Freak October Snowstorm Becoming More Likely

Hello, Snow!

This evening’s snow is a rare enough event. It looks as if the greater Hartford area has picked up measurable snow in October for the first time since 1979 and for only the 4th time in the last 100 years. We will need to wait to hear from the weather observer at Bradley Airport to get the official word.

This may be just a prelude for a significant and high impact winter storm that appears to be brewing for the weekend. All day I’ve spoken to meteorologist friends who have all said the same thing, “I’ve never seen anything like this.”

Obviously things can change and a variation in the track could mean only a little bit of snow. As of right now, however, the model consensus is a major winter storm that has the potential to bring down trees, tree limbs, and power lines given the amount of foliage still on the trees.

As we’ve seen tonight even though it’s October the sun angle is quite low and given a heavy enough snow rate snow can accumulate on the grass and on the roads. The GFS and the NAM computer models along with the Euro show substantial snow totals (most certainly “plowable”) even down to the shoreline.

For entertainment purposes here’s a look at the >12″ snow probability from our SREF guidance suite. The blue shading is 25 percent chance. Obviously this isn’t what I’m forecasting but this shows just how incredibly bizarre, rare, and unusual this storm could be.

By midday Friday we should have a better handle on this storm. At this point it looks like this storm has the potential to be unlike anything we’ve seen in recent memory.

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2 Snow Threats? Yup.

Tracking one snow threat in October is unusual but two is pretty rare. We have two storm possibilities, one on Thursday and another on Saturday.

Storm one will be mainly rain. I’m pretty confident about that. The temperatures through the low levels of the atmosphere are, not surprisingly, too warm for snow. If the storm tracks in the perfect spot and is strong enough to tug down enough cold air it’s possible we see some snow flakes at the tail end. Above 1,000 feet maybe a slushy accumulation?

18z NAM Forecast for 3z Friday. 850mb Temperature and 3-hour QPF.

The 18z NAM which is known for its wild, and sometimes comically snowy solutions, shows the worst case scenario for the Thursday storm with rain changing to snow and accumulation occurring in the higher elevations. For 95 percent of people in the state the Thursday event will feature little or no accumulation even if the most extreme scenario came to pass.

And then there’s Saturday. A convoluted series of interactions between upper level disturbances is going to make this forecast a bear. In addition the impact of Hurricane Rina will make this all the more challenging to forecast.

Our ECMWF model (the Euro as we call it) has been banging the big snow drum for the last couple runs. In fact the run today would drop a substantial amount of snow even in metro Hartford. With leaves on the trees it would be an exceptionally high impact event that is virtually unprecedented in October.

12z Euro SLP and 6-Hour QPF Forecast for 00z Sunday / Courtesy: WSI

Most of our other models show a much weaker storm out to sea with very little impact. Getting a snowstorm like this to occur on October 29th would mean every little piece would need to come together just right. Since we’re more than 100 hours out I wouldn’t count on it.

This is certainly worth watching given the unusually active weather pattern developing along with an unusually cold airmass and storm track setting up. Odds are pretty good that most of us see no snow accumulation over the next 7 days – but there’s a chance some of us see something pretty rare for late October.

Watching Irene

Woke up with an awful stomach ache last night and haven’t been able to sleep much so I’ve had lots of time to watch Irene on the laptop. The storm has become the first hurricane of the 2011 season and lashed Puerto Rico overnight with heavy rain and damaging winds. Over 1,000,000 homes and businesses are in the dark.

San Juan Terminal Doppler Radar Courtesy: Weather Underground

The storm is pulling away from Puerto Rico and will likely pass north of or scrape the northern coast of the Dominican Republic. The island of Hispaniola is very mountainous so the amount of interaction with land will determine the strength of Irene over the next 24-36 hours.

Beyond there it’s a difficult forecast. The National Hurricane Center brings Irene up along Florida’s east coast and into Georgia as a 95 knot hurricane. The model trend, however, is for the storm to move even more to the east which indicates a South Carolina or North Carolina landfall.

5 a.m. August 22 NHC Forecast

In the overnight weather porn department the 00z GFS ensembles and even the 00z Euro showed the possibility of some impact in southern New England next weekend.

I don’t think the pattern looks like that of a classic New England hurricane but rather one where a “scraper” or an “inside runner” could happen. That means a storm that either passes to our east like Earl last year or a storm that makes landfall in the Carolinas, weakens over land, and travels along the coast toward New England like Bertha or Floyd. A direct hit like Gloria, Bob, or Carol seems quite unlikely given the currently forecast setup.

It will be important to watch Irene closely in the coming days.

00z GFS Ensembles

What an Odd Day

Doesn’t get much weirder than this in the weather world. The 12z GFS sent a shot heard around the meteorological world with an exceptionally dramatic blizzard with no other model support. The shots kept coming through today with the American models going crazy with an extreme westerly track that pummels the Mid Atlantic and southern new England with snow.

Shortly after all of this model insanity the Hydrometeorological Prediction Center sent out this statement (they run the American models) saying to basically ignore them.

INITIALIZATION ERRORS IN NUMEROUS DIAGNOSTIC QUANTITIES… INCLUDING HEIGHT/VORTICITY FIELDS/RH…ARE EVIDENT IN
BOTH THE 12Z NAM/GFS WITH SMALL BUT LIKELY SIGNIFICANT SHORTWAVE TROUGHS OVER SOUTH DAKOTA/NEBRASKA ALONG WITH SASKATCHEWAN/MANITOBA…WITH THESE AREAS ALSO NOT PARTICULARLY RESOLVED OR PREDICTED WELL BY THE 00Z ECMWF. THUS…THE SPECIFIC PREDICTIONS BY ALL DETERMINISTIC GUIDANCE ARE IN QUESTION…WITH THE RECOMMENDATION TO FOLLOW CONTINUITY…WITH THE FINAL OUTCOME MOST BELIEVED TO LIE BETWEEN THE 06Z GFS AND 00Z ECMWF…WITH ALL ENSEMBLE GUIDANCE INCLUDING THE SREF MEAN/GEFS MEAN (EXCEPT NOT
THE 12Z VERSION)/ECMWF ENSEMBLE MEAN ALSO CONSIDERED USEFUL TO ADDRESS THE CONTINUED UNCERTAINTY. THIS APPROACH DISREGARDS THE SUBSTANTIALLY DEEPER AND WESTWARD SHIFT OF THE 12Z GFS REGARDING THE POWERFUL LOW TRACKING UP THE EASTERN SEABOARD…AND TO A LESSER EXTENT THE 12Z NAM WHICH LIES NEAR THE FAST EDGE OF THE GUIDANCE WITH THE DEVELOPING LOW.

Though the 12z GFS may have been an aberration it was quite a shock to many of us to see all subsequent American models come west at 18z. In fact the ensembles (both the GEFS and SREF) are west as well. Every GEFS member comes close to bringing blizzard conditions to parts of Connecticut.

It’s important to note that if the 12z data assimilation and initialization was wrong the GFS subsequent run can be impacted. The 18z GFS and NAM use the 12z GFS 6-hour forecast as a first guess. From there additional data is assimilated (at 18z we’re talking about surface obs, remotely sensed or satellite data, and aircraft data) and the model is re-initialized. An egregious error with the 12z initialization could reappear at 18z. By 00z the additional data that’s assimilated includes 00z RAOB data which should help things significantly.

The 12z GFS (and 18z) both show 2 very strong shortwaves phasing and blowing up a monster storm. The 12z Euro (with a superior initialization scheme – no one disputes that) initialized both shortwaves weaker than the 12z GFS. I’d go with the Euro right now but I’m sweating this one out.

It’s hard to go against the foreign global models in a situation like this. If you like snow we’re rooting for a 1980-style Lake Placid miracle.

Wow

Not much else to say about some of the latest computer model runs other than, “Wow!” The 00z Euro continues to show a major snowstorm/blizzard Sunday night 12/26 into Monday 12/27. Many other models are further southeast with a flatter jet stream pattern that doesn’t let the storm move far enough north.

Though the Euro has been slowly ticking southeast the 12z GFS appears to be ticking back northwest bringing blizzard conditions to Cape Cod and scraping southeastern Connecticut with significant snow.

Too early to say how this one will play out. Looks like there’s a decent chance, probably 40% or so, that we could be dealing with a big winter storm right after Christmas. If this does track in just the right spot this could really be a monster. The 12z GFS deepens the storm to 959mb just off Cape Cod!!!!!! That’s incredible!