Outlook for Thanksgiving

The much heralded “pattern change” is still on track for just after Thanksgiving. I’m still thinking we will see a trend toward cooler and more normal late November weather with some bouts of below normal temperatures during the first week of December. Nothing has really changed in my thinking here.

As for the Wednesday/Thursday time frame we still have some kinks to work out. The 12z GFS develops a major low over southern New England phasing 2 shortwaves as a massive trough/closed low moves toward the coast. The shortwave responsible for the forecasted major cyclogenesis is still hundreds of miles west of Vancouver, Canada so it’s going to take a few more model runs to pin this down.

Backing up a bit, on Wednesday we should have quiet weather in the northeast with no travel issues. Ridging overhead to start the day with a digging trough to the west will mean quiet weather from Maine to the Mid Atlantic. I’m not expecting a lot of sun with warm advection and increasing moisture bringing in plenty of cloudiness. Even with a big cut-off low over the Great Lakes, in terms of high impact weather, there’s not a whole lot to talk about on Wednesday. The only issue I can see in the Lower 48 is a period of snow in the upper midwest (Minneapolis and maybe some light snow near Chicago?). This could cause some minor aviation issues but at this point I don’t think it’s a big deal.

As that big trough rumbles east toward the northeast it looks like we’ll see a storm develop over New England as some upper level energy interacts with some baroclinicity off the east coast and a strong low develops near Long Island. The low will occlude, and move north and northwest toward Quebec and Ontario. The 12z GFS and Euro both say this is will happen and result in a period of rain late Thanksgiving followed by scattered showers and blustery conditions by Friday. With strong cold advection by late Friday temperatures will drop and there could even be some light snow showers on Saturday behind this storm.

As always it’s not that easy as some of our other computer models are not showing much. The 18z GFS is weaker with the low and develops it further north (sparing us from any notable rain) as the shortwaves don’t phase in time. The 12z GGEM also shows a weak (no phase) solution while the 12z UKMet is in the camp on the 12z Euro and 12z GFS.

My thinking right now is a period of rain late Thursday into early Friday morning. Winds shouldn’t be an issue on Thursday but behind the storm on Friday they will pick up and may be quite gusty if some of the strong model solutions come to pass. The strength of this storm should dictate how cold we will become over the Thanksgiving weekend. We’ll see what happens.


Torch Cancel – Looking Cooler By Thanksgiving

Torch! Torch! Torch! The weather pattern since November 8th has been very warm in Connecticut. At Bradley Airport (BDL), where official records are kept, the average temperature this month has been 46.8º or 3.2º above normal. Since November 8th the temperature has averaged nearly 6.6º above normal. The biggest reason for this has been a strong Pacific Jet Stream that has flooded the continent with warm air. On the right you can see how the atmosphere looks at 500 mb. The orange/red shades are unusually high heights (higher heights means a warmer airmass) with the blue/purple shades meaning unusually low heights or a cold airmass. A strong pacific jet is an example of a +EPO (Eastern Pacific Oscillation). There are some indications that this will break down in the next week or so which will have major implications on our weather.

On the left is a look at 1, 4, 7, 10, and 13 day forecasts of the EPO since July 25th. The current (and forecast) times are on the right with July 25th on your left. Notice how high on the bar graph the EPO readings have been lately. The bottom graph extends 13 days into the future (first week of December) and shows that the +EPO becomes a -EPO which will reverse the current pattern.

Instead of cold weather over Alaska, British Columbia, and the Pacific Northwest warm weather will be found there with colder weather east of the Rockies.

Another way to look at how the pattern will change is to look at an 8-10 day forecast from 2 of our computer models the GFS and ECMWF. Both computer models really change the Pacific weather pattern quite a bit. Instead of the low heights (blues) over Alaska and the Gulf of Alaska they’re shifted west toward the Aleutians or even eastern Russia. This has a huge difference in our weather and as you can see the high heights in the east have been replaced by low heights (colder weather). Obviously there are some differences in the details (it is 8-10 days out, afterall!) but there is general agreement that the warm weather of the last 2 weeks is going to be leaving and a more seasonal weather pattern is on the way.

So how cold are we talking here? Well, not that cold! For several reasons I’m not expecting a surge of true Arctic air to move toward southern New England. For one there is a tremendous lack of snow cover across Canada which will modify a colder airmass that tries to move south. The other issue here is that even the model on the right (the GFS) which is a colder than average pattern the real cold from the North Pole appears to want to head toward western Europe (UK, France, etc) and not down toward the east coast. Given how warm Canada is currently and the lack of a solid snow pack even up to southern Hudson Bay I have a feeling it’s going to be hard to get truly Arctic air to Connecticut.

Either way the pattern is changing. The Pacific has gone from torch to freezer and that is definitely a good thing for winter lovers. If I had to guess right now I say the first week of December (December 1st-7th) Averages -1ºF (or 1 degree below normal) at BDL.


Surging Nino? What’s it Mean?

Here’s my attempt at a blog. Hopefully it doesn’t end up on failblog. I’m going to try and keep it updated as much as possible about different kinds of things – from weather to life to work (but mainly weather).

What better way to kick it off then a post about meteorology! When most people think about El Nino they think about a mild winter in Connecticut and strong storms pounding California (remember the video of houses falling into the Pacific about 10 years ago). That perception is only partially true.
El Nino is an area of warm water near the Equator generally between the International Dateline and South America. Here’s an animation that stretches over a year. Watch the water near the Equator and notice how the colors go from blue (below normal water temperatures – La Nino) to red (above normal temperatures – El Nino). The reds are getting more and more prominent and El Nino is now solidly “moderate”.
El Nino media hype reached a peak in ’97-’98 when we saw one of the strongest El Ninos ever recorded. It was so strong it flooded almost all of North America with mild Pacific air and absolutely pounded California with a never ending parade of storms. That Nino wasn’t typical. Most El Ninos are actually cold and snowy here in southern New England but the strongest of Ninos tend to be mild. The big question now is where does this Nino go?
A bunch of moored buoys in the Pacific measure water
temperatures at the surface and below the surface allowing us to get a look at the structure of a Nino or Nina. Specifically, we can look at daily measured temperature anomalies across the pacific. 180 is the international Dateline and 100 degrees is near the coast of South America. The red shading shows temperatures that are above normal… in some cases nearly 10 degrees above normal about 100 meters below the surface! That’s a massive warm bubble of water that eventually will probably warm the surface some. So for now it looks like this El Nino is still going to intensify (especially in the eastern Pacific) as opposed to the central Pacific. Computer models also show an intensifying Nino through the next few weeks or month and I see no reason to disagree based on the impressive subsurface warmth (that’s heading east toward South America)
The strength of El Nino is key for our winter. A strong El Nino (which almost always spikes in the east Pacific) really argues for a warmer than normal winter. A moderate, and especially a weak, El Nino would keep us colder than normal particularly the second half of the winter. You can see this by taking a look at 2 different Ninos I posted. 2002-2003 was a weak/moderate Nino and a very cold and snowy one in the eastern US. 1997-1998 was a very strong El Nino (actually record-breaking) and resulted in all out blow torch across the northern US and virtually no snow in southern New England. For winter lovers it was a disaster. Fail.
So where is this Nino going? I don’t think it’s done strengthening yet but I do think it will slow down. With the impressive warmth below the surface this thing ain’t done. It should peak in the next month or so and then slowly begin to weaken as waters cool in the Equatorial Pacific. What does it mean for our winter? Right now it’s strong enough that I am not comfortable in forecasting below normal temperatures but I do think it will be a snowy winter!