Good morning to you from Southern Connecticut Weather!
Where we stand today
This is the second of our two week outlook feature, and before diving in, I want to take a step back and look at the month that’s been. It has been a scorcher, with warm and dry conditions dominating the state and no significant wintry precipitation for anyone.
Where we stand today
This is the second of our two week outlook feature, and before diving in, I want to take a step back and look at the month that’s been. It has been a scorcher, with warm and dry conditions dominating the state and no significant wintry precipitation for anyone.
Above, you see a region wide “torch” that has been the result of a very persistent warm pattern that dates all the way back to November.
At Hartford’s reporting station (BDL—Bradley Airport), the temperature departure is +8.3 degrees through December 13th. Every day but December 1st has been above normal. Precipitation through this same period is .99” below normal.
At Bridgeport’s reporting station (BDR—Sikorsky Airport), the temperature departure is +8.6 degrees through December 13th. Every day has been above normal. Precipitation through this same period is .70” below normal.
By this time of the month, the average high temperatures in Connecticut range from the upper 30s in the hill towns to low 40s elsewhere. With days of double digit positive departures, days where the low temperature was higher than the average maximum temperature, and occasional maximum temperatures that are between 15 and 20+ degrees above normal, it is no wonder that many places in the eastern third of the US are on pace to match or exceed their current warmest December records.
Grading the last outlook
In doing my first two week outlook, I was concerned that I would end up missing something significant. Fortunately, I was pleased in my accuracy. I fell short in terms of predicting precipitation, as the rain events that looked possible at the time all floundered and failed, but I hit the parts that mattered. As we will see below, I also missed on my speculation of the pattern after two weeks. Chalk that up to a rookie out kicking his coverage. Overall grade: B
Week one—Tuesday December 1 to Monday December 7
Temperatures—near to slightly above average (high confidence) Check
Precipitation—above average (high confidence) Wrong
Wintry Precipitation—nothing significant (high confidence) Check
Week two—Tuesday December 8 to Monday December 14
Temperatures—above average (high confidence) Check
Precipitation—average (moderate confidence) Wrong
Wintry Precipitation—nothing significant (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—Tuesday December 15 to Monday December 21
Temperatures—above average (high confidence)
Precipitation—average (high confidence)
Wintry Precipitation—nothing significant (high confidence)
The start of this week brought a brief period of rain, and the latter half of the week brings the possibility of more substantial rain as a strong cold front pushes through and a wave of low pressure rides along the front. Guidance is still trying to resolve how strong the low is, but they have come around to something forming. To me, the pattern this month has shown rain makers to be less than impressive come game time. Maybe this one is different, but either way we should be on our way to an average week in terms of precipitation. Once the front clears, we will see a brief cool down with temps near or slightly below our average. It will feel like December...for a day or two. Perhaps we see a few snow showers around this weekend, but nothing significant is expected and we begin warming up next week. Despite the cool down, we’re almost certainly above average this period.
At Bridgeport’s reporting station (BDR—Sikorsky Airport), the temperature departure is +8.6 degrees through December 13th. Every day has been above normal. Precipitation through this same period is .70” below normal.
By this time of the month, the average high temperatures in Connecticut range from the upper 30s in the hill towns to low 40s elsewhere. With days of double digit positive departures, days where the low temperature was higher than the average maximum temperature, and occasional maximum temperatures that are between 15 and 20+ degrees above normal, it is no wonder that many places in the eastern third of the US are on pace to match or exceed their current warmest December records.
Grading the last outlook
In doing my first two week outlook, I was concerned that I would end up missing something significant. Fortunately, I was pleased in my accuracy. I fell short in terms of predicting precipitation, as the rain events that looked possible at the time all floundered and failed, but I hit the parts that mattered. As we will see below, I also missed on my speculation of the pattern after two weeks. Chalk that up to a rookie out kicking his coverage. Overall grade: B
Week one—Tuesday December 1 to Monday December 7
Temperatures—near to slightly above average (high confidence) Check
Precipitation—above average (high confidence) Wrong
Wintry Precipitation—nothing significant (high confidence) Check
Week two—Tuesday December 8 to Monday December 14
Temperatures—above average (high confidence) Check
Precipitation—average (moderate confidence) Wrong
Wintry Precipitation—nothing significant (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—Tuesday December 15 to Monday December 21
Temperatures—above average (high confidence)
Precipitation—average (high confidence)
Wintry Precipitation—nothing significant (high confidence)
The start of this week brought a brief period of rain, and the latter half of the week brings the possibility of more substantial rain as a strong cold front pushes through and a wave of low pressure rides along the front. Guidance is still trying to resolve how strong the low is, but they have come around to something forming. To me, the pattern this month has shown rain makers to be less than impressive come game time. Maybe this one is different, but either way we should be on our way to an average week in terms of precipitation. Once the front clears, we will see a brief cool down with temps near or slightly below our average. It will feel like December...for a day or two. Perhaps we see a few snow showers around this weekend, but nothing significant is expected and we begin warming up next week. Despite the cool down, we’re almost certainly above average this period.
The latest GFS model shows a fair amount of rain this week.
Using a five day average, we see from the GFS ensembles a warmer than normal period likely through the 19th.
Week two—Tuesday December 22 to Thursday December 31
Temperatures—above average (high confidence)
Precipitation—above average (low confidence)
Wintry Precipitation—below normal (moderate confidence)
I have the highest confidence in my temperature projections. If anything, this coming period could be even more impressive than the current stretch we are in, even if we do not reach the same high temperatures. This is because it is historically harder to maintain these kind of departures at this time of the year. We are likely to stay above normal, perhaps well above normal, throughout the forecast period. The precipitation pattern looks to be more active than we have seen thus far, as a couple of cutters and areas of low pressure make their way through the center of the country and our region to bring us some rain. The chance of wintry precipitation is below normal, but not nonexistent. A well placed area of low pressure and well timed cold air in the region could open the door to a minor event or two, but this looks like a very low likelihood at this time.
Week two—Tuesday December 22 to Thursday December 31
Temperatures—above average (high confidence)
Precipitation—above average (low confidence)
Wintry Precipitation—below normal (moderate confidence)
I have the highest confidence in my temperature projections. If anything, this coming period could be even more impressive than the current stretch we are in, even if we do not reach the same high temperatures. This is because it is historically harder to maintain these kind of departures at this time of the year. We are likely to stay above normal, perhaps well above normal, throughout the forecast period. The precipitation pattern looks to be more active than we have seen thus far, as a couple of cutters and areas of low pressure make their way through the center of the country and our region to bring us some rain. The chance of wintry precipitation is below normal, but not nonexistent. A well placed area of low pressure and well timed cold air in the region could open the door to a minor event or two, but this looks like a very low likelihood at this time.
Incredibly impressive departures and near unanimous agreement in the guidance and the overall pattern make this a high confidence forecast.
Technical Discussion
Week one
Technical Discussion
Week one
 The GFS ensemble projection of the North Atlantic Oscillation, projecting a sharp rise in the index and a continued positive state. |  The GFS ensemble projection of the Arctic Oscillation. It also projects a very sharp rise in the index until it begins to drop (possibly) at the end of the month. |
Let’s recap a bit. Remember that when looking in the longer range, using the ensembles—the GEFS and EPS (Euro ensembles) are particularly useful because they are run with individual members attempting to account for inherent forecasting errors in time by slightly changing initial conditions within each individual member. When there is consistency in each run, and agreement between the guidance, it makes it much easier to believe the output.
What do the two charts above show? That warm weather with mild storms are likely to continue for the foreseeable future. the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) both look to be strongly positive. For those reading for the first time, the AO is an index measuring pressure anomalies in the Arctic, and is correlated with temps for our area for the winter months. A +AO suggests above normal temps, and a -AO below normal temperatures. The NAO is a close relative of the AO, and it measures roughly the same thing in the North Atlantic. The NAO has a correlation with blocking in the atmosphere for storms; -NAO usually implies more blocking is available, +NAO represents a pattern with less room for storms to amplify.
A negative AO when negative usually means that the polar jet stream is weaker and more easily disturbed, which can allow cold air to filter south. The NAO when negative usually means blocking over Greenland, which historically has been present for some of our larger winter storms.
Even though warmer than normal temperatures will dominate this period, there will be a period of seasonable weather. By Thursday, a cold front will be approaching as a trough pushes eastward. We haven’t seen many real opportunities to be seasonably cold recently, so when the colder air does arrive by the weekend it will come as a shock to some. Snow showers in the wake of the front and area of low pressure are possible (especially in areas north and west) but unlikely.
What do the two charts above show? That warm weather with mild storms are likely to continue for the foreseeable future. the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) both look to be strongly positive. For those reading for the first time, the AO is an index measuring pressure anomalies in the Arctic, and is correlated with temps for our area for the winter months. A +AO suggests above normal temps, and a -AO below normal temperatures. The NAO is a close relative of the AO, and it measures roughly the same thing in the North Atlantic. The NAO has a correlation with blocking in the atmosphere for storms; -NAO usually implies more blocking is available, +NAO represents a pattern with less room for storms to amplify.
A negative AO when negative usually means that the polar jet stream is weaker and more easily disturbed, which can allow cold air to filter south. The NAO when negative usually means blocking over Greenland, which historically has been present for some of our larger winter storms.
Even though warmer than normal temperatures will dominate this period, there will be a period of seasonable weather. By Thursday, a cold front will be approaching as a trough pushes eastward. We haven’t seen many real opportunities to be seasonably cold recently, so when the colder air does arrive by the weekend it will come as a shock to some. Snow showers in the wake of the front and area of low pressure are possible (especially in areas north and west) but unlikely.
GFS 500mb heights map for early Saturday. Notice the ridging in the west (black lines bend upward) and the trough in the east. This suggests colder weather on tap.
GFS 850mb temperature map for the same time period. This map shows temperatures at about 5,000 feet. With a trough in the east, temperatures above are cool enough to give us a chance at a brief cold shot.
Week two
Week two
The GFS Ensemble mean, averaging out the various members that make up the model, projecting temperatures out in time. Images courtesy of Weatherbell.
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.
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.
If you like cold and snow, this is about as bad a pattern as it gets for a wintry feel for Christmas. On this map you can see a couple of features that add up to a very warm Christmas in the east. You see ridging in the southeast, higher heights to our north, and a deep trough that extends from the southwest US all the way to Alaska. That looks like a track for both warm weather and warm storms that cut to the west should they form. That is just what all of the models that matter are showing in the long range for the period around the holiday.
By the time we reach the end of the month, maybe the pattern looks marginally better, but it still isn’t one that is all that conducive real seasonable weather. We could see much more in terms of activity and precipitation, but unless we see something well timed, we are staring at a historically warm December with no significant widespread winter weather events in Connecticut.
In my last outlook, I said that there were hints that the regime could break down a bit during the last half of the month. While most sensible forecasters expected an above normal December (as a number of El Nino events have) I don’t think anyone saw the persistence and intensity of this current pattern. I do not see a significant breakdown of the pattern in this latter half of the month, and the pattern may continue into January. For those that enjoy the warmth—enjoy it and all the real positives that come with it—lower heating bills for one. For those that want winter to arrive, only time will tell when the pattern truly shifts. I think the transition to winter will be a long and potentially grueling process that may not take shape for a while.
As always, don’t forget to like us on Facebook and share our discussions, and follow us on Twitter @southernctwx and retweet our posts! I encourage you to provide feedback so I know what I can do better.
Thanks for reading SCW.
-DB
In my last outlook, I said that there were hints that the regime could break down a bit during the last half of the month. While most sensible forecasters expected an above normal December (as a number of El Nino events have) I don’t think anyone saw the persistence and intensity of this current pattern. I do not see a significant breakdown of the pattern in this latter half of the month, and the pattern may continue into January. For those that enjoy the warmth—enjoy it and all the real positives that come with it—lower heating bills for one. For those that want winter to arrive, only time will tell when the pattern truly shifts. I think the transition to winter will be a long and potentially grueling process that may not take shape for a while.
As always, don’t forget to like us on Facebook and share our discussions, and follow us on Twitter @southernctwx and retweet our posts! I encourage you to provide feedback so I know what I can do better.
Thanks for reading SCW.
-DB
