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Area forecast discussion
National Weather Service Taunton Massachusetts
1034 am EST Tue Jan 23 2018

Synopsis...
freezing rain across portions of northern Massachusetts will change to
plain rain by early afternoon. Otherwise...heavy rain is the
main story this afternoon along with strong winds across
portions of eastern Massachusetts and Rhode Island. Blustery, dry and colder weather
follows Wednesday through Friday, then a warming trend next
weekend. A cold front may bring showers next Sunday or Monday.

&&

Near term /until 6 PM this evening/...

*/ highlights...

* freezing rain changes to plain rain across northern Massachusetts by 1 PM
* heavy rain/isolated thunderstorm risk this afternoon
* brief poor drainage street flooding possible
* period of strong wind gusts along and southeast of bos-pvd corridor

Freezing rain...

Moderate to heavy freezing rain being reported across portions
of central and northeast Massachusetts. While surface warm front is still
quite a distance to the south of this region...latent heat
release was slowing bringing temperatures into the 30 to 32
degree range but still some upper 20s in extreme northeast Massachusetts.
Some locations may pickup an additional 0.15 inches of ice
accretion...but latent heat should do its trick and change the
area to all rain by 1 PM. Greatest icing risk will be in far
northeast Massachusetts near the New Hampshire border...where a few locations could
see total ice accretion of one quarter inch.

Dense fog...

Areas of dense fog persisted away from areas of heavier
precipitation. Dense fog has reformed on the South Coast with
mild/moist air over running the relatively cold ocean.
Also...areas of dense fog still impacting some of the region so
opted to extend advisory until 1 PM and then re-evaluate.

Heavy rainfall...

Closed low over the Ohio Valley with emerging warm conveyor belt (wcb)
advancing up the eastern Seaboard. Strong jet dynamics associated
with this feature as 925 and 850 mb wind anomalies increase to +3 South Dakota
this afternoon across this area. Subtropical moisture associated
with this wcb increases to +3 South Dakota as well. The combination of strong
forcing for ascent, subtropical moisture and steepening mid level
lapse rates supports periods of heavy rain along with the risk of a
thunderstorm or two. The progressive nature of the system will
limit heavy rainfall duration to about 6 hrs and also cap
rainfall totals to about 0.75 to 1.25 inches.

Strong wind threat...

Impressive low level jet up to 85 kts at 925 mb develops this
afternoon along the South Coast. This results in very strong low
level warm air advection and a Stout inversion developing, limiting the risk of
strong winds aloft from reaching the surface. However with dew pts
rising into the mid 50s along with steepening mid level lapse rates
models generating a few hundred joules of MUCAPE. In addition, most
of the hi res guidance generating impressive model simulated
reflectivity this afternoon with a broken line of low top convection
with embedded stronger elements. This low top convection may result
in an isolated T-storm with strong gusty winds aloft reaching the
surface. Will continue with the Wind Advisory for the coastal plain
of Rhode Island and southeast Massachusetts as warm sector likely overspreads this area
yielding the greatest risk for strong winds aloft mixing to the
surface.

Temperatures...

Very strong warm air advection yields +12c temps at 925 mb across Rhode Island and southeast
Massachusetts this afternoon. Despite showers highs will likely approach 60
across Rhode Island and southeast Massachusetts. Record high for pvd today is 64/1906,
thus there is a very low probability of approaching this
record. However...portions of northern Massachusetts and parts of the CT
River Valley may not be able to mix out completely so its
possible some of these locations only see high temps reach into
the 40s. Coolest high temps expected in far northern Massachusetts.

&&

Short term /6 PM this evening through 6 am Wednesday/...
425 am update...

Tonight...

Frontal passage occurs this evening with strong Post frontal drying,
so expect decreasing clouds and a drying trend from west to east
early. Temps may initially jump upward across the interior where
shallow cold air was unable to scour out during the day, as Post
frontal winds mix down warm air aloft initially before cold air advection develops.
However core of cold air is delayed until Wed night/Thu. Thus only
seasonably cold tonight.

&&

Long term /Wednesday through Monday/...
*/ highlights...

- slightly unseasonable, breezy through the remainder of the week
- mild conditions along with wet weather return early next week

*/ overview...

Fairly benign pattern for the remainder of January. Progressive flow
across the Continental U.S. With colder, Arctic air locked up around the Hudson
Bay / Davis straight region. 300 mb jet streak with wave break out over
the north-central Pacific, 500 mb ridge into the Bering straight, downstream
500 mb trof into the Gulf of Alaska into the west conus, but Overall Flat, an
unimpeded flow downstream, not greatly amplified, so long as traffic
does not bottle up across the North Atlantic. Milder pattern lies ahead
of any synoptic disturbances, wet weather as well, followed by cold
that is not as deep, slightly unseasonable, lacking a deeper Arctic
connection. However, watching early February closely. Aforementioned
300 mb wave break progressing E, potential 500 mb ridge into the west conus, a
nod to ensemble signals of a +pna pattern emerging. Winter isn't
over just yet.

*/ Discussion...

Through Friday...

Quiet and cold. Cyclonic flow persisting aloft, additional mid-level
energy rotating through, cold air advection enhanced and maintained,
boundary layer mixing up around h9 through which northwest flow prevails,
looking at slightly below seasonable conditions (typically mid 30s
for highs, around 20 for lows) and breezy conditions. Talking wind
chills as low as the single digits, possibly below zero for the north/west
high terrain. Scattered cloud decks, flurries over the Berkshires,
northwest wind gusts as high as 30 to 35 mph, otherwise quiet. Some thought
as to refreezing ice jams, but cold not as deep, so perhaps river
flows elevated by Tuesday rains are uninhibited as ice jams would
not be expected to refreeze so quickly.

Weekend into early next week...

Expunging cold air prior to the onset of the next Pacific-origin
disturbance. Question progressive nature and subsequent morphology
with the potential downstream traffic. Certain Arctic air remains
locked up around the Hudson Bay region, the approaching system warm-
core, exhibiting inside-runner behavior along regions of better baro-
clinicity north and W, looking at another period of mild conditions and
wet weather over much of the NE Continental U.S. Followed by return colder air
however not exceptionally deep. However, acknowledge the spread in
ensemble member solutions, nothing is certain. Preference to slower
ec/UKMET solutions, parent with gefs beginning to signal anomalous S-
influx trends. Cold ground prevailing, certain of fog / visibility
issues, potential for flooding with the possibility of moderate to
heavy rain, more so with swollen and/or ice jammed river basins.
Some uncertainty how quickly cold air is scoured out prior to and
with potential onset of wet weather.

&&

Aviation /15z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through tonight/...

Today...moderate to high confidence. Mainly IFR to LIFR
conditions in periods of heavy rain and areas of fog which was
locally dense. Vsbys should improve some this afternoon with the
heavy rain and perhaps an isolated T-storm or two. Still
dealing with freezing rain across parts of northern Massachusetts...which should
change to plain rain by 1 PM. Strong low level wind shear present over the
shallow inversion. While the interior will struggle to mix
out...should see a period of southerly 35 to 40 knot wind gusts
along the coastal plain during the mid to late afternoon.

Tonight...

Big improvement with any leftover IFR/LIFR eastern Massachusetts around 00z
quickly improving to VFR by 03z or so. Elsewhere VFR with
developing gusty SW winds. Any leftover showers over Cape Cod
and Nantucket at 00z quickly moves offshore. Thus dry runways
overnight.

Kbos terminal...high confidence in taf on overall trends but
lower confidence on exact details. Heavy showers with possibly
embedded thunder 17z-22 and low level wind shear.

Kbdl terminal...high confidence in taf on overall trends but
lower confidence on exact details. Heavy showers with possibly
embedded thunder 15z-18z

Outlook /Wednesday through Saturday/...

Tuesday: mainly IFR, with local MVFR possible. Strong winds
with gusts to 40 kt. Shra, areas fg, freezing rain likely, isolated
thunderstorms and rain.

Tuesday night: mainly VFR, with local IFR possible. Windy with
gusts to 35 kt. Areas fg, slight chance rain showers.

Wednesday: VFR. Windy with areas gusts to 30 kt.

Wednesday night: VFR. Breezy.

Thursday through Thursday night: VFR. Windy with local gusts to
30 kt.

Friday: VFR. Breezy.

Friday night through saturday: breezy.

&&

Marine...
forecaster confidence levels...

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

Short term /through tonight/...

Today...

Southerly gales develop with strongest winds along the waters of Rhode Island
and southeast Massachusetts this afternoon. Showers and fog limit vsby.

Tonight...

Front sweeps across the region early this evening with winds
shifting from S to west. Thus southerly gales diminish with the wind
shift along with vsby improving.

Outlook /Wednesday through Saturday/...

Tuesday: moderate risk for gale force winds with areas of gusts
up to 45 kt. Rough seas up to 13 ft. Rain showers, areas fog,
isolated thunderstorms. Visibility 1 nm or less.

Tuesday night: low risk for gale force winds with gusts up to
35 kt. Rough seas up to 12 ft. Chance of rain showers, areas
fog. Local visibility 1 nm or less.

Wednesday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

Wednesday night: winds less than 25 kt. Local rough seas.

Thursday: moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Areas of seas approaching 5 ft.

Thursday night: moderate risk for Small Craft Advisory winds
with local gusts up to 30 kt. Local rough seas.

Friday: winds less than 25 kt. Seas locally approaching 5 ft.

Friday night: winds less than 25 kt.

Saturday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of seas approaching 5 ft.

&&

Hydrology...
the heavy rain will mainly just result in typical brief nuisance poor
drainage street flooding. However...a Flood Watch has been issued for
the Millers river near Athol where an ice jam remains frozen in place
and has the potential to cause additional flooding. A Flood Warning
also remains in effect for the CT river at Middle Haddam...where this
heavy rain may result in increased flooding problems as a result of
the ice jam.

For details on specific area rivers, including observed and
forecast river stages, please visit the advanced hydrologic
prediction service (ahps) graphs on our website.

&&

Box watches/warnings/advisories...
CT...dense fog advisory until 1 PM EST this afternoon for
ctz002>004.
Massachusetts...dense fog advisory until 1 PM EST this afternoon for
maz002>024-026.
Wind Advisory until 7 PM EST this evening for maz013-015>024.
Winter Weather Advisory until 1 PM EST this afternoon for
maz002>008-012-014-026.
Flood Watch until 6 PM EST this evening for maz003-004.
Rhode Island...dense fog advisory until 1 PM EST this afternoon for
riz001>008.
Wind Advisory until 7 PM EST this evening for riz002>008.
Marine...Gale Warning until 8 PM EST this evening for anz232>235-237-
250-254>256.
Gale Warning until 6 PM EST this evening for anz230-231-236-
251.

&&

$$
Synopsis...Frank/nocera/sipprell
near term...Frank/nocera

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