2013 Fall Medium Range Discussion

[ORH_wxman]

2 out of the 13 years were neutral years.

Washington: 18.0"

Baltimore: 17.6"

NYC: 14.7"

Boston: 24.5"

These two years did feature strong AO blocking, so that wasn't the issue. My general point is the AO isn't as important to winter snowfall as one might think.

I had 3 years as neutral....'59-'60, '62-'63, and '85-'86. Though two of those years (the latter two) were almost La Ninas.

[OSUmetstud]

I had 3 years as neutral....'59-'60, '62-'63, and '85-'86. Though two of those years (the latter two) were almost La Ninas.

Thanks, yeah I missed 1959-1960.

Revised to include 1959-1960:

Boston 30.0"

NYC 22.8"

Baltimore 23.1"

Washington 20.4"

Yeah, we run into the problem of small data sets once again with this treatment. Though I don't think it's fair to include moderate Ninos, either.

[donsutherland1]

How about just a neutral filter? There's probably some solid weak/moderate Nino years that could be contaminating the data set.

Only two winters from the dates you provided featured R3.4 values above -0.5°C and below +0.5°C: 1959-60 and 1962-63. The mean snowfall figures didn't differ much for Washington, D.C., Baltimore, and New York City (22.9", 26.9", and 27.8" respectively) but fell off for Boston (35.9").

[Isotherm]

Don, good research. I agree that this blocking episode could very well persist into the middle of January. I think we'll see some help from the stratosphere for the late Dec-Jan period as we get a warming event to develop in the next few weeks IMO. The severe blocking in early December is correlated strongly to the DJF AO and NAO averaging on the negative side.

[OSUmetstud]

Only two winters from the dates you provided featured R3.4 values above -0.5°C and below +0.5°C: 1959-60 and 1962-63. The mean snowfall figures didn't differ much for Washington, D.C., Baltimore, and New York City (22.9", 26.9", and 27.8" respectively) but fell off for Boston (35.9").

I included 1985-1986 since CPC didn't consider it a Nina even though the trimonthly did hit -0.5C.

[donsutherland1]

With regard to the 11 blocking cases I noted in Message #25, seasonal snowfall figures were:

Baltimore: Mean: 30.1"; Median: 23.6"

Boston: Mean: 56.0"; Median: 51.9"

New York City: Mean: 34.0"; Median: 24.6"

Washington, DC: Mean: 21.8"; Median: 17.6"

All said, even with limitations concerning the sample size, it's probably likely that Winter 2012-13 will feature more snowfall in all of those cities than last winter. I do believe there is more upside risk (DCA/BWI 20" or more; NYC 30" or more; Boston: 50" or more) than downside risk ( DCA/BWI < 10", NYC < 20", and Boston < 40").

[OSUmetstud]

With regard to the 11 blocking cases I noted in Message #25, seasonal snowfall figures were:

Baltimore: Mean: 30.1"; Median: 23.6"

Boston: Mean: 56.0"; Median: 51.9"

New York City: Mean: 34.0"; Median: 24.6"

Washington, DC: Mean: 21.8"; Median: 17.6"

All said, even with limitations concerning the sample size, it's probably likely that Winter 2012-13 will feature more snowfall in all of those cities than last winter. I do believe there is more upside risk (DCA/BWI 20" or more; NYC 30" or more; Boston: 50" or more) than downside risk ( DCA/BWI < 10", NYC < 20", and Boston < 40").

Well I'd we would get more than last winter.

And yeah I'd agree with the upside chances. I'd feel a lot better if we managed to a weak Nino, though.

[CoastalWx]

Nice stuff Don and Nick.

[uncle W]

years with the lowest AO daily index value...

year...AO index...date...

1976-77...-7.433...01/15/77

1969-70...-6.365...03/05/70

1984-85...-6.226...01/19/85

2009-10...-5.821...12/21/09

1977-78...-5.291...02/05/78

1968-69...-5.282...02/13/69

2010-11...-5.172...12/18/10

1965-66...-5.130...01/28/66

1962-63...-5.010...01/21/63

2000-01...-4.854...02/25/01

1955-56...-4.564...02/15/56

1963-64...-4.470...12/20/63

1956-57...-4.473...02/21/57

1961-62...-4.417...03/04/62

2003-04...-4.387...01/17/04

1978-79...-4.387...01/25/79

On or near the dates of these AO minimums it was either very cold, snowy or both...

[OSUmetstud]

years with the lowest AO daily index value...

year...AO index...date...

1976-77...-7.433...01/15/77

1969-70...-6.365...03/05/70

1984-85...-6.226...01/19/85

2009-10...-5.821...12/21/09

1977-78...-5.291...02/05/78

1968-69...-5.282...02/13/69

2010-11...-5.172...12/18/10

1965-66...-5.130...01/28/66

1962-63...-5.010...01/21/63

2000-01...-4.854...02/25/01

1955-56...-4.564...02/15/56

1963-64...-4.470...12/20/63

1956-57...-4.473...02/21/57

1961-62...-4.417...03/04/62

2003-04...-4.387...01/17/04

1978-79...-4.387...01/25/79

On or near the dates of these AO minimums it was either very cold, snowy or both...

What happens when you remove 76-77?

[skierinvermont]

Comparing this winter to a -.5 is just as bad as comparing it to a +1.5 strong Nino. A -.5 and +.5 are totally different. It's not the classification as neutral that matters. It won't make much difference at all if we end up +.4 or +.5. R3.4 will still be close to a full degree C warmer than 2 of the 3 samples.

Why not just do 0 to +1 since we are likely to end up around +.5. Or to expand the sample size a bit do -.2 to +1.2.

I belive Don's range of 0 to +1.5 is pretty reasonable but perhaps skewed slightly to the Nino side. This could be meteorologically justified though if a +1.5 is more similar to a +.5 than a -.5.

(One thing to remember is that "neutral" is the broadest classification. A weak or moderate Nino/Nina classification all have ranges of .5 [.5-.9 and 1.0-1.4] and a strong Nino has a range of 1.0 [+1.5 to +2.4] and a strong Nina has a range of .6 [-1.5 to -2.0]. A neutral has a range of .9 [-.4 to +.4] or even bigger in this case since 2 of OSU's 3 samples reached -.5 and are counted as neutral. The point is Neutral is a very broad classification and a +.5 is nothing like a -.5.)

[usedtobe]

Don, good post. I was hoping you'd post something on the strong neg Ao cases. I may use some of it in an article. Wes

[uncle W]

What happens when you remove 76-77?

it's still below average across the country but a little less on the dark blue's...

[OSUmetstud]

it's still below average across the country but a little less on the dark blue's...

cool. I figured 76-77 might be throwing the temperatures into the blue heavily. It was one of the coldest winters of more modern times.

Two of Buffalo's only true blizzards of the last 35 years occured just after those peak blocking regimes in January 1977 and January 1985.

[uncle W]

cool. I figured 76-77 might be throwing the temperatures into the blue heavily. It was one of the coldest winters of more modern times.

Two of Buffalo's only true blizzards of the last 35 years occured just after those peak blocking regimes in January 1977 and January 1985.

1969-70 was a very cold winter also...NYC usually gets it's coldest temperatures or biggest snowfall of the season around the AO minimum with some exceptions...

http://www.americanwx.com/bb/index.php/topic/37768-increased-october-blocking-and-record-to-historic-weather/

[Ed Lizard]

I remember 76-77 well. Of course 77-78. BTW, nobody will guess who just tweeted the concept of an early Winter apocalypse from the Korean model.

[Bob Chill]

Very nice research Don. I wish I read this thread before I put together my AO thread in the MA subforum. I pulled a good bit of data and put together some nice daily graphs for various -AO Decembers.

[tacoman25]

Comparing this winter to a -.5 is just as bad as comparing it to a +1.5 strong Nino. A -.5 and +.5 are totally different. It's not the classification as neutral that matters. It won't make much difference at all if we end up +.4 or +.5. R3.4 will still be close to a full degree C warmer than 2 of the 3 samples.

Why not just do 0 to +1 since we are likely to end up around +.5. Or to expand the sample size a bit do -.2 to +1.2.

I belive Don's range of 0 to +1.5 is pretty reasonable but perhaps skewed slightly to the Nino side. This could be meteorologically justified though if a +1.5 is more similar to a +.5 than a -.5.

(One thing to remember is that "neutral" is the broadest classification. A weak or moderate Nino/Nina classification all have ranges of .5 [.5-.9 and 1.0-1.4] and a strong Nino has a range of 1.0 [+1.5 to +2.4] and a strong Nina has a range of .6 [-1.5 to -2.0]. A neutral has a range of .9 [-.4 to +.4] or even bigger in this case since 2 of OSU's 3 samples reached -.5 and are counted as neutral. The point is Neutral is a very broad classification and a +.5 is nothing like a -.5.)

In the research I have done, years that are in the weak neutral ENSO range (.5 to -.5) tend to be quite variable and do not have nearly as strong a signal as official Nino events. So I would suggest a .5 ENSO year is more comparable to years in the 0 to -.5 range than years in the 1.0 to 1.5 range. Take a look.

-ENSO neutral years...cold overall for the country, but not really a strong signal as to what area is favored.

+ENSO neutral years...very mixed and weak signal overall.

As opposed to official weak/moderate Ninos.

[Isotherm]

Agree taco. Mid/northern latitude teleconnections exert a stronger influence nationwide in the neutral ENSO years, hence quite a bit more variability. There's a reason why Ninas and Ninos, particularly mod/strong, are generally more predictable for LR forecasters. This is especially the case for the southern tier.

[skierinvermont]

Taco, the two maps you posted don't really look at all alike and although the signal is fairly weak (almost no signal in the 2nd map) I would still conclude that there is a substantial difference between +neutral and -neutral years based on the two maps. The primary difference is that -neutral years have a modest Nina-ish signal while +neutral has almost no signal (you can detect a vague and obscured Nino signal mostly warm north some cold south).

Also this year will be at the top end or even slightly above the +neutral sample. It might be more accurate to compare ENSO events between .3 and .7 vs -.3 and -.7 to accurately summarize the difference between. I would suspect that on average a +.5 ENSO event behaves more similar to a Nino event than does a +.2.

I would suggest that the +neutral map looks almost half way between the -neutral and the Mod Nino maps. If we looked only at events at or near +.5 instead of including +.1s and +.2s I would guess an even more Nino-ish picture would emerge.

In short, a better comparison would be -.5 to 0 VS +.3-7 VS +1.0-1.5. Even in the -.5 to 0 VS 0-.5 VS 1-1.5 I would suggest that +neutral looks almost halfway between -neutral and Mod Nino. One would actually expect the first two to be more similar than the latter given they are closer on the ONI. It's not really a fair comparison given that 0- +.5 is not a centered representation of +.5. Centered would be +.3-7.

[Met1985]

Don great stuff as always.

[skierinvermont]

When I took +.3-.7 years, the signal is very Nino-ish and similar to the +1-1.5. I would conclude the opposite of you Taco, that a +.5 is actually more similar to a 1-1.5 than to a 0 to -.5.

Based on this, I would strongly prefer Don's use of years with 0 to +1.5 ONI and -AO Novembers peaking below -3 than OSU's use of -.5 to +.5. 0 to +1.5 is much more representative of this year's ONI than -.5 to +.5.

Just to repeat Don's numbers for Novies with daily AOs peaking below -3. I believe this would form a good starting point for a winter forecast.

DJF Average: Positive but less than +1.5:

Baltimore: 30.3"

Boston: 48.9"

New York City: 29.0"

Washington, DC: 21.6"

[tacoman25]

When I took +.3-.7 years, the signal is very Nino-ish and similar to the +1-1.5. I would conclude the opposite of you Taco, that a +.5 is actually more similar to a 1-1.5 than to a 0 to -.5.

Based on this, I would strongly prefer Don's use of years with 0 to +1.5 ONI and -AO Novembers peaking below -3 than OSU's use of -.5 to +.5. 0 to +1.5 is much more representative of this year's ONI than -.5 to +.5.

Just to repeat Don's numbers for Novies with daily AOs peaking below -3. I believe this would form a good starting point for a winter forecast.

DJF Average: Positive but less than +1.5:

Baltimore: 30.3"

Boston: 48.9"

New York City: 29.0"

Washington, DC: 21.6"

I think it's overly simplistic to look only at .3 to .7 ENSO events, but if you do, this is the resulting map.

And here is 1-1.5 ENSO.

[tacoman25]

And here you have 0-1.0 ENSO.

Again, a considerably different picture (and it's not as clearcut a signal as it appears, as the range on the map is quite small). I think the bottom line is that any time ENSO is neutral/weak, the results are extremely variable and there are other factors that become much more important than the exact ENSO numbers.

Comparing a weak/neutral ENSO year to strong (1.5) ENSO years should be done with great caution.

[Wow]

What about +0.15 to +0.85? Just kidding...

I agree with tacoman's end assessment. Instead of getting overloaded with the anomaly maps, we should draw from just a couple of broad conclusions about the severity of ENSO and where its greatest levels of correlation occur. No more and no less.

[WXeastern]

Great stuff as usual Don

[skierinvermont]

I think it's overly simplistic to look only at .3 to .7 ENSO events, but if you do, this is the resulting map.

You left off quite a few years with DJF ONIs of .3-.7. I did exclude 06-07 and 87-88 even though the ONI was .7 in DJF, because both peaked at 1.0 or 1.1 in NDJ which I agree is too Ninoish. The resulting map has a significant Nino signal (I should have posted it the first time). Based on this I would conclude a +.5 is more similar to +1-1.5 than to a -.5 to 0. A -.5 to 0 has a significant Nina-ish signal, while a +.5 has a significant Nino-ish signal.

You left off 51-52, 69-70, 76-77, 77-78

ALL years with a DJF ONI of +.3-.7 (except 06-07 and 87-88):

[skierinvermont]

What about +0.15 to +0.85? Just kidding...

I agree with tacoman's end assessment. Instead of getting overloaded with the anomaly maps, we should draw from just a couple of broad conclusions about the severity of ENSO and where its greatest levels of correlation occur. No more and no less.

I agree the signal is weaker for a weaker event, however ~ +.5s often behave fairly Ninoish, unlike -neutrals which are fairly Ninaish. As such, I believe Don's use of 0-1.5 is preferable to OSU's -.5 to +.5. The latter includes many years which behaved fairly Nina-ish in contrast to the Nino-ish signal of ~ +.5s.

Many of the -neutrals include substantial SE ridging through the winter, which explains the much lower snow totals at DC and BWI despite the -AO. Years with an ONI near +.5 look much more Ninoish and have better snowfall in the SE.

[Wow]

Ok, and then you may as well see what the long term progression of ENSO has been. i.e. has it been coming out of a mod/strong/weak Nino/Nina or long term continuation of neutral +/- ? Where do we break that line?

[Srain]

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

342 AM EST TUE NOV 27 2012

VALID 12Z SAT DEC 01 2012 - 12Z TUE DEC 04 2012

==================================================================

= EXTREME PRECIPITATION AMOUNTS FOR NRN CALIFORNIA INTO SUNDAY =

==================================================================

GENERAL FLOW PATTERN & MODEL PREFERENCE

=======================================

LATE THIS WEEK, THE FLOW ACROSS THE LOWER 48 WILL FLATTEN AS TWO

OUT-OF-PHASE STREAMS OF THE WESTERLIES MOVE ACROSS THE COUNTRY.

THE DEEP TROUGH ACROSS THE EASTERN PACIFIC IS EXPECTED TO FINALLY

MOVE INTO THE WEST COAST SUNDAY AND PROGRESS TO THE MIDDLE OF

NORTH AMERICA TUESDAY MORNING. UPSTREAM, A REBUILDING POSITIVE

ANOMALY OVER THE BERING SEA/SIBERIA WILL ENSURE THAT TROUGHING IN

THE EASTERN PACIFIC RELOADS DURING THE MIDDLE OF NEXT WEEK.

THE DETERMINISTIC AND ENSEMBLE MEAN GUIDANCE WERE IN GOOD

AGREEMENT EARLY THIS MORNING, WITH ONLY MINOR DETAIL ISSUES NOTED.

TO DEAL WITH THE LINGERING UNCERTAINTY, THE PRESSURES WERE BASED

ON A 40/30/30 BLEND OF THE 00Z UKMET/00Z GFS/00Z ECMWF THROUGH

SUNDAY BEFORE SWITCHING TO A 50/50 COMPROMISE OF THE 00Z ECMWF/00Z

GFS THEREAFTER.

WEATHER IMPACTS

===============

STARTING WEDNESDAY, HEAVY PRECIPITATION WILL BEGIN IN EARNEST

ACROSS NORTHERN CALIFORNIA, ONLY TO INCREASE IN INTENSITY THURSDAY

THROUGH SUNDAY BEFORE WANING THEREAFTER AS THE RESPONSIBLE UPPER

TROUGH MOVES INTO THE WEST AND THE ONSHORE FLOW FROM THE PACIFIC

DECREASES. AREAL AVERAGE LIQUID EQUIVALENT (LEQ) AMOUNTS OF 10-15

INCHES ARE STILL ANTICIPATED FOR THE FAVORED TERRAIN ACROSS

NORTHERN CALIFORNIA, WITH LOCAL LEQ AMOUNTS OF 20+ INCHES

POSSIBLE. THIS WOULD LEAD TO EXTREME SNOW AMOUNTS (POSSIBLY WELL

IN EXCESS OF TEN FEET) ACROSS THE HIGHEST TERRAIN OF THE SISKIYOUS

AND NORTHERN SIERRA NEVADA, WHICH COULD LEAD TO AVALANCHES WELL

AFTER THE SNOW HAS ENDED. LESSER, THOUGH STILL SIGNIFICANT,

PRECIPITATION AMOUNTS ARE EXPECTED ACROSS THE PACIFIC NORTHWEST

(WHERE AREAL AVERAGE LEQ AMOUNTS OF 4-8 INCHES ARE POSSIBLE) AND

NORTHERN CONTINENTAL DIVIDE (WHERE AREAL AVERAGE LEQ AMOUNTS OF

3-5 INCHES ARE ANTICIPATED).

AS THE EASTERN PACIFIC TROUGH MOVES OUT OF THE WEST INTO THE

PLAINS, SOME GULF MOISTURE SHOULD BE TAPPED LEADING TO MODERATE TO

HEAVY RAINS FROM EASTERN TEXAS THROUGH THE MID-MISSISSIPPI VALLEY

INTO THE GREAT LAKES FROM MONDAY INTO NEXT TUESDAY.

ROTH

http://www.americanwx.com/bb/index.php/topic/37940-the-big-west-coasts-event/