Scientific Forecaster Discussion
fxus61 kbox 200920
Area forecast discussion
National Weather Service Boston/Norton Massachusetts
420 am EST Wed Nov 20 2019
low pressure passing southeast of southern New England to bring
continued overcast skies and a period of light showers today
into early tonight. Rain may mix with wet snow in the Worcester
Hills into the Berkshires but with little to no accumulation.
High pressure building in from the west Thu yields dry
conditions and seasonable temperatures. Milder and breezy Friday
ahead of an approaching cold front that may be accompanied by
scattered showers late Friday/Fri evening. Cool dry weather lingers
much of Saturday, followed by coastal low pressure bringing a risk
of rain/snow Sat night into Sunday morning. As this low exits, a
drying trend with seasonable temperatures should follow early next
Near term /until 6 PM this evening/...
early this morning, a mid/upper-level low analyzed per water vapor
imagery over the PA/Maryland border is helping to draw moisture northward
across much of southern New England, amid a weak northerly near-
surface drainage flow regime. This mid/upper feature is also
contributing to surface cyclogenesis southeast of the 40n/70w benchmark
early this morning, with infrared satellite and GOES-east glm
products indicating cooling cloud tops and even some lightning, an
indication of ongoing organizing/deepening. While this distant
coastal system remains that way today - southern New England will
feel some fringe influences from this system over the next day or
Over the next few hours through, we continue to monitor for the
potential for trace icing associated with pockets of spotty freezing
drizzle, mainly in the hills in northern Worcester County and into
the eastern slopes of the Berkshires. Special Weather Statement remains in effect to
address spotty icing impact into this morning's commute. Mesonet
observations early this morning indicate temperatures in these areas
have more-or-less remained in the low to mid 30s, coolest readings
in western Hampden/Hampshire/Franklin counties. With moisture being
shallow and below the ice Crystal nuclei activation region per 00z
raobs and BUFKIT forecast soundings, suspect the very light echoes
moving northward per radar this morning could result in spotty
freezing drizzle. Marginal temps will likely mitigate to spotty
potential - thus not envisioning a need for a short-fused winter
advisory. Temps elsewhere early this morning are above freezing and
could see some light drizzle as precip bands lift north but most
areas stay cloudy/dry into the am commute.
Into the rest of today, looking at a pretty cool/raw day with
cold advection most of the day and northerly flow tending to
increase through the day. Most models and ensembles show the 500
mb trough closing off as it pulls off the New Jersey coast into the
waters south of Nantucket by late this aftn. Though spotty light
rain or snow showers possible through mid-day, most global and
several high- res guidance sources including the href mean, hrrr
and the NAM-3km nest tend to Blossom precip into the mid/late
afternoon from a Westfield-Providence line North/East. Looks
like this occurs as moisture from the distant coastal low wraps
around and interacts with progged 700-500 mb inverted trough
extending northwest from center of the closed low in the vicinity of
Nantucket. Moisture depth fills over time and thus could see
rain mix with wet snow at times with negligible if any
accumulation from the Worcester Hills into the Berkshires where
temps may be marginal. Should be mostly rain south/east and
tending wetter closer to the coast one gets. By late in the day,
coverage of precip should be mainly confined to the coastal
plain and perhaps as far west as I-395.
Northerly winds will increase as well, tending more north/northwest in the by
afternoon. Should see winds around 10 mph in the interior, though
speeds are even stronger towards eastern coastal MA, cape and the
islands with speeds 10-15 mph with gusts 20-25 mph coastal Massachusetts to low-
30 mph gusts towards the cape and islands.
Biased temperatures towards the colder end of guidance given
persistent overcast, cold advection much of the day and northerly
winds. Only showed daytime highs in the mid-upper 30s to lower-mid
40s, which are only a couple degrees warmer from current values if
Short term /6 PM this evening through 6 PM Thursday/...
Early-evening showers should remain mainly confined to eastern MA,
Cape Cod/islands and adjacent waters. Followed the href/sref mean in
showing a sharp pop gradient with general trend for improvement west-east
as the nighttime hrs progress. All told, shown event-total quantitative precipitation forecast from
a few hundreths across central Massachusetts/NE CT into RI, around a tenth or
so into the Massachusetts coastal plain and the North Shore/Boston area with up
to a quarter-inch towards the cape, some of which could be boosted
By midnight, most areas except for the cape should be clearing out
affording good radiational cooling. Showed lows upper 20s to near
freezing in the interior, to the mid/upper 30s towards the Massachusetts coast,
Boston area into the cape and islands. Continued northerly winds
will make it feel pretty chilly as well with wind chills in the 20s.
North/northwest winds to subside towards light/variable levels into the middle
part of the day on Thursday with progged pressure gradient slackens
as ridging building in from New York. Thermal advective pattern also
changes from one of weak cold/neutral to modest warm advection by
afternoon. With full sunshine, should see temperatures moderating
back into the 40s, and there may be a few spot 50s toward the
Hartford Metro area into southern Rhode Island. Certainly, a lot better
weather than we've been experiencing over the last couple days!
Long term /Thursday night through Tuesday/...
* mild (55-60) & breezy Friday along with a few showers possible late
* Saturday the pick of the weekend, cool but dry & light winds
* rain/wet snow possible Saturday night into early Sunday
Thursday night ...
Change in airmass as warm front lifts across the area. Deep layer
moisture is lacking so any showers will be limited in areal
coverage. Thus most locations remain dry. Not as chilly as tonight
given low level warm air advection and some mid level cloudiness. In fact min temps
likely to occur during the evening hours given high pres overhead
providing light winds and mostly clear skies, enabling radiational
cooling to commence. Temps will then rise second half of the night
as southwest winds increase.
Strong low level warm air advection continues ahead of Great Lakes short wave and
attending cold front. Models continue to advertise +8c airmass at
925 mb advecting across CT/RI/MA Fri afternoon. This should support
highs from the upper 50s to lower 60s before clouds and scattered
showers arrive west to east late afternoon/early evening. Deep layer
moisture is lacking so not expecting widespread showers, just a few
spot showers. Friday night...fairly strong Post frontal cold air advection for late
Nov with with -10c air at 850 mb and -6c at 925 mb over the region
by 12z Sat. Thus a cold night but at least dry weather with the
exception of possibly lake effect snow showers tracking into western
Saturday definitely the pick of the weekend with short wave ridging
building into the region as maritime low exits, allowing heights to
rise and support dry weather in southern New England. Chilly start
to the day with many locations in the 20s and only a modest temp
recover with highs 40-45, upper 30s high terrain. About 5-10 degs
colder than normal.
00z models continue to delay any precip until Saturday night. Thus
dry weather should prevail for the daylight hours Saturday. Also 00z
models have trended a bit farther north with frontal wave late Sat
night into early Sunday, tracking wave along the southern New
England coast or slightly inland. If this track were to verify ptype
would be mainly rain. However still 4 days away so Worth watching.
Early next week ...
Probably cool and dry Mon as coastal low Sunday exits into the
Maritimes. Then gradually moderating Tue as central Continental U.S. Trough
evolves yielding downstream riding along the eastern Seaboard.
Aviation /09z Wednesday through Sunday/...
forecaster confidence levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short term /through Thursday/...moderate confidence.
09z taf update:
Mainly MVFR ceilings, best chance at IFR towards the interior
(w/northwest of bed/pvd and north of bdl). Should see precipitation
Blossom towards rain showers by afternoon, though air could
support a mix to wet snow at orh. Moving into the late-
aftn/early evening, precip should begin to focus more into
eastern Massachusetts terminals. Light north/northwest winds strengthen thru the day
today, 7-10 kts away from the cape, increasing to 10-15 kts
gusts to 20-25 kts for Cape Cod airports.
General theme will be for west to east improvement in ceilings
and less precipitation coverage. Initial MVFR ceilings/VFR-MVFR
visbys eastern sections should transition to VFR. Northwest winds to
continue around 7-15 kts, with gusts on the cape starting to
subside to 20 kt levels.
VFR under high pressure. Gradient slackens into Thursday with
decreasing north winds towards light/variable (tending west-SW late).
Kbos taf...moderate confidence in taf. MVFR predominantes, with
low prob of IFR ceilings late overnight thru late am Wed.
Kbdl taf...high confidence in taf.
Outlook /Thursday night through Sunday/...
Thursday night: VFR. Breezy. Slight chance freezing rain.
Friday: mainly VFR, with areas MVFR possible. Windy with gusts
up to 35 kt. Slight chance rain showers.
Friday night: VFR. Windy with gusts up to 35 kt.
Saturday: VFR. Windy with local gusts up to 30 kt.
Saturday night: mainly VFR, with areas IFR possible. Chance sn,
chance ra, slight chance freezing rain.
Sunday: mainly VFR, with local IFR possible. Breezy. Chance ra,
chance fzra, chance snow.
short term /through Thursday/...moderate confidence.
Scas continue due to residual 5-7 ft seas offshor waters.
However, an expected increase in north/NE winds to Small Craft Advisory levels is
anticipated especially for the latter half of today as a coastal
low passes well east. Have added Cape Cod Bay and Nantucket
Sound into a Small Craft Advisory mainly from winds.
Today: north/NE wind speeds increase to 15-25 kts, with gusts to
25-30 kts, highest offshore waters. Winds around 10-15 kts gusts
to 20-22 kts into Buzzards Bay/Rhode Island Sound. Seas subside to 3-5 ft
on southern waters, though continue around 5-7 ft eastern
Tonight: north winds remain 15-25 kts gusts to 25-30 kts. Building
seas eastern offshore waters to 6-9 ft, 3-6 ft in coastal waters
in eastern Massachusetts/Cape Cod Bay. Southern waters should see seas 4-6
Thursday: decreasing north winds to around 10 kts, gusts to 15-25
kts by afternoon. Seas 4-7 ft outer offshore waters.
Outlook /Thursday night through Sunday/...
Thursday night: winds less than 25 kt. Areas of seas
approaching 5 ft.
Friday: low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Slight chance of rain showers.
Friday night: moderate risk for gale force winds with gusts up
to 35 kt. Rough seas up to 11 ft.
Saturday: low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of rough seas.
Saturday night: winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain.
Sunday: winds less than 25 kt. Local rough seas. Chance of
Marine...Small Craft Advisory from 4 PM this afternoon to 4 am EST
Thursday for anz232.
Small Craft Advisory from 1 PM this afternoon to 7 am EST
Thursday for anz231.
Small Craft Advisory until 4 PM EST Thursday for anz250-251-
Small Craft Advisory until noon EST Thursday for anz255-256.