Blizzard of 2013 – Friday Morning Update

Screen shot 2013-02-08 at 5.28.11 AM

Here’s the blizzard! A beautiful looking storm is streaming north with snow ready to overspread Long Island by 6:30 and moving ashore here in Connecticut shortly after 7:00.

There still remains uncertainty with whether or not this storm will be a mere “major” storm with widespread 12″+ snows or will it enter the pantheon of historic storms with widespread 20″+ totals. There are several reasons for the uncertainty including the influence that large thunderstorms off the coast of North Carolina will have on the eventual track.

Here are the updated snow probabilities. I have changed very little other than to bump up northeast Connecticut and New Haven’s probabilities slightly. I think the forecast from the NWS in Boston of 2+ feet statewide is too bullish at this point. In fact for any specific location I have the odds of >24″ of snow generally 25% or less (which is actually quite high for any snowstorm).

chart_3 (1)

Here’s the bottom line

  • 15″-25″ of snow statewide. It’s possible someone in southern New England gets 30″-36″ of snow but it’s too early to say where that will be or if it will occur.
  • Wind gusts to 60 m.p.h. in southeastern Connecticut and 40-50 m.p.h. elsewhere will result in isolated to scattered power outages. Not a huge deal but some people will be in the dark.
  • Blizzard conditions (wind gusts >35 m.p.h. and visibility <1/4 mile) will be possible in parts of the state.
  • The storm begins as light snow after 8 a.m. A steadier and heavier snow overspreads the state after noon.
  • The heaviest snow will be during the evening and overnight when snowfall rates may approach 3″ or 4″ an hour.
  • Travel will be difficult so stay off the roads if you can.
  • A period of mixing with sleet is possible in coastal Connecticut but it’s possible that this remains an all snow event in many areas including New Haven.

Technical Discussion

The embarrassing run of modeling for U.S. numerical weather prediction continues. Just hours before snow starts falling here’s the difference between the 6z GFS and 6z NAM QPF forecasts.

QPF

No question that the NAM is a garbage model. It’s of limited use to anyone. The GFS, however, has been pretty inconsistent with this storm altogether. The European has been much more reliable and consistent over the last 5 days.

The GFS shows no stall with this storm off of the Cape and keeps it trucking northeast. In addition, it appears to be suffering from some convective feedback with the thunderstorms over the Gulf Stream. This may be resulting in a track too far offshore.

The NAM, on the other hand, is about as wild a weather porn run as you’ll see. A widespread 20″-40″ across southern New England.

The more measured, and consistent, solution has been found with the ECMWF and the SREF. I like this blend of global model with non-hydrostatic short range ensembling. Blend with the best of both worlds! The SREF shows generally 1.5″ to 2.25″ of QPF and is fairly close to the Euro. Run with it friends!

Advertisements

Blizzard of 2013 – Thursday Evening Nemo Update

chart_3

15″-25″ of snow with gusty winds will make the blizzard of 2013 one to remember. A beautiful phase between the Polar jet and sub tropical jet will result in a powerful nor’easter just off the coast. The storm will stall and do a loop-de-loop off of Cape Cod which is a characteristic of some of our most powerful and memorable storms.

Here’s the bottom line

  • 15″-25″ of snow statewide. It’s possible someone in southern New England gets 30″-36″ of snow but it’s too early to say where that will be.
  • Wind gusts to 60 m.p.h. in southeastern Connecticut and 40-50 m.p.h. elsewhere will result in isolated to scattered power outages. Not a huge deal but some people will be in the dark.
  • Blizzard conditions (wind gusts >35 m.p.h. and visibility <1/4 mile) will be possible in parts of the state.
  • The storm begins as light snow after 8 a.m. A steadier and heavier snow overspreads the state after noon.
  • The heaviest snow will be during the evening and overnight when snowfall rates may approach 3″ or 4″ an hour.
  • Travel will be difficult so stay off the roads if you can.
  • A period of mixing with sleet is possible in coastal Connecticut but it’s possible that this remains an all snow event in many areas including New Haven.

Technical Discussion

Here’s the 15z SREF plume for BDL which shows a mean QPF of about 2″. This matches well with the European model (though is a bit less) and is a bit higher than the GFS. Each line here represents an ensemble member’s forecast with the black line representing the mean.

Screen shot 2013-02-07 at 8.02.15 PM

 

There still remains uncertainty as to whether the blizzard of 2013 will be an historic storm or a more pedestrian (yet major) snowstorm. The two questions that remain are

  • Whether the southern stream disturbance (which is firing impressive convection and being modulated by strong latent heat release and PV generation) will truck east a bit and stay farther offshore.
  • How mesoscale banding (and associated subsidence) will modulate snowfall totals.

To answer question one here’s a look at the 18z GFS and 18z NAM 700mb height and RH forecast for 00z Saturday. Notice the NAM (which actually agrees with the Euro) is much closer to the coast with the center of the 700mb low than the GFS. The GFS – off the coast of Nantucket – is too far east for monster snow totals here in Connecticut.

700MB

The second point, about mesoscale snow bands, is just about impossible to pin down ahead of time. Given the strong frontogenesis and -EPV signal we know there will be strong banding and the potential for 3″ or 4″ per hour rates but where and how transient those bands are remains to be seen. 

Enjoy the storm! I’ll see you on Twitter and I’ll be on WNPR tomorrow around 7:10 a.m.

Finding Nemo – Blizzard Forecast to Impact New England

9hva

For some reason I think it’s just hilarious that The Weather Channel has named our Friday blizzard Nemo! While naming storms is just a silly enterprise it looks like Nemo may really be a beast!

Earlier today we were all having fun with the 12z NAM that was showing 40-60″ of snow in parts of New England. No big deal, right? The NAM is just not designed to be used for rip and read snowfall forecasts. It’s a curiosity and is of no use. Toss it. You can toss other QPF forecasts from non-hydrostatic models out the window at this juncture as well.

The global models are in exceptional agreement that this storm is going to be huge. The GFS/Euro combination along with their respective ensemble members have honed in on an impressive solution. Here’s my latest thinking in a probabilistic way.

chart_1

While a chart like this would give TV news consultants heart palpitations it’s really the best way to express forecast uncertainty! I know my blog readers have a lot of weather geek in them… so enjoy! If you notice here the odds of more than 18″ of snow are pretty low… there’s a reason for that! The greater Hartford area has only recorded 5 snowstorms (officially) of 18″+ in the last 108 years! The Bridgeport coop observer has never recorded an 18″ snowstorm since the 50s! They’re just not all that common. We’re also still 36 hours before the storm’s onset and a lot can change.

Before I get accused of being a debbie downer. Let me now talk about how amazing this storm looks meteorologically. Here’s the 18z GFS valid at 6z Friday.

f36

Here’s the GFS which is in fair agreement with the Euro (though the GFS is a bit more impressive with an earlier phase/capture). Synoptically, a digging northern stream disturbance mananges to be timed and located perfectly to dig and capture a moisture laden southern stream disturbance. Beauty! Without blocking downstream there’s not much wiggle room. The timing has to be PERFECT for this to work out for Connecticut. 6 hours in either direction will make a huge difference (keep in mind the northern stream disturbance is over Montana and the southern stream is over Texas).

All of our models show the perfect phase though the Euro is a bit late and therefore a bit less impressive in Connecticut compared to places around Boston. So assuming that actually occurs and it’s not late (a late phase would still clobber the Cape and eastern Massachusetts but give us a more pedestrian storm) let’s watch the beauty unfold at 700mb from 18z Friday to 6z Saturday in 6 hour increments on the 18z GFS.

700mbEvolution

I mean if that’s not breathtaking I don’t know what is. We even manage a little loop-de-loop there as the 700mb low tightens and matures. Exceptionally powerful frontogenesis on the northwest flank of that mid level low would result in a super band the likes of which you rarely experience. All of this is taking place under an area of strong divergence thanks to a coupled jet streak (classic KU setup).

The result of this “perfect scenario” is a large swath of 1.5″ to 3.0″ of liquid and likely a snowfall on the order of 1 1/2 to 3 feet.  Wowzers.

The perfect scenario is only one such possibility, of course, and small changes in the next 24 hours with the 2 disturbances we’re watching can make a large difference down the line. In order to start picking up over 15″ of snow in this part of the country you need small-scale (mesoscale) features on your side. These are notoriously challenging to forecast even 6 hours ahead of time!

That said, as of right now this has all the makings of a classic. Odds are better than 50/50 that many inland areas see a foot of snow. Along the shoreline some sneaky mid level warmth may  bring a period of sleet and a bit of mid level drying may promote some dry slotting. Big “IFs” here though with plenty of potential for a crippling snowstorm if the shoreline is able to hold the sleet and dry slotting at bay.

Will this turn into an historic storm? It’s possible. Too early to say for sure. The amount of liquid being generated by the normally reliable models (like the GFS and Euro – ignore the NAM) are staggering. I’m excited for this one 🙂

Don’t You Miss January?

I finally got around to uploading some clips from the January 2011 snowstorm that dropped near-record amounts of snow in the greater Hartford and greater New Haven. The storm was also one of several that lead to the snowiest month on record in many areas.

Major Snowstorm on the Way (Again)

It’s been a snowy start to the winter for sure. Though the western part of the state has cashed in the most in recent storms I think everyone gets hit hard by this storm and right now I’m forecasting 8″-14″ of snow.

The SREF (short range ensemble forecast) probabilities show greater than an 80% chance for 8″+ of snow. That’s extremely impressive. The 00z NAM is going bonkers with this storm (as usual) dropping 15″ or more of snow statewide. This is likely overdone (a good rule of thumb is to cut the NAM forecast by about 25%) but can sometimes signal the potential for the storm to really go to town.

700mb NAM 36 Hour Forecast

One thing to watch here is how quick and how close to the coast the mid level low forms. If the mid level low really goes bonkers along the Jersey Shore like the 00z NAM does than I expect 12″-20″ of snow across the state. If, however, the mid level low takes a bit longer to organize and scoots a bit east I think the heaviest snow will wind up northeast of Connecticut (just west of Boston?). This seems like the most likely scenario at this point. The 00z GFS continues the trend from previous GFS runs with a track a solid 75 or 100 miles east of the overly-amped NAM.

Wherever the cold conveyor belt starts to rip someone in southern New England is going to get hit very hard and probably pick up 18″ or so. At this point I think 8″-14″ is a reasonable forecast for most areas though I wouldn’t be surprised if those numbers are bumped up in some areas, particularly northeast of Connecticut.

One additional note. Unlike the last storm blizzard conditions are unlikely. The heaviest wind and snow will likely be out of phase so even though snow totals will likely be more impressive than the blizzard after Christmas the wind will not arrive until the heaviest snow ends.