Tonight’s update focuses on the setup, model analysis, timeline and impacts from a snowstorm that is modeled to impact the area from Monday night into Wednesday morning. Considering the short lead time from which this storm has developed, we would be grateful if you would share with friends and family to raise awareness of this potentially major event. Enjoy the discussion! –Greg and Spencer
Overall pattern and setup overview:
An anomalously strong Alberta Clipper system will dive down from Canada then track into Appalachia, before redeveloping off the east coast. As it does so, it is expected to ingest energy from the Southern jet stream. This should aid in strengthening the low pressure system and also in developing very heavy precipitation near the storm center. The biggest question at this point is not precipitation type- it looks cold enough for snow in all areas, but where the low pressure system begins developing and where it will ultimately stall or drift to the west. There also doesn’t seem to be much question as to whether or not the storm will be strong- all computer model solutions currently show a strong low pressure system offshore of the Northeastern United States. So, for now, I have included a preliminary model discussion, breaking down each model and discussing what each model shows.
Preliminary model discussion regarding the upcoming Monday/Tuesday storm..
As you know, there are several operational computer models that meteorologists and forecasters use to aid them in forecasting the weather. This discussion will provide information as to what each model shows and what it could potentially mean for weather here in Connecticut.
GFS: The American medium range forecasting model, or the GFS, shows the Alberta Clipper racing through, without much interaction of the two jet streams, until the Clipper system is pretty far offshore. This would result in accumulating snow for everyone from the clipper, but the coastal low (which would be capable of producing the biggest accumulations), would be too far offshore to really bring significant accumulations to anyone except far Eastern Connecticut.
GGEM: GGEM is a model produced in Canada by Environment Canada. This model produces a solution sort of in between the GFS and UKMET- which is more aggressive than the GFS, but nowhere near as aggressive as the ECMWF.
ECMWF ENSEMBLES: For those who don’t know, ensembles are runs of the same model run with slight alterations to their equations. You may wonder why this is done. The reason it’s done is to provide a check with the operational, or main, run of the model. In other words, if an operational model shows something, and the ensembles look vastly different, or are skewed one direction or another, it gives us a clue that the operational model is not correct and that the forecast should take that into consideration. However, the ECMWF ensembles looked very much like the operational ECMWF! This would generally increase confidence that the operational model is correct. Also, keep in mind, that an ensemble mean is an average of all the “members” of an ensemble package, of which there are many. So, as you might expect, to get an average to show something big is significant. Because there are almost always a few members that show next to nothing.
UPDATE: The newer GFS has just arrived and looks very similar to the ECMWF… therefore, potential impacts from the new GFS are obviously much higher.
Light snow would move into the area Monday night, perhaps clipping the tail end of the evening rush but not causing any major issues there. Precipitation would be light throughout much of the evening and overnight hours, but don’t get too comfortable with that, because it wouldn’t last. Towards the morning hours, the low would begin to bomb and strengthen, promoting the development of what is known as a CCB(Cold conveyor belt, or a large band of intense precipitation) on the west side of the low. While it remains unclear where in the state has the best chance to be hit with the brunt this CCB, model guidance generally favors eastern areas for the heaviest snows. However, the entire state should see rates increase, and areas that see the best banding could see rates of 1-2” per hour!
What happens next depends on where the low stalls out. All guidance stalls the low somewhere off the New England coastline and allows bands of precipitation to rotate around it, but exactly where it stalls will be critical to who sees the highest totals. A stall further to the east would benefit eastern areas while western areas are mainly dry or seeing light snow, while a stall closer to the coast would allow for the entire state to get into the heavy banding and for western areas to have the highest totals. This portion of the storm will have the heaviest snow rates for whoever gets under the strongest bands, and it’s possible that we could see rates of over two inches per hour. The precipitation shield will be more banded though, because the strong bands create subsidence zones on either side of them and the result is the areas outside the bands see only light precipitation instead of a more widespread precipitation shield. Where exactly these bands set up will determine who jackpots for this event, and that’s not something we will know until much closer to the event.
We’ll see the low continue to be stalled and slowly rotting right through Tuesday evening, before moving out overnight Tuesday. Some lingering snow showers are possible right through the morning rush on Wednesday.
In terms of snow totals, the answer right now is really who knows? All guidance is in good agreement on at least warning level snowfall for most of the state(6”), so that’s probably a good baseline to start with on the low end except for far western areas which could see a bit less if a far eastern track was to verify. On the high end though, the numbers are potentially staggering. Both the 18z GFS and 12z EURO print out two feet or more of snow for parts of the region, and quite frankly, with the setup, we don’t think this is unreasonable. However, the question of where we would see those amounts is still very much up in the air, and we won’t know where that is until go time really when the bands begin to form. For this reason, the snowfall map will have very wide ranges and be a very low confidence forecast. We’ll have it out tomorrow morning after we see another round of data. Most likely, the majority of the state will be in the range of 8-16”, but if the 0z models continue to trend stronger, all bets are off. Of course, it could go back to a complete whiff, but I’m not buying that.
· Warning level snows
Widespread significant accumulations are expected from this system. Thankfully, this will be a lighter snow than what we saw today which will make it easier to remove.
· School/Job closures
There is the potential for a snow day on Tuesday for the entire state, and quite possibly on Wednesday as well for the areas that are hit the hardest.
· Power outages
Heavy snow along with strong winds will lead to potential power outages
· Coastal Flooding
Strong winds will result in potential coastal flooding at times of high tids.
· Potentially extreme travel conditions from Monday night to Wednesday morning
Rapidly accumulating snow combined with cold temps will allow for instant accumulations on roads, causing a major snafu.
Lots of it in every possible direction. That about sums that one up.
Next steps from SCW
· First call map and discussion: No later than 3 PM tomorrow afternoon
· Second call map and discussion (Potentially): Monday morning, may skip directly to final call if no major changes.
· Final call map and discussion: No later than 7 PM Monday night
· Live updates: Every 2-3 hours through the event. We have a forecaster scheduled to be on duty from 7 PM Monday night until noon on Wednesday to bring you up to the minute coverage.
Considering the rapid nature of which this storm came into our viewfinder, please share with friends and family to get the word out! We’ll see you tomorrow afternoon, and as always, thanks for reading SCW!