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Forecasters Discussion for 2/11/2015

2/12/2015

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Good evening to you from Southern Connecticut Weather!

Burrrrr! That’s what many were saying today, and you’d better get used to saying it, as we’re locked into a frigid pattern that shows no signs of going away anywhere in the forecast period. That cold will be accompanied by snow, with tomorrow afternoon bringing a round of light snow to the region and then this weekend potentially features a larger system that could bring a more widespread plowable snowfall. There’s a lot to talk about, so let’s jump right into the dailies.

Thursday

A clipper system tracks out of Canada and across Western NY before passing south of Long Island tomorrow afternoon, bringing us a light snowfall on it’s northern flank. The Euro model was ultimately correct in the handling of this shortwave and as a result it does not blow up into a strong storm until it is well out to sea, but it will still deliver a round of light snow tomorrow afternoon from the clipper with isolated pockets of brief moderate snow. As far as timing goes, expecting snow to start early tomorrow afternoon from west to east and continue through the evening commute before tapering off tomorrow night. The snow will be showery in nature, and so accumulations will be a bit spotty, but in general, expecting a coating to two inches of snow across the region, highest in eastern areas.  The 12z UKMET argues for accumulations of up to three or four inches in eastern areas, but as it is an outlier with it’s inverted trough like solution, it is not being weighed for the purposes of the forecast. As far as temps go, another very cold day is on tap, with highs in the upper 20s to around 30(roughly ten degrees below normal).

Here’s a look at the clipper system on tonight’s RGEM model.

Friday

An arctic airmass moves in behind the clipper and brings us our first of several cold shots in the forecast period. Expect widespread below zero lows and highs in the low to mid teens at best, except right along the shoreline where temps may just crack the 20 mark(Which is still 20 degrees below normal!). To make things worse, we’ll have blustery winds throughout the day, allowing daytime windchills to never crack the positive side of zero. At least we’ll have sunshine to take a bit of the sting off, but still, bundle up!

Saturday into Sunday

Good things come in threes? Or fours? Or however many snowstorms we’ve had plus one, because I’ve lost track. Yes, another coastal storm is modeled to impact the area late Saturday into Sunday, although the envelope of solutions is still relatively open at the moment. This is a Miller B type system, which is when a clipper system dives out of Canada, tracks from west to east across the Northeast, and redevelops into a coastal low as it hits the ocean. The question with this system, as it usually is with Miller B’s, is how fast the new secondary low can mature and “bomb out”, expanding the precipitation shield and creating dynamic bands of snow, and how far south the new low will form, which then determine how far north it will be when it bombs and slows down. Let’s explore the three possible scenarios depicted by guidance.

Scenario 1: The Late Bloomer

This scenario is currently depicted on the GFS, which tracks the initial clipper low further to the north compared to the other guidance, and as a result, does not redevelop the secondary into a mature cyclone until it is near or north of our latitude. The end result is that it develops too late for our area to see the heaviest snows, and instead, a lighter event is depicted, with the highest totals in northern areas as they are closest to the low and hence are able to get into the heavier precipitation for a time. With this scenario, we’d see a couple of inches of snow in southern areas and several in northern areas(With a low risk of 6”+), but the snow would generally be on the lighter side, and as a result, while annoying for some, the storm wouldn’t be anything out of the ordinary. Here’s a look at the system on the GFS model. Notice the snow confined to the northern portion of the state in the third image, and the generally lighter shades of blue indicating less intense snow overall.

Scenario 2:  The Direct Hit

This scenario is currently depicted on the Euro, which tracks the initial low much further south compared to the GFS, and as a result, by the time the redeveloped low reaches our latitude, it is a mature cyclone with a well defined strong precipitation shield. As a result, the Euro depicts a gradient from east to west as opposed to north to south, since eastern areas will be closer to the low and will get the brunt of the precipitation shield as a result. Eastern areas would see six or more inches of snow on the Euro, with amounts of over a foot possible, while western areas would see several inches with an isolated risk of over 6”. We can’t show the individual panels of the Euro due to copyright issues, but here’s the MSLP for Sunday morning. Look how much further SW it is compared to the GFS(shown above!). This scenario has support from the GGEM and UKMET models, although both are a bit more tempered in eastern areas than the Euro.

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The Wildcard Scenario: The Inverted Trough

Adding to all this mayhem is the possibility of an inverted trough developing with the storm. IVT’s are notoriously difficult to predict, which is unfortunate, because they can bring heavy snow to a localized area very quickly, but models are incredibly poor with the handling of their features and as a result, our confidence on where one might occur if it did set up is very low. Models have sort of been hinting at the south coast potentially being a target for one, but at this range, all we can do as acknowledge it as a possibility that could significantly enhance snowfall totals for some. Here’s a look at that south coast IVT on todays GGEM model.

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First thoughts

As of now, I’m leaning towards the GFS model. MillerB systems(Like the blizzard that wasn’t for western areas a few weeks ago), tend to end up developing slightly NE of model consensus, and the Euro has been too far SW with these systems several times this winter. I can’t rule out the Euro being correct because it is the strongest model we have and it has very strong ensemble support, but in general, I think it’s a bit overdone. For now, I’m favoring a blend of two thirds GFS and one third Euro, which results in a plowable snowfall for the entire state and a gradient from a couple of inches in SW areas to perhaps a 6”+ snowfall in NE areas. These are very early thoughts though, and can and will change, so don’t get too attached to this just yet.

Another thing to mention about this event is the winds. Winds are modeled to be very strong throughout the storm, especially on the shoreline, and as a result blowing and drifting of snow is expected which will serve to significantly reduce visibilities. This only complicates travel and snow removal, and so this event may feel like a larger one then the totals would indicate. We’ll also continue to have very cold temps throughout the storm.

As far as timing goes, snow moves in Saturday afternoon, heaviest overnight, and moves out Sunday morning. Some travel impacts are likely, but how severe will depend on which track the storm ultimately takes. Our confidence is high on some sort of snow event, but as to how impactful, it is quite low.  We’ll try to nail this down more over the next few model cycles, and will update tomorrow night with potentially a first call map depending on confidence and otherwise with more details and model analysis.

Sunday-Monday

After snow moves out Sunday morning, the main theme is cold, with temps crashing on the backside of the storm and staying crashed for quite a while. Sunday afternoon will feature temps in the single digits to low teens, and Monday’s highs might not make it out of the single digits away from the shoreline, with teens possible right on the water. Lows Monday morning will be below zero statewide. Here’s a look at forecast highs on Monday from the GFS model, which are over 30 degrees below normal! We don’t expect temps to be this extreme, but regardless, it will be very very cold.

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Tuesday-Wednesday

Models show another system in the period, but very strong disagreement on what it could be. Some track the low over the state and bring a boatload of rain, while some keep it further SE and as a result we are all snow in the state. There is of course the compromise which is snow to rain to snow, also shown by some of the models. In general, another storm appears likely, but beyond that, all options are still up in the air as of right now.  Temps will depend on what happens with the storm track.

We’ll have more on the weekend storm in the next day or two, and of course will get to next week in due time. Until then, we’ll update tomorrow to cover the clipper as needed, so keep an eye out on Facebook for that info. Thank you for reading SCW!

-SA

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