Tuesday Update

Thought it was time to update a few of the posts in the last several days with some of my latest thinking.

Friday Night/Saturday Morning Storm
The models have backed away from the 12z Euro showing a major “bomb” over New England with impressive CCB snows down to the coast. I’m not surprised as sometimes you can get one run that really shows things exploding then everything backs off. With a deep closed low and plenty of dynamics I still think there will be some wraparound flurries but accumulating snow doesn’t seem terribly likely. Wind will be an issue overnight Friday and I think 50 mph wind gusts are possible in some towns with rapid pressure rises and a strong pressure gradient as the low departs to the northeast.

Pattern Change – Delayed But Not Denied?
The key to this pattern change is what’s going on in the north Pacific and particularly in the Gulf of Alaska. For the last 2 weeks a very strong series of upper level lows has brought brutal cold and storminess to Alaska and has driven a monster jet into British Columbia. Whistler ski area northeast of Vancouver has had their snowiest November ever. This jet stream setup as flooded the continent with warm, Pacific air. No good.

The 12z GFS Ensembles do show this pattern breaking down by day 7 (next Monday or Tuesday) with the trough over Alaska being replaced by ridging which essentially kills the north Pacific jet. The +EPO which has flooded North America with warmth will switch signs and become negative. This teleconnects to big cold in the northern Plains and northern Rockies as it allows the Polar Vortex to swing south east of the continental divide. On the right you can see the surfadce temperature and 500 mb height anomalies with a +EPO pattern. Our pattern the last several weeks resembles this. The models agree on no sustained blocking in the North Atlantic, but a wholesale shift in the Pacific. On the left is a composite for a -EPO/+NAO regime and you can see near normal height anomalies in the northeast and strong negative anomalies in the northern Rockies/northern Plains. What El Nino???????? At least for December 1-7 this is what the GFS ensembles and Euro ensembles seem to indicate so though the pattern has changed I don’t think we’re going to do much better than average in the northeast with the potential for above normal (+1/+2) given an awful storm track through the Great Lakes.

Madden-Julian Oscillation

As I expected the MJO keeps on trucking. Should be entering Phase 6 by Turkey Day and out of the Maritime Continent toward more favorable SSTs over the west Pacific. You can actually see today the MJO index gained quite a bit of amplitude putting to rest to thought that this MJO wave was going to die out. Eventually this wave will reach the Dateline and given high SST anomalies back in the Indian Ocean I have no reason to believe we won’t see another MJO wave develop on this one’s heels.

December 1-7th Call
Given the GFS/Euro ensembles decent agreement in a strong -EPO ridge developing with little sign of north Atlantic blocking I’m reasonably certain that the northern Plains/Rockies will average below average in this time frame. Here in southern New England I’m expecting just above normal temperatures thanks to a storm track that will favor the dreaded Lakes Cutters.
BDL +1.5F
I’ll try and have a month of December call out in the next few days!

The MJO Keeps on Truckin’

The Madden-Julian Oscillation is a weather/climate phenomenon near the Equator which can have big impacts on the weather up here in the Mid Latitudes. The MJO has been linked to strong oceanic Kelvin waves, the onset of an ENSO (El Nino) event, and even the development of tropical cyclones. The MJO is something that can help bridge weather and climate and give us an idea what is happening in the future. For example, the location of an MJO wave can also have an impact on our weather (for example phase 8/1/2 is favorable for cold weather in the northeast this time of year).

The MJO has been active recently with a substantial MJO wave that started near Africa and the western Indian Ocean and is now near New Guinea and Indonesia. In the Outgoing Longwave Radiation image posted to the left you can see strong negative OLR anomalies (which is a proxy for convection) now centered near Indonesia. The big question is whether this MJO wave (which has weakened will continue east toward the International Dateline which would teleconnect to a pattern change in North America.

The graphic on the right shows the progression of the MJO (counter clockwise or easterly) from the African coast, through the Indian Ocean, and now toward Indonesia. The wave which was quite substantial and had a high amplitude has fizzled some (the further from the origin – the higher the amplitude and stronger the wave) but it is trucking along toward Phase 5. I expect this wave will continue toward the Dateline and it’s amplitude should increase a bit as it heads toward more favorable Sea Surface Temperatures.
You can see negative SST temperature anomalies between the north coast of Australia and New Guinea which is likely stifling MJO activity for the time being but as the wave propogates east it will run into more favorable SSTs and should increase in amplitude. If the MJO enters into phase 7/8/1 this should favor an increased chance for cold during the first half of December. This dynamical MJO forecast from the GFS ensembles indicates the MJO weakens quite a bit but they have been showing this for the last week or two and that has yet to happen. My guess is that this wave will continue and we will see a pattern change as the convection teleconnects to a different east pacific/north american wave train.

A White Black Friday?

Quick update here for some of the new data I’m looking at this afternoon. The 12z Euro develops a major storm (sub 980mb in western Maine) by Friday afternoon which is similar to what the models had yesterday but much further east. Some of our other computers had shown a strong storm as I mentioned yesterday but were trending west with it (which would be warmer/wetter). It appears today that the trend last nighta nd today is a sizable one offshore and that makes big snow a possibility in the Adirondacks and Green/White Mountains with some snow a possibility in southern New England.

Here in Connecticut the Euro shows a substantial cold conveyorbelt snow event on Friday (maybe a couple inches) statewide. This seems overdone to me with the storm being overphased and too strong but I feel like Friday night/Saturday morning will be sharply colder, quite windy (50 mph?), with some snow possible. Whether or not we see accumulation remains to be seen. We’ll have to see what the shortwave in question wants to do.

The 12z GFS and GGEM both have some snow in here late Friday or early Saturday. Now that the shortwave is onshore in British Columbia (and not over the data sparse Pacific) the model runs should begin to converge on a solution.

I’ll keep you posted.


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.