Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 041947

Area Forecast Discussion
National Weather Service Boston/Norton MA
347 PM EDT Wed Oct 4 2023

Other than overnight and morning fog, high pressure continues to
provide dry and very pleasant weather through Thursday. A strong
frontal system then slowly moves into Southern New England Friday
night into Saturday. While rain amounts are still uncertain, there
is growing confidence on widespread showers for late Friday into
Saturday evening. Rain could be heavy at times, as tropical moisture
from Philippe tracks northward. Rain comes to an end early Saturday
night, ushering in blustery conditions and a cooler air mass to
Southern New England for Sunday into early next week.


330 PM Update:

* Another mild night with fog more widespread tonight

This evening & overnight...

Gorgeous late afternoon/early evening in progress, courtesy of
a high amplitude ridge (590 dam) remains across SNE, providing
dry, mild and very pleasant conditions into this evening. Dew
pts in the 60s combined with light onshore flow will promote
areas of fog to develop after sunset (621 pm Boston, 628 pm
Hartford). Given the light onshore flow and stronger/lower
subsidence inversion, the fog overnight is likely to be more
widespread (and locally dense at times) than last night. Higher
dew pts will also result in a mild night, with lows only 55-60.


330 PM update...

* Morning fog eventually burns off to afternoon sunshine

* Warm and humid for October, highs 75-80 & dew pts in the 60s


Expecting morning fog to be more widespread (and locally dense) than
previous mornings, therefore it may take until late morning to burn
off and perhaps midday-ish for coastal areas. Column is fairly dry
with PWATs below 1 inch, so as blyr warms some of this dry air aloft
should mix down and help erode fog. Thus, partly to mostly sunny
conditions should develop. Still a warm airmass over the region,
however with SE winds more established blyr not as warm as previous
days, with 925 mb temps down from 20/21C Wed to 17/18C Thu. This
will support highs in the mid to upper 70s away from the coastline.
Still about 10 degs warmer than normal. Looks to be another
beautiful late morning and afternoon, with sunshine, light SE winds
and a warm away from the coast. Even at the shoreline, despite the
light onshore winds, it will feel mild with dew pts in the 60s.

Thursday night...

As ridge axis moves farther offshore, low level moisture begins to
stream northward toward SNE. This is evident on both NAM and GFS
bufkit time sections. This should translate to widespread low clouds
and fog overnight. All the guidance has some very light qpf. Given
the moisture is very shallow, most likely looking at areas of
drizzle/mist. Another mild night given relatively high dew pts. Lows
mainly 55-60. SE winds persist.




* Increasing clouds Fri, with mainly light rain showers for interior
  MA/CT. Heavier rain arrives overnight.

* Steady and heavier rain Sat morning to Sat early evening. Locally
  heavy rain totals are possible in interior Southern New England,
  although there is more uncertainty on rain amounts in eastern MA
  and RI.

* Cooler than normal weather and blustery/breezy Sunday. Remains
  cooler and unsettled for early next week.


Friday through Sunday...

You`ve heard it before and here we are we approach the
weekend more rain is on the way. Friday through Saturday night looks
to be the most active period of weather in the extended forecast
period as a frontal system from the Great Lakes combined with
moisture from what is now Tropical Storm Phillipe brings soaking
rain and even some thunderstorms to southern New England. Friday
will be a bit of a transition day between the drier pattern we`ve
enjoyed to the very wet pattern of Saturday. This, as the surface
ridge breaks down with the arrival of a mid level trough digging
into the eastern Great Lakes. Eventually this trough will become
negatively tilted as it crosses SNE and ushers the remnants of what
is now Tropical Storm Phillipe into Nova Scotia. So conditions will
begin to deteriorate on Friday as isentropically forced showers move
in with warm advection on E/SE winds. This direction of flow will
also favor orographic ascent which serves to enhance rainfall
amounts over the high terrain of central and western MA/CT. Overall,
though, not expecting big rainfall amounts out of Friday`s showers,
most likely a few hundredths to a few tenths. The heavier and
steadier rain then arrives overnight Friday and especially on
Saturday. As for placement of the heaviest amounts (1+inches)
ensemble guidance is continuing to highlight two maxima, one over
western MA/CT associated with the frontal system and another either
fully offshore or scraping eastern MA associated with Phillipe. This
leaves much of central/eastern MA and RI in the area of greatest
uncertainty as to how much rain we`ll see. There will exist a decent
amount of instability Friday night into Saturday as well which
introduces some variability because anywhere that sees convection
could see very localized high rainfall amounts. Overall, rainfall
amounts for our area are do not scream "flash flooding concern". The
cold front then ushers the bulk of the moisture out of the area
sometime around Saturday night/Sunday morning. Cold air advection
behind the front then steepens the lapse rate and brings a starkly
colder and breezy post frontal airmass on Sunday. There remains a
good deal of uncertainly on the timing of the front and arrival of
the dry slot, though, so there`s a chance rain sticks around for
some of Sunday morning. Even beyond Sunday morning, the upper low
remains overhead and this cyclonic flow/cold pool aloft will promote
clouds and widely scattered rain showers on Sunday.

Monday through Wednesday...

The upper low mentioned above isn`t in any hurry to exit and will in
fact stick around through at least the first half of the week. Thus,
while it won`t be a washout, a cool and unsettled pattern will be
with us for the duration. Given 850 mb temps just a few degrees
above zero this puts us solidly in the cooler than average boat,
with highs only in the mid to upper 50s or low 60s each day.


Confidence Levels:

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

18z TAF Update:

Thru 00z...high confidence.

VFR, light SE winds and dry weather. Only uncertainty is how
quickly does MVFR conditions develop with fog development toward

After 00z...High confidence in trends but lower on exact details.

Widespread fog developing and likely at least MVFR with areas of
IFR/LIFR. Light SE winds.

Thursday...High Confidence in trends but lower on exact timing

IFR/LIFR at 12z in fog but slowly trending upward toward MVFR
and eventually VFR between 15z-18z. Winds SSE less than 10kt.

Thursday night...high confidence in trends but lower in exact
timing details.

VFR/MVFR at 00z in developing fog, then trending IFR/LIFR
overnight in light SSE winds. Could be some patchy drizzle/mist
in the areas of dense fog.

KBOS Terminal...high confidence in TAF trends, but uncertainty
on how quickly fog develops this evening and then how quickly
erodes Thu morning.

KBDL Terminal...high confidence in TAF trends, but uncertainty
on how quickly fog develops this evening and then how quickly
erodes Thu morning.

Outlook /Friday through Monday/...

Friday: MVFR/IFR conditions possible. Slight chance SHRA.

Friday Night: Mainly IFR, with local MVFR possible. Chance
SHRA, isolated TSRA, patchy BR.

Saturday: IFR. Breezy. SHRA, isolated TSRA, patchy BR.

Saturday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SHRA, isolated TSRA, patchy BR.

Sunday: VFR. Windy with areas of gusts up to 30 kt. Slight
chance SHRA.

Sunday Night through Columbus Day: VFR. Breezy.


Forecaster Confidence Levels:

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

330 PM update...

Tranquil boating weather late morning through the afternoon, then
fog develops late evening and overnight. Fog could locally be dense
at times with vsby less than 1/4 mile. Mainly dry weather prevails
until Thursday night, when mist/drizzle accompanies another round of
fog. With high pressure offshore, seas only 1-3 ft on the ocean,
even less in the bays/harbors/sounds.

Outlook /Friday through Monday/...

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

Friday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 11 ft. Rain showers likely, patchy
fog. Visibility 1 to 3 nm.

Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain
showers, patchy fog. Local visibility 1 to 3 nm.

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 10 ft. Slight chance of rain

Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft.

Columbus Day: Moderate risk for Small Craft Advisory winds with
gusts up to 20 kt. Seas up to 5 ft.


Record Daily High Temperatures for October 4th

BOS 86 in 2007
BDL 86 in 2007
PVD 85 in 1941 and 1959
ORH 85 in 1898 and 1931




NEAR TERM...Nocera
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