Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 251110 

Area forecast discussion
National Weather Service Taunton Massachusetts
710 am EDT Mon Sep 25 2017

high pressure covering the northeast USA will bring fair warm
weather to southern New England through Wednesday. A cold
front combined with moisture from Maria may impact the region with
possibly scattered showers Wednesday into Thursday. Behind the
front, turning much cooler and lower humidity later Thursday and
continuing into the weekend. Hurricane Maria will bring dangerous
rough surf and rip currents to the South Coast this week, before
passing well southeast of New England late this week.


Near term /until 7 PM this evening/...

7 am update...

Summer-like morning with temps already in the low 70s in a few
locations along with dew pts in the 60s! The exception is across
Cape Cod and the islands where low clouds and fog exist. This
low level moisture may take most of the morning to burn off
given the lower sun angle now that it's late Sep.

Near record highs today with temps soaring to 85-90 away from
the coastline. Dry weather prevails given deep layer ridge over
the area. However Storm Prediction Center mesoanalysis indicates very moist 850 mb
and 925 mb dew pts across the region. Despite the absence of a
forcing mechanism, this abundant moisture may combine with
differential heating across the high terrain for a spot shower
this afternoon. Previous forecast captures these details nicely
so no major changes with this update.


Lingering fog will dissipate this morning. High pressure will
provide subsidence and maintain a warm humid airmass over US.
Thus we expect another sunny day. Dew points remain in the 60s,
so the humidity will be noticeable.

The mixed layer per the GFS reaches to about 850 mb, similar to
yesterday. The European model (ecmwf) is similar, but more like 880-890 mb.
Temps at the top of the layer are about 16-17c, with a few hints
of 18c. This would support Max sfc temps in the upper 80s and
around 90 inland. Weak winds will again allow a seabreeze, which
will buffer temps this afternoon and keep places near the coast


Short term /7 PM this evening through 6 PM Tuesday/...
high pressure means light wind continue. This means fair
weather with patchy fog inland. Meanwhile, the coastal fog and
stratus should again advect up across Cape Cod and islands.
There is a low risk that the fog could advance farther northwest
into southeast mass.

High pressure remains in control Tuesday, with a light wind
inland and light southeast wind at the shore. The NAM and ggem
show showers moving into south coastal Massachusetts and Rhode Island tonight. The
ggem then spreads showers across all of southern New England
Tuesday. Dynamic features show no support for this, and
convective parameters are stable through the period. We will
favor the GFS and European model (ecmwf) which keep any showers offshore, and
will show slight chance pops along the South Coast late in the

With dew points in the 60s, min temps should also be in the 60s.
Sunshine and mixing on Tuesday will again bring the layer up to
about 850 mb, where temps are forecast at 16-17c. This favors
mid 80s inland and cooler toward the shore.


Long term /Tuesday night through Sunday/...

* very warm and humid weather persist into Wednesday
* scattered showers possible Wednesday into Thursday
* pattern change to much cooler and less humid weather late
Thu into the weekend

Overall good model agreement on the large scale flow between the ec,
GFS, their ensembles, the UKMET and NAM. Thus above average
forecast confidence this period. Ridge lingers across the region
into Wed and will result in warm (highs 80-85) and humid conditions
(dew pts 65-70!).

Despite Hurricane Maria remaining well south of New England mid
level moisture advects (k indices on the rise) northward into our
area beginning Wed and continuing into Thu. Not much forcing for
ascent Wed given ridge axis lingers across the area. Thus perhaps
dry weather prevails Wed.

However by Wed night and especially into Thu approaching short wave
and attending cold front will act on pwats of +2 Standard from Maria and
provide a focus for showers late Wed into Thu. Some signs this could
take the form of a pre - predecessor rainfall event given frontal
boundary and upper level jet streak. Thus looks like a small window
of opportunity for a period of heavy rain over southeast Massachusetts Thu
especially Cape Cod and the islands. Will have to watch closely
given tropical airmass.

Then big improvement with a noticeable cool down late Thu into the
weekend as low level flow becomes north-NE behind departing fropa and
Maria. Seasonable for this time of year with highs 65-70 Fri/Sat/sun
and lows in the 40s along with low humidity. A touch of fall for
sure. Mainly dry too with the exception of a few isolated brief
diurnal showers possible Sat with cold pool aloft and cyclonic flow.


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/...

Today... high confidence.

7 am update...

VFR and mainly dry weather today, other than a spot shower over
the high terrain this afternoon. Seabreezes develop. IFR
conditions over Cape Cod and the islands may take much of the
morning to dissipate. Earlier discussion below.


VFR. Areas of IFR/LIFR early on Cape Cod and islands due to fog,
but the fog will lift and thin during the morning. Light east to
southeast wind.

Tonight... moderate-high confidence.

VFR inland with patchy fog late. Meanwhile, fog and low clouds
move back over Cape Cod and islands with areas of 1/4 mile
vsbys. Areas of IFR/LIFR in any fog.

Tuesday... high confidence.

VFR. Areas of IFR/LIFR early on Cape Cod and islands due to fog.
Light southeast wind.

Kbos taf...high confidence in taf. Seabreeze redevelops by 15z,
becoming south toward 00z-02z.

Kbdl taf...high confidence in taf.

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

Tue night...VFR but trending toward MVFR late South Coast,
along with low risk for some rain South Coast.

Wed...marginal MVFR-VFR with very low risk of rain.

Thu...marginal MVFR-VFR southeast Massachusetts along with risk of
showers. Elsewhere improving to VFR and mainly dry.

Fri...VFR, dry weather and light winds.


forecaster confidence levels...

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

Short term /through Tuesday/...high confidence.

Winds will remain light through Tuesday with high pressure
overhead. Meanwhile, increasing long period south swell from
Hurricane Maria will be moving into the waters with potential
for 5 to 7 foot seas over southern waters tonight and 7 to 9
feet on Tuesday. Small Craft Advisory for hazardous seas will continue. In
addition, areas of fog will result in poor vsbys at times,
especially south and east of Cape Cod.

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

Tue night and Wed...light winds with ridge overhead however
increasing large southerly swells from Hurricane Maria. Low risk
of scattered showers especially southern waters. Given moist
airmass rounds of fog expected.

Wed night into Thu...some heavy rain possible southeast Massachusetts
waters as moisture from Maria combine with approaching cold
front. In addition areas of dense fog may be an issue.

Friday...big improvement with front offshore and high pres
building in.


Tides/coastal flooding...
long period swell from Hurricane Maria will be moving north
into the south coastal waters. Wnawave guidance indicating
increasing swell of 5-7 feet with a period of 15 seconds moving
reaching the south coastal waters tonight and up to 9 ft on
Tuesday. This will result in increasing high surf and dangerous
rip currents. High surf advisory will continue and will extend
through Tue. It is likely the high surf will continue through
the week even as Maria likely recurves out to sea well southeast
of New England.


record high Sunday was broken at bdl with a temp of 92 degrees.
Record high Sunday was broken at orh with a temp of 86 degrees.

Two of four climate sites broke Max temp records yesterday.
Another chance for record high temps again today, when records
are 85-90. Records Jump Up Tuesday to 89-95, while less mixing
will lead to lower Max temps. So the chance for new records
diminishes Tuesday. The current record Max temps for the two and Tuesday...are:

Bos 89/1926 95/1881
orh 85/1970 91/1930
bdl 90/2007 93/2007
pvd 89/1920 89/2007

Also, dew points in the 60s, while high for this time of year,
are not unprecedented. The daily extreme high values for dew
points are still in the low 70s, except for a couple of 68 and
69 values at Worcester.


Box watches/warnings/advisories...
Massachusetts...high surf advisory until 6 PM EDT Tuesday for maz020-022>024.
Rhode Island...high surf advisory until 6 PM EDT Tuesday for riz006>008.
Marine...Small Craft Advisory for hazardous seas until 6 PM EDT Tuesday
for anz235-237.
Small Craft Advisory for hazardous seas until 7 am EDT
Wednesday for anz254>256.


near term...wtb/nocera
short term...wtb
long term...nocera

National Weather Service Glossary of Abbreviations