- Category Archives EPO
Model data continues to suggest a Greenland block will develop as we progress into late-November. This kind of pattern creates a “log jam” of sorts in the weather pattern and is the type pattern notorious for unseasonably cold regimes across our region. The overall agreement between various models raises our confidence in this pattern unfolding as Thanksgiving nears.
Such a pattern illustrated above, per the European ensemble (image 1) and the GFS ensemble (image 2), would help drill a tongue of unseasonably cold air through the northern Plains, into the Mid West, and across the East.
A look at the 00z teleconnections this morning shows 3/4 “big boy” drivers going to that cold look for late-November, as well:
We’ve been discussing early snow cover across Canada and the northern tier for weeks and how models would have to “correct” colder as they realize the air masses traveling over the snowpack won’t be able to modify as they normally would without that snowpack. The differences between this November and last are startling and show how the early snowpack is beginning to “feedback” on itself leading to early-season cold air.
2016 snowpack and temperatures anomalies through the first week of November:
2017 snowpack and temperatures anomalies through the first week of November:
Given the overall look to the pattern downstream, I anticipate the cold will continue to “press” and eventually overwhelm the pattern east as we progress through the second half of the month.
To close, we expect a developing Greenland Block to help drive an unseasonably cold late-November, including the Thanksgiving holiday. This is the type pattern that can also help generate early season wintry “fun and games,” however it’s far too early to be specific with any sorts of potential wintry events that may eventually come in this pattern. Stay tuned.
December-to-date is running colder than normal (to the tune of 2.2 degrees at IND), but the past (7) days has seen a flip in the frigid 1st half of the month.
The “relaxation” is temporary. Modeling continues to advertise the recent “thaw” will give way to increasingly bitter times as we get deeper into the New Year. By New Year’s Day we note the positive heights continuing to establish themselves across Alaska and Greenland (cold and stormy signal). We also note the southeast ridge present, though to a lesser degree than over the past week.
By Day (10), the cold pattern is well established over the Lower 48. This is a coast-to-coast cold signal (heart of the cold centered over the west and central) depicted by the European ensemble, along with other modeling.
Teleconnections support a cold pattern returning.
The agreement amongst teleconnections is nice to see and ups confidence in the overall direction of where this pattern is heading in regards to colder than average times looming. The negative PNA correlates nicely with the SE ridge that continues to make itself heard from time to time over the next few weeks. It should also be noted that the phases of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) become more of a factor for mid and late winter.
As far as storminess goes, we’ll have to handle those as they come. The overall pattern screams towards the idea of an active Ohio Valley to interior Northeast storm track as we move forward (continuing deeper into mid and late winter, as well). That doesn’t mean one or two storms won’t bypass our local region to the south, due to strong, cold high pressure north, but the mean storm track should put areas through the Ohio Valley in the “sweet spot” from a snow perspective throughout the majority of January, and the rest of winter, for that matter. Depending on the position and strength of the Greenland Block will have a lot to say about things. Needless to say, storms cutting NW into the central Lakes should be few and far between after the New Year. Speaking of storms, we have to continue to keep an eye on the second half of next week. At the time of this discussion, the threat is still beyond the 7-day period, but circle late next week and weekend for the potential of wintry “mischief.”
As we rumble through the remainder of 2016, a “transient” weather pattern awaits. Cooler, more seasonable, air is working itself into the Ohio Valley today and will be followed by another (stronger) cold front Thursday. That front will pack more of a punch in the cold department, along with providing opportunity for snow showers, as well. That said, we’re still about a week off from more of a sustained cold pattern.
With the arrival of the new year, a new weather pattern will emerge as well…
The EPO (East Pacific Oscillation) and WPO (West Pacific Oscillation) will flip back to negative phases as the New Year arrives. This will help drive the shift, initially, to a colder regime, locally.
Accordingly, we see the ensemble data flipping to a colder pattern over the upcoming (10) days. Note the low anomalies in the higher latitude regions today (Image 1) versus Day 10 (Image 2).
The pattern developing by Day (10) is one capable of producing another frigid regime- only January style. Cross-polar flow sets up shop and, unlike, December, some blocking is noted, as well. This can help the mean storm track shift further south. (Bye-bye Great Lakes cutters, though Mid Western and Ohio Valley Snow Lovers will find a new worry in the form of suppression potential ;-)). Individual storms will have their respected challenges, as always. As a whole, it’s a very cold, stormy look and a pattern capable of leading to an expanding snow pack across the Lower 48.
Notes: The new European Weeklies are in and reflect the general idea here of a more sustained cold, wintry pattern unfolding as January arrives. The Weeklies are very cold through Weeks 2-3, in particular. As far as snow goes, they also suggest an active storm track with numerous storms leading to an increasingly snowy regime through the middle parts of January, as well. That said, we’re a bit hesitant to focus too much on the long-term snowfall details as the Weeklies have been too generous in the snow department over the past several weeks. As a whole, it’s very tough to argue the pattern isn’t one that should yield the snowy “goods” in the coming weeks though.
Before we get into the updated thinking on the pattern, lets review what we have out:
- Step-down process to cooler/ colder weather begins in mid-November.
- Thanksgiving-Christmas period, as a whole, turns wintry and is snowier than average.
- Our complete 2016-2017 Winter Outlook can be found here.
The first week of November has featured an incredibly warm start to the month. (Image courtesy of MRCC).
Speaking of warmth, 2016 has been a very warm year.
(The cold of 2014 seems so long ago…)
Back to present. We’ve targeted the middle part of November to finally beginning “bucking” the recent warm trend. This won’t happen overnight and will be a battle of back and forth, initially. Thus, the “step-down” label. To be clear, November, as a whole, will finish much warmer than average. It’s virtually impossible to counter the incredibly warm start. That said, we do anticipate “jabs” of colder air working in here over the next couple weeks. For instance, this weekend will feature lows in the 20s for most and highs not making it out of the 40s Saturday afternoon. (The average low and high at IND Saturday are 37 and 54).
Despite being in a weak La Nina, the pattern is taking a while to respond. Remember, we’re coming off one of the strongest El Ninos on record. Until we slow the PAC jet, significant, long-lasting, changes won’t occur. We can lean on the AAM (Atmospheric Angular Momentum) forecast for clues as to when this may occur. You can read more about the AAM here. My fellow local weather compadres, Michael Clark, Ed Valley, and Kirk Hinz have also written/ blogged extensively about the AAM and resulting impacts.
When we look at the AAM forecast (above), we note the westerlies may begin to slow (indicative of the negative values) in the 8-10 day period. This is crucial and, simply put, has to happen for the pattern to begin shifting into more of a position to allow sustained cold to enter the equation. We want to reiterate that this, in and of itself, doesn’t create the cold, but instead allows the pattern to begin shifting away from the Nino-like (warm) regime into more of a La Nina pattern, as a whole. – Hey, you have to start somewhere.
If we can finally get the westerlies to slow, other elements are in play that could (and should) lead to a colder pattern as we move forward. Our (3) big teleconnections are in a position favorable for cold for mid/ late November, into early Dec.
Additionally, the EPO is forecast negative off the GEFS and EPS. (Images courtesy of Weatherbell.com).
Again, this is a cold signal. (Image courtesy of Madusweather.com).
The ensemble data is also beginning to key-in on higher heights (blocking) developing over the top. Notice the significant changes in the overall look to the pattern between now and days 11-16. (Images courtesy of Weatherbell.com).
In summary, and in the face of *most* seasonal data that is screaming warm, warm, warm, we still don’t have any significant changes to our overall thinking of “step-down” mid-November giving way to more sustained wintry-like conditions in the overall sense from the Thanksgiving-Christmas period. Time will tell and only the Good Lord knows what the future holds, but we’ve done far too much work and research to throw the “game plan” in the trash before the game even begins…