The Pattern Change After the Pattern Change

If you were to look at the 7 day forecast you’d probably fall asleep due to boredom. For weather lovers it doesn’t get much more dreadful than this.

WVIT Forecast 7 Day 2012

Even though this is about as dull as it gets for January there are tons of changes going on across the globe. In fact, the jet stream is about to undergo a really monstrous change between now and 10 days from now. This is an (overly) simplistic way of looking at it.

WVIT_Jet Stream

There’s a whole lot that will go into this pattern change and virtually every signal is banging the drum for a wholesale change of the pattern by January 15th. The odds of a significant Arctic outbreak over a portion of the country are good and the odds of a significant snowstorm in Connecticut during the last 2 weeks of January are better than normal.

– Meteorological Discussion Below –

If you had a box of Crayolas and had to draw medium range weather porn – this is what you’d draw.

18z GEFS Day 11-15 500mb Height Anomalies

18z GEFS Day 11-15 500mb Height Anomalies / Courtesy: Alan Huffman

I mean… does it get more beautiful??? A gorgeous -EPO ridge dislodging the already split PV (see yesterday’s post) and a phenomenal looking ridge bridge from the -NAO region straight across the North Pole over into Canada.

Not surprisingly, the D11-D15 850mb temperature anomalies are approaching -10C over Saskatchewan and Manitoba! The GEFS today aren’t alone. By D15 the Euro Ensembles are equally impressive with a beautiful +EPO/-AO/-NAO combo. This is a FRIGID COLD setup for portions of the lower 48 with some impressive cold not too far from southern New England.

m500z_f360_bg

While it’s too early to get into specifics regarding where the core of the coldest weather will setup I’m excited. Cross-Polar flow will deliver the goods to this side of the globe and the signal for strong ridging over Greenland (-NAO) starts raising the specter of a decent snow pattern for the northeast.

While the stratosphere is doing some good things upstairs near the Arctic Circle, tropical forcing from the MJO is also working its magic. There’s renewed vigor to the somewhat sleepy MJO thanks to a burst in MJO-driven convection near Indonesia.

ECMF_phase_51m_small

The ECMWF Ensemble MJO forecast shows the tropical convection rounding the equatorial Pacific after leaving Indonesia and winding up toward phase 7 by 1/20. Many of the dynamical and statistical MJO forecasts are similar.

These plots, courtesy of Alan Huffman, show the 500mb anomalies that correspond to each MJO phase in January.

Phase 5 / Phase 6 / Phase 7

Notice how mild phases 5 and 6 are for the northeast – and how cold (and stormy) phase 7 can be. While the initial Arctic dump may be to our west in the D11-D15 time range as long as the MJO keeps trucking toward the dateline we shouldn’t have much problem getting into the fun stuff. The change is coming – we just may need to be a bit patient!

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Beginning of Winter Not Looking Wintry

December seemed to have so much potential! Arctic cold had been dislodged from the Arctic, snow cover in North America was well ahead of last year, the Pacific jet stream appeared willing to cooperated. But then everything said “hell no” to winter’s arrival. This is how a friend of mine who’s a meteorologist put it on Twitter.

Screen shot 2012-11-30 at 10.30.31 AM

That was followed by this.

Screen shot 2012-11-30 at 10.31.28 AM

We all know that’s true. While I rarely forecast beyond day 10, at least to the public, medium and long range forecasting is a challenge. Hell, short term forecasting can be quite challenging as well (see the snowstorm from earlier in November!).

The month will start on the cold side. However, a chilly December 1st will quickly transition to torchville by December 2nd.  Through next week the GFS MOS has temperatures solidly above climo.

Screen shot 2012-11-30 at 10.35.17 AM

Hideous. But why so hideous? Here’s a look at the day 1-5 Euro Ensemble 500mb mean heights. It’s a pretty instructive chart for why we’ll be torching.

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The first thing to note is the huge ridge (above normal heights) from the Aleutians through the North Pole and even into the North Atlantic near Iceland. This Bering Sea block has effectively become a ridge bridge traversing the pole and into the North Atlantic. This correlates to a strongly negative Arctic Oscillation (AO) and can be favorable for cold in the eastern U.S.

However, there is one feature overwhelming everything else in the U.S. and that is on the west coast. An exceptionally powerful Pacific jet stream is flooding the country with warm, maritime air. Jet streams form due to a gradient in temperature and you can see that gradient between above normal heights around the 4 corners and well below normal heights with the storm to the northwest of Seattle. This is an UGLY pattern.

The question is, however, where do we go from here? Here is day 6-10 on the Euro ensembles. Same map as above with 500mb height anomalies colored.

Screen shot 2012-11-30 at 10.47.25 AM

Same deal here. Large negative height anomalies over British Columbia and the Pacific Northwest and Bering Strait block remains though it has retrograded a bit toward Russia. This is a somewhat more favorable pattern for us for wintry weather but not really for cold. Here are the 850mb day 10 Euro Ensemble temperature anomalies.

Screen shot 2012-11-30 at 10.50.04 AM

The cold has begun to invade the northern Plains while the warmth hangs on in New England. This is not a terrible pattern for getting some storminess around after a dry stretch. If we can keep the storm around the 10th from being too strong and too far west maybe we can squeeze out some wintry weather? The best chance would be to our north, however. I’m a little worried about the lack of NAO ridging for any storm around the 10th. It could turn into a mild cutter pretty easily.

Past the 10th the models show a period of chill and maybe a wintry event for mid-month. While the pattern isn’t great it’s better than what we’re looking at for the next 10 days. The cold will ooze east from the northern Plains across then northern tier of the U.S. and probably provide a boundary capable of producing some snow.

Will it last through Christmas? I have my doubts. It appears the -AO, that at one point was signaling a really wintry start to December, will get replaced by a +AO. The Bering Strait ridge that helped dislodge the cold appears to retrograde into Kamchatka (it’s like playing Risk with weather features!) and then mainland Siberia by Day 15. In the process it gets eaten away and eventually disappears.

Screen shot 2012-11-30 at 11.06.43 AM

The bottom line is that I do think we’ll see a period between 12/10 and 12/20 with the potential for wintry weather. In addition, I do think we’ll see a period of modest winter chill. The chances for snow aren’t by any means a slam dunk. A shift in storm track to the west could leave winter lovers tying nooses with strands of Christmas lights here in New England.

There are some signs we begin to warm back up by Christmas as the AO switches to positive and the northern Pacific remains rather hostile (low heights in Gulf of Alaska). That said, we’ll have to see if the MJO decides to wake up after a dormant period – that could reshuffle the Pacific and we’ll have to see if the NAO wants to play nice. Either of those could provide a mid to late December surprise.

Special thanks to Alan Huffman’s model site for the ensemble anomaly images. Awesome site… check it out!

Near Record Warmth Overspreads Nation for March

An unbelievably strong signal has been showing up for the last 1-2 weeks of an extremely mild/warm pattern across a large chunk of the Lower 48 next week and into St. Patrick’s Day weekend.

If you want to see a TORCH here it is:

Wow! That’s all you can say about that with an exceptionally warm pattern setting up for most of the central and eastern U.S. This kind of pattern would allow us to make a run at 80 degrees away from the coast.

The long range forecast has been fairly easy over the past couple weeks thanks to good model agreement and a very strong MJO wave that’s dominating tropical forcing. Here’s a look at the last 90 days of the MJO and the Euro forecast.

A brief cool down here in the northeast this weekend as we transition from phase 4 into phase 5 of the MJO (teleconnects to troughing) followed by the screaming sou’westerly torch.

The strong MJO wave/tropical forcing signal makes this a high confidence forecast. Check out the 2M temperature anomalies for given phases as the MJO wave emerges from Indonesia and into the Pacific Ocean.

At least initially our foray into Phase 6 and Phase 7 should allow the southeast ridge/west coast trough couplet to really establish itself.

However, I will caution, by the end of the month if this wave continues to show such incredible staying power we may wind up toward phase 8/1 which corresponds to cooler than normal weather along the east coast. The Euro weekly forecasts also show the big warmth backing off by the end of the month which is something to watch out for.

Either way – enjoy the warmth that’s moving in. Nationwide we may be setting the stage for this March to be one of the warmest on record.

 

Pattern Change Coming Into View

What a change! The atmosphere across the northern hemisphere is going to undergo a major transformation as winter finally appears ready to arrive. The current pattern (which has been remarkably persistent) features low heights over Alaska, the Gulf of Alaska, the Bering Strait, and Kamchatka. This +EPO pattern is essentially flooding the United States with mild Pacific air.

In addition the Arctic Oscillation has been strongly positive since October but is finally falling to near neutral numbers.  You can see the changes over the North Pole over the last 7 days. Here’s a look at 500mb height anomalies from 1/1/12 across the northern hemisphere.

You can see the negative height anomalies over the North Pole and across the Arctic with huge positive height anomalies across the mid latitudes. Here is the composite for Arctic Oscillation phases and you can see how closely the pattern fits the +AO.

Fast forward to 1/7/12 and you can see the huge changes underway in the Arctic. The negative height anomalies over the North Pole are gone and heights are rising thanks to a ridge north of the Caspian Sea across Russia and into the Arctic Ocean.

As we move forward the neutral AO state we have presently will become negative with a huge ridge developing over the Aleutians/Bering Strait by 1/15.

The height rises over the Aleutians is very impressive with a large omega block developing. Winter lovers rejoice! This will effectively dislodge the polar vortex and the cold from the Arctic and send it south.

With little upstream blocking this will not be a prolific snow producing pattern. It will, however, be a chilly pattern and with an active northern stream of the jet stream I expect some snow threats to be around.

The question becomes how long does this pattern change stick around? I’m fairly confident a strong +AO will  not return. One reason for this is a stratospheric warming event that’s ongoing. Temperatures are beginning to warm in the Arctic stratosphere and zonal wind anomalies are beginning to drop and in some cases reverse.

With the Arctic Oscillation on our side I doubt we’ll see a return to the December and early January torch. That said, I’m not sure the Pacific remains favorable for cold. For example the omega block over the Bering strait may retrograde into Kamchatka which will lower heights over Alaska and bring a return to the +EPO.

GFS Ensemble Mean 500mb Height Anomalies Jan 21st 00z

Though this may result in a warmer pattern overall by January 20th without the +AO I doubt it is anywhere near as warm as we’ve been. In addition renewed MJO convection over Indonesia (as forecast by the Euro weeklies) may help skew the pattern warmer over the U.S. by February 1 even with a neutral or negative AO.

Bottom line is that winter weather is coming with seasonable to below normal temperatures and some threats for snow. This won’t be an “epic” stretch of winter weather by any means but I do expect more winter than we’ve seen in since Halloween. What’s to be determined is how the pattern shakes out by the end of the month. Will stratospheric warming lead to a sustained -AO? Will a renewed push of MJO convection teleconnect to a warmer pattern overall? Will we see the +EPO vortex return? We shall see!

No Festivus Miracle – No Sign of Winter

What a dull stretch it’s been! The weather pattern across the northern Hemisphere has returned to where it was in the beginning of December. Low pressure over Alaska and Greenland means an exceptionally warm +EPO/+NAO signal for the northeast.

December so far has been near 6 degrees above normal in greater Hartford and though we’ll shave a bit off that over the next week there’s no question the month has been an unmitigated torch.

Here’s the GFS ensemble mean anomalies for 1/1/12 (the Euro ensemble means are fairly close).

The substantial negative height anomalies over Alaska and Greenland show this pattern isn’t going to get much better for snow lovers. Transient ridging in the +PNA regions (western NOAM) may deliver brief cold shots and keep New England a bit cooler but nothing too cold. I fully expect the next 15 days to average above normal and likely most of January.

To show you how bad the +EPO/+NAO (negative heights over Alaska and Greenland, respectively) here are the sfc T correlations.

Put them both together and that’s a pretty lethal combination for cold. At the same time there doesn’t appear to be a mechanism to dislodge the current pattern. For example the MJO has entered a dormant phase and does not look like tropical forcing will be able to dislodge the Alaskan death vortex.

Torch on!