Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 301529
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1129 AM EDT Sun Apr 30 2017

.SYNOPSIS...
Strong high pressure over southern Quebec will build southeast
across New England today, bringing drier and much cooler air.
This high pressure moves off the coast this evening, and a warm
front moves north into our region Monday. A cold front will
move through Tuesday. Another storm moves toward southern New
England late Thursday or Friday, and could linger nearby into
Saturday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1125 AM update...
Updated forecast to increase PoPs and add thunder to western MA
given latest radar trends. SPC mesoanlysis indicating marginal
MUCAPES 250-500 J/kg across western New Eng so cant rule out a
rumble of thunder as this complex moves through next 1-2 hours.

Previous discussion...
Small area of convection lifting NE from central NY expected to
weaken as it moves into more stable environment. However, weak
theta-e advection may support a few sprinkles or light shower,
especially north of the Pike. Otherwise, mainly dry conditions
with increasing clouds as area of low/mid level moisture moves
across New Eng in developing warm advection pattern. Much cooler
today with low level easterly flow. Temps ranging from the
lower 50s across east coastal MA to lower 60s in the CT Valley.
Temps will be around 30 degrees cooler than yesterday in east
coastal MA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Tonight...
As high pressure moves offshore, a warm front will approach SNE
from the south and west. SREF probabilities are near 100 percent
for low cloudiness to rapidly develop across the entire region.
Expect patchy fog along the south coast as higher dewpoint air
moves in over colder sea surface temperatures. Models are
generating some light QPF which is likely some drizzle given the
abundant low level moisture and dry air aloft. As the night
progresses, there could also be some scattered showers, as a
southwesterly low level jet of 40 kt develops, accompanied by an
increase in K Indices...to near 30. Lows will be mainly in the
mid 40s.

The astronomical tide will be on the high side again...11.45
feet at Boston at 3:35 AM, but little in the way of storm surge
is expected, with southeast winds less than 20 kt, so am not
expecting much in the way of splashover. Will keep an eye on
this possibility.

Monday...
The warm front will continue moving northeastward but may have
trouble making it all the way into the Merrimack Valley.
Have gone with a model blend of temperatures...which are mainly
in the 60s but range from near 70 in the CT Valley to the upper
50s in Essex County, MA and over outer Cape Cod and the
Islands. The day will start will start with low clouds, fog, and
areas of drizzle. The surge of higher K indices exits northern
MA by mid- morning, and the risk of any showers will end from
south to north along with it. Much drier air aloft moves in from
the south, actually, for a time, allowing for some breaks of
sunshine through mid-afternoon. Then, clouds will increase and
there is a chance of showers late in the afternoon, well in
advance of an approaching cold front.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Overview...

Still seeing variations in the model solutions for later this
week, although some details are starting to emerge with greater
confidence into Thursday morning. 30/00Z operational GFS
continues to be out of step with the GEFS mean, as well as the
ECMWF and CMC. Favored a consensus approach through Wednesday,
then leaned a bit more toward a non-GFS solution Friday into
Saturday. Lower than average confidence in the Friday-Saturday
forecast.

Details...

Monday night-Tuesday...Moderate confidence.
Low pressure will push across the Great Lakes into Ontario and
western Quebec during this timeframe.

Strong SW low level jet will result in excellent moisture
transport, and help to organize modest instability ahead of a
cold front. Not expecting severe weather, since the primary time
period would be Monday night, but with 45-55 kt winds, cannot
completely dismiss the possibility.

Showers move out of our region Tuesday morning, but the cold
front will lag a bit longer. Gusty southwest winds should
continue through the day. Once the sunshine breaks out,
expecting another day of above normal temperatures.

Wednesday...Moderate confidence.

This is still looking like a mainly dry period. Cyclonic flow
aloft will mean a period of diurnal clouds, mostly toward NW MA.
Any isolated showers which might develop would be confined to
far western MA. Near normal temperatures.

Thursday-Friday...Moderate confidence.

Have greater confidence early Thursday morning will start out
dry. Lots of ingredients lining up for a period of wet weather,
the question which is harder to pin down is the timing. Have
increasing rainfall chances from SW to NE through the day
Thursday, leading into the more likely period of rainfall
Thursday night into Friday. Rainfall could be heavy at times.

Saturday...Low confidence.

This period remains complicated. GFS still has a very wet
solution, while the CMC, ECMWF, and GEFS suggest a closed 850 mb
low passes by to our west, which would force a dry slot into
southern New England during the. As previously mentioned,
favored the drier non-GFS solutions, but did not go with a
completely dry forecast. It will likely be another day or two
before this discrepancy start to get resolved.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

Short term...through Monday.

Today...High confidence. VFR. Low risk for a brief
shower/sprinkle north of the Pike. Easterly winds 5-15 kt.

Tonight...Moderate confidence. Conditions deteriorating to
MVFR/IFR around midnight as stratus and patchy drizzle
develops. Areas of fog along the south coast.

Monday...Moderate confidence. MVFR-IFR CIGS through mid to
late morning in areas of drizzle and fog. Some improvement to
VFR mainly south of the Mass Pike from late morning through mid
afternoon. Becoming MVFR again with scattered showers late in
the afternoon, mainly in western sections, well out ahead of an
advancing cold front.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday night...High confidence.
CIGS lower to mainly MVFR across most of the region, with local
IFR in heavier SHRA. Scattered TSTMS. SW LLWS up to 45-55 kt at
2000 ft AGL along the south coast, including the Cape and
islands.

Tuesday...High confidence.

MVFR-IFR conditions linger early morning in leftover showers,
then improving to VFR through midday. LLWS with SW winds
45-55 kt across south coastal areas possible through 16Z,
highest across the islands.

Wednesday...High confidence. VFR.

Wednesday night-Thursday...Moderate confidence.

VFR expected through the period, although CIGS lower during
Thursday. Increasing coverage of rain from SW to NE Thursday,
with MVFR VSBYs in heavier rain during the afternoon. -RA and
patchy fog lingers with areas of MVFR CIGS/VSBYS into Thursday
night.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Monday/...High confidence.

Today into tonight...NW-N winds may gust to near 20 kt early
this morning. Winds then become N/NE later this morning and veer
to the E/SE by mid-late afternoon. Speeds will diminish to 15
kt or less. Winds become SE to S tonight. Seas below Small Craft
Advisory thresholds. Vsbys lowering to below 3 miles in fog
developing after midnight over the southern coastal waters.

Monday...Moderate confidence.
Warm front moves across the waters Monday. SE winds ahead of the
front become S-SW behind the front, mainly over the southern
waters. Visibility restrictions in areas of drizzle and patchy
fog through early Monday afternoon. Seas could build to 5 ft
over the southern waters late in the afternoon. May need to
issue Small Craft Advisories...but still a little too early.

Outlook /Monday Night through Thursday/...

Monday Night...Moderate confidence.

Increasing SW winds ahead of a cold front approaching the waters,
with gusts up to 30 kt. Rough seas building across the outer
coastal waters, too. Showers likely with scattered
thunderstorms. Visibility restrictions in precipitation. Small
Craft Advisories likely.

Tuesday...Moderate confidence.

Improving conditions as showers move out of the area during the
morning. Gusty SW winds up to 30 kt continue, before
diminishing Tuesday night. Rough seas linger across the outer
coastal waters. Small Craft Advisories likely for the southern
coastal waters.

Wednesday...Moderate confidence. Winds continue to diminish
through  Wednesday night, but seas will take a while longer.

Thursday...Moderate confidence.
Winds expected to remain less than 20 kt, with seas less than
4 feet.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Belk/GAF
NEAR TERM...KJC/GAF
SHORT TERM...GAF
LONG TERM...Belk
AVIATION...Belk/GAF
MARINE...Belk/GAF



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