Christmas Week Weather Bomb Update Two

000

FXUS61 KCAR 211737

AFDCAR

Area Forecast Discussion

National Weather Service Caribou ME

1237 PM EST Tue Dec 21 2021

.SYNOPSIS...

A cold front will cross the area this morning. High pressure

will briefly build into the region this evening before moving

east tonight. Low pressure will strengthen southeast of the

area Wednesday and lift across the Maritimes Wednesday night.

High pressure will build over the area Thursday into Friday. A

warm front will approach the area this weekend.

&&

NEAR TERM /THROUGH TONIGHT/...

1230pm update:

First issue is the cold front exiting Aroostook County in the

next two hours. Expect scattered snow showers and blowing snow

in the open agricultural areas of Aroostook County and northern

Penobscot County. The winds will persist into late afternoon,

but quickly diminish in the evening. Temperatures will be

dropping behind the front.

Radiational cooling will be the second issue this morning with

temps rapidly dropping, but should stabilize by midnight due to

increasing clouds.

The third issue...with the most impact across the forecast

area...is tomorrow`s storm. It`s a very dynamic situation.  A

baroclinic zone is expected to rapidly set up over the area as a

northern stream shortwave approaches and begins to develop neg

tilt. Deep southern stream moisture is pulled northward and

moderate precip develops across the area. P-type and amounts

remain a challenge. Aroostook County will receive mostly snow

and the greatest amounts will be in the NE corner of the county

where up to 10 inches is possible. The mixed precip corridor is

expected across southern Piscataquis and Penobscot counties

towards northern Washington County and the southern tip of

Aroostook County. This corridor will maintain freezing rain and

sleet throughout much of the event and it looks like up to an

inch of mixed sleet and freezing rain could result. Further

south along the coast, all rain is expected. Low level warm

advection is not strong and looks like above freezing temps will

have a hard time moving north of a line from around Bangor

towards a bit north of Calais.

Previous discussion:

Warm air advection ahead of a cold front is producing areas of

light snow across the north early this morning. A strong cold

front west of the Saint Lawrence River early this morning will

approach the western Maine/Quebec border by 12Z. The timing of

the front appears to be an hour or two slower compared to what

most of the guidance was indicating last night. The front will

cross the Caribou/Presque Isle areas by around 15Z and move to

the Downeast coast by 20Z. The main concern will be for snow

showers and perhaps a snow squall with the front and a few hours

of strong wind just behind the front. The lapse rates steepen

and the BTV snow squall parameter is still indicating the

possibility of squalls, although it has backed off just a bit

compared to last night. The most likely areas for heavier snow

showers and a possible squall will be across Aroostook County

and into northern Piscataquis County and northern Penobscot

County. Will plan to issue a heads up special weather statement

early this morning. Although the snow depth is meager with a

lack of deep snow berms, the high fluff factor of the recent

snow will make it easy to blow and drift, especially across open

areas. There could also be short periods, i.e. less than an

hour of intense snowfall rates, although any local accumulations

should remain under 2 inches, but higher amounts can`t be ruled

out in very localized squalls. Once the front clears, there may

also be a few streamers that move off the Saint Lawrence River.

All this makes for a very changeable day, but with high

pressure quickly moving in late in the day the wind will rapidly

drop off toward evening.

High pressure crests over the region around 00z Wednesday and moves

rapidly well east of Nova Scotia by 12Z Wednesday morning. During

the course of the night low pressure across the Great Lakes will

move into southwest Quebec as a southern branch low off the south

Carolina coast begins to move up the coast and to a position a few

hundred miles south/southeast of Long Island by 12Z Wednesday

morning. Expect a short window for radiational cooling through late

evening before clouds increase. Most areas remain dry through 09Z

Wednesday, but snow will break out rapidly between 09-12Z across

southern portions of the FA, with mixed precipitation along and

near the coast.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...

Guidance is in better agreement with Wednesdays winter storm.

Per the day shift, an amplified northern shortwave trough

should phase with the southern shortwave long the Eastern

Seaboard. 00Z Canadian model run shows an increase in QPF along

the phasing boundary, thus increased precip chances in the south

early Wednesday morning. Model and WPC guidance also points to

slightly higher QPF in the southern areas and in previously

forecasted eastern regions. However, some changes in the

Wednesday afternoon temps and QPF has slightly decreased snow

totals. In addition, recent upper air model sounding indicated a

layer of warm air along the transition from rain to snow

Downeast and possibly into Southern Aroostook. Thus, chances of

freezing rain and sleet have been added to the forecast. These

changes do match up fairly well with the 50th percentile for

snow amounts and is in good agreement with WPC. These changes

not impact the Winter Storm Watch that remains in effect for

Wednesday.

By Wednesday night models show the shortwaves sort of merging

and moving eastward, which will taper snow showers to flurries.

As the high pressure behind the low moves in, the pressure

gradients will compress, increasing winds to gusty conditions.

With higher snow ratios possible, areas that received only snow

could see patchy blowing snowing throughout the day on Thursday.

By Thursday night, winds should calm and skies should clear,

allowing temps to drop into single digits, with some temps below

zero in the north.

&&.....

URGENT - WINTER WEATHER MESSAGE

National Weather Service Gray ME

1115 AM EST Tue Dec 21 2021

MEZ013-014-021-022-025>028-220015-

/O.CON.KGYX.WW.Y.0019.211222T0600Z-211223T0000Z/

Southern Franklin-Southern Somerset-Kennebec-Interior Waldo-

Sagadahoc-Lincoln-Knox-Coastal Waldo-

Including the cities of Farmington, New Sharon, New Vineyard,

Temple, Wilton, Chesterville, Jay, Athens, Cornville, Skowhegan,

Palmyra, Pittsfield, Embden, Madison, Augusta, Sidney, Windsor,

Vassalboro, Waterville, China, Palermo, Brooks, Jackson, Knox,

Liberty, Montville, Morrill, Waldo, Winterport, Unity, Arrowsic,

Bath, Phippsburg, Bowdoinham, Topsham, Bowdoin, Whitefield, Dresden,

Alna, Bremen, Bristol, Damariscotta, Newcastle, Boothbay Harbor,

Wiscasset, Waldoboro, Owls Head, Rockland, Appleton, Camden, Hope,

Rockport, Thomaston, Belfast, Northport, Searsmont, and Lincolnville

1115 AM EST Tue Dec 21 2021

...WINTER WEATHER ADVISORY REMAINS IN EFFECT FROM 1 AM TO 7 PM EST

WEDNESDAY...

* WHAT...Mixed precipitation expected. Total snow and sleet

  accumulations up to 2 inches and ice accumulations around two

  tenths of an inch.

* WHERE...Portions of south central and western Maine.

* WHEN...From 1 AM to 7 PM EST Wednesday.

* IMPACTS...Plan on slippery road conditions due to snow covered

  roads. The hazardous conditions could impact the Wednesday morning

  and evening commutes.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling. The latest road

conditions for the state you are calling from can be obtained by

calling 5 1 1.

&&

$$

Legro