NWS Forecast Area Discussion - New England Area

000
FXUS61 KBOX 231759
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1259 PM EST Fri Feb 23 2018

.SYNOPSIS...
High pressure over Maine moves east today. A frontal system
approaching from the west will bring another round of rain and
mixed precipitation this afternoon and evening. Active weather
pattern continues this weekend with more rain and interior mixed
precipitation Saturday night and Sunday. A near- seasonable,
quiet pattern for early next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Forecast remains on track with spotty rain showers moving into
the region. Many of the showers are not reaching the ground due
to the dry air aloft, but some areas are reporting light rain.
We have also received reports of sleet along the eastern slopes
of the Berkshires.

*** A period of light icing likely later today and early this
 evening over higher elevations in central and western MA ***

Spotty showers will overspread the region before the large
swath of rain moves in from the west. Main time frame of the
freezing rain looks to be between 1pm and 9pm. Area of heavy
rain however will likely not enter the region until 3pm.

A Winter Weather Advisory remains in effect for the higher
terrain through this evening due to the potential for freezing
rain. Sounding profiles show the best chance for freezing
rain/sleet to be across the higher terrain given the warm front
aloft with cooler temperatures at 925mb. There still stands a
low potential for ice accumulations up to a quarter inch on the
eastern slope of the Berkshires.

Given a large area of PWATs just to our south and southwesterly
winds by 21Z, this moisture will likely be advected over the
region, bringing areas of heavy downpours into the evening. Most
models are suggesting precip accumulations just over a quarter
inch.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tonight...

Rain will be exiting in the evening from west to east as mid
level drying moves in behind departing surface wave and winds
shift to west. Temps rising through the 30s, and into the 40s
in the coastal plain. Patchy low clouds and fog will develop
tonight with some clearing possible toward daybreak.

Saturday...

Surface ridging builds into New Eng bringing dry weather.
Sunshine will give way to increasing afternoon clouds in
progressive pattern, with just a low risk for a few showers
moving into SW New Eng by evening. A rather mild day expected in
the coastal plain. 925 mb temps range from +2C in NW MA to 8C
near the south coast. With NW flow, temps will reach well into
the 50s in the coastal plain with a few locations in RI and SE
MA possibly near 60. Cooler 40s over higher elevations NW MA.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
*/ Highlights...

 - Wintry mix transitions to freezing rain Saturday night into Sunday
 - Quiet, dry, near-seasonable early week period
 - Stormy pattern emerging for the beginning of March

*/ Overview...

Upstream Pacific flow flattening, SE CONUS sub-tropical H5 ridge
weakening, SW-NE thermal wind axis and storm track along the better
baroclinic zone shifts S/E along which mid-level impulses eject out
of a preferred H5 trof pattern across the W CONUS. An active weather
pattern with a series of disturbances delivering mixed precipitation
events thru the weekend. Building up over the N Atlantic signaled
by a strongly -NAO, initial omega-block transitions to a rex-block,
retrograding W. The preferred region of storm development shifting,
a quiet early week period looks to turn stormy for the beginning of
March. Preference to high-res guidance through the weekend capturing
2m temperatures in more detail, with ensemble means thereafter. Hit
on targets of opportunity below.

*/ Discussion...

Saturday night into Sunday...

An over-running precipitation event associated with a classic warm
occlusion into S Canada. Transitioning precip-types as a warm nose
around H8 becomes pronounced, deepening above a shallow surface cold
airmass, maintained by interior S funneling ageostrophic flow aided
by a secondary coastal surface low invoked by strong synoptic lift /
forcing as cold surface high pressure is situated N/E. Whew. Overall
a favorable synoptic setup for an initial onset of snow and/or sleet
before changing over to freezing rain, mainly across the interior.
Change-over if not already rain towards the coast.

No surprise consensus forecast guidance edged colder, more high-res
guidance becoming available. CIPS analogs a higher probability of a
>6 hour freezing rain event, yet notably a large spread in the top 5
analogs. While leaning N/W MA holding below freezing throughout, and
that sub-freezing wet bulb conditions could extend as far S as N CT
and NW RI, hesitation given a decent slug of precip falling through
an ever increasing warm layer above a shallow cold layer.

Forecast trend accordingly, entrenching cold overnight but chipping
away into Sunday morning with increasing warm air advection aloft
through which precipitation intensity reaches its peak. A retreat of
mainly freezing rain outcomes N/W over time, reiterating that areas
in N/W MA are likely to see freezing rain throughout after a brief
burst of snow and/or sleet. Ice accretion amounts upwards of 0.1 to
0.2 inches given less dry air intrusions and deeper lift / forcing.
This an precipitable waters in the 0.75 to 1.00 inch range, looking
at storm-total precipitation amounts that can be well up around 0.50
to 0.75 inches, locally higher along SW facing high terrain slopes
and along the anticipated kinked surface warm front.

Early next week...

Continued preference to ensembles. N Atlantic traffic build up, an
omega-block evolves lending to a strongly -NAO. Evolution towards a
rex-block retrogressing as energy continually emerges from upstream
out of a W CONUS H5 trof pattern, indications the initial region of
preferred storm development off SE Canada alters W closer to the E
CONUS. The slowed pattern allowing cyclones to mature and later
occlude in our neighborhood, forecast model consensus trending with
a deep, strong storm in our vicinity for the beginning of March. Way
out in time, can hardly touch on details and specifics, continued
ensemble member spread. However can`t ignore such robust signal when
tides are reaching their peak (Boston around 11.5 feet). Until then
will keep it dry and near-seasonable right on up through Thursday.
Then all eyes are upon a potential storm system.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Saturday/...Moderate confidence.

Through today...MVFR/IFR conditions will overspread the region
by mid afternoon, with rain, pockets of sleet and freezing rain
developing across interior MA. Greatest risk of FZRA over
higher elevations.

Tonight...MVFR prevails with rain this evening, and pockets of
FZRA at higher elevations in northern MA. RA/FZRA will end by 3z
along the eastern coast. Fog will settle in behind the precip,
keeping conditions MVFR in the valleys.

Saturday...Fog may linger along the southern coast and islands
past 12z. Conditions will improve to VFR across the region by
early morning.

KBOS Terminal...Moderate confidence. MVFR through this evening
with onset of rain near 21z. Rain ending near 3z with improving
conditions around 6z.

KBDL Terminal...Moderate confidence. MVFR/IFR through this
evening. Patchy fog in the AM, burning off by 9z. VFR conditions
to follow.

Outlook /Saturday Night through Tuesday/...Moderate confidence.

Saturday: VFR. Breezy.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance RA, FZRA, chance SN.

Sunday: Mainly IFR, with areas MVFR possible. Windy with local
gusts to 30 kt. RA, FZRA, patchy BR.

Sunday Night: Mainly VFR, with local IFR possible. Breezy.
Patchy FG.

Monday: VFR.

Monday Night: VFR. Breezy.

Tuesday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Saturday/...High confidence.

Today...NE winds veering to SE in the afternoon. Gusts to 20 kt
over eastern waters late in the day. Vsbys lowering in rain and
fog late.

Tonight...A brief period of southerly gusts to near 25 kt
possible NE MA waters in the evening, otherwise winds shifting
to west with gusts to 20 kt. Rain exits in the evening with
improving vsbys, but patchy fog may develop over southern
waters.

Saturday...Diminishing west winds becoming northerly in the
afternoon. Seas below SCA.

Outlook /Saturday Night through Tuesday/...

Saturday: Winds less than 25 kt.

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft. Chance of
rain.

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas. Rain, patchy fog. Local
visibility 1 nm or less.

Sunday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain, patchy fog. Local visibility 1 to 3 nm.

Monday through Monday Night: Winds less than 25 kt. Seas up to
5 ft.

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Winter Weather Advisory until 9 PM EST this evening for
     MAZ002>004-008-009.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...KJC/Sipprell
NEAR TERM...KJC/Nocera/Sipprell/Correia
SHORT TERM...KJC/Nocera
LONG TERM...Sipprell
AVIATION...KJC/Nocera/Sipprell/Correia
MARINE...KJC/Sipprell

NWS BOx Office Area Forecast Discussion