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donsutherland1

Winter 2015-2016 Medium-Term Discussion

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In Fyodor Dostoevsky’s Crime and Punishment, Dostoevsky wrote of Rodion Raskolnikov, who conceived and carried out a plan to murder a pawnbroker for her money, “At times he was a prey to agonies of morbid uneasiness, amounting sometimes to panic.” Such sentiments seem to arise from time to time when the meteorological outcomes and evolving operational model/ensemble forecasts seem not to fulfill the potential of a promising pattern. They seem especially prevalent following long periods of unseasonable warmth. In the wake of a searing December that left dreams of cold and snow in charred ruins and a transitional period in January that has trimmed but not eliminated warm anomalies in parts of North America that had experienced December’s historic warmth, such sentiments appear widespread as the operational models continue to struggle on the synoptic details related to a potential storm for the January 16-18 timeframe. That some of the guidance has shifted from snowy or out-to-sea solutions to a cutting system have exacerbated such concerns.

 

At the same time, the latest guidance no longer shows quite as extreme a blocking situation as suggested earlier. Rather than forecasting the AO to bottom out at or below -5.000, the latest run of the GFS ensembles shows the AO reaching a minimum near -4.000.

 

Should those in the East simply assume a “rule” by which forecast warm anomalies will verify, cold ones won’t, rainy solutions will, snowy solutions won’t? In other words, should we write off Winter 2015-16 as a failure now that we’re approaching the mid-point of meteorological winter?

 

Even with the reduced magnitude of blocking, not to mention El Niño climatology, doing so would be perilous. Although there are no guarantees of a very snowy outcome similar to winter 1957-58, a notable scarcity of snowfall along the lines of 1997-98 also appears unlikely.

 

At the same time, the PNA+ will likely lead to a warming in the West. Nevertheless, it does appear likely that parts of the drought-stricken region will continue to experience opportunities for beneficial rains.

 

Below are some charts related to less extreme blocks that occurred in the January 15 +/- 10-day range related to February.

 

AO01112016_1.jpg

 

AO01112016_2.jpg

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It could turn out to be a very active February. The Great Lakes will not be freezing over or chilling to their usual low values, so that should be one factor helping to energize weather systems over the northeastern U.S. Another factor will be the higher than average offshore SST values. But if the atmosphere goes into a sharper mean trough than we've seen so far in this transitional January, I could imagine some very active storm systems as there seems to be a fair bite to the arctic air masses so an even stronger than normal air mass contrast may develop for these systems. This regime may not show its hand much through the rest of January but could begin to appear after the 20th. I think the most active zone will probably be the northern Mid-Atlantic to western New England. I would expect this regime to persist into the first half of March. There could be three to five decent winter storms in the seven week period from late January to mid-March. My optimistic conclusion is that it's too early to pronounce the winter of 2015-16 a dud although we can pretty much remove the 2015 part of it.  

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Over the past 5 days, a very stable AO-/PNA+ pattern has prevailed. During that time, the AO has ranged from -3.608 to -3.399 and the PNA has ranged from +0.736 to +1.014. During that time, a clipper system streaked across the Northern Tier and bombed out in the Gulf of Maine bringing up to 10” of snow to parts of Maine and lesser amounts from Pennsylvania across southern New York State (excluding New York City and its immediate suburbs) and southern New England. In short, those snow-starved cities had a “near miss.” However, there are no consolation prizes.

 

Over the next 5-7 days, another storm will head to the Great Lakes region while a strong secondary system moves north-northeastward along the East Coast. The primary system will be sufficiently strong (<995 mb) that it will drive a lot of warmer air northward, once more depriving snow-starved cities such as New York, Philadelphia, and Washington of a meaningful snowfall. In its wake, Arctic air should again knock down temperatures from the Plains States to the East Coast.

 

However, if one looks out to the Pacific, some of the guidance is suggesting that the SOI will rebound to positive and possibly strongly positive values within 10 days. During strong or super El Niño events, that development can coincide with the development of strong ridging over some part of Ontario or Quebec.

 

The ECMWF ensembles and GFS ensembles are in agreement about the development of just such ridging during the 240-hour to 288-hour timeframe. If that occurs, what should have been the locking in of a colder pattern on account of the blocking—something I had expected—could wind up being a more variable pattern with shots of cold alternating with warmer conditions from the Plains States to the East. The Middle Atlantic region, New England, and Quebec might have the highest probability of seeing net warm anomalies in the extended range if such a pattern develops. This issue will need to be revisited in coming days.

 

Finally, on the stratospheric front, a strong Wave 2 pulse is likely to develop over the next 10-15 days. However, it’s far too soon to be sure whether the wave will have the amplitude necessary to trigger a sudden stratospheric warming event. The ECMWF argues against such an event through the next 10 days, but 10 days is beyond a reasonably accurate forecasting horizon. Such events are only forecast with reasonable accuracy within a few days of their onset, so aside from noting the forecast development of the wave, more data will be needed to reach any conclusions about the likelihood of such an event. The infrequency of such events—about one every two winters—argues for holding off on conclusions until more data is available.

 

SOI01132016.jpg

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Alex became a hurricane this morning. It's the first hurricane in the Atlantic basin in January since Alice (which formed in December 1954) and the first to develop in January in the Atlantic basin since 1938.

 

From the NHC:

000WTNT41 KNHC 141434TCDAT1HURRICANE ALEX DISCUSSION NUMBER   4NWS NATIONAL HURRICANE CENTER MIAMI FL       AL0120161100 AM AST THU JAN 14 2016Remarkably, Alex has undergone the transformation into a hurricane.A distinct eye is present, embedded within a fairly symmetric massof deep convection.  Water vapor imagery shows that the upper-leveltrough is now west of the cyclone, with divergent flow over thecenter - indicative of a tropical transition.  It is very unusual tohave a hurricane over waters that are near 20 deg C, but theupper-tropospheric temperatures are estimated to be around -60 degC, which is significantly colder than the tropical mean.  Theresulting instability is likely the main factor contributing to thetropical transition and intensification of Alex.  With thesechanges, the government of the Azores has issued warnings for mostof the Azores islands.The initial intensity is set to 75 kt in accordance with theanalyzed Dvorak T-number of 4.5.  Only slight additionalintensification seems possible since the system will be passingover even colder waters during the next day or two.  In 36 hours,the global models suggest that the cyclone will becomeextratropical as it begins to merge with a large low pressure areaat high latitude.  The post-tropical cyclone is then likely to loseits identity after 48 hours.The initial motion is north-northeastward or 020/17 kt.  Alex isbeing steered by a shortwave mid-level trough that is rotatingaround a larger trough to the northwest.  This should cause thecyclone to turn northward and north-northwestward and accelerateover the next couple of days.  The official track forecast is verysimilar to the previous one and also quite close to the consensusof the tightly-packed dynamical model forecast tracks.Alex is the first hurricane to form in the month of January since1938, and the first hurricane to occur in this month since Alice of1955.FORECAST POSITIONS AND MAX WINDSINIT  14/1500Z 31.5N  28.4W   75 KT  85 MPH 12H  15/0000Z 34.3N  27.7W   80 KT  90 MPH 24H  15/1200Z 38.9N  27.7W   75 KT  85 MPH 36H  16/0000Z 45.3N  28.6W   60 KT  70 MPH...POST-TROP/EXTRATROP 48H  16/1200Z 53.0N  31.5W   60 KT  70 MPH...POST-TROP/EXTRATROP 72H  17/1200Z...DISSIPATED$$Forecaster Pasch

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In #185 yesterday, I noted that some of the guidance was indicating that the SOI could go positive or even strongly positive down the road and posted the 500 mb pattern that has often prevailed during such cases with strong El Niños.

 

The 18z GFS ensembles have centered above normal height anomalies very close to the predominant position in December.

 

GFSEnsembles0114201618z.jpg
 
It should be noted that the height anomalies are nowhere near as pronounced as they were in December. Nevertheless, the GFS ensembles are providing a hint that a milder pattern could attempt to reassert itself toward the close of January. However, should blocking regain strength  and then hold through much of February, such a pattern could be temporary.
 
Right now, odds may still lean toward a blocky February, especially if the AO drops to -4.000 or below over the next few days as still modeled. Nevertheless, any return of milder conditions could prove disconcerting in sections of North America that have experienced an unseasonably warm winter overall and a noted lack of snowfall. 

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With today being day 46 of meteorological winter, we have now moved past the midpoint of the winter season. Of course, winter weather can occur in March and sometimes April. So far, the highlights have been:

 

  •  An historically warm December
  • A massive flood along the Mississippi and Missouri Rivers
  • A late-November snowstorm in the Midwest
  • A blizzard that moved out of New Mexico and Texas
  • A lack of snowfall in the East (To date: Albany: 4.3”;  Baltimore: Trace; Boston: 1.2”; New York City: Trace; Philadelphia: Trace; Providence: 0.9”; Richmond: None; Washington, DC: Trace)

 

Until January, the predominant synoptic pattern featured an AO+/PNA+ combination. Since January, an AO-/PNA+ has taken hold. The AO has been negative for 14 consecutive days and at or below -3.000 for a week. That has tempered the warm anomalies in the East and contributed to some snowfall in New England.

 

Overall, the AO has averaged +0.133 for meteorological winter to date. It has been positive on 61% of days. However, it has been at -3.000 or below on 15% of days vs. +3.000 on 7% of days. The positive AO anomaly will very likely be wiped out by Sunday.

 

Right now, given the strong blocking that developed, it remains more likely than not that February will feature blocking, as well. Were the AO to fall to -4.000 or below in coming days (and some of the guidance still takes it there this weekend), that probability would increase.

 

In the meantime, the super El Niño continues to fade slowly. A gradual fade is likely to continue over coming weeks and perhaps pick up a little. Typically, such a development, especially with a basin-wide rather than East-based El Niño should favor more opportunities for cold in a large part of North America.  However, the picture going ahead is less certain than usual.

 

What happens may well be highly dependent on the MJO. To date, winter 2015-16 has featured an abnormally strong MJO signal for super El Niño cases. This outcome may, at least in part, be the result of the widespread warm SSTAs in the Pacific.

 

MJO01152016.jpg

 

If the past two super El Niño cases are representative, the amplitude should be somewhat lower during the remainder of meteorological winter. However, a sharp decline would not be likely. Therefore, one may cautiously expect a continued stronger than usual MJO signal and depending on the Phase, that signal could counter or even override the blocking (perhaps leading more to normal temperature departures than cold ones if unfavorable MJO Phases coincide with the blocking).

 

Finally, the long-range ECMWF guidance appears favorable for cold in the eastern part of the CONUS. However, if one takes the GFS MOS projections through January 20 and the actual temperatures from 1/1-14, it now appears that the CFSv2 may wind up with the better January temperature forecast for that section of North America than either the ECMWF or JMA, as warm anomalies now appear to be more likely than not for the monthly period in such cities as Philadelphia, New York, and Boston, even considering next week’s possible Arctic shot. Furthermore, the PNA+ will likely lead to warm anomalies developing in the Pacific Northwest near January 20 and that warmth could trim or even erase the cold anomalies that have accumulated to date there.

 

CFSv201152016.jpg

 

In contrast to the other guidance, the CFSv2, which is still outside its skillful range, is featuring more widespread warm anomalies. Right now, that does not appear to be the most likely scenario when one considers ENSO climatology, the location of best ENSO forcing during the current event, and potential for a blocky February, but it is a plausible one that cannot be dismissed. Should the MJO move into predominantly unfavorable phases and/or the SOI remains near neutral or positive for large parts of February, the warmer CFSv2 idea could prevail. It’s still too soon to embrace such a prospect, but that prospect cannot be ruled out.

 

Across much of Canada and the Pacific Northwest, warm anomalies could prevail in February courtesy of the PNA+. With a strong PDO+ persisting (December’s value was +1.01, an increase from November’s +0.86), a PNA+ is likely to predominate.  The southern tier running from southern California to the Southeast could be on the cooler side of normal on account of an active subtropical jet.  North of there, especially from the Plains States to the Middle Atlantic and New England regions is uncertain right now. Blocking would argue for colder outcomes in parts of that area, but a high-amplitude MJO in unfavorable phases (a risk not certainty) would argue against that outcome.

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The ECMWF Ensembles are forecasting that the MJO will likely predominate in Phases 2 and 3 through much of the rest of the second half of January. The forecast 500 mb pattern on the GFS ensembles for 240 hours and even farther out to 360 hours bears some similarities and also some differences from the composite MJO pattern for strong El Niño events (1/15-2/15 timeframe).

 

Note: All GEFS maps are from Tropicaltidbits.com

 

MJO01152016_2.jpg

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The ECMWF Ensembles are forecasting that the MJO will likely predominate in Phases 2 and 3 through much of the rest of the second half of January. The forecast 500 mb pattern on the GFS ensembles for 240 hours and even farther out to 360 hours bears some similarities and also some differences from the composite MJO pattern for strong El Niño events (1/15-2/15 timeframe).

Note: All GEFS maps are from Tropicaltidbits.com

MJO01152016_2.jpg

Don,

First and foremost I learn so much from your posts, love reading your explanations and forecasts.

Any thoughts on February? Is it looking like a crapshoot? Are you seeing a blockbuster February setting up for the Mid Atlantic similar to 2010? I'm sure it comes down to blocking obviously and AO,NAO, PNA.

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Don,

First and foremost I learn so much from your posts, love reading your explanations and forecasts.

Any thoughts on February? Is it looking like a crapshoot? Are you seeing a blockbuster February setting up for the Mid Atlantic similar to 2010? I'm sure it comes down to blocking obviously and AO,NAO, PNA.

Thanks for the kind words.

 

Today's AO was -4.820. That's the lowest AO figure since March 23, 2013, when the AO stood at -4.855. The last reading of -5.000 or below was March 22, 2013 (-5.240).

 

Typically, such a strong AO- reading at this point in January has been followed by a generally blocky February. The guidance breaks down the blocking the extended range, but if past experience is representative, that outcome should be temporary. However, given the super El Niño and abnormally high MJO amplitude that has prevailed for the most part during the winter season, there's a lot more uncertainty than usual. El Niño and blocking climatology would argue for cool anomalies from the Midwest eastward, but that outcome is much less certain than usual. We'll have to see where things stand as we get closer to February.

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Today's AO is -4.916. That's the lowest figure since March 22, 2013 when the AO was -5.240. That figure has pushed the AO's average for meteorological winter to -0.075. To date 58% of days have been positive and 42% negative. However, 19% of days have been at or below -3.000.

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Going forward, I think the pattern evolution is generally in alignment with prior posts, though, time will tell regarding the extent to which the reversal amplifies.

 

[1] The NAM transition into a predominately negative state has occurred over the past couple weeks, via tropospheric forcing mechanisms [i.e., Kara Sea ridge development, potentially instigated by a couple of background factors], stratospheric polar vortex elongation in response to initial strong wave-1 attack which has warmed the lower/mid stratosphere over the Pacific side of the Pole.

 

[2] Thus far, the severe -AO has not yielded any snowfall or extreme cold. The upcoming week will feature colder than normal temperatures. The rapid upward trend in both the AO and NAO modalities for the 18th-22nd period is a noted Archambault indicator for enhanced storminess / cyclogenesis along the East Coast. So the detection of a possible storm later in the week would coincide with statistics on prior sharp AO/NAO rises, and severe -AO dailies. However, if the western ridge amplitude is not sufficiently meridional and/or oriented more NE-SW rather than N-S, it will tend to force cyclogenesis too far S/E and push the storm offshore. This remains a possibility due to the off the charts +AAM state which has infused the Pacific Jet with incredible westerly momentum. The AAM tendency has been negative recently, but it is still very high. If the ridge remains amplified, there is enough downstream Atlantic residual blocking to prevent a warm/rainy scenario. Confluence appears strong. Largest risk is a S/E miss, in my view.

 

[3] The targeted period for robust wave activity [Jan 20-30] will be occurring with the strongest wave-1 pulse to date, in accordance with the discussed precursors. Forecasted wave-1 heights, historically speaking, would be sufficient to induce a vortex displacement. Typically, the initial wave-1 hit is separated by a couple weeks of depressed flux prior to the second, stronger pulse. A potent +MT event in East Asia could develop as wave-1 increases concurrently, and this would enhance pressure on the vortex. The one wildcard remains the anomalously strong condition of the vortex this winter, which may require stronger wave activity than is typically needed to force SSWs. With that being said, I think the probability is mod-high for at least a minor SSW, whereby zonal winds slow significantly and 10hpa temperatures rise sharply. I am not certain that we will achieve a major SSW displacement, but the time frame continues to be near the end of January for that potential.

 

[4] Regardless of stratospheric progression, other tropospheric indicators are suggestive of the overall maintenance of high latitude blocking in February. I expect that the Western ridge reload will be extremely transient. A classic Nino NPAC looks probable for the end of the month with the Aleutian low and +PNA. GWO orbit and heightened AAM state support the aforementioned regime of S/E US troughiness and Rockies ridging as the month closes. The expectation for February continues to be the gradual retrogression of the GOA with a -AO and -NAO in the means. Depending upon the evolution of the stratosphere, this AO/NAO blocking could be either moderately robust or severe / similar in magnitude to the January episode. An official displacement would heighten the probability of protracted blocking.

 

Overall, it does not appear to me that we are paralleling the Nino winters which were torchy / snowless from front to back. The second half transition still looks on track. January is falling in accordance with the analogs; generally a near normal temperature departures with improved high latitude indicators.

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Snowstorm Possible for Parts of the East Friday into Sunday…

 

If one examines the data for January snowstorms going back to 1950, there have been 17 cases in which a storm brought 10” or more snow to one of the following cities: Boston, New York City, Philadelphia, Washington, DC. However, there are just 3 cases during which the storm brought 10” or more snow to at least 3 of those cities (January 1978, January 1996, and January 2005) and just one case in which all four of those cities received 10” or more snow (January 1996).

 

The 1950-2015 data is below:

 

January_Snowstorms01192016.jpg

 

With respect to the just-concluded and ugly 12z ECMWF run, I believe it's too soon to write off the potential storm, particularly in the northern Middle Atlantic region and southern England areas. The continued continuity of the other guidance suggests that the upcoming storm may still bring 10” or more snow to 3 or even all 4 of those cities. Moreover, that such a storm is forecast to occur during an AO-/PNA+ synoptic pattern is consistent with January cases during an El Niño event for the January 23 +/- 15 day period.

 

Taking into consideration all of the ECMWF and GFS runs from 1/18 12z through 1/19 12z (3 runs of the ECMWF and 5 runs of the GFS), with greater weight applied to more recent runs, it appears that Baltimore and Washington, DC could experience a potentially major to historic snowfall event where both cities could approach or exceed 20” snowfall.

 

Finally, the 12z ECMWF dramatically cut back the QPF for such cities as New York and Boston from its 0z run, but it remains to be seen whether this big change is reasonable, especially as the GFS and GFS ensembles retained good run-to-run continuity.

 

Nevertheless, various scenarios are incorporated for the weighted model data, so a look what might be a worst-case may be useful. For purposes of comparison, I’ve provided the lowest QPF output from the ECMWF or GFS for the timeframe noted above, as well as the lowest QPF for any of the scenarios that were applied to the weighted series of model runs (e.g. 3σ below the weighted average figure from the model runs). Of course, we’re still fairly far out from the event, so a lot of uncertainty remains.

 

Worst_Case01192016.jpg

 

The 12z EPS and then 18Z GFS could provide early insight into the possible validity of the 12z ECMWF run.

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Some early thoughts on the January 22-24 Snowstorm…

 

So far, most of the guidance, excepting yesterday’s 12z run of the ECMWF, which was an outlier, indicates that the upcoming snowstorm could bring 10” or more snow to Washington, DC to New York City. Since 1950, only three January snowstorms have brought 10” or more snow to Washington, DC, Philadelphia, and New York City, including the one that was underway today in 1978.

 

At this point in time, the consistency of the guidance, including yesterday’s 12z ECMWF run, strongly suggests that the Baltimore to Washington, DC region could experience one of its five biggest snowstorms on record since at least the late 19th century. If the guidance holds, that region could be facing a 20”-30” snowfall. It’s too soon to reach firm conclusions right now, as details concerning the storm remain to be worked out, but that’s where the guidance has been over the past 48 hours.

 

My initial thinking is below:

 

BWIDCA01202016_2.jpg

 

The five biggest snowstorms on record for Baltimore and Washington, DC are below:

 

BWIDCA01202016.jpg

 

This storm is likely to reach blizzard proportions along parts of the East Coast. Moreover, the combination of a full moon and very high onshore winds could create significant coastal flooding and beach erosion. Such an impact will be a notable aspect of this storm aside from its prolific snows in parts of the Middle Atlantic region.

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Overnight, details concerning what will likely be a major-to-historic Middle Atlantic snowstorm have come into greater focus. Right now, the two dominant aspects of the guidance are persistent fairly strong confluence and the interaction of system’s coming into the Pacific Northwest and the eastern trough that will likely limit the storm’s ability to gain latitude as that incoming system serves to “kick” the storm out to sea. Whether the storm reaches North Carolina’s Outer Banks and then heads out to sea or reaches the northern Delmarva Peninsula/southern New Jersey before heading out to sea will make a large difference for snowfall amounts from northern New Jersey into southern New England. The incoming system’s influence will likely reduce prospects of the storm’s stalling for a time, something that had been seen on some of the earlier guidance.

 

The worst-case scenario is that the storm would depart after reaching the vicinity of the Outer Banks. Under such a scenario, 6” snowfall amounts would likely be limited to a line running roughly from Trenton to Asbury Park in New Jersey and southward. Several inches of snow could still fall 50-75 miles north of that line, but little or nothing 100-125 miles north of it on account of the persistent confluence.

 

At this time, I’m assuming a sort of middle ground scenario in which the storm moves offshore somewhere between Salisbury and Ocean City and then heads eastward out to sea. I also favor the ECMWF’s colder thermal profile given its superior resolution, but could still envision some temporary precipitation-type issues along the New Jersey Shore, Delmarva, Long Island, and even into NYC and its nearby suburbs.

 

Considering these assumptions, my initial thinking for accumulations is as follows:

 

Baltimore: 18”-24”

Boston: 1”-2”

New York City: 6”-10”

Newark: 6”-12”

Philadelphia” 12”-18”

Sterling: 20”-30”

Richmond: 6”-10”

Washington, DC: 20”-30”

White Plains: 4”-8”

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Historic Blizzard Imminent for Middle Atlantic Region...

 

At 8 am, the first impressive wave of precipitation had moved into southern sections of Virginia while farther north mid-level clouds were mostly obscuring the sun in Washington, DC with only a few streaks of orange left in the sky.

 

Radar_RDUNWS012220160809am.jpg

 

These developments mark the early stages of what will likely be an historic and crippling blizzard for such cities as Washington and Baltimore. Both cities could approach or exceed their modern snowfall records. 30" or greater snowfall amounts are likely across parts of the area. A widespread outbreak of thundersnow appears likely given some of the soundings. In the Blue Ridge where orographic lifting could enhance snowfall rates, a few spots could approach or exceed 40".

 

To illustrate how tremendous the potential QPF is, below are the last four figures for Washington, DC (DCA) from the GFS:

 

1/21 12z: 2.69"

1/21 18z: 2.44"

1/22 0z: 3.27"

1/22 6z: 3.64"

 

Not only has the model consensus remained remarkably consistent about the potential of a huge snowfall, one has seen some of the guidance expand the precipitation field a little farther to the north. Such guidance includes the 6z GFS, 0z ECMWF, 6z RGEM, and 0z UKMET.

 

My final estimates are as follows:

 

Baltimore: 20"-30"

Boston: 2"-4"

Bridgeport: 6"-12"

New York City: 8"-14"

Newark: 10"-15"

Philadelphia: 14"-20"

Sterling: 24"-36"

Richmond: 8"-14"

Washington, DC: 24"-36"

White Plains: 6"-12"

 

A small deviation in the storm's track could still result in a large increase in snowfall on the northern extent. For example, even a 25-30-mile shift northward could result in New York City's picking up closer to 15" snow than 10".

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Moderation Looms but February May Still Have Snowstorm Potential…

 

Today is the 57th day of meteorological winter. So far, January has featured a remarkable turnaround in temperatures from December in the areas that experienced historic warmth. Some of that region is currently running somewhat colder than normal while other parts are somewhat above normal.

 

AO01262016_1.jpg]

 

Aside from the temperature reversal, which would be notable by itself, there was also a major Mid-Atlantic blizzard during the January 22-24 period. The Washington, DC area (e.g., National Zoo), Baltimore, Philadelphia, and New York City received more than 20” snow.

 

AO01262016_2.jpg

 

Over the next 5-10 days, a milder pattern is likely to prevail. However, toward the end of that timeframe, colder air could return to western portions of North America and then begin to expand eastward. The operational GFS and ECMWF and their ensembles are in good agreement with such a scenario.

 

The longer-term for February is less certain. The 1877-78 super El Niño saw a similar reversal in temperatures in January only to witness a partial return of the widespread anomalous warmth in February. The 1982-83 super El Niño experienced a similar January temperature reversal with the February temperature profile largely resembling the January one.

 

In terms of blocking, the AO fell to -4.916 on January 17. Climatology favors a negative AO for February and the probability of a negative AO is higher than climatology in cases when the AO fell below -3.500 during the January 15-25 timeframe. Nevertheless, probabilities should not be read in a deterministic fashion, so there is a risk, albeit lower than climatology, of a positive February AO.

 

In coming days, a minor stratospheric warming event is forecast by the ECMWF. However such an event is forecast to fall well short of what one witnesses during a typical sudden stratospheric warming event (SSW) and it is not forecast to propagate downward into the troposphere. Hence, as was the case in January when a super Kara Sea-centered ridge displaced the polar vortex yielding a strongly negative AO, one will likely need to look to the troposphere for the largest impact on the AO’s evolution.

 

The ongoing PDO+ suggests that the persistent PNA+ pattern that has prevailed during meteorological winter (88% of days have seen a PNA > 0) will likely predominate through at least the first half of February and perhaps longer.

 

The super El Niño continues to fade, particularly in Region 1+2. The change in anomalies by ENSO region during the past 4 weeks is as follows: Region 1+2: -0.7°C and Regions 3, 3.4, and 4: -0.2°C. The cooling should continue and will likely accelerate a little in coming weeks. Nevertheless, strong El Niño conditions are likely to persist through February.

 

So, at this point in time, given all of the above data, it is plausible that February could see monthly anomalies wind up above normal in much of North America starting somewhere between 35°N and 40°N latitude (but not so warm to preclude opportunities for snowfall, especially when blocking is present during which colder anomalies could also prevail). The continued strong El Niño favors an active subtropical jet and possible storminess. The potential for at least some degree of blocking (which has generally been strong when it has been present) coupled with a PNA+ argues that at least some of this storminess could bring meaningful snow across some parts of North America (especially from the southern tier toward the Middle Atlantic and perhaps southern New England regions.

 

There remains a risk, though a smaller one, of a sort of “worst case” scenario similar to the evolution of winter 1877-78 whereby much of North America would return to a warmer than normal temperature regime. The latest run of the CFSv2 is highlighting that potential. This is something that will need to be watched. If one does not witness a return of the EPO- and later, AO-, the probability of the warmer outcome would increase. 

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The Return of the Strongly Positive AO...

 

This morning, the Arctic Oscillation stood at +3.900 on this 60th day of meteorological winter. The AO has averaged -0.102 through today. Over the next 3-5 days, the average for meteorological winter will very likely go positive, where it had been until January's strong blocking episode. So far, 55% of days have had a positive AO with 42% experiencing an AO of +1 or above. 45% of days saw a negative AO with 35% featuring an AO of -1 or below.

 

The strong blocking that developed earlier this month has often been a precursor to predominant blocking in February. However, the big rebound that has now taken place is a proverbial fly in the ointment. Most cases that saw the AO rebound to strongly positive values in the January 25-February 10 timeframe featured little blocking in February. The new GFS ensemble forecast now has far fewer ensemble members pointing to a return of blocking in early February.

 

AO01292016.jpg

 

Compounding matters is the failure of a significant or major stratospheric warming event to appear in late January. Instead, a relatively minor event will take place over the next 3-4 days with the stratosphere again cooling afterward. Some wave-breaking activity will attempt to displace the polar vortex.

 

Nevertheless, Winter 2015-16 may not fit neatly into what has taken place in the past, even if the AO+ predominates for at least the first half of February or longer. The super El Niño event is only slowly fading after having peaked in mid-to-late-November. The best ENSO forcing is west of where it was during the 1997-98 super El Niño event. The PDO+ persists favoring a PNA+.

 

Put another way, scenarios other than widespread warmth across much or all of North America are plausible, though . There is variability among the cases. For example, 1976 featured widespread warmth in February. In contrast, despite an extremely positive AO, February 1989 did not.

 

Looking more closely, only three of the featured cases saw a PDO+ in February: 1981, 1982, and 1993. Again, there was variability among those cases.

 

Where there is greater consensus is that a predominantly positive AO could limit snowfall opportunities in the Middle Atlantic region. However, there is only a single El Niño case in the mix and that El Niño event was a weak one. Therefore, even this stronger consensus among the cases is subject to a fairly large degree of uncertainty.

 

All said, at least for now, I am cautiously suggesting that the outlook for a blocky February has diminished somewhat (but probably not as greatly as implied by the above historic cases), though considering the earlier January block, it remains possible. The latest EPS continues to support that idea. The specific implications remain to be determined and variables such as the EPO, PNA, and ENSO may either amplify the impact of any reduced blocking or even counter it. For now, it still appears that early February warmth will give way to a colder pattern, starting first in the central portion of North America then moving eastward. Whether that cold will lock in for more than 10-14 days will depend on factors, including but not limited to renewed blocking (which now appears somewhat less likely than even a week ago).

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Don, I agree that we have approached a crossroads with the direction that blocking will go over the next 4-6 weeks but I do want to add something to discussion. The Euro ensembles are currently decidedly in favor of the AO turning negative before the end of the first week of February and remaining that way through the end of the run. Over the last 2-3 days the signal has been growing stronger on the Euro ensembles and last night's 0z run was the most bullish yet. 

 

I know the Euro weeklies should always be taken with a grain of salt but they also support a -AO through at least the 3rd week of February and an even bigger grain of salt...the latest CFS sub monthlies are showing a -AO for all of February. 

 

Time will tell of course but if I had to make my best guess, the current + period will prove to be transient. At the very least I don't believe we are entering a strongly positive phase.  

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post-2857-0-25064000-1454187281_thumb.gi

 

 

 

 

 

 

post-2857-0-97592000-1454187468_thumb.gi

 

 

 

 

Both the 12z GFS and the ECMWF are showing a substantial omega block over the West coast in the 240hr. timeframe. It has a similar 500mb set up seen just before the March 93 super storm. Obviously

a lot can change this far out, but it is of note that both models seem to be hinting at something special

in this period.

 

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Don, I agree that we have approached a crossroads with the direction that blocking will go over the next 4-6 weeks but I do want to add something to discussion. The Euro ensembles are currently decidedly in favor of the AO turning negative before the end of the first week of February and remaining that way through the end of the run. Over the last 2-3 days the signal has been growing stronger on the Euro ensembles and last night's 0z run was the most bullish yet. 

 

I know the Euro weeklies should always be taken with a grain of salt but they also support a -AO through at least the 3rd week of February and an even bigger grain of salt...the latest CFS sub monthlies are showing a -AO for all of February. 

 

Time will tell of course but if I had to make my best guess, the current + period will prove to be transient. At the very least I don't believe we are entering a strongly positive phase.  

Absolutely. I just wanted to highlight larger than normal uncertainty. The rarity of the strong AO+ during El Niños at this time of year suggests that one should not automatically assume that the usual rules (from predominantly neutral or La Niña cases) will prevail. All said, I still believe it is more likely than not that blocking will resume and the potential for fairly strong blocking is there. Such an outcome should lead to opportunities for measurable snowfall in the Mid-Atlantic region, including the chance for significant snowfall that would be higher than climatology.

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I'd be stunned if it remained positive.

The long range has been especially volatile this season, so I wouldn't pay much attention to the shift away from the -AO on the GEFS.

I agree 40/70 Benchmark.

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attachicon.gifgfs_namer_240_500_vort_ht_s.gif

 

 

 

 

 

 

attachicon.giff240.gif

 

 

 

 

Both the 12z GFS and the ECMWF are showing a substantial omega block over the West coast in the 240hr. timeframe. It has a similar 500mb set up seen just before the March 93 super storm. Obviously

a lot can change this far out, but it is of note that both models seem to be hinting at something special

in this period.

There's a lot of potential on the table. That the long-range part of the GFS has swung between a significant snowfall and large rainfall is less important right now than the model's seeing the potential for a significant storm. Details will need to be resolved later.

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