siberia in the media range. That is certainly something to take note of for down the road, in terms of the state of the AO.