Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 211117 

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
717 am EDT Mon Oct 21 2019

low pressure well south of New England and its rain shield will
impact Cape Cod and the islands early this morning. As the low
continues to move seaward, rain will exit and clouds will give
way to increasing sunshine later this morning through the
afternoon. However, some cloudiness may linger over Cape Cod and
the islands. Dry weather tonight lingers into Tuesday morning.
Spotty light showers develop Tue afternoon, then become more
widespread Tue night ahead of an approaching cold front. Behind
the front, dry conditions and seasonable temperatures follow
Wednesday afternoon into Friday. Another cold front may bring a
some showers Friday afternoon and night. High pressure builds
in for most of next weekend.


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

7 am update...

Last of the band of rain from the northern edge of past tropical
storm Nestor is slowly shifting offshore at 11z. Further inland,
areas of locally dense fog have developed during the pre-dawn
hours. Visibility has locally lowered to below 1 mile across
portions of north central and western mass, including korh where the
visibility is down to 1/4sm. Some reduced visibility also
reported across portions of the mid and Outer Cape as well as on
Nantucket and Martha's Vineyard.

East-NE winds have been gusty overnight across the Outer Cape and
the islands as well, but they have been diminishing as winds
back to north away from the cape as seen on latest observations.

Updated to bring conditions current, which were mainly on track
except for some adjustments to winds and reduced cigs/vsbys.
Expect these conditions to improve as the low clouds and fog
burn off from mid morning to midday.

Previous discussion...

As the cloud shield advances east and skies clear early this
morning, expected areas of fog to develop before sunrise across
central CT and central/west mass, which includes the Hartford area
and the city of Springfield. This may have some impact on the
morning commute depending how quickly skies clear. Also there
could be enough blyr mixing via light north winds to preclude
fog from becoming too widespread or dense. Something we will
watch closely over the next few hours.

As ocean storm departs short wave ridging develops across the
area with rain ending and clouds eroding/moving offshore. Thus,
increasing sunshine later this morning into the afternoon from
west to east. Low level northeast flow may result in clouds
lingering longer over southeast especially Cape Cod and the
islands. Airmass relatively mild with 925 mb temps around +9c by
this afternoon. Model soundings show mixing beyond 925 mb so
expecting highs 60-65 this afternoon, perhaps only upper 50s
Cape Cod and islands if clouds linger along with cool northeast


Short term /6 PM this evening through 6 PM Tuesday/...

340 am update...

Tonight ...

Dry weather with short wave ridge over the area along with surface
ridge from Quebec into southern New England. This will provide
mostly clear conditions, light winds and with dew pts in the upper
30s to mid 40s expect radiational fog to develop.

Tuesday ...

Any possible breaks of sunshine early will quickly give way to
overcast conditions as return flow and associated southeast low level jet
increase. Spotty light rain/drizzle may develop in the afternoon
with this increasing moist low level flow. Not a washout but could
get damp in the afternoon and especially late in the day. Cloud
cover and increasing onshore winds will limit highs to the mid and
upper 50s.


Long term /Tuesday night through Sunday/...


* area of showers push across Tuesday night into early
* improving conditions and blustery winds Wednesday afternoon
* dry and mild Thursday/Thursday night
* another front brings scattered showers Friday afternoon into
early Saturday
* dry later Sat into Sunday morning, then another round of
showers possible


Tuesday night through Wednesday...

Cutoff 500 mb low pres over S Ontario and the western Great Lakes
Tue evening lifts north-NE to Hudson Bay Wed. The steering flow
beneath the lifting low at the surface and aloft shifts from S
to west during Wed. This should allow the surface front to shift east
late Tue night and Wed.

00z models also signaling a shift of the deep layer moisture
further east than previous model guidance with the increasing and
shifting deep layer wind flow. Models also showing the remnants
of Nestor well southeast of Nantucket by 00z Wed. This position, along
with an 500 mb short wave wrapping north across north mass into northern New
England, will push the offshore moisture across mass Bay then
the western edge clips east mass early Tue night before shifting
into east NH/Maine. 00z GFS also showing the precipitable water moisture plume
(up to 2-3 South Dakota above normal, or about 1.5 to 1.7 inches) moving
quickly up the eastern Seaboard by 00z Wed to near or east of Cape
Cod and southeast coastal mass before shifting to the Gulf of Maine by
around 06z.

As the front crosses the region, the last of the showers push
offshore by midday Wed. Winds shift to west and become gusty,
upwards to around 20 kt during the afternoon. Clouds give way to
mostly sunny conditions Wed afternoon. Will see temps top off
in the mid- upper 50s across the higher inland terrain, ranging
to the lower-mid 60s across the coastal plain and the lower to
mid CT valley.

Thursday through Sunday...

Mid level steering flow remains rather fast, though noting
another digging 500 mb trough around Thursday, but will keep weather
systems steadily moving across the northeast. Will see dry
conditions and seasonably mild temperatures Thursday into early
Friday as high pressure ridge builds across. Fast moving short
wave and surface front.

The high flattens out as the center shifts off the mid Atlc
coast Thu night/Friday morning. Winds shift to S-SW, which will
allow moisture to work up the eastern Seaboard as another cold
front approaches late Fri into Sat. Have chance pops across the
region, which should push offshore during Fri morning. Dry
conditions forecast for late Saturday into Sunday.

Noting widening model solution spread late Sunday into Monday,
with dry conditions offered by the GFS, while another short wave
moves across the Ohio Valley toward the region around the
Monday timeframe. Low forecast confidence. For now, have carried
chance pops from around mid Sunday through the remainder of the


Aviation /12z Monday through Friday/...
forecaster confidence levels...

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

Short term /through Tuesday/...

11z update...

Today...high confidence.

Areas of IFR-LIFR ceilings/MVFR to locally LIFR visibilities across the
Outer Cape and islands as well as north central and west mass should
improve to VFR from 14z-16z. Any other patchy dense fog should
improve over the next hour or two. Light north-NE winds, bit higher
Cape Cod and islands.

Tonight...moderate confidence, some uncertainty regarding areal
coverage of MVFR late.

VFR to start, dry conditions. However, MVFR cigs may move
onshore late and overspread much of the region.

Tuesday...high confidence on trends, lower on exact

VFR/MVFR then trending IFR/MVFR in areas of low clouds and
drizzle in the afternoon and especially toward evening.

Kbos terminal...
high confidence in taf trends.

Kbdl terminal...
high confidence in taf trends.

Outlook /Tuesday night through Friday/...moderate confidence.

Tuesday night: mainly IFR, with areas MVFR possible. Breezy. Rain
likely, chance shra, patchy br.

Wednesday: mainly VFR, with local MVFR possible. Breezy. Slight
chance rain showers.

Wednesday night: VFR. Breezy.

Thursday through Thursday night: VFR.

Friday: mainly VFR, with local MVFR possible. Breezy. Slight
chance rain showers.


forecaster confidence levels...

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

Short term /through Tuesday/...

340 am update...


Weak low pressure south of 40n/70w will provide NE winds 15-20
kt over the waters south of the islands this morning, possibly
gusting up to 25 kt. Given the long fetch seas will increase 4
to 7 ft. Less wind and waves northward. Light rain before over
the southern waters exits offshore by or shortly after daybreak.
Northeast winds decrease this afternoon.


East swells as wind diminishes with high pres from Quebec
building into New England. Dry weather and good vsby.


High pres moves into the Maritimes with east-southeast winds strengthening
across New England. Vsby lowers in developing areas of

Outlook /Tuesday night through Friday/...moderate confidence.

Tuesday night: low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Rain likely, rain
showers likely, patchy fog. Areas of visibility 1 to 3 nm.

Wednesday: low risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas. Chance of rain showers.

Wednesday night through thursday: winds less than 25 kt. Seas
up to 5 ft.

Thursday night: winds less than 25 kt. Areas of seas
approaching 5 ft.

Friday: winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory until 6 am EDT Tuesday for anz254>256.


near term...nocera/evt

National Weather Service Glossary of Abbreviations