HPC AM Discussion

[Snowden]

DT has hit home about this several times but see below:

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

312 AM EST WED DEC 22 2010

VALID 12Z SUN DEC 26 2010 - 12Z WED DEC 29 2010

...EUROPEAN CENTRE GUIDANCE STAYS THE COURSE ON POWERFUL EAST COAST STORM DECEMBER 26-27...

WILL STICK WITH THE CONSISTENT ECMWF FOR THE PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3-7. FOR THREE CONSECUTIVE MODEL CYCLES...THE DETERMINISTIC ECMWF HAS INDICATED A MASSIVE...DEEP...SLOW-MOVING CYCLONE HUGGING THE CAROLINA AND MID ATLANTIC COASTS THE TWO DAYS FOLLOWING CHRISTMAS. THE ECMWF AND UKMET WERE THE FIRST OF THE GLOBAL NUMERICAL MODELS TO SWITCH FROM TRACKING THIS WAVE ALONG 40N THROUGH THE MIDWEST...TO A SUPPRESSED PATH ACROSS THE DEEP SOUTH. SINCE THIS BREAK-AWAY...THE UKMET SPLIT OFF EVEN FARTHER SOUTH...WITH THE ECMWF LOCKING ONTO AN EVOLUTION THAT TAKES THE DEVELOPING LOW TO THE FLORIDA PANHANDLE AND THEN SHARPLY UP THE EASTERN SEABOARD. THE GEM GLOBAL FOLLOWED THE EUROPEAN CENTRE TRACK ON ITS 00Z/21 RUN...BUT HAS SWUNG THE SYSTEM OUT WIDER OVER THE ATLANTIC THE LAST TWO RUNS. THE GFS HAS SHIFTED TO THE SOUTHERN ROUTE ACROSS THE GULF STATES ON ITS CURRENT RUN...BUT LIKE THE GEM GLOBAL...DIRECTS THE CYCLONE WELL SOUTH AND EAST OF CAPE HATTERAS.

THE ECENS MEMBERS HAVE AVERAGED CLOSE TO THE DETERMINISTIC ECMWF...WITH MANY MEMBERS FOLLOWING IT EXACTLY...AND OTHERS TRACKING A BIT FARTHER OFFSHORE. THE EUROPEAN CENTRE GUIDANCE HAS THE ADVANTAGE IN DEVELOPMENTAL SYSTEMS WITH ITS HIGH RESOLUTION...AND IS FURTHER AIDED BY ITS 4D-VAR ANALYSIS IN GENERAL. ITS ENSEMBLE MEMBERS ARE MORE HIGHLY RESOLVED THAN THE GEFS MEMBERS...AND WITH DYNAMIC...DEVELOPMENTAL SYSTEMS...THE EUROPEAN GUIDANCE SHOULD HAVE THE EDGE. INDEED...THE GEFS MEAN HAS BEEN CONSISTENTLY FLATTER WITH THE PATH OF THE BIG STORM...WHICH IS CERTAINLY IN LINE WITH THE LOWER RESOLUTION. EVEN SO...FOUR 00Z/22 GEFS MEMBERS STILL TRACKED COMPARABLY TO THE ECMWF...SHOWING A DEEP NOREASTER AND A HIGH IMPACT STORM FOR THE MAJOR METROPOLITAN AREAS ASTRIDE INTERSTATE 95 FROM WASHINGTON TO BOSTON. TO WIT...THESE GEFS MEMBERS ARE GOING AGAINST THEIR LOWER RESOLUTION/LESS DEVELOPMENTAL NATURE. THE ECMWF HAS MUCH CLIMATOLOGY ON ITS SIDE AS WELL...WITH ITS TRACK WEST OF THE GULF STREAM...AND THE BOMBING PHASE NEAR AND NORTH OF CAPE HATTERAS. THE MOST UNUSUAL...AND THREATENING...ASPECT OF THE ECMWF FORECAST IS THE RELATIVELY LOW LATITUDE AT WHICH THE STORM MATURES AND STALLS/LOOPS. MORE TYPICALLY...SYSTEMS WILL CLOSE OFF AND HOVER OVER THE WATERS SOUTH OF NOVA SCOTIA...AS WITH THE MOST RECENT CYCLONE STILL AFFECTING DOWNEAST MAINE. THE ECMWF SHOWS THE UPCOMING CIRCULATION COMING TO A HALT JUST EAST OF THE DELMARVA PENINSULA...WHICH PUTS THE VERY POPULATED AREAS OF THE EASTERN MID ATLANTIC...LONG ISLAND...AND SOUTHERN NEW ENGLAND IN A PROLONGED PERIOD OF HIGH WINDS AND HEAVY PRECIPITATION...MOSTLY SNOW. THE EXTRAORDINARY NEGATIVE NAO THIS MONTH COULD CERTAINLY SUPPORT SUCH AN ANOMALY. EVEN BEFORE THE RAPID DEEPENING PHASE OF THE SYSTEM...AREAS OF THE DEEP SOUTH FROM THE INTERIOR GULF COAST STATES TO GEORGIA AND THE MOUNTAINS AND PIEDMONT OF THE CAROLINAS MAY SEE A VERY RARE WHITE CHRISTMAS...AGAIN...CONSISTENT WITH THE REMARKABLE DISRUPTION AT HIGH LATITUDES.

WHILE THE EASTERN VORTEX RELOADS AND EXPANDS...THE FLOW STREAMING OFF THE PACIFIC WILL BE LARGELY SHUNTED FARTHER NORTH THAN RECENT DAYS...WITH THE POLAR JET TAKING AIM AT THE WASHINGTON COAST. SOME FLOW WILL SPLIT INTO THE FAR SOUTHWEST...BUT WITH NOT NEARLY THE ROBUSTNESS OF THE PAST WEEK.

[donsutherland1]

Although I have enormous respect for the expertise and outstanding work done by HPC (and am rooting for the operational Euro solution to verify), I do raise a caveat. Although general climatology would tend to favor the Euro, moderate/strong La Niña climatology does not. Just a small difference in timing when a phase takes place or if it does would have a substantial impact on the outcome. It is no coincidence that since 1871, there have been only two KU-type storms (December 1909 and January 2000) when the ENSO Region 3.4 anomaly was -1 or below. None of those storms brought 10" or more snow in all of the big cities running from Richmond to Boston (RIC, DCA, PHL, NYC, BOS). Although one cannot rule out what would be an unprecedented event for the 1871-present timeframe were the operational 0z Euro to verify, historical odds are against it. That the ECMWF ensemble guidance has shifted south and eastward and a number of other models are well east of the Euro adds to this sense of caution.

[nj2va]

Nice discussion. Easy for this noob to understand.

[A-L-E-X]

Although I have enormous respect for the expertise and outstanding work done by HPC (and am rooting for the operational Euro solution to verify), I do raise a caveat. Although general climatology would tend to favor the Euro, moderate/strong La Niña climatology does not. Just a small difference in timing when a phase takes place or if it does would have a substantial impact on the outcome. It is no coincidence that since 1871, there have been only two KU-type storms (December 1909 and January 2000) when the ENSO Region 3.4 anomaly was -1 or below. None of those storms brought 10" or more snow in all of the big cities running from Richmond to Boston (RIC, DCA, PHL, NYC, BOS). Although one cannot rule out what would be an unprecedented event for the 1871-present timeframe were the operational 0z Euro to verify, historical odds are against it. That the ECMWF ensemble guidance has shifted south and eastward and a number of other models are well east of the Euro adds to this sense of caution.

Don, I mentioned this in your pinned thread, but what kind of ENSO did March 1956 occur in? I believe Feb 1989 occurred in a strong la nina and would qualify as a "near miss."

[donsutherland1]

Don, I mentioned this in your pinned thread, but what kind of ENSO did March 1956 occur in? I believe Feb 1989 occurred in a strong la nina and would qualify as a "near miss."

Alex,

The ENSO Region 3.4 anomaly in March 1956 was -0.78. What had been a moderate/strong La Niña had weakened considerably by February and March. February 1989 is a "near miss" case. Such cases are far more common than KU-type events during moderate or strong La Niñas.

[rainstorm]

do you think we can have a feb 89 storm here this weekend, don, or will this thing just head far out to sea?

[TowsonWeather]

All good points, Don, and I think we would all be wise to proceed with caution for those very reasons.

[donsutherland1]

do you think we can have a feb 89 storm here this weekend, don, or will this thing just head far out to sea?

My early guess is that SE Virginia has a good chance at seeing accumulating snow. How much remains a big question.

[rainstorm]

My early guess is that SE Virginia has a good chance at seeing accumulating snow. How much remains a big question.

so basically, when people say its out to sea they refer to dc north? what fell here in the feb 89 storm?

[donsutherland1]

so basically, when people say its out to sea they refer to dc north? what fell here in the feb 89 storm?

The references to out to sea likely refer to the big cities from DCA northward.

February 1989 saw one of the great stretches of winter weather for Norfolk. 2/17-19/1989 saw 15.4" of snow fall at Norfolk. 2/23-24/1989 had another 9.0" snowfall.

[rainstorm]

The references to out to sea likely refer to the big cities from DCA northward.

February 1989 saw one of the great stretches of winter weather for Norfolk. 2/17-19/1989 saw 15.4" of snow fall at Norfolk. 2/23-24/1989 had another 9.0" snowfall.

now i remember reading about that. didnt norfolk warm up into the 70's inbetween the snows?

[donsutherland1]

now i remember reading about that. didnt norfolk warm up into the 70's inbetween the snows?

Yes. The high temperature on 2/21 was 76°.

[rainstorm]

Yes. The high temperature on 2/21 was 76°.

that was a wild week of weather. i wish we could have variable weather patterns again instead of being locked into one pattern for whole seasons.

[Ender]

THE EUROPEAN CENTRE GUIDANCE HAS THE ADVANTAGE IN DEVELOPMENTAL SYSTEMS WITH ITS HIGH RESOLUTION...AND IS FURTHER AIDED BY ITS 4D-VAR ANALYSIS IN GENERAL.

What about the UKMET? I thought they went to 4DVAR as well, they certainly have with their regional models. Oh, and their resolution is in the Euro's range.

ITS ENSEMBLE MEMBERS ARE MORE HIGHLY RESOLVED THAN THE GEFS MEMBERS...AND WITH DYNAMIC...DEVELOPMENTAL SYSTEMS...THE EUROPEAN GUIDANCE SHOULD HAVE THE EDGE.

Without a doubt.

THE ECMWF HAS MUCH CLIMATOLOGY ON ITS SIDE AS WELL...WITH ITS TRACK WEST OF THE GULF STREAM...AND THE BOMBING PHASE NEAR AND NORTH OF CAPE HATTERAS.

I'm not going to bother...

THE MOST UNUSUAL...AND THREATENING...ASPECT OF THE ECMWF FORECAST IS THE RELATIVELY LOW LATITUDE AT WHICH THE STORM MATURES AND STALLS/LOOPS. MORE TYPICALLY...SYSTEMS WILL CLOSE OFF AND HOVER OVER THE WATERS SOUTH OF NOVA SCOTIA...AS WITH THE MOST RECENT CYCLONE STILL AFFECTING DOWNEAST MAINE. THE ECMWF SHOWS THE UPCOMING CIRCULATION COMING TO A HALT JUST EAST OF THE DELMARVA PENINSULA...WHICH PUTS THE VERY POPULATED AREAS OF THE EASTERN MID ATLANTIC...LONG ISLAND...AND SOUTHERN NEW ENGLAND IN A PROLONGED PERIOD OF HIGH WINDS AND HEAVY PRECIPITATION...MOSTLY SNOW.

Yup, exceptionally, exceptionally unusual. In fact, when did it last happen? I know it has..but pretty darn unusual. Especially in mid winter. Of course, it's happened, or come close to happening, on the Euro a couple times already this December.

THE EXTRAORDINARY NEGATIVE NAO THIS MONTH COULD CERTAINLY SUPPORT SUCH AN ANOMALY.

Well, the Euro isn't just making things up. It's making its forecast for "good reason"...but are those reasons correct?

[WintersGrasp]

Don great posts here. I'm being very cautious with this one. I believe, and we've all seen, storms that the mods trend south with and not ride up the coast be followed by others that do the same. I've also noticed that the models, yes even the euro, may have a huge fee runs, then gradually adjust run by run (in this case east). It's not what I want, but it is what I see happening. Right now, everyone up the east coast could see more than a couple inches, but if I had to bet on it I'd say NC and southern VA stand the best chance at more than 6.

[NorEaster27]

What about the UKMET? I thought they went to 4DVAR as well, they certainly have with their regional models. Oh, and their resolution is in the Euro's range.

Without a doubt.

I'm not going to bother...

Yup, exceptionally, exceptionally unusual. In fact, when did it last happen? I know it has..but pretty darn unusual. Especially in mid winter. Of course, it's happened, or come close to happening, on the Euro a couple times already this December.

Well, the Euro isn't just making things up. It's making its forecast for "good reason"...but are those reasons correct?

The GGEM and NOGAPS have 4D-VAR and the euro ensembles do not agree with the OP....

[A-L-E-X]

The references to out to sea likely refer to the big cities from DCA northward.

February 1989 saw one of the great stretches of winter weather for Norfolk. 2/17-19/1989 saw 15.4" of snow fall at Norfolk. 2/23-24/1989 had another 9.0" snowfall.

Donald, not to bug you about 2/89 too much, but I remember the latter storm delivered a 2-5" accum to NYC and Long Island. Did the earlier storm do anything up here?

[Ed Lizard]

AM19PSU says Cisco at HPC is something of a Euro-phile.

Looks like Rausch has partially dampened out the Cisco oscillation

[A-L-E-X]

Alex,

The ENSO Region 3.4 anomaly in March 1956 was -0.78. What had been a moderate/strong La Niña had weakened considerably by February and March. February 1989 is a "near miss" case. Such cases are far more common than KU-type events during moderate or strong La Niñas.

And the other thing was, I believe you had 1955-56 in your list of analogs, so I think you expect the la nina to weaken considerably by March

Although, with the type of blocking youve been talking about persisting into January, who knows we might have a 1916-17 style mod-strong la nina winter with lots of moderate events adding up to a nice seasonal total.

[OSUmetstud]

AM19PSU says Cisco at HPC is something of a Euro-phile.

Looks like Rausch has partially dampened out the Cisco oscillation

It's likely the Cisco did not see the 00z Euro Ensembles before writing last night's discussion.

[Snowden]

Don great posts here. I'm being very cautious with this one. I believe, and we've all seen, storms that the mods trend south with and not ride up the coast be followed by others that do the same. I've also noticed that the models, yes even the euro, may have a huge fee runs, then gradually adjust run by run (in this case east). It's not what I want, but it is what I see happening. Right now, everyone up the east coast could see more than a couple inches, but if I had to bet on it I'd say NC and southern VA stand the best chance at more than 6.

I agree, and my gut feeling says we'll see the Euro begin to slowly south and east today

[NorEaster27]

Although I have enormous respect for the expertise and outstanding work done by HPC (and am rooting for the operational Euro solution to verify), I do raise a caveat. Although general climatology would tend to favor the Euro, moderate/strong La Niña climatology does not. Just a small difference in timing when a phase takes place or if it does would have a substantial impact on the outcome. It is no coincidence that since 1871, there have been only two KU-type storms (December 1909 and January 2000) when the ENSO Region 3.4 anomaly was -1 or below. None of those storms brought 10" or more snow in all of the big cities running from Richmond to Boston (RIC, DCA, PHL, NYC, BOS). Although one cannot rule out what would be an unprecedented event for the 1871-present timeframe were the operational 0z Euro to verify, historical odds are against it. That the ECMWF ensemble guidance has shifted south and eastward and a number of other models are well east of the Euro adds to this sense of caution.

100% agree very good post.

[A-L-E-X]

In that Rausch link you posted, I noted this:

THE 00Z

GEFS/ECMWF ENSEMBLE MEANS OFFER MORE SUPPORT FOR A SHARPER AND

MORE N-S ORIENTED TROF THAN RECENT GFS RUNS. WHILE THE 00Z AND

12Z/21 ECMWF EVOLUTIONS ARE FAIRLY EXTREME WITH THE DEPTH OF THE

MID LVL LOW THAT CLOSES OFF NEAR THE EAST COAST... THEY APPEAR A

LITTLE MORE COMPATIBLE WITH ENSEMBLE MEAN IDEAS VERSUS GFS RUNS.

AS THE LOW TRACKS ALONG THE EAST COAST THE 00Z ECMWF IS ON THE WRN

SIDE OF THE SPREAD OF 00Z ECMWF ENSEMBLE MEMBERS AND WWD OF ALL

00Z GEFS MEMBERS WHICH ARE ADMITTEDLY SOMEWHAT LOWER IN

RESOLUTION. WHILE THE STRONG DYNAMICS ALOFT MAY WELL SUPPORT THE

OPERATIONAL ECMWF SOLN... IT IS TOO EARLY TO SUBSCRIBE FULLY TO

ITS FCST. A SOLN IN THE WRN HALF OF THE GUIDANCE SPREAD STILL

APPEARS REASONABLE THOUGH. AS A RESULT WILL GO WITH A BLEND

CONSISTING OF 30 PCT EACH 00Z ECMWF AND 12Z/21 ECMWF RUNS WITH THE

REMAINING 40 PCT OCCUPIED BY THE 00Z ECMWF ENSEMBLE MEAN.

[Rainshadow]

And the other thing was, I believe you had 1955-56 in your list of analogs, so I think you expect the la nina to weaken considerably by March

Although, with the type of blocking youve been talking about persisting into January, who knows we might have a 1916-17 style mod-strong la nina winter with lots of moderate events adding up to a nice seasonal total.

Alex,

This is how close the current gwo is going to come to that Feb 89 miss. (I'm assuming a counterclockwise loop continuing, which may be wrong). That yellowish dot were the daily values around the time of that oh so close event.

[WintersGrasp]

If the gfs holds serve here and the euro shifts south, we have a lot to worry about here for anyone north of southeastern Virginia

[Rainshadow]

It's likely the Cisco did not see the 00z Euro Ensembles before writing last night's discussion.

That may be true, I have seen the briefer internal discussions come out as early as 3 am. I don't know the ending time of that shift, but it does start before 11 pm.

[donsutherland1]

Alex,

This is how close the current gwo is going to come to that Feb 89 miss. (I'm assuming a counterclockwise loop continuing, which may be wrong). That yellowish dot were the daily values around the time of that oh so close event.

It had switched from Phase 2 the day before the storm to Phase 3 on the day the storm begain (2/17). It remained locked in Phase 3 for some time afterward.

[Rainshadow]

It had switched from Phase 2 the day before the storm to Phase 3 on the day the storm begain (2/17). It remained locked in Phase 3 for some time afterward.

Don,

Yes that was the one I was referring to Feb 23-24.

[A-L-E-X]

It had switched from Phase 2 the day before the storm to Phase 3 on the day the storm begain (2/17). It remained locked in Phase 3 for some time afterward.

Don, just think about it-- if that storm had materialized for us (I believe it was a bust-- we were supposed to get a foot) it would have been PD2. Then the one in 2003 would have been PD3!

BTW did only one of those Norfolk snowstorms make it up to NYC with accum snow?

[A-L-E-X]

Don,

Yes that was the one I was referring to Feb 23-24.

Sounds like 2/89 featured more than one bust, Tony.