I couldn’t bring myself to call this post “storm speculation”, but given the timing and the fact that this could be our first real snowfall of the season (remember that December 29th was more of an icing event) I wanted to take a moment to provide you with an update on the Tuesday snow potential, as well as briefly discuss the potential for a larger event this coming weekend.
First things first. How did you like our rainstorm? After an event more reminiscent of October than January, Connecticut is slowly drying out after a record warm day in Hartford and Bridgeport that was also plenty wet. Some locations even experienced thunder and lightning!
With the rain departing and cold air rushing in, expect temperatures to drop near freezing at the shoreline and below freezing in interior Connecticut. With windy conditions and continual drying, I expect the roads to be ok, but anything wet could freeze overnight as temperatures drop. Be careful on the roads tonight and tomorrow morning.
On to Tuesday.
The Setup
The setup for Tuesday is pretty straight forward. A shortwave from Canada will move a surface low (the clipper) across northern New England. As this happens, the low will redevelop over the Gulf of Maine.
First things first. How did you like our rainstorm? After an event more reminiscent of October than January, Connecticut is slowly drying out after a record warm day in Hartford and Bridgeport that was also plenty wet. Some locations even experienced thunder and lightning!
With the rain departing and cold air rushing in, expect temperatures to drop near freezing at the shoreline and below freezing in interior Connecticut. With windy conditions and continual drying, I expect the roads to be ok, but anything wet could freeze overnight as temperatures drop. Be careful on the roads tonight and tomorrow morning.
On to Tuesday.
The Setup
The setup for Tuesday is pretty straight forward. A shortwave from Canada will move a surface low (the clipper) across northern New England. As this happens, the low will redevelop over the Gulf of Maine.
GFS showing the clipper to our north at 1pm on Tuesday
Potential Issues
Because of the track of the clipper to our north and redevelopment well to our east, moisture will be limited. The other potential issue could be temperatures, at least early on. With temperatures likely to be above freezing during the day in advance of the clipper, precipitation could be slow to accumulate or even start as rain, especially near the shoreline, before becoming all snow. With light precipitation expected and temperatures above freezing for a time, this would have the effect of cutting down accumulations. Should temperatures fall faster and/or precipitation be heavier, accumulations would occur more efficiently. Let’s take a look at what some of the latest guidance says.
The Guidance
The first image below shows the GFS at 7pm on Tuesday. Light snow is falling statewide as the temperatures in the air column above the ground are cold enough for snow. You will notice however that in the next image surface temperatures are near freezing. This not only implies more warmth than is ideal for accumulations at the surface, but also that temperatures are above freezing in the preceeding hours, where a fair amount of precipitation is falling.
Potential Issues
Because of the track of the clipper to our north and redevelopment well to our east, moisture will be limited. The other potential issue could be temperatures, at least early on. With temperatures likely to be above freezing during the day in advance of the clipper, precipitation could be slow to accumulate or even start as rain, especially near the shoreline, before becoming all snow. With light precipitation expected and temperatures above freezing for a time, this would have the effect of cutting down accumulations. Should temperatures fall faster and/or precipitation be heavier, accumulations would occur more efficiently. Let’s take a look at what some of the latest guidance says.
The Guidance
The first image below shows the GFS at 7pm on Tuesday. Light snow is falling statewide as the temperatures in the air column above the ground are cold enough for snow. You will notice however that in the next image surface temperatures are near freezing. This not only implies more warmth than is ideal for accumulations at the surface, but also that temperatures are above freezing in the preceeding hours, where a fair amount of precipitation is falling.
The next model, the Canadian, is not one I personally prefer, but in this situation it makes sense to blend more guidance to get a sense of what will happen. The Canadian drops a bit more drops more QPF, and as a result more snow likely falls. This image only shows precip, not the rain/snow output, but note the red line crossing the state--that is the freezing line at the surface.
Here we have the high resolution NAM, which is used to help us resolve some of the mesoscale (small scale) issues like precipitation types and temperature that global models may not see with as much detail. The NAM is warmer and as a result shows more mixing.
Finally, the latest run of the European model (which I cannot post) ticked some of the moisture further west. More in line with the Canadian.
Forecaster Thoughts
At this point, I’m leaning toward a blend of the Euro and GFS, with the Canadian and NAM having a bit less influence. Although guidance generally isn’t showing a lot of precip falling during the time I think we have the best chance of accumulation, I think this is going to be a widespread snowfall and minor accumulation event, with a coating to inch for most of the state, with more 1 inch totals appearing away from the shoreline and isolated 2 inch totals in the northwest and northeast hills where temperatures at the surface could allow for better accumulation earlier.
Between now and the time the snow begins, I will be watching how guidance handles the amount of moisture available and temperatures. An increase in the amount of moisture available and/or a downward trend in temperatures, which sometimes happens with clipper systems, could increase snow totals to a more widespread 1-2 inches. Using my gut, I place the odds of that happening at ~50%
Main Takeaways
Ok, let’s talk about the weekend, and by the weekend I mean Friday 16th through Monday the 18th. I know that there has been a lot of chatter in the weather space about the potential during this period. It has been highlighted by SCW and talked about by many. It’s time for Fact vs. Fiction.
Fact: There is a signal for storminess around this time period.
Yes, the various ensembles have shown the pattern being conducive for significant storminess in the east. This signal is strong, it is consistent, and it has been reflected by many of the operational models.
Fiction: There will definitely be a winter storm this weekend.
Although there is a strong signal, that signal is for storminess, and not necessarily a winter storm. That makes a huge difference in sensible weather. No one knows for sure if there will be a storm, what type it will be, and who will get what. There are a lot of things that need to be resolved in the atmosphere first before we have a better sense.
If you are starting to see snow accumulation forecasts from outlets and other folks, don’t buy the hype. In this chaotic setup, do not get hung up over each GFS or European model run. This can be no better illustrated than the last four runs of the GFS. The images are taken from when a low is closest to our location.
Forecaster Thoughts
At this point, I’m leaning toward a blend of the Euro and GFS, with the Canadian and NAM having a bit less influence. Although guidance generally isn’t showing a lot of precip falling during the time I think we have the best chance of accumulation, I think this is going to be a widespread snowfall and minor accumulation event, with a coating to inch for most of the state, with more 1 inch totals appearing away from the shoreline and isolated 2 inch totals in the northwest and northeast hills where temperatures at the surface could allow for better accumulation earlier.
Between now and the time the snow begins, I will be watching how guidance handles the amount of moisture available and temperatures. An increase in the amount of moisture available and/or a downward trend in temperatures, which sometimes happens with clipper systems, could increase snow totals to a more widespread 1-2 inches. Using my gut, I place the odds of that happening at ~50%
Main Takeaways
- A clipper will bring a period of light snow to Connecticut on Tuesday
- This is likely to be a very minor event, with accumulations of a coating to 1” for most, and isolated 2” totals in the northwest and northeast hills where temperatures could be more conducive for accumulations
- Precipitation should begin Tuesday afternoon between noon and 3pm and last through the evening
- The combination of snow and falling temperatures could have a minor impact on the Tuesday PM commute
Ok, let’s talk about the weekend, and by the weekend I mean Friday 16th through Monday the 18th. I know that there has been a lot of chatter in the weather space about the potential during this period. It has been highlighted by SCW and talked about by many. It’s time for Fact vs. Fiction.
Fact: There is a signal for storminess around this time period.
Yes, the various ensembles have shown the pattern being conducive for significant storminess in the east. This signal is strong, it is consistent, and it has been reflected by many of the operational models.
Fiction: There will definitely be a winter storm this weekend.
Although there is a strong signal, that signal is for storminess, and not necessarily a winter storm. That makes a huge difference in sensible weather. No one knows for sure if there will be a storm, what type it will be, and who will get what. There are a lot of things that need to be resolved in the atmosphere first before we have a better sense.
If you are starting to see snow accumulation forecasts from outlets and other folks, don’t buy the hype. In this chaotic setup, do not get hung up over each GFS or European model run. This can be no better illustrated than the last four runs of the GFS. The images are taken from when a low is closest to our location.
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The 00z, 06z, 12z, 18z GFS runs.
All of these runs have significant differences in timing, low location, precipitation type, and temperature, all of which are impacted by each other and critical to making an accurate forecast—and this is just one model! The Canadian and Euro operational models are all over the place as well!
The bottom line? The models at this range are just saying there’s a signal. It will take time to figure out what happens this weekend.
SCW will be following both Tuesday and this weekend's potential and will keep you updated.
Thank you for reading this long post over minor snowfall and potential. Stay tuned. An interesting week may be ahead.
-DB
All of these runs have significant differences in timing, low location, precipitation type, and temperature, all of which are impacted by each other and critical to making an accurate forecast—and this is just one model! The Canadian and Euro operational models are all over the place as well!
The bottom line? The models at this range are just saying there’s a signal. It will take time to figure out what happens this weekend.
SCW will be following both Tuesday and this weekend's potential and will keep you updated.
Thank you for reading this long post over minor snowfall and potential. Stay tuned. An interesting week may be ahead.
-DB
