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Area forecast discussion
National Weather Service Taunton Massachusetts
354 PM EDT Sat Oct 21 2017

high pressure south of New England will provide very warm and dry
weather into Monday. The exception will be across northeast
Massachusetts Sunday where a backdoor cold front will yield cooler
temperatures but still above normal. A cold front with possibly
waves of low pressure will bring gusty showers to the area Tuesday
afternoon into Wednesday. Drier and seasonably cool weather is
expected behind the front for late in the week.


Near term /until 6 am Sunday morning/...
400 PM update...

Deep layer ridge remains just west of New England providing dry
weather thru the night. Light pressure gradient with 1028 mb high
just south of the region along with clear skies and a dry atmosphere
(dew pts in the 30s) will promote temps to fall fairly quickly with
sunset. Thus have leaned toward the cooler bias corrected MOS to
derive min temps tonight. Could be some patchy fog over southeast Massachusetts
where dew pts have come up into the lower 40s from SW winds today
off the ocean. Overall very tranquil conditions for late Oct.


Short term /6 am Sunday morning through Sunday night/...
*** near record warmth CT/western Massachusetts but much cooler northeast Massachusetts ***


Little wrinkle in tomorrow's forecast, that being a backdoor cold
front dropping southward from the New Hampshire/ME coastline. This feature will
be accompanied by a wind shift to the north-NE and result in cooler
temps for northeast Massachusetts including Boston with highs in the 60s.
However how far south this boundary slips is somewhat uncertain
along with how widespread low clouds will become across this area.
Given this is shallow/mesoscale boundary we followed the high res
guidance for this portion of the forecast.

Elsewhere, mostly sunny conditions and warm sector airmass with +17c
at 925 mb will support highs tomorrow 75-80, possibly low to mid 80s
CT River Valley from Hartford to Springfield. Record high tomorrow
for bdl is 85 set back in 1979. Could come close.

Sunday night...

Boundary begins to lift north as a warm front, thus a mild night
with lows 45-55. Still comfortable with dew pts in the 40s and 50s.
Dry weather but could have some low clouds and patchy fog in the
warm sector airmass especially with dew pts higher than the avg
nighttime low.


Long term /Monday through Saturday/...

* heavy showers and gusty winds are possible ahead of a cold front
Tuesday afternoon into Wednesday

Overview and model preferences...
gradually sharpening and building block downstream (ridgeline
is near labrador) allows deepening trof to establish itself
across the east Continental U.S. Through mid week, taking on a negative tilt
and cutting off toward the latter portion of the week. This
yields a much wetter and unsettled setup in comparison to the
very dry/anomalously warm setup this past week. The only break
comes in the form of a secondary, very deep trof near the
Continental Divide which allows the subtropical ridge/Bermuda
high to regain control across the southeast and force the mean jet and
cutoff across New England to the NE late week. A very amplified,
complex flow pattern, so individual guidance is still
struggling to resolve the details especially after Wednesday,
therefore, with this update, will lean most heavily on ensembles
to take into account the full envelope of solutions.


Mon and Mon night...
the final throes of ridging continues to shift east Mon into Mon
night. Column remains generally dry enough to support one final
mainly dry day, although with moisture loading from the top-down
through the column, will likely see increasing cloud cover, and
especially overnight as the bl moistens. Will begin to
introduce some low-end pops late Mon night due to increased
moisture and weak low level jet development. Otherwise, mainly dry through
the daylight hours. Breezy warm flow with increased pres
gradient ahead of the deepening low pres near the Great Lakes.
Mixing to h92 at least, where temps rest around +14c to +15c.
Even with increasing clouds, highs should still reach the low-
mid 70s before.

Tue and Wed...
deepening upper trof takes on strong negative tilt, with parent
sfc low sliding S-north through the Great Lakes, dragging a cold
front into New England. This front slows as the trof tilts
thanks to parallel orienting flow. The system begins a gradual
occlusion process and slows as it does so, allowing the front
remain hung near or over S New England into the day on Thu. Two
weak frontal waves associated with strong low level jet cores slide
across the region, the first mid day Tue into Tue afternoon,
while the second follows early Wed. Given the initial trof is
able to tap Gulf of Mexico moisture, noting high ensemble
probabilities of pwats near, but just below 2.00 inches, or
nearly 3 std deviations above late October climo through the
period, supported by k-indices near the mid 30s. Also, high tt
values (near 50) and modest mid lvl lapse rates suggest
instability, and even show some mu cape values between
300-500j/kg. All this is to suggest that, particularly with each
low level jet passage there is a risk for heavy rainfall, with potential
localized urban flooding. Even if rainfall rates diminish
between each low level jet core, widespread light-mod rain can still be
expected with the unstable profile and high moisture content.
Given the potential convective nature to the precipitation,
widespread quantitative precipitation forecast is likely to remain generally between 1.00-2.00
inches but with locally higher amounts possible.

The h92 low level jet early Tue reaches near 40-45 kt, while the second,
early Wed looks to be stronger, potentially above 50 kt, nearly
4 std deviations stronger the climo. With the destabilized
sounding, will need to watch for strong winds at the sfc should
at least some of this momentum be efficiently transferred. A
convective fine line, especially along the frontal boundary is
possible, which could lead to localized strong winds. Overall
the pattern does suggest the possibility of wind headlines.

cooler, drier air is finally allowed to move into S New England
as the trof continues to wrap up and begin a slide to the north in
response to the ridge building across the southeast Continental U.S.. this dry
slow moves in aloft first, trapping moisture in the low lvls.
Given strong cyclonic flow aloft and cold advection, could see
continued, but less widespread rain showers through the daytime Thu, so
pops will be decreasing with time. Could even see some small
hail or graupel as fzl lowers with the influence of cooler air.
H92 temps drop to an average near +7c. Which should keep daytime
temps in the low-mid 60s.

Fri into Sat...
high pres noses in as modest ridging builds across the NE in
advance of yet another very deep longwave trof through the west.
Mainly dry conditions favored. The cold air influence is short-
lived, given the ridge building is associated with warmer air
attendant to the subtropical ridge across the southeast. Therefore,
looking at still seasonably mild temps by day (mainly mid-upper
60s). Airmass suggests seasonal lows, mainly near the mid 40s.


Aviation /20z Saturday through Thursday/...
forecaster confidence levels...

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

Short term /through Sunday night/....

18z update...

Thru tonight...high forecast confidence.

VFR, dry runways and light west-SW winds becoming light and
variable after sunset.

Sunday...high confidence except low confidence across northeast

VFR, dry weather and light winds. However lots of uncertainty
across northeast Massachusetts where low clouds (mvfr-ifr) along the coast
of New Hampshire/ME may slide southward into northeast Massachusetts. Forecast
confidence was not high enough to go with IFR/MVFR conditions so
left tafs VFR but need to watch this closely.

Sunday night...moderate confidence.

Uncertainty on how quickly MVFR-IFR conditions overspread the
area from the northeast and from the southwest. Mainly dry
conditions prevail along with light winds.

Kbos terminal...high confidence in taf through Sunday morning
then uncertainty on MVFR-IFR cigs from New Hampshire/ME coast sliding

Kbdl terminal...high confidence in taf through Sunday.

Outlook /Monday through Thursday/...

Monday...high confidence.
Mainly VFR, although with a low risk for early am fog and lower
clouds with isolated IFR conditions possible.

Mon night into Wed...moderate confidence.
Mainly a mix of IFR/MVFR in low cigs, fog and rainfall.
Occasional strong S wind gusts. Low level wind shear likely, especially during
the day on Tue and Wed.

Thu...moderate confidence.
Some improvement to VFR, although lingering IFR/MVFR possible.


forecaster confidence levels...

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

Short term /through Sunday night/...high confidence.

Very tranquil boating weather for late Oct continues this period
with light winds, dry weather and good vsby. Only wrinkle will be
backdoor front that drops southward from New Hampshire/ME coastline into Massachusetts
waters Sunday, resulting in a wind shift to the N-NE. Post frontal
winds speeds generally 10 kt or less especially given mild water
temps of 55-60.

Outlook /Monday through Thursday/...moderate confidence.

increasing S winds should remain generally below 25 kt through
Mon evening and seas below 5 ft through Mon night. Advisories
not likely to begin until after this period.

Tue into Wed...
occasional southerly gales with wind gusts 35-40 kt possible.
Seas, building 8-10 ft mainly S and southeast waters. Even in periods
where gales not experienced, high end small craft advisories
likely. Rain/fog lead to vsby restrictions. Some thunderstorms
possible over the waters.

gradual improvement with winds shifting around to the west. A few
gusts still to 25 kt at least, along with lingering seas/swells.
Small craft advisories likely to follow gales.


Fire weather...
dry weather continues through at least Sunday with minimum relative humidity values
25 to 35 percent, lowest values over CT and western Massachusetts. However with
high pressure nearby winds will be very light. Thus fire weather
parameters remaining below headline criteria.


record high temperature for Sunday, October 22: only bdl is in

Bdl 85 in 1979


Box watches/warnings/advisories...
Rhode Island...none.


near term...nocera
short term...nocera
long term...doody

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