Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 200810
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
310 AM EST Tue Feb 20 2018

.SYNOPSIS...
A mild southwest flow will bring unseasonably mild temperatures
today with record warmth possible Wednesday. A cold front moves
through Wednesday night followed by much colder weather
Thursday. A wave of low pressure tracking along the front may
bring some rain Thursday, possibly mixed with snow in the
interior. An active wet weather pattern Friday through the
weekend during which there is the possibility of mixed
precipitation, freezing rain.

&&

.NEAR TERM /THROUGH TODAY/...

Dense fog along the CT coast expected to expand east along the
south coast early this morning as higher dewpoint air advects
over colder water with SW flow. HWRF and NARRE-TL both show high
probs of vsbys 1/4 mile or less so we issued a dense fog
advisory for the south coast as well as Hartford county.

Stratus and areas of fog will linger this morning, especially
along the south coast, with improving conditions this afternoon.
GFS and NAM indicate decreasing moisture in the 1000-950 mb
layer which should lead to partial sunshine developing in the
afternoon, especially interior.

Soundings show very shallow mixed layer today, mostly 950 mb or
a bit lower which will limit full heating potential. 950 mb
temps near 12C which would support highs reaching into lower 60s
in the CT valley and interior E MA and adjacent RI if sunshine
develops. Modest SW flow will keep south coastal areas in the
lower 50s. SW gusts to 20-25 mph at times.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/...
Tonight...

Mild SW flow continues tonight. Abundant low level moisture will
lead to areas of stratus and fog redeveloping, most prevalent
along the south coast. Dry air in the mid levels so patchy
drizzle possible. Temps may remain at or above 50 degrees
tonight, except 40s Cape/Islands and immediate south coast.

Wednesday...

Persistent SW flow continues ahead of approaching cold front.
Areas of stratus and fog expected to burn off with at least
partial sunshine developing by afternoon. Soundings indicate
slightly deeper mixing than today, up to 925 mb where temps
15-16C. With full sunshine, potential would exist for low to mid
70s in the interior. However, low clouds expected to linger
through the morning which may limit full potential so expected
highs upper 60s to lower 70s away from the south coast which
would still comfortably establish record highs at BOS,BDL,ORH
and close call at PVD. These temps are up to 30 degrees above
normal. SW flow with gusts to 25 mph will keep temps in the 50s
along the immediate south coast.

Cold front approaching from the west may bring a few late day
showers to western MA.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...

*/ Highlights...

 - Showers Wednesday night
 - Cold rain, wet snowflakes Thursday
 - Active weather pattern Friday through the weekend
 - Watching for potential mixed precipitation, freezing rain
 - Pattern change early next week

*/ Overview...

Persistent SE CONUS sub-tropical H5 ridge maintained by parked N-
Central Pacific split flow and downstream H5 trof over the W CONUS
generating a warm-moist atmospheric river from the Central Pacific
NE to SE Canada. But nothing lasts forever. Breakdown of upstream
pattern, thermal wind flattens through which impulses stretch, dip
southward. A brief midweek warm-up is followed by an active weather
pattern late week into the following week. Along a parent frontal /
baroclinic zone, sulked S, stretching across the NE CONUS, thermal
profiles in question as intriguingly ensembles signal an evolving
blocky N Atlantic pattern per forecast strong -NAO into March. Will
hit on targets of opportunity below. Ensemble guidance preferred.

*/ Discussion...

Wednesday night into Thursday...

Leaning with the cold front pushing S, suppressed via high pressure,
sinking mid-level air. Showers overnight. Attention turns to a wave
ejecting along the baroclinic zone into Thursday. Daytime event, 2m
temperatures wavering around 34. An over-running event, perhaps some
vertically-staggered W-E banding pressed up against the 1040+ high,
as cool, dry air undercuts. Expect a cold rain event, wet snowflakes
mixed in, but no accumulation. More activity/outcomes closer to the
S-coast of New England.

Thursday night...

Hold with an influential near 1040 high and hold off on any weather.
With that, light winds, mostly clear conditions, favor radiational
cooling and will lean towards cooler 2m temperature guidance.

Friday into Friday night...

Lifting warm frontal disturbance with surface high pressure settled
to the E. Noting ageostrophic wind profiles, wet-bulb temperatures,
low level thermal profiles, will be monitoring for potential shallow
cold air to lock-up briefly across N/W MA especially within interior
sheltered valleys. Can`t rule out a short period of freezing rain,
confidence gained via CIPS analogs. Otherwise rain and warming
temperatures, non-diurnal trend during the overnight period.

Saturday into Sunday...

More potent CONUS disturbance ahead of which high pressure builds
over E Canada. Will be monitoring for precipitation-type issues once
again with the possibility of a near-shore secondary low developing
despite the thrust of stronger dynamics N/W across the Great Lakes
Region. Beyond 120 hours, notable ensemble member spread, confidence
low at this time. CIPS analogs indicate freezing rain, mainly N/W MA
per a top analog from early February 2008. Snows further N/W.

Early next week...

Perhaps a breather before the pattern begins to change as noted in
the OVERVIEW section above.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Wednesday/...Moderate confidence.

Through 12z...Widespread MVFR/IFR. Areas of LIFR in fog,
locally dense, developing along the south coast. Showers will
lift north of the region.

Today...IFR/MVFR stratus and patchy fog improving to VFR by
midday. LIFR fog may linger into early afternoon over the
islands. SW gusts to 20-25 kt.

Tonight...Stratus and patchy fog redeveloping with MVFR/IFR
conditions. Areas of LIFR along the south coast. Patchy drizzle.

Wednesday...IFR/MVFR to start, improving to VFR by afternoon. SW
gusts to 25 kt.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

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

Wednesday Night: VFR. Breezy. Chance RA.

Thursday: VFR. Chance RA, chance SN.

Thursday Night: VFR. Slight chance RA, slight chance FZRA,
slight chance SN, slight chance PL.

Friday: VFR. Chance RA, chance FZRA, chance PL.

Friday Night: MVFR/IFR conditions possible. Chance RA, chance
FZRA, patchy BR.

Saturday: Mainly VFR, with local MVFR possible. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Wednesday/...High confidence.

Persistent SW flow. Modest low level jet over the waters
through Wed but strong inversion will prevent winds from mixing
down. Expect gusts mostly below SCA but up to 20kt at times.
Poor vsbys in fog expected for most of the period, mainly over
south coastal waters.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt. Local rough seas.
Slight chance of rain.

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain.

Thursday Night: Winds less than 25 kt. Chance of rain, slight
chance of freezing rain.

Friday: Winds less than 25 kt. Chance of rain, chance of
freezing rain.

Friday Night: Winds less than 25 kt. Chance of rain.

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain.

&&

.CLIMATE...
Record Highest Observed Temperature for February...(since
records began)

Boston.........73 (2/24/2017)
Hartford.......73 (2/24/1985)
Providence.....72 (2/24/1985)
Worcester......69 (2/24/2017)

Record High Temperatures...

February.......2/20......2/21

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

Record Warmest Min Temperature...

February.......2/20......2/21

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

Extreme High Dew Points...
Dew Point forecast has values in the 50s Tuesday and Wednesday.

February.......2/20......2/21

Boston.........54 (1991) 56 (1953)
Hartford.......53 (1981) 55 (1989)
Providence.....58 (1939) 56 (1989)
Worcester......53 (1981) 54 (1953)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Dense Fog Advisory until 9 AM EST this morning for CTZ002.
MA...Dense Fog Advisory until 9 AM EST this morning for MAZ020>024.
RI...Dense Fog Advisory until 9 AM EST this morning for RIZ006>008.
MARINE...Small Craft Advisory from 7 PM this evening to 7 PM EST
     Wednesday for ANZ235.
     Small Craft Advisory until 7 PM EST Wednesday for ANZ250-
     254>256.

&&

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



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