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December 14/15 winter storm threat part II


Typhoon Tip

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Not crazy about the mid level track... not sure if it might suggest dryslot here or an underplayed icestorm for Hfd/Spfd though.  m/l warmth does tend to rocket up the valley.

 

This is what is highly intriguing.  Going back to past post about the HP, if that does end up being stronger than what was advertised, that just further enforces colder air locked in towards the sfc but then again, a track even further east also means less WAA aloft.  Really a tough call right now.  

 

The dry slot potential is also rather intriguing but it does appear the dry slot wouldn't occur until after the heaviest of the precipitation has passed...but you know how dry slots can be 

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The more NW solutions really haven't changed my forecast much...since we never really had a redeveloped mid-level center before them...save for maybe 1-2 weenie NAM runs. All it does it push the eventual "ending as sleet and ZR" line further north, but it doesn't really discourage the big front end thump. It might lower my accums by an inch or two at most.

Lots of panic and crying over nothing
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Shh you will jinx us ;)

 

The key will be the 00-06z period... where the best frontogenesis goes right over us (and actually over CT, RI, MA and most of the coastal states). This will the period where we could be cranking out 1-2" per hour snowfall rates at times. Afterwards we fight both the dry slot aloft (moisture become shallow and outside of the snow growth temperature range) and the warming profile (although we just barely stay below freezing in the entire column in ALB). The latter fact won't matter when we only have low level vertical velocities generating precipitation in a shallow column that is outside of the snow growth zone, so expect to see more sleet/freezing rain in the 09-12z period even in ALB. 

Do you buy the 12Z NAM'?  Everyone was thinking that it was a NW outlier, but it seems like it might have lead the pack.

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Those surprised by the early starting time for the snowfall and the early significant accumulations should take it as a sign the more inland solutions have some validity. Already we are seeing mid-level frontogenesis starting to squeeze out mesoscale snow bands that could drop some significant snowfall in the next 3-6 hours across CT, RI and MA. This band 24 hours ago was suppose to be a good 50-100 km south of where its affecting now. Heck we are on the edge of a snowband in ALB right now when we really aren't expecting any significant precipitation till after 18z. If there is a stronger upper-level system downstream, you would expect a corresponding increase in mid-upper level heights upstream helping to tighten up the temperature gradient against the arctic air (frontogenesis). This is what is happening right now.

Yea but Phil it also can mean significant accumulations and fronto before the massive warming takes place, the dry slot just flies through. 

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thanks, will check that out, I used this 

http://www.wpc.ncep.noaa.gov/sfc/usfntsfcwbg.gif

 

but position of the high is critical also right?

 

Yes it is, especially for the flow to allow colder air to be locked in towards the sfc.  Once the HP moves slightly east, that is a stronger signal for keeping cold air locked in and reinforcing it.  

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Lots of panic and crying over nothing

 

 

Well if you wanted to stay 100% dendrites, then it is discouraging having a bit more NW solution....but I never really expected to stay 100% snow. It is still basically a SWFE with just a more rapidly developing sfc reflection along the coast than is typical...the mid-levels often win out in this situation. But the battle before that happens is where we make hay.

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Do you buy the 12Z NAM'?  Everyone was thinking that it was a NW outlier, but it seems like it might have lead the pack.

 

I think its too aggressive with precip, but the track might not be too far off reality given the more amp up nature of the southern stream s/w. This is allowing the initial low in this miller-b solution to be more dominant for longer before it transfers energy to the coast. 

 

Yea but Phil it also can mean significant accumulations and fronto before the massive warming takes place, the dry slot just flies through. 

 

Oh I agree... again most of the precipitation falls before the warming takes place... just ending with some light sleet/freezing rain/rain depending on how close a person is to the surface coastal front. All I am saying that the main event will probably be earlier than guidance was pointing yesterday with a greater chance of liquid precipitation towards the end of the event. 

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Thank you, I was pretty sure it was January but I couldn't remember the year.

 

It's a good example for all the "but it's so cold at the surface" weenies out there that don't think mixing can happen with this kind of air mass.

I was 9 degrees and ripping rain, talk about dumbfounded in my hallow that day. The shotgun shells lasted all night to wake up with probably the most beautiful glimmering sunrise of my life, and  you know what happened after. The return of Leon

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