A very active and stormy weather pattern is setting up this week. We have several events to deal with- first, a snow threat Thursday, snow squalls Friday, snow showers for NY EVE Night, and then maybe ice Monday? A map is being issued for the upcoming Thursday threat. After coordination with TW and DB... more details below.
Currently: The cold front has now cleared the entire state. A secondary push of cold air, which will set the stage for a winter storm threat, is over Central Ontario and Quebec, will move through tomorrow. Just a wind shift is associated with this cold front, so its passage should be dry.
Tonight: Cooler air begins to seap in, and temperatures won't be so warm as they've been. Look for low temperatures within a few degrees of 30.
Tomorrow: Generally sunny, with highs 40 to 45. Quiet and nice day for the time of year. Clouds increase tomorrow night ahead of the storm, with lows generally from the low 20s to low 30s. I think clouds will increase late enough to allow for radiational cooling.
Now for the storm potential for Thursday:
The various model solutions are as follows. The ECMWF suite, which includes the UKMET, very aggressively develops a strong low pressure system way down by the VA Capes and explodes it near the coast. This would almost always favor significant snow for most, if not all, of the area. However, most other models, including the newest NAM, GFS, and GGEM models show the low develop much further north and weaker. This would result in less precipitation and less cold air.
Years ago, I would have been inclined to just ride the ECMWF and wait for other models to come to it. However, the ECMWF's performance has struggled lately, while the GFS has gotten much better.
There isn't a lot of cold air available at the surface. If there were more, it would be a question of more snow vs. less snow. However, with a VERY marginal surface air mass, we would need very heavy precipitaiton to pull down colder air from aloft and cool the column- a process known as evaporational cooling.
Because of the lack of cold air available, if any "fluke" heavy bands of snow set up, one area could get signifcantly more snow than another, even if it's an area that shouldn't be "snowier". If a band like that sets up, there's often another area that gets much less precipitation near the heavy band. That area would then receive much less snow as a result. It is impossible to speculate where such bands will or will not be. Therefore, this forecast is of much lower confidence than normal.
Here's a look at our first call snow map for this event
Currently: The cold front has now cleared the entire state. A secondary push of cold air, which will set the stage for a winter storm threat, is over Central Ontario and Quebec, will move through tomorrow. Just a wind shift is associated with this cold front, so its passage should be dry.
Tonight: Cooler air begins to seap in, and temperatures won't be so warm as they've been. Look for low temperatures within a few degrees of 30.
Tomorrow: Generally sunny, with highs 40 to 45. Quiet and nice day for the time of year. Clouds increase tomorrow night ahead of the storm, with lows generally from the low 20s to low 30s. I think clouds will increase late enough to allow for radiational cooling.
Now for the storm potential for Thursday:
The various model solutions are as follows. The ECMWF suite, which includes the UKMET, very aggressively develops a strong low pressure system way down by the VA Capes and explodes it near the coast. This would almost always favor significant snow for most, if not all, of the area. However, most other models, including the newest NAM, GFS, and GGEM models show the low develop much further north and weaker. This would result in less precipitation and less cold air.
Years ago, I would have been inclined to just ride the ECMWF and wait for other models to come to it. However, the ECMWF's performance has struggled lately, while the GFS has gotten much better.
There isn't a lot of cold air available at the surface. If there were more, it would be a question of more snow vs. less snow. However, with a VERY marginal surface air mass, we would need very heavy precipitaiton to pull down colder air from aloft and cool the column- a process known as evaporational cooling.
Because of the lack of cold air available, if any "fluke" heavy bands of snow set up, one area could get signifcantly more snow than another, even if it's an area that shouldn't be "snowier". If a band like that sets up, there's often another area that gets much less precipitation near the heavy band. That area would then receive much less snow as a result. It is impossible to speculate where such bands will or will not be. Therefore, this forecast is of much lower confidence than normal.
Here's a look at our first call snow map for this event
We're expecting little if any, snow accumulations along the south coast, 1-3" in the central portion of the state, and 4-6" in the northern part of the state. For now, it looks like the Windham hills will be the big winner, as they'll have both elevation and be further east and closer to the storm. 6-8" could fall in those areas. Of course, as always, this is subject to change up until the storm, and we'll have a final call map out tomorrow evening. Some areas could see large "parachute" snow flakes falling, but not really accumulating, if the surface is in the mid 30s and the upper levels are cooler. For now, I'll call for highs mostly in the upper 30s on Thursday.
As far as the timing goes, I expect snow to move into the state on Thursday morning before mixing with and changing to rain from south to north across the state. Rain may flash back to snow across the state later in the evening as colder air works in from the deepening system. Best chance for that is in the NE hills, contributing to the higher snow totals there.
After a cold frontal passage, as a secondary cold front approaches Friday, aided by lake effect streamers, a band of snow squalls could move through during the afternoon. As is always the case with snow squalls, accumulations would be limited to areas that get heavier squalls. The Litchifeld hills would be the favored areas, but any area could get a rogue squall. High temperatures on Friday should again be in the upper 30s.
An Alberta Clipper system will pass to the north New Year's Eve. A band of snow showers will accompnay this feature. Minor accumulations may accompany this feature, since it will be passing through at night. Look for highs on Saturday to also be in the upper 30s.
New Year's Day should feature fair weather and warmer temperatures in the mid 40s. Then on Monday, a new system will track to our west and spread overrunning moisture ahead of it. Models tend to underestimate low level cold air at this range, and there is a very strong high pressure system over New Brunswick province. This is a recipe for light freezing rain or freezing drizzle and a potentially very treacherous day. Fortunately, it is a federal holiday and many do not have work. Monday's highs should be in the upper 30s, but those highs may occur very late at night.
Beyond that, as the storm tracks to our west, much warmer air will move in for Tuesday, with high temperatures getting into the mid 40s. After that storm pulls out, the pattern will gradually realign and a large ridge over Alaska will help transport more cold air into the region. In fact, the overall pattern could be quite interesting, as the Southeast Ridge will still be present, which could set up a battleground and create a rather stormy pattern for our area.
Now, let's take a look at some of our weather in graphical format. First, let's look at something different. These are analog composite snowfalls for storms that had similar upper air patterns leading up to the Thursday system. This doesn't mean it will happen exactly this way, but it looks fairly similar in distribution to our map and is a good check tool to use to see if your forecast makes sense.
As far as the timing goes, I expect snow to move into the state on Thursday morning before mixing with and changing to rain from south to north across the state. Rain may flash back to snow across the state later in the evening as colder air works in from the deepening system. Best chance for that is in the NE hills, contributing to the higher snow totals there.
After a cold frontal passage, as a secondary cold front approaches Friday, aided by lake effect streamers, a band of snow squalls could move through during the afternoon. As is always the case with snow squalls, accumulations would be limited to areas that get heavier squalls. The Litchifeld hills would be the favored areas, but any area could get a rogue squall. High temperatures on Friday should again be in the upper 30s.
An Alberta Clipper system will pass to the north New Year's Eve. A band of snow showers will accompnay this feature. Minor accumulations may accompany this feature, since it will be passing through at night. Look for highs on Saturday to also be in the upper 30s.
New Year's Day should feature fair weather and warmer temperatures in the mid 40s. Then on Monday, a new system will track to our west and spread overrunning moisture ahead of it. Models tend to underestimate low level cold air at this range, and there is a very strong high pressure system over New Brunswick province. This is a recipe for light freezing rain or freezing drizzle and a potentially very treacherous day. Fortunately, it is a federal holiday and many do not have work. Monday's highs should be in the upper 30s, but those highs may occur very late at night.
Beyond that, as the storm tracks to our west, much warmer air will move in for Tuesday, with high temperatures getting into the mid 40s. After that storm pulls out, the pattern will gradually realign and a large ridge over Alaska will help transport more cold air into the region. In fact, the overall pattern could be quite interesting, as the Southeast Ridge will still be present, which could set up a battleground and create a rather stormy pattern for our area.
Now, let's take a look at some of our weather in graphical format. First, let's look at something different. These are analog composite snowfalls for storms that had similar upper air patterns leading up to the Thursday system. This doesn't mean it will happen exactly this way, but it looks fairly similar in distribution to our map and is a good check tool to use to see if your forecast makes sense.
You can see the accumulation distribution, ranging from 1-2" along the south coast, to 6-8" in the far north- not all that different from our map!
Finally, let's look at the setup for Monday.
Finally, let's look at the setup for Monday.
You can see the high pressure near Caribou, Maine, holding in cold air. In fact, that new high out near Manitoba may suppress the other low further south, so as to keep Tuesday colder! We'll see, as that's a long way out and not included in our discussion yet!
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-GP!
Please like us on Facebook, retweet our map/disco on Twitter @SouthernCTWX and ask questions! We're here for you!
-GP!
