Final Report on Tropical Storm Irene Released

The Tropical Cyclone Report for Hurricane Irene was released this week by the National Hurricane Center. There’s not much in here we didn’t already know. Not surprisingly the New Jersey landfall has been downgraded from a hurricane to a 70 mph tropical storm (note: the highest winds were offshore and not on land).

What was a bit of a surprise to me was that Connecticut garnered just 1 mention in the body of the 45-page report. Besides the historic flooding in Vermont and the Catskills the worst impact from Irene in terms of wind damage and storm surge was here in Connecticut.  Here’s the closest reference to Connecticut about the surge that destroyed countless homes, businesses, and roads along our shoreline.

Glad that New York City escaped severe damage but why not mention areas that did experience severe damage?

Connecticut is covered by 3 National Weather Service offices. One in Albany, one near Boston, and one near Long Island. It’s easy to be forgotten here on the outskirts of the 3 service areas. It looks like even the NHC forgot about us too.

The National Weather Service in Taunton, Massachusetts does a nice job including us in emails and communications. I can’t even remember the last time I heard from the other offices.

White Christmas? Probably Not

There’s been little to post about on this blog since October 30th since the weather pattern has been so quiet and so mild and so boring! There are many indications that this tranquil and relatively mild weather pattern will continue through New Years and probably into the beginning of January.

The climatological odds of a white Christmas (based on 1981-2010 normals) range from about 20% in Groton to 70% in far northwest Connecticut. The I-84 corridor has a slightly less than 50/50 shot at a snow depth >1″ on Christmas morning. The exact percentage is probably close to 40 or 45% in metro Hartford.

This year given the pattern, and the tendency for storms and air masses to trend warmer than forecasted by models, I’d say you can probably lop about half off your climatological chances for a white Christmas. Here’s a rough estimate for Christmas 2011:

  • New Haven – 10%
  • Hartford – 20%
  • Torrington – 30%

Not very good. Across northern New England there’s a chance for a little snow on 12/21 which may be enough to spare Vermont, New Hampshire, and interior Maine from a brown Christmas.

Sneaky Snow?

For people who love winter this weather pattern just plain sucks. Surprisingly, I haven’t been complaining about it. After October a break from winter has been nice – and it’s been nice for our heating bills too!

It appears that this may be one of the rare times that we are able to get a couple inches of snow to fall in a hostile early season weather pattern.

12z NAM / 48 Hours 500mb Vorticity & Height Forecast

Our computer models are showing a very powerful area of upper level energy ejecting from the southern Plains toward southern New England by Thursday. This vorticity maximum gets deamplified as it is crushed by a growing area of confluence over the Canadian Maritimes and the North Atlantic.

Occasionally this kind of setup can deliver what I like to call a drive-by snowstorm. A 6 hour window of snow in a somewhat localized swath. The storm will never become a powerful or mature cyclone as its upper level energy is zipping along and weakening. In addition in the mid levels of the atmosphere a low pressure system never really closes off and you’re left with an “open wave” effectively limiting the amount of precipitation that can fall.  See the 700mb NAM forecast to the left.

So what’s the bottom line? In a storm like this there’s little room for error. The storm has to “thread the needle” so to speak with a perfect track of the 500mb shortwave. At this point our models are in fairly good agreement with a track just to the south of Connecticut. With warm waters and a period of upper level divergence we should see a deepening surface low and a period of warm advection produce precipitation along and north of the shortwave’s path.

At this point things look cold enough for a rain/snow mix or snow as long as the storm maintains its current forecast track. Any adjustment north would back winds near the surface enough to warm the boundary layer and result in more rain especially for the valleys and shoreline.

The maximum amount of snow we can reasonably expect in a setup like this is around 6″ given an “ideal” track. Something less than ideal will result in less snow whether it’s due to mixing or due to the storm tracking too far south. Odds favor less than ideal but it’s worth watching.

By midday tomorrow we should have a better idea how this “drive-by” snow event will play out. It would be pretty incredible if such a mild meteorological autumn and beginning of winter was able to produce 2 plowable snowfalls before December 10. If you like snow don’t get too excited yet and if you don’t like snow don’t worry nothing is set in stone at this early juncture.

4th Warmest Autumn on Record?

Sort of. The average mean temperature in Windsor Locks was 55.8º for meteorological autumn. September, October, and November (SON) was also the 2nd snowiest on record.

The official “Hartford area” records have SON 2011 going down as the 4th warmest on record.

  1. 57.5º in 1931
  2. 56.0º in 1927
  3. 55.9º in 1946
  4. 55.8º in 2007 and 2011

If you look at the data something jumps out. Notice all the previous warmest falls were decades ago (odd, considering the climate has warmed in the last 100 years). Before the official records were kept at the airport they were kept in downtown Hartford. If we still kept records in downtown Hartford this year probably would have been the warmest on record.

With some at the National Weather Service showing indifference about the climate record (see October snow total debacle) and the movement of sites it’s challenging to compare years, months, seasons, or even storms. Though this is the 4th warmest fall officially it’s likely we are actually close to the warmest on record in reality.

Bridgeport (records post 1948) recorded their warmest fall on record as well as Boston.

Will It Stay This Warm?

The easy answer is no. Monday was a full +20 above average in the greater Hartford area which is an impressive departure for normal. The month as a whole so far is +3.1 in metro Hartford which is nothing to sneeze at either.

To figure out if it will stay this much above average we have to look back and see why it has been so warm.

November 500mb Departure From Normal

The 500mb height anomalies show substantial negative departures over Alaska and the Pacific Northwest. Ugly if you like cold and snow in New England. This -PNA/+EPO combination is in general a very warm pattern for the northeast. Inversely, across Alaska, this has been a record cold pattern!

In addition to the cold vortex that’s been spinning near Alaska the stratosphere has become exceptionally cold over the Arctic.

30mb Height Anomalies

Up in the stratosphere the polar night jet has gone berserk with a powerful polar vortex. This +AO configuration effectively will mean no sustained high latitude blocking for the foreseeable future. We will need some type of stratospheric warming (possible later in the winter – a SSW?) or some other mechanism (like Rossby wave train breaking) to break up this vortex. Until that happens it will be a challenge to get sustained cold and wintry weather in the northeast unless the Pacific cooperates.

Here’s an example of what we saw last year from Dec 15, 2010-Jan 30, 2011 with that epic 45 day stretch of weather.

You can see the high latitude blocking with an impressive -NAO that brought the record snow into southern New England for nearly 2 months last year.

So where do we go from here? Winter lovers will have some reason to rejoice heading into December as it appears our substantially above normal weather pattern will be changing to something more average.

Finally we’re beginning to see some improvement in our computer models for those who like snow and cold. Ridging is showing up in the PNA region and some ridging over Alaska to help flip the EPO and bring some cold out of northern Canada. Since we can’t rely on blocking in the North Atlantic seeing changes out in the Pacific are important.

Although many of these features appear to be transient this is a reversal from the sustained warmth we’ve been having. We’re getting there. I expect the Day 6-10 (Dec 5-9) and Day 11-15 (Dec 10-14) to average near normal with some transient bouts of below (maybe even much below) normal temperatures.

As for snow chances it doesn’t appear like Connecticut will see anything significant through December 10. It’s possible after that point we become a bit more wintry. The good news for skiers is that there may be several snow chances across northern New England over the next 1-2 weeks which, when combined with colder temperatures, should help boosting the base.