2013 Fall Medium Range Discussion

[Srain]

Some of the analog dates suggested via the CPC Super Ensembles certainly raise an eyebrow.

[WEATHER53]

Some of the analog dates suggested via the CPC Super Ensembles certainly raise an eyebrow.

This has looked very promising at least a half dozen times this winter and, at least for Rich-Phil corridor, never materialized.

[Ian]

This has looked very promising at least a half dozen times this winter and, at least for Rich-Phil corridor, never materialized.

 

Good news is I don't think any are particularly great for us tho there are a few storms within a few days of some of the dates.

[Heisy]

The block showing up on the euro & ensembles today looks really good, one issue is I still don't see a big snow threat for Mid-Atlantic until at least Day 12+

[pcbjr]

Regardless and however late to the party - it is all a good model step in the right direction. Let's hope there isn't a banana peel or a cube of ice on the dance floor for the models to trip over or slip on.

[easternsnowman]

 

This has looked very promising at least a half dozen times this winter and, at least for Rich-Phil corridor, never materialized.

 The western burbs of philly and also south jersey have done ok with snow just the city has'nt and most of delaware too.

[donsutherland1]

Some late evening thoughts...

 

Perhaps lending support to the ideas expressed in Message #631, some of the ensemble guidance is now suggesting that the EPO could go negative during the first week in March. If that happens, prospects of at least a period of cross-polar flow could increase.

 

The 2/22 0z run of the GFS is suggesting that a very cold air mass could move into the eastern U.S. during the first week in March. The forecast 2 meter temperatures on that model would be the coldest since March 2009. What's more that model forecasts such readings with little or no snow cover in the Mid-Atlantic region. The GFS has sometimes been too aggressive with the cold, so even if such readings do not materialize, the idea that the month could get off to a cold start is not unreasonable.

 

The blocking (AO-) regime that got underway on February 6 is likely to persist for some time. Since 1950, there have been 6 cases on which February blocks formed, the AO fell to at least -2.5 in February, and December had also seen the AO average -0.50 or below. In 67% of those cases, the blocking regimes that commenced in February lasted 36 days or longer. 50% of those blocking regimes lasted more than 40 days. The mean figure was 34.3 days and the median figure was 39.5 days. Hence, it is plausible that the ongoing blocking could last into the March 10-20 timeframe. That outcome would further reinforce the idea of a cold start to the month. The six prior cases were 1962, 1964, 1969, 1970, 1986, and 2001.

[donsutherland1]

With the GFS having led the way in "calling off" what once looked to be a promising southern New England snowstorm, the ECMWF and finally NAM have moved into agreement with the GFS today. I suspect that the storm's great "vanishing act", in spite of strong blocking (AO: -1.957; NAO -1.149), is the result of the MJO. At last word, the MJO was in Phase 4 and at high amplitude (1.949).

 

Phases 4 and 5 are terrible for KU snowstorms in the February-March timeframe. Since 1950, the following is the breakdown of KU snowstorms based on MJO phases:

 

Phases 1-3: 50% (includes the Blizzard of 2013)

Phases 4-5: 7%

Phases 6-8: 43%

 

Some of the guidance keeps the MJO locked in Phases 4 or 5 through March 8. If that's the case, prospects for a KU snowstorm during the first week of March could be low. That does not mean that it cannot snow, just that a KU-type snowstorm would be unlikely.

 

Having said that, given the analog cases that have been coming up, I continue to have reasonable confidence that March 2013 could be the snowiest since March 2009 in some parts of the East. Whether or not a KU storm would occur is a different matter, but at least one of the analog cases had such a storm.

 

The idea of a colder than normal start to March remains on track. With blocking forecast to grow stronger through the medium-term, one cannot rule out the prospect of an Arctic air mass moving down out of Canada at some point during the first 7-10 days in March.

[Srain]

It certainly appears a very chilly start to March is ahead with freezing to near freezing temps well S into Texas/Louisiana as well as the Deep South. We will need to monitor these trends as freezing temps may come awfully close to the Coastal Counties late next week into next weekend that may extend into Northern Florida as well.

 

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
200 AM EST SAT FEB 23 2013

VALID 12Z TUE FEB 26 2013 - 12Z SAT MAR 02 2013

 

...OVERALL PATTERN AND SENSIBLE WEATHER THREATS/HIGHLIGHTS...

 

THE MODELS AND ENSEMBLES POINT TO AN ACTIVE AND TRANSITIONAL
MEDIUM RANGE FLOW PATTERN STARTING TUE/WED INTO THU WITH THE
LIFTING OF A WELL ORGANIZED MID-UPPER LEVEL TROUGH AND SURFACE LOW
SYSTEM/WINTER WEATHER SWATH FROM THE MID-MS VALLEY TO THE
MIDWEST/GREAT LAKES/NE US AS MOISTURE WRAPS INTO THE SYSTEM...ALSO
THEN ENHANCED BY LAKE EFFECT.  A TRAILING COLD FRONT APPROACH
ACROSS THE SE/ERN US WILL ALSO FOCUS PRECIPITATION.

 

MEANHWILE...ANOTHER DYNAMIC MID-UPPER LEVEL SHORTWAVE TROUGH DIGS
WINTER PCPN SEWD OVER THE WRN US MON/TUE BEFORE EJECTING EWD
ACROSS THE CENTRAL AND ERN STATES WED/THU...POSSIBLY LEADING TO
SOME EAST COASTAL SURFACE LOW RESPONSE. ANOTHER TROUGH IN THIS
SERIES IS ON ITS HEALS BACK ACROSS THE WEST MIDWEEK...BUT EXPECTED
RAPID UPSTREAM FLOW AMPLIFICATION OUT FROM THE ERN PACIFIC HAS
GOOD GUIDANCE SUPPORT TO LEAD TO DEVELOPMENT OF AN AMPLIFIED WRN
US MID-UPPER LEVEL RIDGE BY LATE NEXT WEEK. THIS MAY FORCE THE
LEAD IMPULSE TO AMPLIFY WITH NRN STREAM ENERGY INTO QUITE AN
AMPLIFIED AND COLD E-CENTRAL US MID-UPPER LEVEL TROUGH IN A
POSITIVE PNA PATTERN. DOWNSTREAM...TRENDS CONTINUED TOWARD AN
INCREASINGLY BLOCKY (NEGATIVE) NAO PATTERN EMERGING IN THE NRN
ATLANTIC HEADING INTO NEXT WEEKEND WITH HIGH LATITUDE HEIGHT RISES
FEEDING WWD ACROSS SRN GREENLAND TOWARD ERN CANADA.

 

...GUIDANCE EVALUATION AND WEATHER SYSTEM PREFERENCES...

 

MODEL AND ENSEMBLE MEAN GUIDANCE HAS OVERALL CONVERGED UPON A MORE
COMMON/BETTER CLUSTERED MID-LARGE SCALE SOLUTION FOR MUCH OF THE
FORECAST DOMAIN NEXT WEEK COMPARED TO THE LAST FEW DAYS WITH THE
LAST COUPLE GFS/GEFS RUNS MORE IN LINE/LESS PROGRESSIVE.  LOWER
FORECAST SPREAD BOLSTERS FORECASTER CONFIDENCE DESPITE A
TRANSITIONAL PATTERN.  THE ECMWF ENSEMBLE MEAN EVEN SO HAS PROVEN
THE MOST RUN TO RUN CONSISTENT THROUGH MEDIUM RANGE TIME SCALES
RECENTLY AND NOW SITS ON THE SLIGHTLY SLOWER/MORE AMPLIFIED SIDE
OF THE FULL ENVELOPE OF GUIDANCE ALOFT.  THIS SOLUTION REMAINS
WELL SUPPORTED BY UPSTREAM AMPLITUDE OVER THE PACIFIC AS DEPICTED
IN RECENT WATER VAPOR IMAGERY LOOPS.

 

SCHICHTEL

 

 

 

[donsutherland1]

The latest run of the NAEFS is now in good agreement with the temperature anomalies suggested by the CFSv2 and analog cases that were posted a few days ago (#631).

 

CFSv2/Analogs:

 

NAEFS (2/23/2013 0z):

 

In short, support for at least a cold start to March in the East, consistent with the dual PNA-AO/NAO blocks consistently signaled on the ensembles, continues to grow. If the MJO can finally break out of its "Phase 4-Phase 5 prison," opportunities for a widespread moderate to significant snowfall could increase.

[GaWx]

In my opinion, the MJO is not useful in predicting the chance for a major winter storm in the SE US.In short, support for at least a cold start to March in the East, consistent with the dual PNA-AO/NAO blocks consistently signaled on the ensembles, continues to grow. If the MJO can finally break out of its "Phase 4-Phase 5 prison," opportunities for a widespread moderate to significant snowfall could increase.

 

Don,

 I know that your emphasis is on the NE when you talk about KU storms. However, for the SE US, phases 4-5 have had three of the six major S/IP for KATL and KRDU for the period 2/20-March since when the MJO phases historical record started:

 

-3/1/2009: phase 4

-2/26-7/2004: phase 5

-3/13/1993: phase 4 (Storm of Century)

 

  Looking at the broader picture for all of winter (21 major S/IP since 1974), there is still no suggestion of correlation between the MJO's supposed favorable phases and the chance for a major SE winter storm.

 

 In my opinion, the MJO is not useful in predicting the chance for a major winter storm in the SE US.

[donsutherland1]

Don,

 I know that your emphasis is on the NE when you talk about KU storms. However, for the SE US, phases 4-5 have had three of the six major S/IP for KATL and KRDU for the period 2/20-March since when the MJO phases historical record started:

 

-3/1/2009: phase 4

-2/26-7/2004: phase 5

-3/13/1993: phase 4 (Storm of Century)

 

  Looking at the broader picture for all of winter (21 major S/IP since 1974), there is still no suggestion of correlation between the MJO's supposed favorable phases and the chance for a major SE winter storm.

 

 In my opinion, the MJO is not useful in predicting the chance for a major winter storm in the SE US.

 

I agree with you and saw your earlier post about a lack of correlation between the MJO and Southeast snowstorms. I'm strictly referencing wider-scale KU snowstorms for February-March. The March1993 superstorm is the lone exception since 1950 in that regard. There are some decent regional/localized storms and some that fell short of KU stature.

 

Hopefully, after this winter, I'll be able to put together a list of notable SE snowstorms since 1950 and also notable snowstorms in southern Canada. I'd like to become more familiar with the patterns/setups for such storms for subsequent winters.

[Ottawa Blizzard]

This pattern is reminding me of January 2010 and early January 2011 when northeast Canada was torching and the U.S. was experiencing winter weather more akin to Ottawa. At least it isn't December and we've got through most of the winter without this pattern.

[cbmclean]

This pattern is reminding me of January 2010 and early January 2011 when northeast Canada was torching and the U.S. was experiencing winter weather more akin to Ottawa. At least it isn't December and we've got through most of the winter without this pattern.

Mr. Blizzard (or can I call you Ott)  this isn't exactly in your neighborhood so to speak but I figure it might be worth a mention here.  In one of our previous threads we discussed cold temperatures, or lack thereof in far northern Canada.  I have noticed today that Eureka on Ellesmere island has quietly been having a spectacularly cold February.  The current temperature is sitting at -54 F and yesterday their low was -57 F, which is very impressive for them.  In fact it may be the lowest temp that I remember seeing for them in my years of noting their weather.  The monthly avg for the month overall is -43 F which is pretty spectacular , especially for this present warm climate.  Quite interesting.  

[ORH_wxman]

Mr. Blizzard (or can I call you Ott)  this isn't exactly in your neighborhood so to speak but I figure it might be worth a mention here.  In one of our previous threads we discussed cold temperatures, or lack thereof in far northern Canada.  I have noticed today that Eureka on Ellesmere island has quietly been having a spectacularly cold February.  The current temperature is sitting at -54 F and yesterday their low was -57 F, which is very impressive for them.  In fact it may be the lowest temp that I remember seeing for them in my years of noting their weather.  The monthly avg for the month overall is -43 F which is pretty spectacular , especially for this present warm climate.  Quite interesting.  

 

That portion of Canada is having a very cold February...in the range of -8 to -10C below normal. Def in contrast to what they have seen recently.

[donsutherland1]

That portion of Canada is having a very cold February...in the range of -8 to -10C below normal. Def in contrast to what they have seen recently.

 

The Arctic region north of 80°N is also having its coldest spell since 2010 with some much below normal readings:

 

[Ottawa Blizzard]

Mr. Blizzard (or can I call you Ott)  this isn't exactly in your neighborhood so to speak but I figure it might be worth a mention here.  In one of our previous threads we discussed cold temperatures, or lack thereof in far northern Canada.  I have noticed today that Eureka on Ellesmere island has quietly been having a spectacularly cold February.  The current temperature is sitting at -54 F and yesterday their low was -57 F, which is very impressive for them.  In fact it may be the lowest temp that I remember seeing for them in my years of noting their weather.  The monthly avg for the month overall is -43 F which is pretty spectacular , especially for this present warm climate.  Quite interesting.  

Yes, the high arctic has had a very cold winter this year, which is good news for those of us hoping to avoid future catastrophe caused by melting ice caps. ;-) Hopefully these colder temperatures in the high arctic are a sign of things to come. Interesting how it hasn't been getting much media attention though...

[wxmx]

And with the pattern favoring a rather strongly negative EPO, this cold could unleash into the CONUS past day 10.

[ayuud11]

And with the pattern favoring a rather strongly negative EPO, this cold could unleash into the CONUS past day 10.

Do you think we can get one more sub -20c arctic air cold shot? 

[donsutherland1]

Since February 19 (#631) when I discussed the CFSv2 model's coming into agreement with the ENSO-teleconnection analogs, that model has continued to trend colder nationwide for March. At the same time, the GFS ensembles have moved into strong consensus that a deep blocking regime is about to unfold and that the blocking regime likely will last for an extended period of time. The idea of a long-duration block that could last into the March 10-20 period was set forth in #639.

 

Below are the latest forecasts from the CFSv2 for the March anomalies (the CFSv2 has demonstrated skill at this timeframe) and the GFS ensembles for the Arctic Oscillation.

 

 

1960 remains among my leading analogs. In terms of the objective analogs, 3/11/1958, 2/17/1969, and 2/17/2010 are showing up for the 8-day period centered around March 6. KU snowstorms occurred in all three years 5-8 days after the dates shown. March 1960 also had a blizzard. In short, the pattern is a potent one and I would be surprised if snowfall totals from at least Philadelphia to Boston are not above normal for March. The above normal figures could extend south to Washington, DC, west into the Ohio Valley, and north into southern Ontario and southern Quebec. Later in the month, perhaps in a fashion not dissimilar from how the pattern evolved in March 2009, I suspect that the Plains States could again be at risk of a significant snowfall.

[donsutherland1]

Briefly, the 2/26 18z run of the GFS was quite mild in parts of the U.S. during the March 5-12 timeframe. IMO, the colder look on the 12z operational ECMWF and 12z ECMWF and GFS ensembles is probably more likely to verify assuming the blocking develops as forecast.

 

If one examines the GFS ensembles, there is strong agreement that a period of severe blocking (AO of -3 or below) is likely. That outcome, if it materializes, is typically cold almost nationwide.

 

 

The latest run of the CFSv2 (Message #652) is in reasonable agreement with the composite temperature anomalies associated with that magnitude of blocking. Hence, at this point in time, I believe the 18z run of the GFS is likely to be an outlier.

[donsutherland1]

Back on 2/19 (Message #631), the analog pool that I used was indicating the potential for a snowy March in parts of North America. At that time, the analog pool was indicating the potential for a snowy March in parts of the Mid-Atlantic region and New England. Those analogs also suggested that the Ohio Valley, southern Ontario and southern Quebec would likely seek their most snowfall in March since 2011.

 

A week later, the analog pool was still bullish on that idea. As a result, I stated in #652 that the pattern is a potent one and I would be surprised if snowfall totals from at least Philadelphia to Boston are not above normal for March. The above normal figures could extend south to Washington, DC, west into the Ohio Valley, and north into southern Ontario and southern Quebec.

 

The major theme remains the blocky start to March. If the historic cases are representative, the blocking could persist through the March 10-20 timeframe. The 3/2 run of the GFS ensembles is pointing to such a scenario.

 

Some of the guidance, despite less than stellar run-to-run continuity, is now providing growing support for the idea of a significant March snowfall in interior portions of the Mid-Atlantic region. For example, the 3/2 18z run of the GFS suggests that Sterling, Virginia (IAD) could pick up 6" or more snow. It also brings some accumulations into the Washington, DC (DCA) area, along with a very large amount of sleet. What's important to note is that is according to the soundings. However, springtime snowstorms can have stronger dynamics, so the notion of a larger accumulation of wet snow cannot be excluded. In short, there is probably some possibility that Washington, DC could pick up 4" or more snow.

 

Since 1950, there have been 10 March snowstorms that brought 4.0" or more snow to Washington, DC (DCA). In 7/10 (70%) of those cases, the Arctic Oscillation (AO) was < 0. The AO is likely to be strongly negative this time around. In addition, 40% of cases saw an AO-/PNA+ combination. That combination is forecast to be in place for the upcoming storm.

 

A snapshot of Washington, DC's major March snowstorms since 1950 is below:

 

 

In the wake of the increasingly likely March 5-7 event, the pattern is likely to remain a potent one for winter weather, even if a temporary relaxation occurs. Hence, even if New York City and Boston miss out on the snow this time around, that that is not yet a foregone conclusion, the month could provide some additional opportunities given the persistent blocking.

 

In short, I have little reason to change my thinking concerning March at this point. If anything, I'm encouraged how things have been shaping up thus far.

[cbmclean]

Yes, the high arctic has had a very cold winter this year, which is good news for those of us hoping to avoid future catastrophe caused by melting ice caps. ;-) Hopefully these colder temperatures in the high arctic are a sign of things to come. Interesting how it hasn't been getting much media attention though...

Eureka on Ellesmere Island continues to go off the charts with its bizarre (to me at least) cold spell. February finished with an avg temp of -44 °F, which would be healthy cold for the middle of the Greenland Ice Cap (Summit camp).  It's still going strong; the low on March 1st got down to -60 °F, which is spectacular for this day and age.  It's sitting at -54°F right now. 

 

Does anyone have any idea what's going on up there?  This part of the world does not get much mainstream meteorological attention.  What is causing this?

[donsutherland1]

Correction...

 

My list in Message #654 omitted the March 9, 1999 snowfall, which brought 8.4" to DCA.

 

Since 1950, there have been 11 March snowstorms that brought 4.0" or more snow to Washington, DC (DCA). In 8/11 (73%) of those cases, the Arctic Oscillation (AO) was < 0. The AO is likely to be strongly negative this time around. In addition, 45% of cases saw an AO-/PNA+ combination. That combination is forecast to be in place for the upcoming storm.

[donsutherland1]

Eureka on Ellesmere Island continues to go off the charts with its bizarre (to me at least) cold spell. February finished with an avg temp of -44 °F, which would be healthy cold for the middle of the Greenland Ice Cap (Summit camp).  It's still going strong; the low on March 1st got down to -60 °F, which is spectacular for this day and age.  It's sitting at -54°F right now. 

 

Does anyone have any idea what's going on up there?  This part of the world does not get much mainstream meteorological attention.  What is causing this?

I haven't had a close look at the pattern up there, but it has been impressive. Moreover, the Arctic region above 80°N has had its longest and deepest spell of below normal readings since 2008.

[Ottawa Blizzard]

Back on 2/19 (Message #631), the analog pool that I used was indicating the potential for a snowy March in parts of North America. At that time, the analog pool was indicating the potential for a snowy March in parts of the Mid-Atlantic region and New England. Those analogs also suggested that the Ohio Valley, southern Ontario and southern Quebec would likely seek their most snowfall in March since 2011.

 

A week later, the analog pool was still bullish on that idea. As a result, I stated in #652 that the pattern is a potent one and I would be surprised if snowfall totals from at least Philadelphia to Boston are not above normal for March. The above normal figures could extend south to Washington, DC, west into the Ohio Valley, and north into southern Ontario and southern Quebec.

 

The major theme remains the blocky start to March. If the historic cases are representative, the blocking could persist through the March 10-20 timeframe. The 3/2 run of the GFS ensembles is pointing to such a scenario.

 

Some of the guidance, despite less than stellar run-to-run continuity, is now providing growing support for the idea of a significant March snowfall in interior portions of the Mid-Atlantic region. For example, the 3/2 18z run of the GFS suggests that Sterling, Virginia (IAD) could pick up 6" or more snow. It also brings some accumulations into the Washington, DC (DCA) area, along with a very large amount of sleet. What's important to note is that is according to the soundings. However, springtime snowstorms can have stronger dynamics, so the notion of a larger accumulation of wet snow cannot be excluded. In short, there is probably some possibility that Washington, DC could pick up 4" or more snow.

 

Since 1950, there have been 10 March snowstorms that brought 4.0" or more snow to Washington, DC (DCA). In 7/10 (70%) of those cases, the Arctic Oscillation (AO) was < 0. The AO is likely to be strongly negative this time around. In addition, 40% of cases saw an AO-/PNA+ combination. That combination is forecast to be in place for the upcoming storm.

 

A snapshot of Washington, DC's major March snowstorms since 1950 is below:

 

 

In the wake of the increasingly likely March 5-7 event, the pattern is likely to remain a potent one for winter weather, even if a temporary relaxation occurs. Hence, even if New York City and Boston miss out on the snow this time around, that that is not yet a foregone conclusion, the month could provide some additional opportunities given the persistent blocking.

 

In short, I have little reason to change my thinking concerning March at this point. If anything, I'm encouraged how things have been shaping up thus far.

Don, interestingly, the record high in Sept-iles Quebec today dates from 1962. It looks as though early March 1962 saw a similar high latitude blocking setup to the one we're currently experiencing. Toronto was much colder than Sept-iles on that day, as it is today.

[donsutherland1]

Don, interestingly, the record high in Sept-iles Quebec today dates from 1962. It looks as though early March 1962 saw a similar high latitude blocking setup to the one we're currently experiencing. Toronto was much colder than Sept-iles on that day, as it is today.

 

At least as far as the AO is concerned, the blocking was similar. On March 3, 1962, the AO was -3.699. Today, the AO was -2.797.

[uncle W]

At least as far as the AO is concerned, the blocking was similar. On March 3, 1962, the AO was -3.699. Today, the AO was -2.797.

todays AO is around -3.400...This is a list of March's with a daily ao of -3.000 or lower and the monthly average...Snowfalls or cold spells around the time of the ao minimum in NYC...

the lowest reading this year was -3.902 on 12/8..I'm hoping it gets to -4 because it raises the chances for a cold wave, snowstorm or both...

I made a quick search and came up with these numbers for March...

year....low AO date....monthly AO

-6.365... 3/05/1970...-2.084...cold month...4" snow 3/29...

-4.417... 3/04/1962...-2.848...Ash Wed. storm 3/6...a little snow...

-4.318... 3/04/1981...-1.645...8" of snow 3/5...

-4.202... 3/24/2001...-1.687...a little snow on 3/26...

-4.030... 3/11/1958...-2.522...4" snow 3/14...12" snow 3/21...

-3.856... 3/10/1999...-1.492...4" of snow 3/15...

-3.822... 3/21/2006...-1.604...cold but no snow...

-3.805... 3/04/1952...-1.859...4" on 3/2...

-3.766... 3/04/1957...-2.013...3" of snow 3/1-2...

-3.758... 3/21/1955...-1.568...3" of snow 3/18...

-3.706... 3/13/1984...-2.386...7" of snow 3/9...

-3.469... 3/19/1969...-1.582...3" of snow 3/7...

-3.381... 3/09/1991...-0.527...cold spell with no snow...

-3.320... 3/31/1996...-1.483...4" of snow 3/29...

-3.254... 3/01/1965...-0.905...2" of snow 3/21...

-3.217... 3/04/1978... 0.502...5" on 3/3...only month with a plus ao average...

-3.200... 3/10/1960...-1.625...14" on 3/3...

-3.200... 3/21/1987...-1.746...2" 3/13...

-3.188... 3/17/1980...-1.433...5" of snow 3/13-14...

-3.032... 3/16/1979...-0.814...cold spell with only flurries...

I think we have a good chance the AO ends up averaging negative and if we can get as low as -3.500 we have a good chance of seeing a significant snowfall

[donsutherland1]

Some additional thoughts on the possible 3/5-7/2013 storm...

 

1. The strong blocking that has been in place since the start of the month has strenghtened further overnight. The AO is now -3.470. The current blocking regime has now lasted 27 consecutive days.

 

2. The computer guidance is in strong agreement that interior portions of the Mid-Atlantic region will likely pick up a significant snowfall. Baltimore and Washington, DC could also pick up 4" or more. Some of the guidance is more aggressive with snowfall amounts for Washington, DC and Baltimore. The heaviest snows, where one-foot or larger amounts could occur will likely cover western/central Virginia and western Maryland. Such cities as Charlottesville, Sterling, and Frederick could be in the area where some of the heaviest snow falls.

 

The NAM brings a foot of snow to Washington, DC (DCA). Since 1840, there have been four storms that brought 10" or more snow to Washington, DC in March:

 

March 16-17, 1843: 12.0"

March 27-28, 1891: 12.0"

March 7-8, 1941: 10.7"

March 29, 1942: 11.5"

 

3. There is major disagreement on the computer guidance as to whether appreciable or even significant snows could extend from the northern Mid-Atlantic region into New England. The ECMWF has consistently argued against such an outcome. The GFS has argued for such an outcome in its last three runs in a dramatic switch that is almost reminscent of its taking the lead on what turned out to the be the Boxing Day Blizzard of December 2010. The pattern is sufficiently complex and the pieces sufficiently close that either the ECMWF or GFS could score a dramatic coup or a dramatic bust.

 

Climatology would argue for a more northward extent of the precipitation. Not all of the precipitation would fall as snow, along coastal regions.

 

At the same time, historic experience with storms that dumped 4" or more snow in Washington, DC (DCA) in March with an AO-/PNA+ setup would support the ECMWF.  Since 1950, there have been 5 such cases:

 

March 5-7, 1962: DCA: 4.0" (much heavier amounts farther west); NYC: 0.2"; BOS: 0.4"

March 30-31, 1964: DCA: 5.8"; NYC: None; BOS: None

March 3, 1978: DCA: 4.1"; NYC: 5.0"; BOS: 9.2"

March 1-2, 1980: DCA: 4.9"; NYC: None; BOS: None

March 9, 1999: DCA: 8.4"; NYC: None; BOS: None

 

In terms of the blockbuster Washington, DC storms cited earlier, only the March 1843 and March 1941 storms brought significant snow to New York City and Boston.

 

Hence, at least at this point in time, I lean toward a scenario somewhat closer to the ECMWF when it comes to the northern Mid-Atlantic and New England, but with not quite as sharp a cutoff and 6" or greater snows extending into metro Washington, DC. The possibility of at least some accumulation of snow in the northern Mid-Atlantic and southern New England areas exists. There remains a smaller chance (probably about 1-in-3) that a 6z GFS-type solution works out.

This post has been promoted to an article

[donsutherland1]

To expand on my points in Message #661, the 3/4/2013 0z run of the GFS ensembles paint a 500 mb pattern that is remarkably similar to that of the March 5-7, 1962 storm for the 72-hour and 96-hour period. Weatherbell meteorologist Joe Bastardi had early on discussed the 1962 storm as a possible analog storm. Afterward, by 120 hours, the GFS ensembles shift the center of the 500 mb trough to the north and east of what occurred in 1962.

 

 

 

This solution, if it proves correct, lends support to something closer to the 0z ECMWF than the 6z operational GFS with some adjustments that would bring at least some precipitation to parts of the northern Mid-Atlantic and New England areas (especially southeast New England). The 3/6 12z run of the NAM might offer some reasonable insight into the precipitation in the northern Mid-Atlantic and New England areas. Not all of the precipitation would fall as snow there. Nonetheless, there remains about a 1-in-3 chance, IMO, of an outcome close to the 6z GFS. I suspect that by the 18z and 0z runs, there will be a trend toward convergence in the guidance.