Currently: A quick peak at the surface analysis reveals not much going on. High pressure over Missouri guiding our weather. Our storm has formed just east of Florida. Yes, parts of Florida are currently in Winter Storm Watches!
Tonight: Temperature guidance is in excellent agreement, and I see no reason to deviate. Aside from a few high cirrus clouds, it should be generally clear. Expect low temperatures to range from 0 to 5 above across the NW Hills, to the mid teens in the urbanized areas along the south coast.
Tomorrow: There is fair agreement in the temperature guidance. Skies should generally be sunny, although clouds should begin to increase toward day's end in southern sections. I'll go with a general compromise in temperatures, but shade toward the cooler guidance, given recent performance. So we'll go with general upper 20s across the state.
Now for the storm. First off, the National Weather Service has issued a Winter Storm Watch for Eastern Connecticut for the potential of 6" or more of snow. The GFS and, to a lesser extent, the ECMWF, do not show much in the way of snow at all west of I 91. After coordination, this solution seems a bit erroneous. Spencer even mentioned to me that the European model looks "like a tropical storm" in how it handles the banding features, and he is right. Now, I am not an expert on model physics, but a thought occurred to me, and that is that it could be possible that the model algorithms see the system more "tropical" because it is developing in the Bahamas. This could cause the models to handle the precipitation placement wrong. Remember, tropical systems have very little precipitation on the NW side. This is something that needs to be considered as well.
Now there are a few concerns with this system: The first, and most obvious concern, is the storm track. 40 degrees north and 70 degrees west is generally referred to as the benchmark for winter storms, because a storm tracking there is in a favorable place to produce significant snowfall in the Northeastern United States. If this storm tracks along or just inside that benchmark, significant snow will probably spread further west than what our snow map is indicating. A current model consensus tracks the storm just east of the benchmark, which is still far enough west to bring significant snow to the eastern half of the state. However, if the storm tracks east of where we have it right now, then western Connecticut, especailly the Northwest hills, may see very little if anything, while amounts would have to be shaved even in Eastern Connecticut. The GFS, and to a lesser extent, the ECMWF, have a track further to the east, while the UKMET and GGEM have a track near where we have it. The NAM and some SREF members, as well as other mesoscale models, have a track further west.
Here are the GFS, GGEM and NAM tracks.
Another concern is that this storm will be intensifying rapidly. While models are in high levels of disagreement regarding the track and precipitation distribution of the storm, models are in excellent agreement that this storm will rapidly intensify and become a monster low somewhere in the Atlantic ocean, and probably south of our latitude. This means a few things: First, there is going to be an explosion of precipitation and intense banding somewhere. Unfortunately for forecasters, the model skill level at predicting where banding is going to be is extremely low. Sometimes we really do not know where the banding will set up until we see it on radar! Related to banding, every time a real heavy snow band sets up, an area of subsidence, or sinking, drying air, also sets up near the band- as if the heavy band robs the other areas of their snow- which it does, in a sense. Since we cannot accurately predict where the bands of snow will set up, we also cannot accurately predict where those areas of subsidence will set up. Secondly, since this storm is strengthening so quickly and becoming so strong, winds will rapidly pick up- perhaps well removed from the storm center. Areas that do get heavy snow could very easily verify blizzzard conditions, as a result. Finally, since this storm is originating in the deep tropics, it will probably carry a lot of warm, moist air with it, which could be undermodeled at this time. This could create heavier precipitaiton than is currently being modeled. Since we have an arctic air mass in place, the temperature contrast between Bahamian air and the arctic air mass we have in place could also create intense precipitation along a coastal front. At this time, precipitation type does not appear to be a concern, but if the storm tracks west of where we have it, the immediate SE coast could mix.
A final concern is snow to water ratios. Given the very cold, dry air mass in place, snow to liquid ratios will be higher than normal. A standard snow to water ratio is on the order of 10-13:1, meaning for every 0.1" of precipitaiton that falls you get between 1 and 1.3 inches of snowfall accumulation. This time, due to the very cold, dry air mass in place, ratios could be on the order of 15-20:1. This is a concern because missing by a small amount in the total precipitaiton expected could yield a larger error than normal.
With all that said, here is our snow map. We are expecting significant accumulations east of Interstate 91, with lesser, but still plowable, snow west of there. Of course, this is preliminary, and updates may and probably will be needed as we get closer to the event. Expect our final call to be issued by tomorrow evening.
I may do a quick update to this discussion later tonight, pending new model runs.
Now, heading beyond the storm.
As the storm pulls out, another Arctic blast- stronger than the last one- will move into the area for the weekend. This Arctic air mass will be worse than the last one for two reasons- First, temperatures will be lower. If that isn't bad enough, winds will be much higher, due to the strong Atlantic low (our snowstorm) pulling out. Winds may gust in excess of 40 MPH Friday and Saturday, and not begin to diminish until early Sunday! With fresh snowpack in place, I'll go a bit cooler than guidance for high temperatures on Friday, keeping the entire state in the teens! Saturday's highs will likely be a couple of degrees lower than those of Friday. Finally, on Sunday, highs may actually surpass 20 degrees everywhere except the NW hills. Lows this weekend may even approach zero on the south coast and will likely go below zero inland, especially if the higher end of snow totals is realized! The combination of the cold and any power outages that develop from the storm will be dangerous, so have a backup plan in place for if you lose power.
Another storm system is expected to affect the state Monday into Tuesday. I did not have a lot of time to really look into that storm system, but it looks to be a more climatological type storm, with precipitation type issues. It should be cold enough Monday morning for precipitation to begin as snow everywhere, before transitioning to sleet and then rain. There could also be a larger area of freezing rain than currently modeled, especially in the CT Valley, since models typically do a poor job with low level cold air. In addition, there is the potential for a frontal wave to develop after the front moves through on Tuesday, which would turn the entire area over to accumulating snow, with flash freeze concerns. As for temperatures, Monday could actually threaten 40 degrees (briefly) for much of the state, and then we'll cool it down by about 10 degrees on Tuesday, to 30-32. Another shot of Arctic air, though probably not as intense as this weekend's, will then follow that system.
Taking a brief look into the long range, temperatures should be more variable than recent, but biased toward below normal. (No it isn't going to stay 20 degrees below normal forever!) However, this contrast should also yield to a more stormy pattern, and with an adequate supply of cold air, most storms should be at least partially frozen. Suffice it to say, there will be a lot of tracking to do in the coming weeks! I
That's all for now! Enjoy the rest of your week, and please share this discussion with friends and family!