Pattern Change

A fascinating pattern change is upon us and we’re going to see a fairly abrupt change in our weather. We can actually trace it all back to a weak system that brought us a bit of rain the weekend after Christmas. Remember that storm? You probably don’t since it was a pretty easy to forget!

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Courtesy: Kyle Griffin / UAlbany

That innocuous storm in New England developed into a monster storm over Iceland with a pressure around 930mb prior to New Years. You can see in the surface map above the sprawling storm retrograded into Iceland and took up a large chunk of the North Atlantic. This system was so powerful it effectively managed to shake up the atmosphere over the Arctic. A large cyclonic wavebreak occurred sending low potential vorticity air north toward the North Pole – substantially increasing the height of the Dynamic Tropopause over the Pole.

Courtesy: Kyle Griffin / UAlbany

Courtesy: Kyle Griffin / UAlbany

This wave break and associated ridging has shattered the positive Arctic Oscillation pattern that had been so dominant in December. This graph of the AO courtesy of Ryan Maue at WeatherBell shows the dramatic shift from a positive to a negative AO regime.

Courtesy: Ryan Maue / WeatherBell

Courtesy: Ryan Maue / WeatherBell

Ridging over the Arctic (-AO) is expected to continue through the next 10-15 days which should give us several bouts of below normal chill and with some luck a snowstorm. You can see that ridging here by day 10 on the Euro Ensembles with a mean trough over the northeastern U.S.

Courtesy: Ryan Maue / WeatherBell

Courtesy: Ryan Maue / WeatherBell

Getting a snowstorm around here takes a bit of luck – though the pattern does support a wintry period. Our first shot comes this weekend and early next week though at this point I’m not overly excited with our first opportunity in the Saturday-Monday time frame.

Here’s a look at the Monday system on the European ensemble and you can see a strong signal for a northeastern U.S. coastal low but the lack of any appreciable high pressure/confluence to the north. Outside of the elevated interior a nice cold and dry high is always an important ingredient. mthk_f180_bg_US

Whether or not the storm threat in the 1/9-1/11 window pans out with a snowy solution the pattern looks good for winter weather going forward – through at least 1/20.

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Cold Shot on the Way

Forecast 7 Day Temp Trend Hartford

The cold shot on Monday and Tuesday is still on track. Your furnace will get a work out and local ski areas will blow an incredible amount of white gold. Today’s GFS MOS has pretty impressive chill by Tuesday morning with a minimum temperature at BDL of 5F on Tuesday!

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So yeah – cold stuff early next week.

What weather weenies like me care about is what happens around 1/10 and beyond when the weather pattern becomes more favorable for some snow. Hell, after the last 2 months just seeing some cold air in Canada is enough to get us excited!

The first chance for something comes in on Saturday or Sunday. There are a number of possibilities here – with the possibility of a warmer system (rainy) being most likely at this early juncture.

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Snow lovers don’t despair yet – there’s a ton of model spread and uncertainty here. Some of the GEFS members (shown above) have a storm cutting way west – which would be warm – and some have a storm getting shunted south with cold high pressure building in. Stay tuned on this one – can’t rule anything out now. The Euro ensemble members also show a tremendous amount of spread ranging from a rain storm Friday night to a nor’easter/snowstorm on Sunday night.

Now – the most epic possible solution is what the 00z GFS is showing for Saturday and Monday with a lighter event on Saturday and a major nor’easter/blizzard on Monday. While the odds of this verifying is exceptionally low it is one possible scenario here. The pattern supports something interesting – getting something to actually occur always takes a bit of luck.

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I doubt we’ll have much clarity here until Monday and the pattern is able to shake out a bit better. One thing I remain confident in is a second shot of colder air after next weekend as the Arctic Oscillation flips negative and an area of large ridging extends up into Alaska. This chart shows the temperature forecast for the Euro Ensemble members at 850mb – well below climatology for a chunk of the extended range.

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Winter’s Here

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For at least 2 days we’ll get a taste of winter next week. I’m expecting temperatures in the 20s both Monday and Tuesday as a sharp dip in the jet stream brings chilly air into New England.

It’s what follows, however, that has me really interested. On December 29th I posted about the long term forecast appearing favorable for some “fun” winter weather near or after 1/10. Now we’re seeing the first signs of some possible storminess in a pattern that looks ripe for New England winter storms.

Let’s start with where we stand in the long range.

ECMWF Ensemble (WMO Essential) / WeatherBell

This pattern setting up around 1/10 looks quite favorable for winter weather in New England. Ridging over western North America sets up a +PNA/-EPO look and that ridging extends across the North Pole (-AO). A cross polar flow and even ridging around Greenland acts as a -NAO. For snow lovers this is good!

It appears we’ll have 2 possible systems to track. The first system is coming into view late Friday or Saturday. The GEFS show several possibilities ranging from snow storm to rain storm to miss. All options are on the table here but at least there’s the possibility of something interesting.

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Regardless of what happens Friday/Saturday there’s another opportunity for snow by Monday with colder air nearby. The Euro Ensemble mean shows some storminess lurking off the coast. With plenty of cold and high latitude blocking this is intriguing.

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The pattern going forward looks pretty exciting for snow lovers. Periods of seasonable cold along with a pattern that should support at least one if not several snow chances. Skiers – be patient – it looks like the goods are coming.

The Epic Torch of December 2015

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For people who love winter this December has been a disaster. If there’s any silver lining for someone like me it’s that we’re going to absolutely obliterate the record for warmest December since 1905. Smashing records is fun – though I’d rather be skiing.

So what the hell caused this torch?

We can start with El Nino. A near record Nino has baked the waters of the Equatorial Pacific. As is typical, warm waters fueled powerful thunderstorms near the Equator south of Hawaii (see red shading below).

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The latent heat release and outflow from these storms, in turn, helped a powerful jet stream to develop across the Pacific Ocean. You can see that here on the zonal wind anomalies for December.

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This active jet stream helped bring milder/maritime air across the lower 48 but the nail in December’s coffin was the giant -PNA trough over the western half of the country. Notice the negative 500 mb height anomalies over the west coast (-PNA) as well as the gradient of above normal heights north of Hawaii and below normal heights over the Aleutians/Bering Sea forcing the abnormally strong Pacific jet.

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An active storm track to our west and a remarkably persistent -PNA pattern flooded the eastern half of the country with the epic torch. Breaking a monthly record by a degree or two is impressive but by 5 degrees? Basically unheard of!

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So where do we stand going forward?

A disturbance in the force (sorry for the lame Star Wars reference) will at least temporarily shake up the pattern. See yesterday’s blog post here. I’m worried, however, any change in the pattern is temporary as the stratospheric polar vortex will remain in place and the background El Nino forcing will stay the same.

Either way at least for now the torch is gone and we have a really sweet looking pattern for snow developing around 1/10. Let’s hope we cash in before the Heat Miser comes knocking on our door.

Real Winter Weather on the Horizon

As we wind down the warmest December on record (by a large and impressive margin) our computer models are now showing an exceptional pattern change that should have cold and snow lovers jumping with joy.

It appears that one of the catalysts for this change is a giant and anomalous block that forms over the Kara Sea. This area north of Siberia in the Arctic Ocean will be ground zero for a pretty big change in the atmospheric circulation.

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This super-block effectively disrupts the tropospheric Polar Vortex over the North Pole resulting in a rapid warming and a switch in the all important Arctic oscillation from positive to negative. You can see that dramatic switch in this Arctic Oscillation plot from Ryan Maue at WeatherBell.

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This is a very impressive signal on an ensemble mean in the 10-15 day range! The flip in the Arctic Oscillation will allow cold to come south and should really kickstart winter. The 500mb anomalies forecast by the GEFS (the Euro Ensembles agree to a large extent) are very tasty with a classic looking northeast cold/snow pattern developing later in January – especially near or after 1/10.

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So how long will the pattern remain “good” for snow? Who knows – but at least there’s a nice looking window for some fun!