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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

FXUS61 KBOX 222025

Area Forecast Discussion
National Weather Service Boston/Norton MA
425 PM EDT Sun Sep 22 2019

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 RI and MA. Showers and a few thunderstorms 
will accompany the front late Monday afternoon and Monday night.
High pressure settles in through midweek with mild days and 
cool nights. Swells from Jerry will cause increased rip current
risk along the coast especially Monday through Wednesday.


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 RI and southeast MA, mainly after
midnight. It could become dense in some of these
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.


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 MA and southern RI between midnight and 6 AM Tuesday.
Lows will range from the mid 50s in northwest MA 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.


*/ Highlights...

 - Showers likely Monday night
 - Warm-up and dry through midweek
 - Another sweeping cold front around Thursday night
 - Low confidence forecast into the following weekend

*/ Overview... 

Tropics are active. Multiple cast members supported by a phase 1 MJO 
crew. As members are drawn into the mid-latitude production they in 
part bring chaos to the show. From the NW Pacific to the NW Atlantic 
S equatorward, the multitude of systems, accumulated cyclone energy, 
latent heat release, all of which has the opportunity to be drawn N 
as the pattern slows and buckles, the subsequent result of warm air 
advection across Alaska and further downstream over Greenland that 
yields subsequent blocks. A CONUS trof-ridge, near climatological-
record percentiles by the weekend, the NE-CONUS in the NE-periphery 
of the MS/OH Valley ridge with a +1-2 standard deviation temperature 
anomaly through the column, by weeks-end into the following weekend 
it'll be interesting as to the heat and humidity magnitude that'll 
be able to advect into the NE-CONUS beneath prevailing NW-flow aloft 
likely prior to SE-sweeping cold fronts. Rainfall opportunities that 
ensemble-means continue to show synoptically remain uncertain as to 
outcomes as well as how warm it potentially could get. Any nudge in 
the ensemble mean longwave pattern could put us either in a warm-dry 
pattern or a mild-wet setup. Nevertheless temperatures look to be 
above-average into early October as emphasized by CPC forecasts, but 
lower confidence with respect to precipitation outlooks. Dependence 
on the longwave pattern breakdown. Aside we really need some rain. 

For now through the early half of the week, +WPO/+EPO signals with a 
robust N Pacific jet into the CONUS, energy cascades E. Grasping at 
continental-moist airmasses, there's opportunity for some rainfall 
Monday night and again Thursday night (however the latter becoming 
weighed down by increasing heights as the pattern begins to buckle). 
Mild days and cool nights. Break down details below. 

*/ Discussion...

Tuesday into Wednesday...

Clouds lingering. Light showers N beneath the closed mid-upper level 
low slowly working E. Downsloping W/NW flow. Gradual clearing, mild 
days, cool nights. Above-average temperatures when normally for late 
September we should see highs around 70, lows around 50. Expect it 
to be around +5 degrees with respect to the two. 

Thursday into Thursday night...

Sweeping cold front and a chance of showers. However heights on the 
rise as the longwave pattern buckles, a trof digs over the W CONUS 
with the ridge building E. Rainfall outcomes could be suppressed 
prior to ending up on our doorstep. Remaining mild. 

Friday onward...

Low confidence forecast depending on the longwave CONUS setup. We 
could end up warm and dry, or rather mild with on and off rainfall 
chances along sweeping cold fronts.


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 RI and southern MA coast through this evening. SSW 
winds gusting to 15-20 kt.

Tonight...VFR. However, areas of IFR-VLIFR FG 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 SHRA and isolated TSRA during
the afternoon from W to E. MVFR possible with any RA/+RA. SW
winds gusting to 25 kt in the afternoon, especially over the

Monday night...MVFR in SHRA and TSRA. Precipitation ending in
western and central sections after 06Z. Locally heavy downpours

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF. 

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy. Slight chance SHRA.

Tuesday Night through Wednesday Night: VFR. 

Thursday: VFR. Breezy. Slight chance SHRA.


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...SSW 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

Monday...SW winds will increase to 20-25 kt with a few gusts to
30 kt not out of the question late. SCA 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. SCA 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. Local rough seas. Slight chance
of rain showers. 

Tuesday Night: Winds less than 25 kt. Local rough seas. 

Wednesday through Wednesday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. 

Thursday: Winds less than 25 kt. Seas up to 5 ft.


MA...High Rip Current Risk from Monday morning through Monday 
     evening for MAZ023-024.
RI...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 
     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 
     Small Craft Advisory from 1 AM Monday to 6 AM EDT Tuesday for 
     Small Craft Advisory from 1 AM Monday to 6 PM EDT Tuesday for 


LONG TERM...Sipprell