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Office: BOX

FXUS61 KBOX 211811
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
111 PM EST Wed Feb 21 2018

.SYNOPSIS...
Record warmth this afternoon, then a cold front this evening
will be followed by dramatically colder weather Thursday. A wave
of low pressure tracking to the south will bring some
accumulating snow and sleet north of the Pike with rain and
sleet to the south. An active wet weather pattern Friday through
the weekend during which there is the possibility of mixed
precipitation, freezing rain late Friday into Friday night and
again around Saturday night into Sunday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Dense fog and record high temps are the headlines this
afternoon.

Dense fog continues along the South Coast of RI, along Cape Cod,
and across the Islands. The overall pattern of moist air moving
over cold water and then ashore should continue through mid
afternoon. We will extend the Dense Fog Advisory in these areas
through at least 3 PM for coastal RI and Cape Cod and the
Islands.

Morning soundings showed warm air in place at low levels just
off the surface. Yesterday the mixing, per Amdar soundings,
reached about 935 mb. All soundings show the inversion top at
this level, so projecting the same mixing this afternoon brings
850-mb equivilent temps of 10-11C at ALB and GYX, 8C at OKX, and
5.5C at CHH. This supports mostly l-m70s inland, and should be
achievable where there is sun and a land wind. As such, we have
bumped max temp forecast up a couple of degrees with a range in
the upper 60s to mid 70s inland, and 50s along the cloudy south
coast. As per the ALB and GYX soundings, if full mixing were to
be achieved this would suggest high temperatures 77-79F, with
the best chance in northeast Mass and the CT Valley.


Soundings show 25-30 knots in the projected mixed layer,
possibly a few spots approching 35 knots.

Cold front will be moving into western New Eng late in the day
and may be accompanied by a few showers in western MA.

&&

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

Cold front moves south of the coast this evening and may be
accompanied by a few showers south of the Pike. Areas of
stratus and fog may linger near the south coast in the evening,
otherwise improving conditions with much colder air will drain
south across the region as strong high pres builds to the north.
Low temps by morning will range from near 30 in NW MA to around
40 near the south coast.

Thursday...

Dramatically colder weather with afternoon temps 30-40 degrees
colder than today. Strong high pres (~1040 mb) to the north will
provide the cold air with falling temps through the 30s during
the afternoon with temps falling to freezing or below over
higher elevations by late day.

Fast moving shortwave will result in a flat wave tracking along
the old frontal boundary south of New Eng. Underrunning
situation setting up with low level moist and colder air
undercutting somewhat milder air aloft. Result will be an area
of deep moisture and mid level lift along mid level frontal
boundary with area of precip overspreading SNE, especially in
the afternoon.

Ptype will be a challenge as low level cold air pushes south
across the region while the cooling process aloft will be a bit
slower. This will set up potential for snow, sleet and freezing
rain across the interior. Model differences in the thermal
profile will result in lower confidence pytpe forecast. At
this time, we blended GFS/ECMWF thermals which would suggest
more in the way of snow and sleet north of the Pike with rain
mixing with sleet to the south. Some freezing rain is also
possible near or south of the Pike across higher terrain in
northern CT and central and SW MA. Best chance for minor snow
accumulations will be across higher elevations of northern MA
where 1-3 inches possible. Less than an inch on colder surfaces
for remainder of interior.

Forecast remains uncertain and a warmer solution could result in
more ice and less snow for northern MA.

&&

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

 - Active weather pattern Friday through the weekend
 - Watching for potential mixed precipitation, freezing rain
 - N/W interior out towards the Berkshires at greatest risk
 - Quieter, seasonable pattern into the following 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...

Thursday night...

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

Friday into Friday night...

Freezing rain forecast late Friday into early morning Saturday over
the N/W interior. Warm frontal isentropic ascent aided by convergent
forcing per SW low-level jet beneath stretching H5-7 vortmax. Focus
on thermal profiles below the warm nose up around H8, 2m wet bulb
temperatures. Over-running setup, frontogenetical forcing within low-
mid levels upon precipitable waters 0.75 to 1.00 inch, especially
along the W-slopes of high terrain. GFS warmest, NAM coldest, while
EC/Canadian split between the two, though closer to the NAM. Worst
case scenario of around one-quarter of an inch of ice accretion over
N/W MA, upwards of a tenth for surrounding areas away from the
coast. CIPS analogs continue to signal the potential for a 6-hour
freezing rain event over N/W areas of S New England. Some hesitation
given the surface high is more E, ageostrophic flow off the waters
rather than N. However not out of the question if you can get enough
precip outcomes prior to colder air eroding. Going with one to two
tenths of ice accretion mainly out around the Berkshires. Possible
sleet / snow mix before the changeover. Otherwise rain, warming
temperatures, non-diurnal trend during the overnight period.

Saturday into Sunday...

Classic warm occlusion over the Central CONUS with the leading warm
front with secondary low development over the NE kinked by cold air
damming. Once again, focus upon the low-level thermal profile below
H9 and the warm nose, 2m wet-bulb temperatures. Cold front sweeping
through Saturday, near 1040 surface high building NE Saturday night,
perfect setup for N-funneling ageostrophic flow into New England, a
better cold air damming setup. How well does cold air return and
entrench ahead of precipitation expected Saturday night into Sunday
remains a big question. Timing of outcomes as well. To early to say
on specific details, a low confidence forecast, but attention is
again focused out across N/W MA and Berkshires. Otherwise rain prior
to the cold front and dry slot, clearing out as late as Monday morn.

Early next week...

Quiet, more seasonable outcomes as the pattern bottles up across the
N Atlantic. The favorable region of storm development over SE Canada
puts us in a cooler, drier regime with W/NW flow prevailing. Can't
rule out some weak disturbances across the region with time. A low
confidence forecast.

&&

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

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

Short Term /through Thursday/...Moderate confidence.

This afternoon...

Fog is slowly shifting south. Expect low clouds and vsbys to
continue through the afternoon over Cape Cod and Islands,
including Block Island. Southern RI around WST and UUU is
questionable, but with shifting winds later afternoon those
areas should see improvement toward 4-5 PM. Gusty southwest
winds near 25 knots especially at ORH and along the coastal
plain.

Tonight...

IFR fog lingers over Cape Cod and Islands in the evening, but should
lift early in the night as winds shift west and northwest. VFR
conditions remainder of Southern New England. Winds shifting
northwest and then north overnight.

Thursday...

VFR in the morning. Winds turn from the northeast. Clouds lower
and thicken as an area of precipitation moves in from the west.
Afternoon cigs/vsbys lower to MVFR in snow/sleet north and
light rain south. Light accumulation possible north of the Mass
Pike.


Thursday night...

Rain/sleet/snow moves offshore along with the low clouds. Most
of the night should be VFR with continued northeast winds.

KBOS Terminal...High confidence TAF. VFR through Thursday
morning. Cigs/vsbys lower to MVFR in the afternoon in rain,
possible sleet toward evening.

KBDL Terminal...High confidence in TAF. VFR through Thursday
morning. Cigs/vsbys lower to MVFR in the afternoon in rain,
possible mixing with sleet.

Outlook /Friday through Sunday/...Moderate confidence.

Friday: Mainly VFR, with local IFR possible. RA likely, chance
FZRA.

Friday Night: Mainly VFR, with areas IFR possible. RA likely,
FZRA likely.

Saturday: VFR. Chance RA.

Saturday Night: Mainly VFR, with local IFR possible. Breezy. RA
likely, FZRA likely.

Sunday: Mainly VFR, with areas IFR possible. Breezy. RA, FZRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...High confidence.

This afternoon...Southwest flow continues today with gusts to
20-25 kt at times. SCA remains for most of the waters for
combination for wind and seas. Dense fog will result in vsbys
less than 1/2 mile, especially south coastal waters. A SCA has
been added for Narragansett Bay through evening.

Tonight...Winds shift to the north later tonight with gusts to
20 kt. Improving vsbys overnight.

Thursday...Northerly winds with gusts to 20 kt at times. Vsbys
lowering in rain in the afternoon, mixing with snow NE MA waters
and sleet south coastal waters.

Outlook /Thursday Night through Sunday/...

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Rain likely. Areas of visibility 1 to 3 nm.

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

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Rain likely, chance of freezing rain.

Friday Night: Winds less than 25 kt. Rain likely.

Saturday: Winds less than 25 kt. Slight chance of rain.

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Rain likely, chance of freezing rain.

Sunday: Winds less than 25 kt. Areas of rough seas. Rain,
freezing rain likely.

&&

.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.......Today 2/21

Boston.........63 (1906)
Hartford.......63 (1930)
Providence.....63 (1930)
Worcester......59 (1930)

Record Warmest Min Temperature...

February.......Today 2/21

Boston.........45 (1994)
Hartford.......49 (1981)
Providence.....50 (1981)
Worcester......43 (2002)

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

February.......Today 2/21

Boston.........56 (1953)
Hartford.......55 (1989)
Providence.....56 (1989)
Worcester......54 (1953)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Dense Fog Advisory until 5 PM EST this afternoon for
     MAZ022>024.
RI...Dense Fog Advisory until 5 PM EST this afternoon for
     RIZ006>008.
MARINE...Small Craft Advisory until 7 PM EST this evening for
     ANZ231>234.
     Small Craft Advisory until 6 PM EST this evening for ANZ230-
     236.
     Small Craft Advisory until 9 PM EST this evening for ANZ235-
     237.
     Small Craft Advisory until 1 AM EST Thursday for ANZ250-
     254>256.

&&

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