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2/12-13 Potential Coastal Storm Threat


Typhoon Tip

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4pm BOX

 

 

 

THU INTO EARLY FRI...
INITIALLY THE REMNANTS OF A FILLING CLIPPER SYSTEM WILL BE
APPROACHING FROM THE GREAT LAKES REGION. NOTING ENOUGH MOISTURE IN
THE COLUMN FROM THE SFC THROUGH ABOUT H5 TO SUPPORT LIGHT
SNOWFALL ACROSS MUCH OF THE REGION AS THIS SYSTEM CROSSES.
STILL...GIVEN THE WEAKENING DYNAMICS AND SHIFTING OF ENERGY TOWARD
THE DEVELOPING OFFSHORE SYSTEM...OVERALL ACCUMS ARE LIKELY TO BE
GENERALLY AROUND AN INCH OR LESS FOR MOST OF INTERIOR CT/MA/RI.

BY FRI EVENING CONVECTIVELY ENHANCED DEEPENING OF LOW PRES OFF
THE DELMARVA WILL RAPIDLY SHIFT NE UNDER THIS PROGRESSIVE
PATTERN...AND THAT/S JUST IT...IT DEEPENS TO SUB 980HPA TOO FAR E
OF THE REGION FOR A SIGNIFICANT IMPACT. DO NOTE TYPICAL TROWAL
SETUP WRAPPING INTO THE NW QUADRANT...COINCIDENT WITH MODEST LIFT
AROUND -12C ACROSS SE MA. THEREFORE...COULD SEE MORE EFFICIENT
DENDRITE PRODUCTION ACROSS THIS AREA SUPPORTING ADV LVL SNOWFALL
ACROSS THE. MEAN QPF VALUES FROM SRN BRISTOL THROUGH COASTAL
PLYMOUTH COUNTY AND POINTS SE ARE AROUND 0.3-0.4 SO 3-6 INCHES FOR
THIS AREA IS NOT OUT OF THE QUESTION WITH LESSER AMOUNTS FURTHER N
AND W. SOME MINOR OCEAN ENHANCEMENT POSSIBLE TOWARD THE END EARLY
FRI...AS WINDS TAKE A MORE N-NW ORIENTATION AND VERY COLD AIR
BEGINS TO BUILD IN.

 

post-238-0-98832200-1423602036_thumb.png

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That is about how I'd forecast it.... Maybe even knock each section down a notch

Looks good though. Pretty much nuisance snows outside of bos pvd SE where it could be better

Yea I'd knock it down by a factor of 2 at this point. Every cycle seems to be pushing the best moisture/lift further south and east. Expecting maybe an inch here. 2-3" for James
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Sounds like a solidly reasoned approach... Unless something happens on the 00z guidance to later tomorrow, I don't any reason to go ballistic with expectation, ...or even have any for that matter. 

 

Definitely looked much better and more bullish yesterday, but seemingly incrementally dismantled on every run, every model since... 

 

Could still come back.  The mid level impulse(s) are over upper interior Manitoba, where I am sure there is a festoon of NWS balloon launchers.  In fact, ever since the thing left the Alaskan sector it's been waning in the runs..  

 

Heh, long shot.    It's a fun hobby to have right now though; there are other opportunities out there to screech society to a terrorized halt, so don't give up ...

 

haha

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Sounds like a solidly reasoned approach... Unless something happens on the 00z guidance to later tomorrow, I don't any reason to go ballistic with expectation, ...or even have any for that matter. 

 

Definitely looked much better and more bullish yesterday, but seemingly incrementally dismantled on every run, every model since... 

 

Could still come back.  The mid level impulse(s) are over upper interior Manitoba, where I am sure there is a festoon of NWS balloon launchers.  In fact, ever since the thing left the Alaskan sector it's been waning in the runs..  

 

Heh, long shot.    It's a fun hobby to have right now though; there are other opportunities out there to screech society to a terrorized halt, so don't give up ...

 

haha

 

Thursday is dead. Wait and see on Sunday. Lube up for Wednesday.

 

This threat is no longer likely to heavily impact me directly, so the thread can now be locked.

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#1 Theres plenty of forcing and lift even without a coastal.

#2 There's an inverted trough signature ( not relying on that obviously)

#3 looking at 18:1-20:1 ratios so even if it's .20 its 3-6 with 6 inch amounts most likely as you work east

 

Meh, even if I give you the 0.20" QPF (which isn't all that likely as far west as you) 18:1 to 20:1 seems pretty far out on the limb.

 

post-44-0-14121300-1423604723_thumb.png

 

That's your breakdown based on the two latest NAM parameters and the latest GFS. Only one run  gives any hope at seeing better than 15:1, and it's the one model you love to toss.

 

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Meh, even if I give you the 0.20" QPF (which isn't all that likely as far west as you) 18:1 to 20:1 seems pretty far out on the limb.

 

attachicon.gif2015-02-10_16-43-26.png

 

That's your breakdown based on the two latest NAM parameters and the latest GFS. Only one run  gives any hope at seeing better than 15:1, and it's the one model you love to toss.

 

 

Where's that table from? That's interesting

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http://sanders.math.uwm.edu/cgi-bin-snowratio/sr_map_main.pl

 

I mean 20:1 stuff is pretty rarefied, reserved for the mountains and downwind of the lakes. Even if we pull 13:1 that's a big increase from normal around SNE.

 

 

Once in a while we can pull a 30:1 fluff bomb of 1-3" or something. They have the same look in model soundings too with a very deep DGZ with solid omega throughout.

 

This year is the year of sand and sugar snow IMBY. Getting 10:1 is a stretch.

 

Snow ratio climo is sort of a mess though since a lot of the first order sites really "undercatch" the snow. 

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http://sanders.math.uwm.edu/cgi-bin-snowratio/sr_map_main.pl

I mean 20:1 stuff is pretty rarefied, reserved for the mountains and downwind of the lakes. Even if we pull 13:1 that's a big increase from normal around SNE.

Even BTV's area average is 13:1. You really need that good low level assist from orographics in a cold airmass to pop those 20:1-30:1 stuff.

We can usually pull 3-6" from these clippers out of 0.15-.2 QPF.

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It appears the factor that is different between now and yesterday's solutions have to do with overall trough movement and orientation.  Models are now slower in the negative tilt fashion and therefore slow down the potential intensification process of the surface low to a later period closer to Nova Scotia, then per se New England.  These nuances are pretty much present in all storms, this process is just a little slower today and could speed up tomorrow.  That's why this is very dangerous to write off this potential with about 60 hours until first flakes fly.  I would not write off this potential and BOX's map seems reasonable now.

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Once in a while we can pull a 30:1 fluff bomb of 1-3" or something. They have the same look in model soundings too with a very deep DGZ with solid omega throughout.

 

This year is the year of sand and sugar snow IMBY. Getting 10:1 is a stretch.

 

Snow ratio climo is sort of a mess though since a lot of the first order sites really "undercatch" the snow. 

 

The one positive is the 30:1 stuff usually falls with very little wind. When you have wind you have a strong LLJ, and when you have a strong LLJ you're usually advecting air that messes with the depth of the DGZ. So I bet those are accurately captured by COOP, but maybe we're a little too fluffed on the windy systems. People tend to estimate snow, but take liquid verbatim even if it all blew by the can. In the end given that it is an inexact method anyway, we're probably doing a decent job.

 

Even BTV's area average is 13:1. You really need that good low level assist from orographics in a cold airmass to pop those 20:1-30:1 stuff.

We can usually pull 3-6" from these clippers out of 0.15-.2 QPF.

 

That's the key to big ratios. You need a very deep DGZ, so flakes continue to grow as they fall in addition to being produced at all levels of lift.

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This is just an example of the NAM sounding at BOS around 00z Friday (just the closest site I had easy access to).

 

You can see the sounding that is forecast, and the area within the DGZ (in yellow), and lift (white line going to the left is rising motion).

 

post-44-0-32205500-1423608017_thumb.png

 

To get significant ratios around here (or anywhere for that matter) you would want the temp/dew point traces to mimic the dashed lines.

 

Also you can note here that the DGZ is very close to the top of the saturated layer, which introduces some possibility for drying out of the prime dendrite growth region.
 

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Been steadily backing down the past 24hrs... you said warning snows yesterday, then high end advisory/low warning, then 3-6" this morning, then 2-4" a few hours ago, now 1-3", when will the slashing stop?!

 

Why wouldn't he adjust expectations down as modeling comes in lower?

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The one positive is the 30:1 stuff usually falls with very little wind. When you have wind you have a strong LLJ, and when you have a strong LLJ you're usually advecting air that messes with the depth of the DGZ. So I bet those are accurately captured by COOP, but maybe we're a little too fluffed on the windy systems. People tend to estimate snow, but take liquid verbatim even if it all blew by the can. In the end given that it is an inexact method anyway, we're probably doing a decent job.

That's the key to big ratios. You need a very deep DGZ, so flakes continue to grow as they fall in addition to being produced at all levels of lift.

Yeah I always like to see -10C at H85 or lower during orographically driven events as the strongest low level ascent just above summit ridges will punch that layer. That's how we got 10" on Friday night when no model was remotely close, just because of like -14C summit level temps and a deep -10C to -18C column in the lowest 7000ft, with a moist light to moderate westerly flow. Those flakes grew on the way up and on the way down haha. Silver dollar dendrites.

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