Super Band Delivers!

Photo of Libby / Courtesy: Jeremy Keckler

An impressive mesoscale banding featured developed in southern Connecticut that sat and sat and sat over the same area. These things can produce some exceptional totals in a relatively short total and this was no exception. This produced the big totals thanks to a growing and relatively stagnant area of low/mid level frontogenesis that worked in tandem with synoptic scale lift from the right entrance region of a jet streak in central New England.

Here are the totals from my awesome weather watchers:

  • East Haddam – 10.5″
  • Salem – 10.5″
  • North Guilford – 10.0″
  • Woodbridge – 10.0″
  • Montville – 10.0″
  • Haddam – 9.8″
  • Newtown 9.5″
  • Higganum – 9.0″
  • Branford – 8.3″
  • Ansonia – 8.2″
  • Wallingford – 8.0″
  • Old Saybrook – 8.0″
  • New Haven – 8.0″
  • East Hampton – 8.0″
  • Franklin – 7.0″
  • Ledyard – 7.0″
  • Naugatuck – 7.0″
  • Oxford – 7.0″
  • Groton – 6.5″
  • Colchester – 6.5″
  • Wolcott – 6.5″
  • Bridgeport (BDR/Official) – 6.2″
  • Southington – 5.5″
  • Vernon – 5.0″
  • Tolland – 3.9″
  • West Hartford – 3.8″
  • Litchfield – 3.0″
  • Avon – 2.8″
  • Stafford Springs – 2.6″
  • Windsor Locks – 2.4″
  • East Granby – 2.0″

Thanks for the reports! Enjoy the snow :)

Weather Rant: Fluff Factor

Nothing makes me cringe more than hearing a meteorologist say “temperatures will be so cold there will be a fluff factor.” It makes me want to scream!

There’s a big difference between dry and light snow that is easy to move and fluffy snow flakes that are able to accumulate fast! A meteorologist friend of mine in New Hampshire used this analogy:

Think of dendrites as a bunch of tree branches thrown into a pile. The pile gets stacked high the more you add as the branch structure traps air in between. Now throw them through a wood chipper and watch how much lower the pile gets. There’s your columns, needles, bullets, and small plates.

Dendrites (the beautiful and ornate crystals) are the flakes that can pile up quickly and result in high ratios of liquid precipitation to snow totals. Snow flakes grow through deposition. Deposition is the process where water vapor changes state to a solid on the ice crystal. This is the dominant process in producing snow.

The deposition process is maximized when temperatures are between -12c and -18c in the cloud. Besides a more efficient growth process dendrites also accumulate more rapidly due to their large suface area adding to extra space in between each individual flake.

Bottom line is that even though it’s in the teens that doesn’t guarantee good snow growth or a fluff factor!! Not even close!!! Having cold temperatures in addition to saturation and strong lift in the dendritic growth zone (-12ºc to -18ºc) is the key to getting a “fluff factor”.

When temperatures are too cold or too warm in the region of best lift you get other types of crystals that don’t form as efficiently and don’t accumulate as efficiently. The latter will reduce snow:liquid ratios. Snowflakes like plates or columns or needles accumulate slowly and produce a “fine” consistency to the snow.

Looking at a surface temperature and saying the snow will accumulate fast is bad meteorology. Use cloud microphysics folks – it’s the only way to forecast snow!

Saturday Snowstorm

If you don’t want to geek out and read all this… the bottom line is I expect most of us to 4″-6″ of snow in Connecticut and most of southern New England.

Finally some real snow in the forecast! Here’s the 12z NAM valid at 15z (10 a.m.) Saturday with 850mb temperatures (0c solid black) and 3-hour QPF shaded. As usual the NAM is the most robust of all our models in terms of precipitation.

A weak disturbance is ejecting east toward southern New England. Though the shortwave isn’t strong we’ll get a burst of QG forcing (lift) thanks to warm advection and a 60+ m/s jet streak to our north leaving us in the favorable right entrance region.

NAM dynamic tropopause forecast for 15z Saturday. Isotachs shown - note the 60m/s jet streak northeast of Connecticut on the DT.

12z NAM forecast of sea level pressure and 1000-500mb thickness valid 18z Saturday

In the NAM SLP/Thickness map you can see the relatively tight thickness gradient over NY and New England which will help maximize low level warm advection even with a relatively weak low level jet. In addition synoptic scale lift will be present through the column in right entrance region of jet streak to the north.

The bottom line is that snow will overspread the state shortly before daybreak Saturday with 4″-6″ of snow likely across all of Connecticut. I expect snow even down to the shoreline (including the Groton/Stonington snow hole). Snow to liquid ratios will be better than 10:1 with relatively cold soundings and some lift and saturation into the favorable dendritic growth zone. This isn’t a classic setup for good snow growth so I expect 15:1 snow:liquid ratios.

On a side note I couldn’t help but notice this National Weather Service map this morning. I generally don’t look at their forecasts or discussions but this really jumped out at me.

How the hell is this supposed to make any sense to anyone? A winter storm watch for Fairfield County and a winter weather advisory for the remainder of southern Connecticut. Nothing to the north? Why? Will Bridgeport get more snow than New Haven?  Snow should begin around the same time so why do we have watches, advisories, and nothing in effect when the storm appears ready to deliver similar impacts regionwide.

To be honest I don’t even know what the criteria is for each advisory or warning for each county because the definitions seems to change every couple years and they vary from county-to-county and state-to-state.

The NWS does a great job (most of the time) with severe thunderstorm and tornado warnings but maps like this do everyone a disservice. It makes no sense.

2 Snow Threats – Finally!

It’s taken long enough but this evening we have two weather events on our radar. Ironically, the pattern is still a mild one, with well above normal temperatures on the way for much of next week.

Still, well timed (or poorly timed, based on your perspective) disturbances will produce snow across Connecticut tonight and again on Saturday.

Tonight’s system is moisture starved and not terribly dynamic so I wouldn’t expect much. That said, 1″-2″ of snow is possible in some areas with a moist onshore flow keeping southern New England a bit more primed for snow than inland areas to our north and west. A touch of frontogenesis appears to be enough along with QG forcing/ascent to produce some locally heavy bands of snow this evening.

As for Saturday, most years this storm wouldn’t be much of a story, this year it is. A slightly more juicy and dynamic shortwave is ejecting from the Pacific northwest (the one that produced the snowstorm and ice storm near Seattle) will produce some strong lift and a more widespread batch of snow. A bit of mid level warmth gets introduced which may mean some sleet or freezing rain particularly for areas south of Hartford. Details to be determined but at this point I feel pretty good about 2″-4″ of snow on Saturday with the potential for 6″ somewhere though most of us will see less.

Here’s the 15z SREF snow probabilities which aren’t overly impressive though they should bump up in coming runs.

Don’t fret if you don’t like snow. It looks like the torch returns by Monday with a warm pattern setting up. Here’s the 12z GFS MOS for next week:

In the grand scheme of things this winter still is a bit of a downer but I do see some signs of larger storm threats beyond day 10. -NAO????? Stay tuned….

A Different Way to Look at Winter 2011-2012

Besides the October snowstorm this winter has been pretty much nonexistent in Connecticut. Since 10/30 there has been no measurable snow at either Windsor Locks or Bridgeport – which is remarkable for January 15!

Up north the winter has been just brutal for many ski areas in northern New England. Last week’s synoptic and upslope snowstorm was an absolute blessing for struggling ski areas. Here’s a cool way to display snow depth at the famed Mount Mansfield snow stake (just off the Toll Road in the Stowe ski area).

The green is the average snow depth by date and I also plotted this year, last year, and the also ugly 2006-2007 winter. After a very slow start up north this winter has exceeded ’06-’07’s paltry snow depth but remains below average. While last year was an epic snow year in Connecticut it took until March for northern Vermont to really exceed average with a maximum depth around 100″!

Bottom line is hope is not lost for skiers. 2 snow chances and relatively cold this week should boost Vermont bases. Though the Day 8-20 period looks very mild it’s difficult for snow depths in the mountains to take big hits this time of year. Closer to home I don’t see much for winter lovers to get excited about through early February.