Ugly Timing for a Winter Storm

Of all the days for a snowstorm – the day before Thanksgiving is probably the worst. Even I’m finding it tough to get excited about this storm – and I can’t even sleep at night before snow because I’m so excited about it most of the time.

B3PCzq4CMAAV5bQThe forecast isn’t terribly complex – our computer models are actually in pretty good agreement. There are a few reasons why this event will struggle a bit.

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For one, the lack of a cold surface high to the north will keep temperatures on the mild side in the lowest thousand or two feet of the atmosphere. Particularly vulnerable will be the shoreline where there will initially be a bit of an easterly component to the wind off the warm Sound. It’s certainly possible that the snow hole of Groton/New London is unable to get measurable snow due to temperatures a bit too warm near the ground.

A second item of concern is the track of the mid level low – particularly around 10,000 feet above the ground at 700 mb.

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Here on the 18z GFS the 700 mb low closes off to our west across southeastern New York. You generally want the 700mb low overhead or just east to really cash in with the heaviest snow. While the initial thump of snow along the mid level warm front will be impressive (strong isentropic upglide) the “comma head” should stay a bit to the northwest of Connecticut – unless models bring this entire system a bit east.

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A third issue is relatively crummy dendritic growth. Efficient production of snow flakes (dendrites) is maximized in temperatures near -15C. The dendritic growth zone is between -12C and -18C. In this storm the DGZ is quite high in the atmosphere (above 500mb) and there are several sneaky dry layers around. This makes me a bit bearish – I’d much prefer to see good lift/RH in the snow growth zone. This can lead to a period of ice crystals that are ineffecient accumulators (death needles and colums are the worst!!!).

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Another way to view this is in a time-height profile for KHFD on BUFKIT with omega contoured along with RH and the snow growth zone. You can see the omega bullseye and best RH is under the snow growth zone. Things improve a bit from a snow growth perspective in northwestern Connecticut and especially the Berkshires.

Putting it all together there are a number of factors to make us a bit “bearish” on this one than we’d otherwise be.

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The GFS is printing out nearly an inch of liquid for most of Connecticut while the European model has between 1.0″ and 1.5″ across the state. The combination of borderline boundary layer temperatures, a mid level low track that is not particularly favorable, and crummy snow growth we’re shaving quite a bit off what you’d expect from just taking a straight 10:1 snow to liquid ratio.

Obviously things can change – a cooler boundary layer, a mid level low track that’s farther east placing us in an area of better frontogenesis/mid level life, or better snow growth are all things we’ll have to look out for. Conversely, lighter snowfall rates and a warmer boundary layer could yield unimpressive snow totals. Regardless, the Wednesday travel day before Thanksgiving looks like a mess.

Winter Storm Likely on Wednesday

The timing couldn’t be worse – a nor’easter on the busiest travel day of the year. The question now is how close to the coast will it track and how much snow will we see.

It’s a juicy storm with origins in the Gulf of Mexico. Both the European model and GFS model show a substantial storm nearby.

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The European solution – with a strong storm hugging the coast is the solution is the one I think is most likely to verify. About half of the European ensemble members show a low track just south of Long Island.

The Euro scenario would be snow to sleet to rain (maybe freezing rain in the northwest hills?) while the GFS would be mainly snow. The Euro solution – with its ensemble support – is not a blockbuster snowstorm for Connecticut but it would be a royal pain for the day before Thanksgiving.

At the very least plan for an ugly day of travel on Wednesday.

Storm Brings a Bit of Winter and Gusty Winds

Monday looks like an interesting day with a very sharp temperature contrast across the state and a little bit of everything weather-wise. Sleet, freezing rain, rain, thunderstorms, and gusty winds all a possibility depending on where you live.

Let’s start off with the winter weather threat. A bit of moisture moves in after midnight and temperatures near the ground will be close to 32 degrees in the Northwest Hills. We can’t rule out some sleet pellets statewide but any legit impact from wintry weather will be northwest of Hartford.

bufkitprofileHere is a sounding valid tomorrow morning at 7 a.m. off the NAM model. Above the ground there’s a sharp increase in temperature but right near the surface the cold air hangs tough (the red line is temperature… the farther right the line gets the warmer the air… the higher up you go on the graph the higher the elevation above the ground). This is a freezing rain signature and it does appear that some light freezing rain is a possibility during the morning commute – especially in the Litchfield Hills. The setup isn’t great for a long-duration or serious event but in the hills of western Connecticut things could get a bit slippery tomorrow morning.

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After that the focus will shift to winds. By afternoon, milder air will flood in from the south across the shoreline and eastern Connecticut. You can see the milder air in this map with a sharp temperature contrast from northwest to southeast. Also, you can see the cold air wedged and trapped in the valley! 41F at BDL and 59F in Hartford!!! Seems odd but it actually happens more often than you may think.

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How cool! Literally cool if you’re in Springfield, Enfield, or Windsor Locks! Where temperatures warm up gusty winds could really be an issue late tomorrow afternoon into early evening. The GFS model shows 50 knots of wind at 600 feet above the surface at Groton tomorrow at 7 p.m.

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While an inversion (temperatures increasing with height) will keep the strongest winds from mixing down this is too close for comfort. There is the potential for damaging winds in southeastern Connecticut tomorrow given how strong the winds just off the deck are AND the fact the inversion isn’t particularly strong (i.e. temperatures only increase a bit with height – the increase isn’t that dramatic). Isolated power outages and gusts over 45 m.p.h. are certainly possible east of New Haven along the shoreline tomorrow.

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First Snow of the Season!

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It won’t be a big storm by any means but we have some snow on the way. In general only minor accumulation is anticipated but, in the hill towns especially, up to 2 inches is possible which will make roads a bit slippery by morning.

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The issue with this storm will be temperatures in the lowest 2,000 feet of the atmosphere. Here’s the GFS model for later this evening showing temperatures at 925mb or about 2,500 feet above sea level. The 0c line will drop south as freezing levels drop but it will take some time to transition the rain to snow (though above 1,000 feet in elevation the precipitation will likely begin as snow).

gfsNE_925_temp_015We’re not talking about a large amount of precipitation (liquid totals near 0.25″) and we will waste some of the precipitation as rain initially so final totals will be kept down a bit. If you’re feeling lazy tomorrow morning no reason to shovel the driveway as most of the snow will melt during the day tomorrow with highs near 40F!

 

Why Model Snow Maps are Terrible

Of all the computer model data I look at – model derived snowfall totals is either dead last or not looked at at all. They’re about as useful as a piece of garbage.

Take today’s 12z GFS run valid Monday morning. I’m sure this map will make the rounds soon from bad TV weather readers, weather hobbyists, and knowledgeable meteorologists who have sold out their credibility for page views, twitter followers, and/or Facebook likes.

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Are you excited for the 7″ of snow in Willimantic??? Don’t get too excited yet! A look at the GFS model for Willimantic shows that during the height of the storm the freezing level is over 2,000 feet above ground and temperatures are as warm as 2.5C just above the surface. That would be some wet snow for the hills but it certainly wouldn’t be 7″ of snow for Willimantic or Norwich. More like 0″ for Norwich and Willimantic.

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Don’t be fooled by computer generated maps with funky snow algorithms. I haven’t found one that is even remotely useful. Going back to basics with model soundings is the only way to accurately forecast events like this.