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fxus61 kbox 180621 
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Area forecast discussion
National Weather Service Taunton Massachusetts
121 am EST sun Feb 18 2018

Synopsis...
fast moving low pressure will bring a plowable snow to portions
of southern New England overnight. The snow will end by
daybreak with rapidly improving conditions and temperatures
rising well above freezing. Warm frontal showers lift north
across the region for Monday, followed by a warm up for the mid
week period with potential record breaking warmth. A return to
more seasonable conditions by late week.

&&

Near term /until 6 am this morning/...

1250 am update...

Kbox 88d dual pol continues to show correlation coefficient (cc)
values of around 0.8, indicative of wet snow and/or rain across
southeast Rhode Island and S coastal Massachusetts including the mid and lower
cape and Martha's Vineyard. Also noting bright banding on the
0.5 degree reflectivity where the mixed precip lies. Temps in
those areas ranged from 33 degrees from kpvd-kpym, up to 39
degrees at kack at 05z where it continues to lightly rain.

Winds have shifted back to light north across the CT valley where
temps remain in the upper 20s to near 30, while heavier snow was
reported across north central and NE mass down to the Route 128
where visibilities were between 1/2 and 1 mile. Noting snow
amounts of 3-5 inches across north central CT into northwest Rhode Island on public
information statement at 1217 am.

With the mix and change over to rain across S coastal areas,
have ended the the winter storm warnings and winter weather
advisories across those areas.

Noting back edge of precip working into SW CT, moving into the
southern Berkshires as deepening low pressure pushes east-northeast early
this morning.

Have updated to bring conditions current, including headlines to
be in line with the conditions especially across S Rhode Island/S coastal
mass.

&&

Short term /6 am this morning through 6 PM Monday/...

The storm tonight will quickly depart within the progressive mid
level flow. High pressure will build into the mid Atlantic
states, bringing drier and warmer conditions to southern New
England during this period. Expecting a decent amount of snow
melt Sunday afternoon. Good radiational cooling conditions
Sunday night could lead to the formation of black ice on
untreated surfaces.

&&

Long term /Monday night through Saturday/...

*/ highlights...

- showers on Monday
- above average temperatures Tuesday and Wednesday
- following some rain, return to seasonable conditions late week

*/ overview...

Split flow parked out across the north-central Pacific. S-stream
dipping towards Hawaii into the inter-tropical convergence zone where anomalous westerlies
prevail with a lingering phase 7 mjo. North-stream ridging into
Alaska. The two under- going confluence into western North America.
North-stream energy sheared S capturing S-stream mild, moist
westerlies before ejecting NE. A sub- tropical ridge builds off
the southeast Continental U.S. As does the integrated water vapor transport into
southeast Canada, an anti-cyclonic rossby wave break emerges into the north
Caribbean. On the warm side of the thermal wind profile,
looking at a surge of warmer than average conditions, shots of
wet weather suppressed by mid-level subsidence, blustery SW
winds throughout. Will hit on the targets of opportunity below.

*/ Discussion...

Monday...

Warm frontal light to moderate rain late and overnight.
Isentropic ascent, convergent forcing. Precipitable waters
+1-inch, expect higher outcomes north/west along SW-facing high terrain
slopes, away from the building 500 mb sub-tropical ridge. Cold air
eroding with breezy SW winds, gusts up to 30 mph initially
before warmer air aloft inverts mixing to off. Both clouds and
dewpoints increasing, potential fog issues given colder waters,
ground. Non-diurnal temperature trend towards Tuesday morning
as h925 temperatures warm above +10c.

Tuesday into Wednesday...

Potential record-breaking warmth, especially Wednesday. Please
see the climate section below for record highs established on
February 21st and for all of February since records began. H925
temperatures warming to +12-16c, 850 mb temperature anomalies +20c.
Going with the cold front holding off till Wednesday night. A
question of clouds hampering sunshine. Dry above h9, fair amount
of low-level moisture to mix out below that given higher
dewpoints. Breezy SW winds aiding in mechanical mixing along
with anticipated daytime heating, expect cloud breaks over the
interior while socked-in along the S/southeast coast, especially
evening and overnight periods. It's amazing you only have to
look back 1-year to get an idea on potential outcomes. Not the
same synoptic pattern but can gain insight as to possible
impacts. Stay conservative, hold highs in the 60s. SW gusts 30
to 35 mph possible.

Wednesday night into Thursday night...

Showers at first along a sweeping cold front, suppressed in with
its intensity by the sub-tropical ridge. Expect light outcomes.
Then a cool down to more seasonable temperatures beneath high
pressure. It could be into Friday morning we'll see our coldest
temperatures more so if radiational cooling materializes.

Friday Onward...

If the sub-tropical 500 mb ridge weakens, thermal wind profiles
shifting S/E, will be watching waves of energy out of the
confluent base of a 500 mb trof over the west Continental U.S.. on what side of
the envelope and specific timing of individual waves, all
pertinent on potential outcomes that at this time are uncertain.
Preference to the ec ensemble mean.

&&

Aviation /06z Sunday through Thursday/...
forecaster confidence levels...

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

Short term /through tonight/...

Overnight...moderate confidence.
Conditions deteriorating with onset -sn/sn, possible +sn for
bdl to bos and interior terminals S/east away from the coast. Some
mixed -ra/-sn along S coastal terminals, with mainly rain at kack.
Lowering LIFR-vlifr with 1/4sm snow vv002 for some toward
midnight, but some question where the band of heavier snow will
set up. IFR-LIFR for S coastal terminals with mix with, possible
changeover to rain.

Light/variable winds through 07z-08z become north-northwest toward
daybreak.

Today...
brief leftover MVFR-IFR ceilings through 14z, then VFR. Northwest wind
gusts up to 25-30 kt this morning, highest across higher
inland terrain and along the coast, then diminish during the
afternoon.

Tonight...
VFR.

Kbos terminal...moderate confidence.
IFR conditions in -sn, may see conditions briefly lower to
LIFR in occasional periods of snow through 08z-09z. Snow
accumulations along runways of around 2-3 inches. Conditions
improve to VFR by around 12z-14z.

Kbdl terminal...
snow begin reported, will increase in intensity going towards
midnight, diminishing a couple of hours after, light into the
early morning hours. Looking for snowfall accumulations on the
runways potentially up around 6 inches. Airport weather warnings
may be needed for snowfall rates of 1-2 inches per hour.

Outlook /Monday through Thursday/...moderate to high confidence.

Washingtons birthday: VFR. Breezy. Rain showers likely.

Monday night: mainly VFR, with areas IFR possible. Breezy. Rain showers
likely.

Tuesday: mainly VFR, with areas IFR possible. Breezy. Slight
chance dz.

Tuesday night: mainly VFR, with local IFR possible. Breezy.
Slight chance dz.

Wednesday: mainly VFR, with local MVFR possible. Breezy.

Wednesday night: VFR. Chance rain showers.

Thursday: VFR. Slight chance rain showers.

&&

Marine...
forecaster confidence levels...

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

Short term /through tonight/...

Poor visibility with gusty east-southeast winds expected tonight in snow
and rain. Gusts could approach 30 kt. Rough seas expected to
build once more across the outer coastal waters Sunday. Gusty northwest
winds develop in the wake of a departing low pressure, too.
Small craft advisories posted for all the waters at some point
tonight into Sunday.

Outlook /Monday through Thursday/...moderate to high confidence.

Washingtons birthday: low risk for Small Craft Advisory winds
with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance
of rain showers.

Monday night: winds less than 25 kt. Seas up to 5 ft. Rain
showers likely.

Tuesday: winds less than 25 kt. Local rough seas. Slight chance
of drizzle.

Tuesday night: winds less than 25 kt. Areas of rough seas.
Slight chance of drizzle.

Wednesday: winds less than 25 kt. Areas of rough seas. Slight
chance of rain showers.

Wednesday night: winds less than 25 kt. Local rough seas.
Chance of rain showers.

Thursday: winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

&&

Climate...
record highest observed temperature for February...
(since records began)

Boston.........73 (02/24/2017)
Hartford.......73 (02/24/1985)
Providence.....72 (02/24/1985)
Worcester......69 (02/24/2017)

Record high temperatures (tuesday 20th / Wednesday 21st)...

February.......20th......21st.....

Boston.........68 (1930) 63 (1906)
Hartford.......69 (1930) 63 (1930)
Providence.....69 (1930) 63 (1930)
Worcester......65 (1930) 59 (1930)

Record warmest low temperature...

February.......20th......21st.....

Boston.........46 (1930) 45 (1994)
Hartford.......50 (1981) 49 (1981)
Providence.....48 (1981) 50 (1981)
Worcester......47 (1981) 43 (2002)

&&

Box watches/warnings/advisories...
CT...Winter Storm Warning until 7 am EST this morning for
ctz002>004.
Massachusetts...Winter Storm Warning until 7 am EST this morning for
maz005>007-011>019.
Winter Weather Advisory until 7 am EST this morning for
maz002>004-008>010-026.
Rhode Island...Winter Storm Warning until 7 am EST this morning for
riz001>006.
Marine...Small Craft Advisory from 7 am this morning to 2 PM EST this
afternoon for anz231>234.
Small Craft Advisory from 8 am this morning to 1 PM EST this
afternoon for anz230.
Small Craft Advisory from 7 am this morning to noon EST today
for anz236.
Small Craft Advisory from 7 am this morning to 1 PM EST this
afternoon for anz235-237.
Small Craft Advisory until 6 PM EST this evening for anz250-
256.
Small Craft Advisory until 1 PM EST this afternoon for anz251.
Small Craft Advisory until 10 PM EST this evening for anz254-
255.

&&

$$
Synopsis...Belk/sipprell
near term...sipprell/evt
short term...Belk

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