1-29 Possible HECS (historic east coast storm)

1-30 These are the results... 6" here

This was the loop from spc

Euro path

GFS path

Some of the closer snow maps from 72hrs

Euro not too bad

CMC I think is the winner

NAM, as bad as it seemed, not terrible. 

Some misses were the FV3, NAM3k, GFS

And the SREF missed OXC by an inch

Satellite at sunset

Radar shots 10pm, 6am 9am

6am banding setting up

10 pm storm arrives

9am banding just missing us

A couple of the issues we had with this storm, other than there being 4 pieces that were difficult to track and come together completely, was that areas like mine didn't have really good snow growth. The final slr was about 11:1, which is hard to understand when surface temps were 8-10°F.  Further look at the skew showed that the DGZ was really low 925 to 600mb or so, but the theta was 600-500mb.  Some have also argued the wind destroyed the flakes, but videos from the Shelter Island ferry terminal show huge flakes in winds of 50mph with winds on that skew nearing 100mps at 925-850mb. So while it snowed a lot, it didn't add up.  We were constantly stuck between bands.  Oxford had 9"  Shelton 8" Fairfield and Bridgeport airport 10".  To have 50% more snow the next town over is frustrating and hard to predict.  

1-28  Started snowing late morning, didn't really stick even though temps were 30.  Wanted to note some model history. First the GFS ensembles capitulation.  It may not look like much from this far away, but the amount of precip the GFS had was pretty steady for quite a few runs, then last night, it moved into the Euro's range.  This is the ensembles, which isn't usually as extreme.

GFS operational snow had us at 0.5 up to 15 before it leveled out around 11.

And then there was the 6z NAM, lighting up wxtwitter...

So as of breakfast, the outlier low end model was the GFS with 13-15 inches for Newtown.

Euro was in at 20

Then came the short term models. 

Then the 12z runs came out and started halving the amounts, except the GFS which lowered but not half.  No surprise. Here is where the NWS settled.

 

1-27  Well this has been a ride....

NAM came on board right away, then dropped it on the 18z run, only to come back strong.

Euro been pretty steady

GFS windshield wipered

Canadian was more consistent than the GFS which is odd.

But now that they've come together it boils down to when that upper low closes off and which model eliminates the noise over the atlantic.  NAM and Euro close off the low earlier, NAM just off NJ now, and Euro a little further east. GFS was by Cape Cod but shows signs of caving to the Euro.

Ukie came on board this morning, then shifted east again.

It's definitely one of the most challenging storms to forecast with pros on tv, and accuweather unsure up to now. Even the NWS acknowledged 48 hours prior, the challenges.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...

Major winter storm possible for much of the region Friday

night and Saturday...

It has been a live-or-die-by-every-model-timestep sort of night here

at the office. And what the models give, they also take away, which

basically describes the model variability we have seen the past

couple of days with the potential winter storm for our region Friday

night and Saturday. The 00z suite has made a notable consensus shift

westward with the low tracking just off the coast, but the high

volatility/variability remains. The 00z GFS is a far-east outlier

solution and basically brings little snow to the CWA for the whole

event. Meanwhile, the 00z NAM returned the snow to our area, in a

large return of departure from the 18z NAM no-show (no-snow) event.

The 00z CMC brings a blockbuster storm to the area, with widespread warning criteria south and east of the Fall Line; the 00z ECMWF is only somewhat drier than its 12z predecessor run. The 00z UKMET went sharply west, with meaningful QPF/snow for much of the area.

The model volatility with this system has been something to behold. Such run-to-run spread is typical/expected for these types of events, given the highly complicated interdependent phenomena involved. However, simple analysis of the spread in the National Blend of Models is enlightening; the 04z NBM V4.0 (V4.1) 50th percentile storm total snow for the Philly area was around 1.5 (1) inch(es). The 75th percentile storm total snow was around 8 (10)

inches, or roughly an order-of-magnitude difference between the

median and the upper quartile. Bottom line here: the storm total

snow forecast remains highly uncertain and subject to large changes in subsequent forecasts.

Observation-wise, it will be critical to assess three

regions/phenomena as the event unfolds: (1) the strength/depth,

orientation, and speed of a northern-stream digging vort max through the Midwest on Friday morning, (2) the orientation and speed of a southern-stream vort max in the southern Plains around this same time, and (3) the low-level response to the phasing trough near/off

the Southeast coast Friday night (e.g., the 850-mb heights and

winds). The progressive solutions have a more compact and faster

northern-stream vort max and a slower southern-stream vort max,

which results in upper low development farther east (and generally

too far east for our region to see substantive snow); the snowier

solutions acquire phasing and neutral to negative tilt of the large-

scale trough more quickly (and thus, farther west). Trends in the

low-level response are obvious Friday night -- the NAM/CMC (aside

from the errant 18z NAM simulation) are positioning the 850-mb

low/trough farther southwest. The GFS is much noisier, exhibiting

little trend. Notably, the 00z GEFS featured unusually low spread,

which makes me wholly suspicious of the deterministic and ensemble

output from its suite.

With the model camps making the GFS more and more of an outlier,

tonight`s forecast is generally a non-GFS consensus blend. This

preserves a considerable amount of continuity to fields of

importance such as PoPs, QPF, and snow amounts. The main changes

were to sharpen the gradient of snow totals near/northwest of the I-

95 corridor, with 1-3 inch totals northwest of the Fall Line, 3-6

inch totals in the urban corridor and immediately adjacent areas,

and 6-12 inch totals roughly from Easton, MD, to New Brunswick, NJ.

Again, there is enormous uncertainty with these forecast totals. If

the more progressive solutions pan out, very little snow may occur

in a large chunk of the area. If the slower/stronger solutions pan

out, heavier totals would occur at least to the Fall Line. Continue

to monitor the forecasts, as large changes may occur leading up to

the event.

Based on the forecast totals, we have issued a winter storm watch

for all of Delmarva, far southeastern Pennsylvania, and most of

central and southern New Jersey from 7 pm Friday to 7 pm Saturday.

Will fine-tune the timing once warnings/advisories are issued, but

this is the general time window of concern for our area.

Other impacts and forecast considerations...

Winds will be a big factor with this storm, with north winds of 10

to 20 mph becoming northwest 15 to 25 mph on Saturday. Gusts of 30

to 40 mph will be common, with higher gusts possible (especially

near the coast and in the higher elevations). With snow falling for

much of this time, very low visibilities and blowing snow are

possible. Conditions may become very hazardous near the coast on

Saturday.

Wind chills will drop well below zero across the area Saturday night

as northwest winds remain quite strong. Advisory conditions (wind

chills at or below -15) are probable in the southern Poconos and far

northwest New Jersey.

Dry air advecting into the region from the northwest on Saturday

will likely make for a rather abrupt cutoff to the snow. A sharp

gradient in snow totals is possible if this dry air is stronger than

already forecast. This only increases uncertainty with snow totals

northwest of I-95, in particular.

There may be some light snow or a wintry mix on the front-end of the

event on Friday afternoon into the evening. Models remain quite

variable with this potential. Impacts with this are expected to be

limited. The primary period of more substantial precipitation (snow)

is expected to be after the Friday evening rush.

 

1-25  Been watching this for a few days.  The storm hasn't gone away, though it's been in different positions.  Three areas of energy will be diving into a trough and meeting up to round the trough and come up the coast.  The 0z euro is the strongest of these and gives the best example of how it can work.  

The GFS yesterday (1/24) also had a pretty significant 12z run

But in the 18z run one piece of energy got stuck in the SW and ended up missing the trough, which resulted in a less potent storm which relied on the energy from Canada to make it go negative tilt. This happens just a bit too late, resulting in good snow for Maine and Eastern New England.

As I mentioned, the storm has been there for a while, just in different forms.  

Thread on WXDisco opened on the 20th. 

Snow maps from 1/24....

 

Finally

Writing this in retrospect.  We finally got a snow storm on January 7th.  It was originally supposed to be a few inches, ended up with 9.

The storm overperformed in CT 

NSSL had the best call from 48 out 

From 60 out the models struggled.

I didn't get a core sample right after the snow fall so I couldn't determine the ratio, but the qpf seemed to be underdone by all.  

Today is the 15th and we still have about 2" on the ground in the shade with some spots clear in the sunnier areas.  

What happened to winter this December....

 It's not that I've given up completely on this blog, though more attention is paid to Wxdisco.com than here for sure, its just that the month of December was a snoozer.  We got 1.5" of snow from two storms, but one did include snow on Christmas Eve, which stayed on the ground past midnight, so count it. 

Other than that, it was very dry and warm. 

Bridegport had the coolest reading due to the ocean

Oxford and Danbury were warmer and similar to each other.

Hartford and Providence had their 3rd warmest 

Boston and Providence had their warmest year on record, Hartford was 5th.

3 of the 5 warmest years for Boston have been since 2010

First accumulating snow of 2021?

 12/8  Storm is whiffing to the south and east. Ukie is just outside BM closer to 38/70

Euro is further south at 37/70

GFS even further south

NAM furthest north - all is in order

There's a warm air advection chance of snow Thursday then it warms up.  Not much in the way of anything otherwise during the next two weeks.  

12/4 Looking at 12-8 for the first snows.  This has been on and off for the last 10 days or so on the models and they are starting to consolidate somewhat.  UKMET and the Euro are oddly the furthest east while the GFS and NAVGEM are furthest west.  All but the NAVGEM bring minor accumulating snow to the tristate area, in some cases even to the shore areas and LI. 

Ensembles are starting to consolidate. 

Things missing are really cold air and something to slow it down or make the trough go negative. GFS has it going from snow to sleet/rain, NAV is mostly rain, UKIE and Euro are mostly snow, but more of a glancing hit as they are further offshore.  GFS skew shows that the surface temps aren't the problem for north of the Merritt, but that there is a warm pocket around 800mb that melts the snow and refreezes as it falls in the layers closer to the ground.  Temps should be around 30-32 for the event at the surface, mabye 33.  It's not a terribly dynamic storm, so faster moving and weaker, but still noteworthy as its our first real chance at accumulating snow for this season. 

February 1-2

This was the result.  Not bad - LI /CT stayed snow further east than expected. I'd give me an A-

1-31 

The north trend stopped, though I'm sticking with it.  Still not convinced it doesn't mix NYC east and south of Trenton.  There have been some breathtaking model runs today that really make me think I've underdone this.  Trying to figure where the heavy band will set up is like trying to figure out where the heaviest thunderstorm will be a day before.  Based on the upper level low placement, and the progged vertical velocities, I like the red area as having the most chance of being over 18" with some areas getting 24-30" in the hash.  But not surprising if that  hash area shifts east into Bergen or even Westchester, or if the western edge sags down a little.  Mitigating things in SNJ, ELI and SECT/RI/Cape is that there will be some snow, then it mixes and rains.  The low is hugging the coast for most of the heavier precip and that just brings the warm air in.  We may even be dry slotted and go to freezing drizzle as far west as Fairfield County and NYC. 

But the models are putting out crazy amounts. Like this one from the Regional Canadian (NAM) with 50".  

Or the NAM with 40"

Even the GFS as I'm drafting this came in with some big numbers

This was issued at 330 this afternoon

1-30  First snow map is below.  The amounts are higher than the NWS forecast currently, but less than the highest models.  The area of heavies snow is purposely north as we've seen this happen before. It is likely I will extend the 10-18 further south.

1-29 This starts off as a low coming across the country, dropping a swath of 12" across the midwest before it dies out approaching the Apps and reforms off the Carolinas.  Initially the models had the transfer taking place closer to SC than NC, but that has since shifted back to the typical OBX to 40/40 benchmark track.  

Complicating this standard Miller B storm is that an upper low is coming behind it which will "capture" the low and slow it down.  Models having a problem trying to figure what happens to the low, with some stacking them, others putting low to the east or south.  Typically the low either stacks or stays to the east and moves with the upper low.  However, some models, had the low looping and heading south and then east.  This is not common.  Stalling, yes, but a loop that big is a red flag that the model can't figure which surface low to follow.  The shaded area is the 500mb low.

Here is a more typical scenario

But today that seems to be resolved.  The low is coming off NC by OBX, moving northeast (not east), getting captured by the upper low and then moving northeast.

Now that the models agree on the set up, it comes down to positioning of the lows (upper and lower) and that will remain a challenge through the weekend.  Here is where we are right now with the 12z Sat model trends. You can see what we call the windshield wiper effect as the snow shifts south, then back north.  This is pretty typical. Additional shifts are likely but should be less dramatic.  Also note the Canadian's precip output is insane.  But its not impossible, and that area may not be the one to get it. 

Euro

GFS

A little early for the NAM but so far

and Canadian