Where we stand today
In the midst of a historically warm December, Connecticut avoided a rare December without measurable wintry precipitation through a well timed system earlier this week. Nevertheless, December finished as the warmest on record by a mile, as a persistent pattern allowed for strong ridges and western storm tracks that advected incredible warmth both at the surface and in the atmosphere above.
BDL in December
Average maximum temperature—11.3 degrees above normal
Average minimum temperature—12.1 degrees above normal
Mean temperature—43.3 degrees, a new record for December and 11.7 degrees above normal
Snowfall—1”, and 6.4” below normal.
BDR in December
Average maximum temperature—11.3 degrees above normal
Average minimum temperature—12.3 degrees above normal
Mean temperature—47.2 degrees, a new record for December and 11.8 degrees above normal
Snowfall—.7”, and 4.4” below normal.
As I alluded to in my last two week outlook, any pattern change was likely to be drawn out. We saw this in spectacular fashion in late December, as hopes for a pattern change were crushed with record temperatures on Christmas Eve. Today, the change is occurring, however. Winter is here. It has returned. The question is how wintry do we get and how quickly. This two week period is likely to answer those questions.
Now that January has begun, we’re closing in on peak climo for both cold and snow. We certainly hit it for cold as our average high and low begin to rise by the end of January. For snowfall, it gets a bit trickier. Although January is historically when Connecticut sees the most snow on average, February has shown the propensity to be a big snow producer for the state, even with rising average temperatures. Look no further than the years between 2013 and 2015, where February snowfall far exceeded January snow, and the fact that Bridgeport has a higher record monthly snowfall in February than in January.
Here is what history says about January in Connecticut.
BDL (Bradley Airport)
Jan 1 avg high—36
Jan 1 avg low—20
Jan 31 avg high—36
Jan 31 avg low—21
Jan avg snow—12.3”
Jan record snow—54.3” (2011)
Jan 1 avg high—41
Jan 1 avg low—25
Jan 31 avg high—38
Jan 31 avg low—25
Jan avg snow—7.6”
Jan record snow—26.2” (1965)
Grading the last outlook
In my last two week outlook, it was easy to see that temperatures would continue to torch through the end of the month. I was also confident that we’d see average precip, at least during the first week, and accurately called above average precip in the second half of the outlook—even though it was a low confidence forecast. Forecasting wintry precip is where my hangup is with grading myself this week.
“I think the pattern gets marginally better toward the very end of this period, if for no other reason than climo catching up to give folks something minor. That’s not much to bank on however in a historically warm, and hostile pattern for wintry precipitation. It is becoming increasingly likely in my mind that December does not offer any significant wintry precipitation event.”
That’s what I wrote last time. Had I shut up after the first sentence, I’d earn an A, easily. However, I kept talking, and I really did believe we were more likely than not to see a snowless December. Technically, I guess I was right. We did have one wintry event and that was a very minor one. Moreover, the evidence was in my corner, and if presented with the same options I’d almost have to make the same forecast. However, I need to be penalized for out kicking my coverage, again. All and all, a very good outlook however in my opinion. Overall grade: A-
Week one—Tuesday December 15 to Monday December 21
Temperatures—above average (high confidence) Check
Precipitation—average (high confidence) Check
Wintry Precipitation—nothing significant (high confidence) Check
Week two—Tuesday December 22 to Thursday December 31
Temperatures—above average (high confidence) Check
Precipitation—above average (low confidence) Check
Wintry Precipitation—below normal (moderate confidence) Check -
Two week outlook summary
* Note—high confidence (70% or greater belief of event occurring), moderate confidence (36-69%), low confidence (0-35%); nothing significant (less than 1” snowfall and .25” ice)
Week one—Friday January 1 to Thursday January 7
Temperatures—below average (high confidence)
Precipitation—below average (high confidence)
Wintry Precipitation—below normal (moderate confidence)
This first week of the period has already started warmer than normal, but the first hint of a real change in the air will come in the form of a shot of arctic air that arrives Monday and peaks on Tuesday before moderating by the middle to end of the week. Guidance has continued to hone in on the coldest air of the season by far arriving during this period, with temperatures on Monday and Tuesday staying in the 20s all day with low temperatures in the teens and maybe even single digits. Wind chills could also be brutal, especially on Tuesday.
With regard to precipitation and snow, with high pressure dominating most of the period, it does not look like any significant events, wintry or otherwise, are going to happen. I say this with the caveat that there will be a (low) chance of snow showers and squalls in part of Connecticut the next few days that could produce a quick coating if lucky. For this reason, I went with below normal chances for wintry precipitation instead of saying nothing significant would happen.
Week two—Friday January 8 to Thursday January 14
Temperatures—below average (moderate confidence)
Precipitation—above average (moderate confidence)
Wintry Precipitation—above normal (moderate confidence)
Here’s where things could begin to get fun if you like cold and snow. Despite the pattern change beginning earlier in the month, it will take time for the atmosphere, and thus, your sensible weather, to change. While operational models have jumped around on this period, the ensembles, which again, use individual members with modified initial conditions to account for errors that inherently develop the further out you try to look into the future, have been consistent in bringing the east coast a pattern that screams colder than normal and stormy.
I expect that by the time we reach January 8th, temperatures will have moderated from the arctic blast that comes during the first part of the week, and we may even see temps above normal again, but seasonably cold. With a +PNA, -AO, -EPO, and (maybe) -NAO in place or coming into view, there should be ample troughing in the eastern US to allow for cold and a more active storm track. If there is sufficient timing and blocking in place, areas of low pressure could have what they need to amplify and track in a fashion that allows for wintry precipitation.
I have to say however, that you should temper your expectations. Patterns that look this good on paper may not look as good once we are closer, and patterns that are good still have to produce. Talking about potential is always tough in a business where production matters, but if you like winter weather, you just want to have chances—something we didn’t have in December.
I am currently eying a period between the 8th and 11th, and a period around the middle of the month, as guidance (both operational and ensemble) show a window of opportunity for an more than one amplified area of low pressure somewhere in the east.
To best illustrate the change that is already underway, I think it is best to show things in their starkest form.
Now, let’s look at today…
We talk a lot about the Arctic Oscillation (AO), North Atlantic Oscillation (NAO), and Eastern Pacific Oscillation (EPO), but the Pacific/North American Teleconnection Pattern (PNA) is important too. In addition to El Niño driving a strong a strong Pacific jet that allowed for warm air to flood the eastern US, a negative PNA, which featured below normal heights over the intermountain region of North America and areas further west, allowed for higher heights in the east and a flood of warmth. The inverse is generally true for a positive PNA. Translation: a positive phase of the PNA allows for higher than normal heights and ridging out in the west, and below normal heights and thus more troughing in the east. This serves to cut off warm Pacific air from flooding the east. Generally, you need some sort of Pacific pattern cooperation (PNA or EPO) if you want significant cold and snow in the east.
If you believe the ensembles, the PNA is not the only domino to fall in January. By the second week of the month, we are talking about a wholesale pattern change being in the works. First, let’s clarify what I mean by pattern change. It is a subjective term that will mean different things to different people. For this forecaster, a pattern change is an overall shift that does not merely last a day or two. It could be as short as a week or as long as long can be.
In this range, much more weight is placed on the ensembles, as they have better skill (generally) giving us a clue of the evolution of the medium term pattern. When there is consistency in each run, and agreement between the guidance, it makes it much easier to believe the output. The GEFS and EPS have been in good agreement that the pieces come together to give the eastern US a window of opportunity for cold and wintry precipitation.
Let’s look at another map.
Again, if you like stormy, this is another thing of beauty. You don’t need to look closely to see very strong winds over the east coming from the south, signifying a strong southern jet that can bring a lot of moisture for any storm that develops. If you are looking closely however, you can see that on the west coast, there is an area of split flow—essentially where the southern and northern jets separate in the west and come closer to one another in the east. Our biggest storms occur when the southern and northern jet “phase” together at the right time and location.
I don’t really need to post charts to show how much potential really exists with this pattern, but here they are for good measure.
The bottom line? The pattern is changing, but how much we just don’t know yet. Currently, I believe this will be a significant change. The signals are there for at least a brief period where a cold and wintry pattern becomes the dominant regime in the eastern United States.
Caveat emptor (buyer beware) however. Just because a pattern looks good on paper, doesn’t mean that it will produce. Timing of shortwaves, the interaction of the southern and northern jet branches, and amount of cold air in place both at the surface and aloft when a storm does come along will make a big difference in whether we shovel snow or just potential.
We already have periods of interest on the horizon in the long term. I won’t waste your time posting operational model runs (they are not terribly useful at this range), but there is a potential period of interest between the 9th and 11th, and another period of interest a few days after. What happens with those periods, no one knows, but I think the odds are good that we at least have something to talk about and track the first two weeks of January, and it won’t be record high temperatures.
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