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Jan 4-6 Coastal Bomb

Baroclinic Zone

By Baroclinic Zone,
in New England

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RUNNAWAYICEBERG

RUNNAWAYICEBERG

Posted
Posted

This is long and not for the ema crowd. Just the red headed stepchild, SCT. 

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
** Heavy snow with strong winds expected for Suffolk County
and much of Southern CT Wed Night through Thu - Blizzard Conditions
Possible **

** Light to Moderate snow accumulations and strong winds expected
Wed Night through Thu for remainder of the region - Moderate to
Heavy snow accumulation possible **

Polar trough will continue to dig into the SE US, aided by one
strong shortwave/jet streak diving through the Gulf Coast this
morning, and by a second separate vigorous shortwave/jet streak
diving through the lower Mississippi River Valley this morning.
As mentioned over the last few days, there are still subtle
model differences in the timing/location of phasing of the
above shortwave energies as they round the base of the digging
trough this evening/tonight, as well as a final interaction with
a third shortwave/jet streak (diving through the Upper
Mississippi River Valley this morning) off the SE US coast late
tonight into Thursday morning. This interaction will affect the
track and timing of explosively deepening low pressure. The
other factor appears to be models having difficulty with
convection development and vorticity feedback off the US east
coast as this intense mid/upper level energy interacts with a
sub-tropical moisture plume, which also could play a
significant factor in low pressure track.

Operational models have already shifted about 50 miles closer
to LI with track of low pressure by late Thursday than 24 hrs
ago, with consensus track of a 955 to 960 mb low pressure
system tracking over or just se of the 40/70 lat/lon benchmark.
The exact phasing evolution will determine any additional
forecast track adjustment, with GEFS/ECMWF/SREF still showing at
least 150 miles of spread in members within 24-36 hrs. This
range of potential shift would have significant implication on
westward expanse of frontogenetically forced heavy snow banding,
and strong to damaging wind fields with this intense low. In
fact 06z NAM, has taken a significant shift westward from 00z
with its frontogenetic forcing, showing potential for 1 ft+ snow
across the entire area. For this reason, NHC will be doing a
reconnaissance flight and several dropsondes this
afternoon/evening off the Fl/SE US coast to better capture this
phasing and convection latent heat release in the models.

For now, based on above and consensus 00z operational/ensemble
track and uncertainty, expectation for snow to develop from S/SE
to N/NW tonight as polar and southern stream jet energy phase.
This will place the region under deep lift of right rear of 150
kt jet streak, with subtropical moisture being fed by cold
conveyor into the region. Then as phasing shortwave energy and
rapidly deepening low pressure move up the coast tonight, LI
and SE/SC CT are expected to fall under strong low- mid level
forcing late tonight into Thu afternoon. Heavy snow banding is
typically under and just to the NW of that. Also potential for
enhanced updraft/convection through CSI as indicated by negative
epv above the frontogenetic forcing. SPC SREF/SPC HREF
corroborate this through indicating a moderate to high potential
for 1 per hour snowfall rates during this time, and possibly 2
inch per hour. Once again though, this banding could
expand/shift westward by 50 or more miles, which is in the realm
of QPF spread seen in GEFS and SREF, which have a reasonable
range of 1/10 to 1 inch across NYC!

So overall, the probability for a light to moderate accumulating
snowfall event for the entire area is high late tonight into Thu
eve, with a heavy snowfall expected for much of LI and CT. Potential
still exists for the entire region to see a moderate to heavy snow
event.

A good middle of the road compromise for qpf with the
track/banding uncertainty is staying close to GEFS/SREF/ECMWF
ensemble means. This was blended in with WPC for consistency.
This results in 1/2 to 1 inch qpf across LI/SE CT, 1/4th to 1/2
inch across NYC/NJ metro and SW CT, and up to 1/4 inch to the
NW. Snow ratios are a bit tricky with strong omega in the
saturated snow growth and eventually in the warmer riming
saturated region, especially for eastern and coastal areas. So
a blend of snow ratio algorithms and WPC was used that appear to
capture this. This points towards a likelihood of 6 to 12 inch
snowfall for E LI/SE CT, 4 to 7 inches westward to the Hudson
River, and 1 to 4 inches to the NW. As mentioned, this remains a
fluid situation based on model spread, with potential for these
numbers to go down, but still seems more reasonable upwards
based on model trends and mode of SREF/GEFS/ECMWF ensemble
members compared to operational runs. This higher trend is
reflected in latest WFO/WPC snow probs, with high probs of
greater than 6 inches of snow across E LI/SE CT and low to
moderate probs to Hudson River. A significant jump in the
reasonable worse case has also been noted, with 1 in 10 chance
of seeing more than 12-16 inches of snow across much of LI/CT, 8
to 12 inches of snow across NYC/NJ metro to Hudson River, and 4
to 8 inches N & W still in play. In fact, the 06z NAM has come
in with 1 1/2 to 2 1/2 inches of liquid QPF for much of the
region, which is within SREF ensemble spread.

The other hazard with this storm continues to be strong winds,
with a blend between GFS/NAM profiles pointing to likelihood for
30 to 40 mph gusts along the coast Thu aft/eve, and 45-50 mph
gusts for eastern coastal areas. This will lead to blowing and
drifting snow, possibly near whiteout conditions in the warned
areas, as well as some downed tree limbs and power lines.

Based on above, have upgraded to winter storm warning for Suffolk
and SE CT with 6 to 10 inches of snow expected and potential
for 1 ft or more. No blizzard warnings at this time, as
despite likely high winds, heavy snowfall and low vbsy, but low
confidence that sub 1 ft snowfall will have significant enough
impacts. If expected snowfall amounts increase today, and
therefore high end impacts, a blizzard warning will be hoisted.
A Winter storm watch issued for NYC metro, Nassau and SW CT
with 3 to 7 inches expected and potential for widespread in
excess of 6 inches. To the N&W of this region an advisory is
likely, but not enough confidence in 6+" for watch. Have held
off on headlines after collab with surrounding offices in this
region due to 3rd period timing and uncertainty. Again, if 6z
NAM is pre-cursor, we may see the warning upgraded another tier
westward or possibly more.

 

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wxsniss

wxsniss

Posted
Posted
2 minutes ago, sbos_wx said:

I wonder why they didn't in the first place 

Agree.

Maybe part of the hesitation is whether heaviest snowfall (roughly 10am-5pm) matches heaviest winds (latter half of storm) to make 3 hours of criteria, but I'd think Boston certainly has better chance of that than southeast MA.

It'll probably come up this afternoon given Euro held steady.

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jlauderdal

jlauderdal

Posted
Posted
24 minutes ago, wxsniss said:

18z mesoanalysis:

SLP at 1004 mb, placement more similar to 12z Euro/RGEM than 12z NAM

Can see the battle for dominance east of FL on water vapor... NAM favored a more northwest SLP

the euro was throwing off multiple lows yesterday and sure enough there is low analyzed right off the coast of FLL and then another low off of daytona beach which will be the primary low

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Hazey

Hazey

Posted
Posted
Just now, leo2000 said:

That is not me that is Frankie MacDonald is a the Maritime's popular weather man. I got a question Southeastern Mass is expected by some Mets to get hit the hardest with the snow wouldn't that particular track gives Nova Scotia more snow?. 

No. You're on the wrong side of the storm. You warm, you rain. Enjoy the wind

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The 4 Seasons

The 4 Seasons

Posted
Posted

So the NWS throwing out their own definition of a blizzard warning and going with the public definition.... blizzard = foot+ of snow 

No blizzard warnings at this time, as
despite likely high winds, heavy snowfall and low vbsy, but low
confidence that sub 1 ft snowfall will have significant enough
impacts. If expected snowfall amounts increase today, and
therefore high end impacts, a blizzard warning will be hoisted.
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wxsniss

wxsniss

Posted
Posted
4 minutes ago, The 4 Seasons said:

So the NWS throwing out their own definition of a blizzard warning and going with the public definition.... blizzard = foot+ of snow 


No blizzard warnings at this time, as
despite likely high winds, heavy snowfall and low vbsy, but low
confidence that sub 1 ft snowfall will have significant enough
impacts. If expected snowfall amounts increase today, and
therefore high end impacts, a blizzard warning will be hoisted.

Where is that from? Didn't see that on Box AFD.

That's frustrating if true... I see NWS as a scientific expert profession that should not be so influenced by optics in the public eye.

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