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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
447 PM EDT sun Sep 22 2019

Synopsis...
southwest flow ahead of an advancing cold front will make for a
rather warm night tonight and one more very warm and breezy day
on Monday. Areas of dense fog are again likely tonight along
the South Coast of Rhode Island and Massachusetts. Showers and a few thunderstorms
will accompany the front late Monday afternoon and Monday night.
High pressure settles in Tuesday and Wednesday with mild days
and cool nights. Swells from Jerry will cause increased rip
current risk along the coast especially Monday through
Wednesday. Another front approaches Thursday into Thursday
evening, with dry conditions returning Friday.

&&

Near term /until 6 am Monday morning/...
420 PM update...

There were just some high level cirrus clouds across the region
late this afternoon. The only exception continued to be along
the South Coast from Buzzards Bay to Block Island, where a fog
bank persisted, but was beginning to thin a bit. Temperatures
were in the mid to upper 80s inland...with Boston Logan having
hit 89 degrees!

Gusty winds to around 15-25 mph late this afternoon will
diminish to around 10 mph after sunset. Mainly clear skies are
forecast through tonight, except low clouds and fog may spread
inland across southern Rhode Island and southeast MA, mainly after
midnight. It could become dense in some of these locations...so
will have to watch for a possible dense fog advisory if it
develops. With southwest winds remaining around 10 mph
overnight, am not expecting much in the way of radiation fog
farther inland. Dewpoints will be on the rise, reaching the
lower to mid 60s across the area overnight, so overnight lows
should be holding in the mid 60s.

&&

Short term /6 am Monday morning through Monday night/...
with a warm start overnight and still some sunshine Monday
morning, temperatures will soar to the upper 80s again, except
cooler on the South Coast. Cannot rule out a few 90 degree
readings. These will not be records, though, since the Boston
record was 96 set in 1895, bdl record was 93 set in 1914, and
the pvd record was 92 set in 1970.

BUFKIT soundings show the potential for southwest winds to
increase to 20-30 mph for a few hours across the interior Monday
afternoon. Have increased winds in the grids to reflect this.

Models are a bit quicker with development of showers ahead of
the front. Expect a few to develop by 2 or 3 PM in western MA,
then increasing through the late afternoon hours. By 9 or 10 PM
Monday night, showers and a few thunderstorms will be ongoing
across the entire region. K indices reach 33 to 35 but with
little cape, believe that any thunder will be elevated. Locally
heavy downpours are possible. Models show the heaviest rain in
eastern Massachusetts and southern Rhode Island between midnight and 6 am Tuesday.
Lows will range from the mid 50s in northwest Massachusetts behind the
front to the mid 60s in southeast sections.

Expecting increasing swell from the south Monday, this time from
Tropical Storm Jerry. Will issue a high rip current risk
statement for the elevated risk for dangerous rip currents,
mainly over the islands including Block Island, Marthas
Vineyard, and Nantucket Monday. This risk area will likely
expand on Tuesday.

&&

Long term /Tuesday through Sunday/...

Highlights...

* showers linger across eastern areas through mid morning
Tuesday
* dry conditions and mild temperatures through mid week
* a cold front crosses Thursday into Thursday evening
* some showers may approach with another front sometime next
weekend

Overview...

Northern stream mid level steering flow remains progressive
through most of this timeframe as broad mid level high pressure
sprawls across the mid Atlc and southeast U.S. Eastward across the mid
Atlc. Cutoff 500 mb low pres moves along in the northern stream
flow, pushing across northern New England Tue/Tue night. The mid
level heights lower somewhat, but still expect temperatures
through mid week to remain above seasonal levels. Should see a
couple more fronts move along in the progressive flow aloft, but
should not see a lot of precip with either system.

Details...

Tuesday...
cold front clears the coast Tuesday morning, but is slow to
exit as it hangs up in the SW steering flow aloft ahead of the
approaching 500 mb cutoff low. Carried chance pops mainly across Cape
Cod and the islands, with slight chance from the bos-pvd corridor S
and east through mid morning, then should push off the Outer Cape
and Nantucket by midday.

However, there are a couple of features that need to be
monitored. First, a few mainly diurnally driven showers may push
into north central/northwest mass as 500 mb cutoff low moves across northern
New England into early Tuesday afternoon. Also need to keep an
eye on ts Jerry as the system makes its closest westward
approach well southeast of Nantucket on Tuesday, so this may slow the
progression of the back edge of the precip/clouds. At this
point, the leftover showers should push offshore by midday or
early afternoon.

Winds to shift to west during the midday and afternoon hours with
some gusts up to 20 kt possible along S coastal areas. Expect
temps to reach the mid 60s to around 70 across the higher inland
terrain to the mid-upper 70s across the coastal plain and lower
CT valley.

Tuesday night through Wednesday night...
high pressure takes over, with dry conditions during this
timeframe. West-northwest winds expected Tue night and Wed as the high
slowly moves off the mid Atlc coast, then will become light west-SW
on the backside of the ridge during Wed. Expect high temps
mainly in the upper 60s to mid 70s on Wed, up to 5 degrees above
seasonal normals.

Clouds may begin to approach after dark across western areas
Wed night, but expect dry conditions to continue. Temps will
remain on the mild side.

Thursday and Thursday night...
SW winds in place ahead of the approaching cold front Thu
morning through midday. Some questions on the timing and track
of the front, which may tend to slow down while the western Atlc
ridge slows down as well. Rather wide model solution spreads as
to the arrival of showers, if they make it at all. At this
point, have carried slight chance to low chance pops, but could be
quite a bit more depending upon which model one believes. Kept
the chance for some showers into Thu night, which may weaken as
the front pushes offshore and another high approaches from the
Great Lakes. Will still see temps running slightly above normal.

Friday through Sunday...
should see another high build across the eastern Seaboard late
this week into next weekend as another broad 500 mb ridge builds
across. Noting large 500 mb high pres extending from the mid Atlc to
southeast states eastward to the mid Atlc, though position of the high
as well as the cutoff 500 mb low over Nunavut and the northwest
territories and trough extending down across the mid and
northern rockies, or possibly in the Pacific northwest.

At this point, have carried a dry forecast for Friday/Friday
night, then yet another front may approach sometime next
weekend. However, with the ridge to the se, this front may stall
or even wash out as it approaches. Rather low confidence for
this portion of the forecast.

&&

Aviation /21z Sunday through Friday/...
forecaster confidence levels...

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

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

2020z update...

This afternoon/evening...VFR except lingering LIFR/IFR in dense
fog along Rhode Island and southern Massachusetts coast through this evening. South-southwest
winds gusting to 15-20 kt.

Tonight...VFR. However, areas of IFR-vlifr fog may redevelop
and then linger at times along the South Coast. It could extend
inland to about a kpvd-kpym line.

Monday...VFR. Increasing risk for rain showers and isolated thunderstorms and rain during
the afternoon from west to east. MVFR possible with any ra/+ra. SW
winds gusting to 25 kt in the afternoon, especially over the
interior.

Monday night...MVFR in rain showers and thunderstorms and rain. Precipitation ending in
western and central sections after 06z. Locally heavy downpours
possible.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy. Patchy fog.

Tuesday night through Wednesday night: VFR.

Thursday: VFR. Breezy. Slight chance rain showers.

Thursday night: VFR. Slight chance rain showers.

Friday: VFR.

&&

Marine...
forecaster confidence levels...

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

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

420 PM update...

Tonight...south-southwest winds with gusts to 20 kt into this evening and
again late tonight. Areas of dense fog, especially from Buzzards
Bay to Block Island. Dry weather prevails. Seas build across
the outer coastal waters. Small craft advisories posted,
beginning late tonight for the outer waters as seas build to 5
ft.

Monday...SW winds will increase to 20-25 kt with a few gusts to
30 kt not out of the question late. Small Craft Advisory in effect with 5 to 7 ft
seas over the southern and southeastern outer waters, as swells
enter the picture from distant Tropical Storm Jerry. Chance of
showers toward evening. Visibility locally below 1 mile along
the South Coast, especially in the morning, in areas of fog.

Monday night...as a cold front moves through, widespread
showers and thunderstorms. Seas up to 5 to 7 ft over the
southern and southeastern waters. Winds still gusting up to 20
to 25 kt. Small Craft Advisory continues for those areas. Visibilities below 3
miles in locally heavy rain showers.

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

Tuesday: winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, patchy fog.

Tuesday night: winds less than 25 kt. Local rough seas.

Wednesday 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.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...high rip current risk from Monday morning through Monday
evening for maz023-024.
Rhode Island...high rip current risk from Monday morning through Monday
evening for riz008.
Marine...Small Craft Advisory from 1 am to 8 PM EDT Monday for
anz232>234.
Small Craft Advisory from 6 am to 8 PM EDT Monday for anz231.
Small Craft Advisory from 6 am Monday to 6 am EDT Tuesday for
anz235-237.
Small Craft Advisory from 1 am Monday to 6 am EDT Tuesday for
anz250.
Small Craft Advisory from 1 am Monday to 6 PM EDT Tuesday for
anz254>256.

&&

$$
Synopsis...evt/gaf

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