Winter 2014-2015 Medium-Term Discussion

[NJwinter23]

NJwinter -- I agree with the bolded, namely that this was a bottom-up event induced by strong tropospheric wave driving. I think we might be talking semantics as far as the stratospheric warming, but the current event is a minor to moderate warming as westerly winds slowed significantly for a few days in conjunction w/ rapid warming. But yes, we haven't had a major SSW yet which involves the complete reversal of 60N/10mb winds to easterly for 5 consecutive days or more. It appears we cool down over the next several days and attempt another wave 2 / vortex split in mid January. Remains to be seen if that one is major. However, from what I've researched, even minor to moderate stratospheric warming events substantially heighten the probability for the development of a more perturbed tropospheric polar vortex. Should be interesting to see how this month plays out.

 

I may have somewhat mis-interpreted your sentence here before my response: "Both occurrences tend to be precursors to tropospheric perturbation, particularly if we get another spike, which seems possible based upon current data." ...Seems like we are more or less on the same page, hoping for another strato shot to enhance the chances of more ao/nao help end jan/feb

[Weathergun]

The PV split seems part tropospheric and stratospheric warming induced. Some wave downwelling indicated in the zonal winds:

 

[winterymix]

Brief morning update...

1. ENSO conditions remain remarkably similar to those at a similar point in time during winter 2004-05.

2. Some GFS ensemble members are suggesting a large decline in the AO similar to what happened in January 2005.

3. Both the Day 8 and Day 11 GFS ensemble analogs have a date from January 2005.

It seems the MJO prognosis may presage a wintry trend across the eastern US. Unfortunately, the MJO seems to obey a 40 to 47 day cycle. Therefore, after this developing cold paradigm, it could dwindle after two or three weeks and we may have to wait 40+days for the pattern to reload.

[DTWXRISK]

 FIRST  if that was  true  the  QBO   has  -23 or  lower  all of   DEC  where was the Blocking ?

SECOND  values that  extreme   are NOT  supportive but actually  hostile  to blocking  patterns over  North America

 

Would this support more blocking (i.e., -AO and -NAO)?

[WxMidwest]

There was a really small sample of analogs for the extreme -20 or lower QBO values in winter. Now, if the QBO can increase into the -10's, this traditionally means the likely-hood of the NAO can be negative with a higher probabilistic chance of happening. Impact wouldn't be seen till Late Feb / March time period.

[GaWx]

The 1/8-9/15 MJO was the strongest JAN MJO phase 5 on record (back to 1975) and only 2nd to 2/18-21/85 for the strongest phase 5 on record in any DJF. Despite that, 1/8-9/15 was a very cold period in the E US, which is quite interesting considering that phase 5 has been the warmest phase by far overall for at least a decent portion of the E US.

 

http://cawcr.gov.au/staff/mwheeler/maproom/RMM/RMM1RMM2.74toRealtime.txt

[scottmartin49]

....so add MJO to QBO and Siberian snow cover as non-primary indicatives- at least as far as this winters verification will tend. Now consider that the AO also isn't living up to its reputation, and all we're left with are a boiling Pacific and a booming NAO. Sherlock Holmes, something, something... 

[Absolute Humidity]

....so add MJO to QBO and Siberian snow cover as non-primary indicatives- at least as far as this winters verification will tend. Now consider that the AO also isn't living up to its reputation, and all we're left with are a boiling Pacific and a booming NAO. Sherlock Holmes, something, something...

Goes to show how little we really know.

[donsutherland1]

....so add MJO to QBO and Siberian snow cover as non-primary indicatives- at least as far as this winters verification will tend. Now consider that the AO also isn't living up to its reputation, and all we're left with are a boiling Pacific and a booming NAO. Sherlock Holmes, something, something... 

I'm not sure what you mean by the "AO...isn't living up to its reputation." Do you mean that it has been predominantly positive despite the SAI's suggestion of a predominantly negative AO? Certainly, the below normal snowfall that has occurred this month in much of the East, despite the cold, is consistent with a positive AO.

 

Below was a table I posted in the NYC forum on 12/31. The combination of a strongly positive AO to open the month following low December snowfall suggested a higher than climatological probability of below normal snowfall for January (about 30% higher than the 1950-2014 probability of < 6" snowfall for January). It also suggested a much lower probability of above normal snowfall nearly (65% lower than the 1950-2014 probability of 10" or more snowfall for January).

 

 

 

 

The best case for the start of February would be a strongly negative AO. Such a situation combined with positive ENSO Region 3.4 anomalies has produced a much higher frequency of above- to much above normal snowfall for February (relative to the overall 1950-2014 reference period) in the Eastern third of the U.S.

 

On the matter of the SAI, last winter's somewhat inconsistent performance and this winter's dismal (at least so far) performance suggests that the linkage is probably much weaker than had initially seemed to be the case. That increasingly likely outcome would amount to a major blow to attempts to improve seasonal winter forecasts, as the predominant AO state is an important contributor. 

 

Finally, the longer-range guidance shows a renewed strong EPO- regime developing toward the end of January, hinting that the developing period of moderation will probably last 1-2 weeks with cold returning afterward. There still remains no strong signal for a negative AO and the spread among ensemble members remains enormous.

[Isotherm]

The tropospheric AO regime should begin to turn increasingly negative post January 15th, and particularly by the 20th / thereafter. I believe this will occur b/c of a variety of forcing mechanisms, stratospheric trends inclusive.

 

Keep in mind, a stratospheric warming event does not need to be classified as "major" to have impacts in the troposphere. The current situation is in fact a sudden stratospheric warming event of at least moderate magnitude. The development of a warm / very warm stratosphere substantially increases the probability for the persistence and / or initiation of a more perturbed tropospheric vortex. This is evidenced by the fact that the vast majority of winters in which the precursor stratosphere pattern was warm / perturbed led to increased propensity for negative AO conditions in the ensuing winter.

 

Poleward heat flux is now reaching daily maximum levels of approximately 25-26 K m/s, quite analogous to the early 2004 heat flux as depicted below:

 

Current:

 

 

 

 

2004:

 

 

 

 

 

The 2004 SSW event peaked at slightly warmer than -55C for the 90 to 65N region at 70mb:

 

 

 

 

Currently we continue to warm rapidly at 70mb, and based upon forecasts, I think we warm a bit more over the next couple days w/ a peak at approximately -58C or so.

 

 

 

 

 

Tropical forcing, while on the weaker side, is becoming rapidly more favorable for the development of a classic Nino regime in the medium term w/ increased PNA ridging / Aleutian troughing. For the first time this autumn and cold season, we should see more sustained favorable forcing. The control run of the ECMWF is just beginning to detect the possibility for negative AO onset in the 15th-20th period. Any negative NAO development would probably wait until after the 20th.

 

Take this with a grain of salt, though I believe it has decent accuracy and support from other signalling: The long-term tropical forcing based geopotential height forecast suggests a strong negative NAO / Greenland blocking signature in early February.

 

 

 

Earlier this month, I posted about the potential for an AO modality reversal in late January, particularly by the 20th and thereafter, as a more Nino-like global pattern begins to develop. I continue to believe that should be the case for a number of reasons as outlined below. The NAO state is more uncertain; however, there should be a significant improvement w/ a neutralization of the index by late January, which would certainly be a far cry from the strongly positive / low height field dominating the north Atlantic so far this winter.

 

 

[1]   Pacific-tropical forcing: A major "problem" over the past several months has been a lack of real Nino-like tropical forcing in the Pacific. SST's have gradually warmed to weak El Nino criteria, and the SSTA profile is indicative of a strongly positive PDO signal; however, tropical convection has been more reminiscent of a La Nina pattern, and this had has implications as far as the mid-latitude regime. As noted before, this will be changing as we finally see an eastward propagation of tropical convection / upward motion into the central tropical Pacific, which should initiate downstream changes in the mid latitude 500mb pattern.

 

Note the tendency for suppressed convection over the central tropical Pacific over the past several months. Forecasts for the next few weeks indicate a significant change to this tropical forcing pattern as stronger upward motion / lift translates ewd.

 

 

 

200mb velocity potential and OLR forecasts suggest that the above tendency persists throughout the remainder of January.

 

 

[2] Global budget of atmospheric angular momentum: An important indicator of whether the atmosphere is in a Nino or Nina-like state is the AAM budget of Earth, namely as AAM increasing or decreasing, particularly in the tropical regions, this has significant ramifications as far as the mid latitude ridge / trough response. Lower AAM tendency represents a more Nina-like state while increasing speeds suggest a more Nino-like state. If one notes prior Nino winters, generally one finds that a Nina-like pattern occurs more frequently in Nino's when the AAM budget is suppressed. However, the Nino's which feature increased AAM tend to resemble more closely a "typical" El Nino height configuration at 500mb. This is a relationship that exists which must be utilized in concert with all other variables as well. November-early December featured a predominately +AAM, during which time, high latitude blocking and Eastern troughiness was present. That reversed to a strongly negative AAM by mid December, at which time a +EPO / +AO regime initiated. Currently, AAM has spiked significantly, at levels higher than we've seen over the past 50-60 days. This seems to coincide with the development of more Nino-like tropical forcing.

 

 

[3] Stratospheric improvement: The minor SSW event which transpired last week significantly warmed the stratosphere and can often act to warm / perturb the tropospheric vortex, thereby reversing the modality of the northern annular mode. This process tends to take at least 2 weeks, which further points to the 20th and beyond time frame I've been referencing for an AO state shift. We may not initially see a strongly negative AO, but the AO should neutralize by the 20th, then turn negative for the final 10 days of January as heights build across the pole from both the Eurasian and Pacific sides. The NAO state will likely lag due to the maintenance of a stratospheric vortex near Greenland and recent enhanced geomagnetic activity; however, it should undergo a significant negative trend toward neutral at the very least by late January. Model guidance is now in agreement on height rises beginning first in the EPO region by the 19th, and the Arctic after the 20th. Heights should improve significantly in the NAO region, but I wouldn't expect a monster Greenland block this month.

 

[4] ENSO state / progression analogs: the tendency in warm/positive ENSO years is for a mid to late winter negative AO / NAO state. Even in warm ENSO positive winters, the NAO often shifted to a negative state for February.

 

 

In conclusion: the current cold January has clearly diverted this winter from poor/warm +ENSO year and indicates that the global state remains favorable for NPAC / EPO blocking, as has been the case since autumn. Improvements in global, tropical, and stratospheric forcing implicate an AO shift after the 20th. The NAO state should improve significantly (neutralize) but blocking in that region may remain unimpressive for the time being. Sensible weather wise: anticipate a transient thaw period of approximately 3-5 days as the global regime transitions, however, the cold January should resume for the CONUS by the last week of January, with the development of a -EPO/-AO. Since the negative AO state has not been present thus far, this will likely increase the potential for wintry precipitation in the East which has largely been absent. At this point, I expect the late January transition to continue and amplify for the month of February. We'll see how it goes.

 

 

[illinois]

I'm not sure what you mean by the "AO...isn't living up to its reputation." Do you mean that it has been predominantly positive despite the SAI's suggestion of a predominantly negative AO? Certainly, the below normal snowfall that has occurred this month in much of the East, despite the cold, is consistent with a positive AO.

Below was a table I posted in the NYC forum on 12/31. The combination of a strongly positive AO to open the month following low December snowfall suggested a higher than climatological probability of below normal snowfall for January (about 30% higher than the 1950-2014 probability of < 6" snowfall for January). It also suggested a much lower probability of above normal snowfall nearly (65% lower than the 1950-2014 probability of 10" or more snowfall for January).

The best case for the start of February would be a strongly negative AO. Such a situation combined with positive ENSO Region 3.4 anomalies has produced a much higher frequency of above- to much above normal snowfall for February (relative to the overall 1950-2014 reference period) in the Eastern third of the U.S.

On the matter of the SAI, last winter's somewhat inconsistent performance and this winter's dismal (at least so far) performance suggests that the linkage is probably much weaker than had initially seemed to be the case. That increasingly likely outcome would amount to a major blow to attempts to improve seasonal winter forecasts, as the predominant AO state is an important contributor.

Finally, the longer-range guidance shows a renewed strong EPO- regime developing toward the end of January, hinting that the developing period of moderation will probably last 1-2 weeks with cold returning afterward. There still remains no strong signal for a negative AO and the spread among ensemble members remains enormous.

Love all of your analysis. I would say the SAI is very solid, based on the previous results. I would argue that there is another piece that in years like this and last we are currently missing that would indicate when the correlation does not work.

[donsutherland1]

To provide some details on the Arctic Oscillation (AO), the below tables show the distribution of days so far this winter and the average AO required to reach various winter averages. A winter average of -1 or below appears very unlikely at this point in time. Even a more modest figure (-0.5) may be difficult to achieve.

 

 

This does not mean that there cannot be a prolonged period of strong blocking. What it does mean is that the kind of robust winter averages suggested by the SAI and OPI will be very difficult to achieve. Furthermore, if just half the days this winter are to have a negative AO, just 26% of the remaining days can have a positive AO. Even that figure may be difficult to attain, also suggesting the growing possibility that the AO would be predominantly positive in terms of daily outcomes.

[donsutherland1]

Love all of your analysis. I would say the SAI is very solid, based on the previous results. I would argue that there is another piece that in years like this and last we are currently missing that would indicate when the correlation does not work.

I thought it was solid given the paper--and still hope things work out--but am cautious.There are numerous cases where hindcasts work out very well and then things fall apart in a forecasting environment.

 

My guess is that the SAI, as currently constructed, may have a weaker relationship to the winter AO than had initially appeared to be the case. Some other variable or set of variables may be important. Some candidates include near end of month Eurasian snow cover changes (one AmWx member picked up on this possible issue early on, I believe it was GaWx) and late summer sea ice cover in part of the Arctic (something Dr. Cohen has mentioned in a few of his blog articles).

 

The SAI is still a promising tool, but probably needs to be coupled with some additional variable or variables to increase its predictive power.

 

It will be interesting to see Dr. Cohen's assessment at the end of the winter, especially if the AO winds up having been predominantly positive.

[donsutherland1]

Morning thoughts...

 

1. The EPO is forecast to go negative or strongly negative in the extended range. Such a development, if it occurs, would result in cold returning to the Plains States and eastward following the 7 to possibly 14-day thaw beginning around mid-month.

 

2. The AO forecast remains uncertain with no strong negative signal. It will be interesting to see how the upgraded GFS ensembles handle this situation beginning later today. While such a development would likely have less impact on Midwest snowfalls (e.g., the greater Chicago area), it would have potentially major implications for February snowfall in the Middle Atlantic and New England areas, with a higher probability of below normal monthly snowfall.

 

3. To illustrate how the possibility of a negative winter AO average continues to slip away, after today's +1.689 figure, the remainder of the December-February period would need an average AO of -1.840 to achieve a winter average of -0.500 and a mean figure of -2.818 to have a winter average of -1.000. Yesterday, those respective averages were -1.765 and -2.722. Through today, 45% of the days this winter have seen the AO at +1.000 or above, while 7% of days saw it at -1.000 or below.

[DTWXRISK]

Great post... strongly agree

[stadiumwave]

We are now seeing a downward propagation of the most recent stratospheric warming event towards the troposphere.

 

 

 

 

 

 

 

https://twitter.com/WSI_Energy/status/555031003040055297

[WidreMann]

What does it mean when the EPV flux points to the right on the FU Berlin site?

[InstantWeatherMaps]

What does it mean when the EPV flux points to the right on the FU Berlin site?

From what I hear that's good for propagation.

[DaculaWeather]

What does it mean when the EPV flux points to the right on the FU Berlin site?

Polar flux propagation are heat eddies moving poleward. That's what we like to see as it's pounding on the PV, and generally causes a weaker PV. It looks like this flux episode is kinda weak though. The longer the line the stronger, so this one is fading.  We have had a fairly long warming episode, it wasn't major or sudden, but fairly prolonged. It will be interesting to see what effect it will have on our sensible weather. I suspect that it is possible that some of the upcoming -AO and -NAO signals may be because of the warming we just went though.

[donsutherland1]

The AO: Where Does It Go For February?

 

January 14 is the midpoint of meteorological winter. That does not mean that cold and snow cannot occur beyond meteorological winter. However, it is a good time to see where things stand with respect to the Arctic Oscillation (AO). Through the first half of meteorological winter, the AO has averaged +0.903. 7 out of every 9 days (78%) saw a positive AO.

 

For the AO to average -0.500 for the winter, it will need to average -1.903 for the January 15-February 28 period. For the AO to average -1.000 for the winter, it will need to average -2.903 during that same timeframe.

 

Some ensemble members suggest that the AO will go negative down the road, but the model solutions have been generally inconsistent.

 

 

Climatology would argue for a negative February AO average. Since 1950, almost two-thirds of February cases saw the AO average < 0. More than a third saw it average -1.000 or below.

 

If one examines only the AO cases that saw a positive average for the first 45 days of meteorological winter,just over half of February cases had a negative AO and a quarter had an AO average of -1.000 or below. Put another way, the risk of a positive February AO was approximately 35% higher than the 1950-2014 baseline.

 

At the same time, there was a clear signal that differentiated the negative and positive February cases for winters during which the first half had witnessed a positive AO. If the AO fell to -2.000 or below on at least one day during the January 10-February 10 timeframe, 80% of February cases had a negative AO average. If, on the other hand, the AO did not reach -2.000 or below during that same timeframe, 89% of February cases had a positive AO average and the risk of a +1.000 or above February average was more than twice the 1950-2014 baseline.

 

Below are charts showing February AO scenarios following a positive AO during the first half of winter and respective 500 mb and temperature anomalies for select cases (when the 1/10-2/10 AO either reached -2.000 or below on at least one day or it didn't).

 

For now, one should watch the ensemble guidance and also the actual AO values.

 

 

[Ender]

The AO: Where Does It Go For February?

 

At the same time, there was a clear signal that differentiated the negative and positive February cases for winters during which the first half had witnessed a positive AO. If the AO fell to -2.000 or below on at least one day during the January 10-February 10 timeframe, 80% of February cases had a negative AO average. If, on the other hand, the AO did not reach -2.000 or below during that same timeframe, 89% of February cases had a positive AO average and the risk of a +1.000 or above February average was more than twice the 1950-2014 baseline.

 

As always an outstanding post.

 

Now all we need is for the deprecated GFS' 6Z, or the upgraded GFS' 12Z, or ECMWF's 12Z AO forecast to verify for late next week (-2.2, -2.2 and -3.7 respectively) and we'll be all set. 

 

Edit: Looks like the 6Z CFSv2 ensemble mean would almost do the trick as well.   

[donsutherland1]

As always an outstanding post.

 

Now all we need is for the deprecated GFS' 6Z, or the upgraded GFS' 12Z, or ECMWF's 12Z AO forecast to verify for late next week (-2.2, -2.2 and -3.7 respectively) and we'll be all set. 

 

Edit: Looks like the 6Z CFSv2 ensemble mean would almost do the trick as well.   

I agree, at least if the past is representative.

[Ender]

I agree, at least if the past is representative.

It's ironic that things are often most exciting and always most interesting when the past isn't.

[uncle W]

todays ao forecast has one member at +4 and another at -4...that's a wild spread...the forecast is for a negative ao over the next few days but it's a wait and see with the ao the end of January...

[donsutherland1]

Morning thoughts...

 

1. The AO is currently down to +0.212. As a result, for the winter average to come out to -0.500, the AO will need to average -1.951 during the 1/16-2/28 period. For it to have a winter average of -1.000, the 1/16-2/28 average will have to come to -2.974.

 

2. The closing 7-10 days of January is likely to see the EPO negative or strongly negative. Hence, there may be opportunity for Arctic air to get involved. If so, one can't rule out a bout of severe cold.

 

3. Many GFS ensemble members are clustered in the -2.0 to -0.5 range for the AO during this timeframe, but there remains a very large spread, even when the two most extreme members are not considered.

 

4. If one looks to the 1981-2010 period for similar EPO and AO values, coupled with a PNA that fluctuates between -0.5 and +0.5 for the last 10 days of January, the following years show up: 1985, 1988, 1995, 2004, and 2010. 4/5 (80%) of those cases had a negative February AO average (1995 was the exception). The sample size is very small, so one should be cautious. However, if the AO drops to -2 or below in the 1/10-2/10 period following a positive average for the first half of meteorological winter, 80% of a larger set of cases (12/15 cases) had a negative February AO. If one looks at the MJO, 2010 had the closest similarity to where things might be for the closing 10 days of January (Phase 7 for 2010). The other four years ranged from Phase 2 to Phase 5.

 

In sum, mid-month moderation (relative to the very cold conditions that had recently prevailed) will probably last 7-14 days (10 days is a reasonable midpoint estimate). Afterward, there could be another bout of cold to possibly very cold conditions, assuming the forecast teleconnections verify and cross-polar flow develops as suggested on some of the guidance. Beyond that, there should be at least cautious optimism that February could have a predominantly negative AO (probably accompanied by a generally positive PNA). If so, the eastern third-to-half of the CONUS and southern Canada could have a mean trough. Were severe blocking to develop, then a larger part of Canada (especially eastern Canada and perhaps northern Canada) could have a mean ridge.

[donsutherland1]

AO update...

 

This morning's figure: +0.033

 

Average needed during the remaining days of meteorological winter for a December-February average of 0: -0.950; Probability of outcome based on 1950-2014 data: Somewhat unlikely

 

Average needed during the remaining days of meteorological winter for a December-February average of -0.500: -1.997; Probability of outcome based on 1950-2014 data: Unlikely

 

Average needed during the remaining days of meteorological winter for a December-February average of -1.000 -3.043; Probability of outcome based on 1950-2014 data: Extremely unlikely (~ 3%)

 

In sum, especially when the latest ensemble data is considered, the probability of a negative AO average for meteorological winter, especially an average of -0.500 or below, is continuing to decrease. The likelihood of a negative AO average of -1.000 or below for the December-February timeframe is now extremely low.

 

The above does not mean that February can't have a predominantly negative AO. Whether or not the AO drops to -2 or below on at least one day between now and 2/10 could provide a strong signal, if the past is representative.

[mrgolf]

I have a question for someone that can answer. I read cohen's update from yesterday. He mentioned about the barents/kara low. That its been a constant figure so far this winter. He said the models are hinting at it being absorbed. If it did that, would it help us with the ao and nao? Im just thinking of possibilities of it turning in our favor before we run out of time

[icebreaker5221]

While we overall appear to be in a multi-decadal -PDO cycle, we have been in a +PDO phase since early 2014.  The PDO correlates nicely with positive heights in the PNA and EPO regions, and negative heights across the eastern US.  While these correlations exist in Dec, they are much stronger in Jan/Feb.  As long as the PDO doesn't weaken too much (it's trending less + since Dec), I suspect we'll see a slightly better pattern for east coast snow lovers moving forward.  On the other hand, this does not bode well for the west coast drought. 

 

Also note that while there is some significant cross correlation with ENSO, it certainly does not account for the entire signal.  That said, +ENSO combined with +PDO gives the best odds of resembling the mean pattern. 

 

In any event, there is always significant fluctuation about the mean / base state, but the state of the North Pacific has a pretty significant pull on the means. 

 

Dec cor Z500

 

Jan cor Z500

 

Feb cor Z500

 

Just for fun...

Day 5-10 12Z GEFS:

 

[donsutherland1]

Morning thoughts...

 

A sense of panic set in on some sites yesterday, with pattern perceptions switching wildly like a pendulum with a change in model runs that suddenly showed a milder closing week of January. In the long-range, one should not switch wildly with each model run. The runs work toward details. What matters is the larger synoptic setup. The details will vary from day to day. Such caution is even more imperative when one is dealing with a period of time when run-to-run continuity has been poor.

 

Therefore, one should resist the temptation to swing wildly from one model run to the next when volatility in the guidance is so high. To illustrate the "windshield wiper" effect that unfolded on some sites, which compounded some of the negative sentiment in recent weeks at AmWx, just imagine the following scenario:

 

Sunday-Monday Forecasts for New York City:

Forecast time: 1/16 6 am: Mainly cloudy with a shower or two. (6z GFS forecast: 0.02")

 

Forecast time: 1/16 12 pm: Rainy and windy. Rainfall amounts will range from 1"-2" (12z GFS forecast: 1.53")

 

In contrast, if one had stayed with the ensembles and also more consistent ECMWF, both forecasts would have read something along the lines of "Rainy with the potential of 1" or more rainfall."

 

How would one perceive the two forecasts that varied with each model run? Would one prefer the more stable second one, even if it were changed slightly as the details grew clearer e.g. if it shifted from "the potential of 1" or more rainfall" to "1" or more rainfall is likely?"

 

Back to the guidance. What happened overnight?

 

The 0z and 6z guidance moved back toward the colder scenarios. In fact, the new GFS showed the first fantasy range snowstorm since it supplanted the earlier version of the GFS. For posterity's sake, the relevant frames are:

 

 

Of course, that's so far out, one should not even be taking it too seriously right now (though one can always dream and the image is pleasing after what has been a grueling first half of winter with a noted absence of snowfall, even if the image is virtual).

 

The far more important thing is that the period of moderation (less severe cold than has been the case earlier this month), will probably give way to another very cold period as the month approaches its close courtesy of a new EPO- block. Given the pattern evolution that appears more likely than not, I remain cautiously optimistic about February.

 

When it comes to February KU-type snowstorms, some statistics:

- 70% commenced with an AO < 0

- 60% commenced with a PNA > 0 (75% of PNA- storms occurred after February 10)

- Most common setup: AO-/PNA+ 45% (January figure: 85%)

- Second most common setup: AO-/PNA- 25%

- Favored MJO Phases when the ENSO R3.4 anomaly was positive: Phases 7, 8, 1, 2 (80% of KU snowstorms during those phases occurred when there was a positive ENSO R3.4 anomaly.

- Most notable early February storm with an AO+: February 2-5, 1961

[WidreMann]

If it makes anyone feel any better, the AAO is also forecast to become positive.