NWS Scientific Forecaster

C&P from NWS Scientific Forecaster

Area forecast discussion

National Weather Service Gray ME

1204 PM EST Fri Dec 23 2016

Synopsis...

high pressure builds across the region today, providing mostly

sunny skies, and above normal temperatures. Another fast moving

system brings some rain and snow to the area for Saturday. High

pressure will build back into the area for Christmas day into

early Monday before our next weather maker arrives with mixed

precipitation by late Monday into Tuesday. Temperatures will be

at or above seasonal norms through early next week.

&&

Near term /until 5 PM this afternoon/...

1201 PM...minor estf update to reflect current mesonet in near

term grids.

 

 

930 am...outside of some lingering low cloud below the subsidence

inversion noted on 12z kgyx raob...a mostly sunny day on current

GOES visible imagery. For this estf...I adjusted sky grids to

reflect current satellite low cloud trends and ingested the 14z

mesonet into near term grids.

Prev disc...

645 am...skies clearing outside of the mountains and have adjusted

forecasts accordingly. Also made some tweaks to T/TD based on

current obs.

Previously...stratocu is hanging tough in some areas downwind of

the mountains, and it may linger through sun rise before increased

mixing breaks it up, as a weak inversion lingers. Once the clouds

break up should see mainly sunny skies outside of the mountains

through the day, while in the mountains the clouds will linger

through the morning before they start to dissipate. Highs will

range from the low to mid 30s in the north to low 40s in south.

&&

Short term /5 PM this afternoon through 6 PM Saturday/...

another fast moving system will approach from the west Friday

night, but overall precip should hold off until around daybreak.

Look for some rad cooling as skies will remain mostly clear in

the evening, with lows around midnight or so, ranging from the low

20s in the mountains, to the upper 30s in srn New Hampshire and along the ME

coast.

 

 

Models have been in general agreement over the last several runs

that two waves will approach from the west, one in the nrn stream

and one in the southern stream before phasing over US and to our

east. This will keep the heaviest precip to our south and east as

triple point low from larger scale low to out north forms over

the Gulf of ME and deepens over Nova Scotia. The fast moving

system will limit precip to the 24/12z - 25/00z period, and really

bulk of precip looks to be 14-22z. P-type will like start as snow

inland, and maybe briefly as snow/rain on the coast and in far southeast New Hampshire.

The snow will gradually change to rain from south to north during

the course of the day, with little to no accums on the coast and

southeast New Hampshire. Could see up to an inch inland during the the morning on

the inland coastal plan, and just and inch or two in the mountains.

So overall, nothing too significant, but may cause some travel

issues inland during the day, especially during the morning before

temps rise above freezing across almost all the County Warning Area. Highs will

range from the mid to upper 30s in the mountains, to around 40 on

the coastal plain and along the coast.

&&

Long term /Saturday night through Thursday/...

high impact weather potential: mixed precipitation possible

Monday night into Tuesday.

Overview: taking a look at the big picture to start off, the

hemispheric flow is unblocked allowing a series of short waves to

pass through our region in the next week. The core of the cold air

has retreated to Greenland (the danish island, not the place in

NH!) Keeping our temperatures comfortably seasonable. Across North

America the flow is quite zonal to start the weekend and then a

strong trough digs down along the coast of British Columbia on

Sunday. This trough eventually closes off over Colorado by Monday

before weakening and retreating back to James Bay by Tuesday.

Accompanying this trough is a strong surface low which will bring

precipitation to the region on Monday night into Tuesday. The

zonal flow returns for Wednesday and Thursday before the next

batch of cold air aloft dives southward out of the northwest

territories at the end of next week.

Sunday: Christmas day will bring northwesterly flow and mountain

showers as saturday's front moves off into the Maritimes. Wind

profiles favor precipitation near the crest of the mountains and

have increased the pop and snow amounts for far northern New Hampshire into

the Quebec/Maine border. High pressure will build into the region

overnight Sunday into Monday allowing for temperature to drop into

the single digits. With the calm conditions and clear skies expect

good radiational cooling. Have gone colder than most guidance for

the mountain valleys and would not be surprised to see readings

as low as -10f in some northern valleys.

Mon- tues : the focus of this forecast is on Monday into Tuesday.

A potent storm develops in the Lee of The Rockies on Sunday in

association with the upper closed low. Dropping at close to 1mb/hr

it rapidly intensifies into a very strong cyclone over eastern

North Dakota in the early hours of Monday. By Monday afternoon

the system becomes vertically stacked and occludes over Lake

Superior and begins to weaken as the cloud shield moves over

northern New England. On Monday night the low passes to our north

allowing warm air to push northward into the region. This system

is unusual in a few ways. It is both anomalously warm and moist

with an impressive 3 sigma anomaly in precipitable water and 850 temperature

anomalies around 2 sigma. There is also very good agreement on

the track and intensity through midday Monday when the storm

reaches maximum intensity over North Dakota. These factors combine

to give moderate confidence in a freezing rain/mixed precipitation

scenario for the overnight hours of Monday into Tuesday.

With the low center well to our north overrunning precipitation

associated with the warm front will move through the northern

portion of the County Warning Area Monday night. The trailing cold front will then

pass through Tuesday morning brining an end to precipitation by

midday Tuesday. The temperatures will be consistently increasing

across the area from Monday morning all the way into Tuesday with

consensus of numerical guidance having the region rising above

freezing by 06z Tuesday. With temperatures aloft up to 8c moving

in ahead of the surface warming expect a few hours of freezing

rain Monday night. Cips analogs also show a number of freezing

rain reports. Of greatest concern for freezing rain are the

northern mountain valleys where it will be hardest to get the cold

air out and also the foothills of Maine as far south as Augusta

and Fryeburg where cold air may be dammed during Sunday night into

Monday. Any lingering cold air would increase the icing. However

at this point have low confidence in the cold air damming and

have gone with the increasing overnight temperature trend. The

potential for stronger cold air will need to be monitored over the

next several days.