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fxus61 kbox 200224 
afdbox

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
1024 PM EDT Thu Sep 19 2019

Synopsis...
high pressure remains in control through the weekend with
summerlike temperatures returning. A cold front brings the
next chance of showers early next week. More seasonable
temperatures follow for the rest of the week with a risk of
showers on Thursday as another cold front approaches. Distant
Hurricane Humberto will bring high surf and dangerous rip
currents through Friday.

&&

Near term /until 6 am Friday morning/...

Rather quiet weather continues. Only minor tweaks to the ongoing
forecast to reflect observed trends.

Previous discussion...

Expecting another good radiational cooling night with high
pressure well in control - clear skies (high clouds approach
late/overnight), dry air mass and light winds. With lows in the
mid/upper 30s still on track in the more sheltered valleys and
colder spots in western MA, still may be a few patches of frost,
but quite localized and not enough anticipated coverage to
warrant frost headlines. As with last night, with the radiation
inversion setting up and planetary boundary layer decoupling, radiation fog looks to
develop again tonight in locales adjacent the CT River Valley.

&&

Short term /6 am Friday morning through Friday night/...
high pres remains in control. A weak shortwave riding over the
ridge will bring some mid/high clouds during Fri but still
mostly sunny. After a chilly start, a significant warmup is
expected during the afternoon. 925 mb temps 18-19c will support
highs reaching the mid/upper 70s. Mainly clear skies Fri night
but not as cool as airmass moderates. Lows will be mainly in the
50s.

Swell from Humberto will also continue the threat for rough
surf and dangerous rip currents. With warming conditions Friday,
will continue the high surf advisory through much of Friday
along ocean-exposed portions of the coast.

&&

Long term /Saturday through Thursday/...
highlights...

* dry weather, mild days and seasonable nights for the weekend.
Elevated threat for lingering rip currents Saturday.

* Cold front brings at least showers to the area later Monday into
Tuesday.

* Brief dry weather Wednesday, turning unsettled late next week.

Details...

Saturday - Sunday...

Still anticipating a great weekend weather-wise, as an amplified
ridge aloft (approx. 1-2 Standard deviations above normal
geopotential height anomalies per gefs) builds and crests over the
region. Abundant sunshine, dry weather and 850 mb temperatures
around the mid-teens celsius support above-normal temperatures for
late September, with good diurnal temperature ranges. Of the two
days, Sunday projects to be the warmest areawide given warmer 850 mb
temperatures and more of a southerly gradient component to the flow
affording less inland penetration of sea breezes near the coast.
Looking for highs in the mid-upper 70s to mid 80s on Saturday
(coolest along the coast/cape and islands), with highs well into the
80s on Sunday. Lows mainly upper 50s to low-mid 60s.

With potential for several to be heading to the beaches on Saturday,
still will be some concern for rip currents lingering from
Humberto's passage. Seems likely a rip current statement would be
needed. High surf issues don't look as likely, with wave heights
generally under 5 feet and a lowering trend to waves.

Monday - Tuesday...

Cold front continues to be a Focal Point for more active weather in
this period. Past couple GFS deterministic model runs have slowed
the front's eastward progression down by a few hours, though it
still is on the faster side compared to the Gem and European model (ecmwf). So still
some timing issues to Iron out, but some loose consensus that Monday
late-afternoon Monday through overnight/early Tuesday as an
approximate frontal passage. European model (ecmwf) is still slower than that and
would lead to a continuation of wet weather on the South Coast, cape
and islands through a larger part of Tuesday.

Dynamics look favorable and low- and mid-level wind fields are
pretty robust monday; however guidance lapse rates in mid-levels are
weak, and it would take greater heating/instability to trigger
thunderstorms at this point. Will continue to leave as showers for
now but the thunder potential would be greater if more instability
is realized then currently progged. Pwats climb to about 1.4-1.7"
supporting at least a brief downpour threat. Regardless, this
continues to be the next bonafide chance at rains.

Midweek:

Larger disagreement in model solutions then becomes apparent for
Wednesday into Friday. Some of this disagreement comes from models'
varied handling of shortwave energy digging into the intermountain
west/southern rockies Tuesday. International guidance keeps this
disturbance closed off and detached from the larger westerlies,
which in turn keeps our area dry with seasonable temperatures. On
the other hand the GFS shows less amplitude to this shortwave trough
aloft and would verbatim indicate a brief spell of quiet weather
early Wednesday before isentropically forced showers enter the
picture for Wednesday night.

While the Gem and the GFS bring a strong cold frontal passage
through on Thursday with seasonal early Fall-like weather for Friday
- the European model (ecmwf) washes the front out Thursday and instead amplifies an
upper-level ridge over the East Coast, which would bring above
normal temperatures back into southern New England by late week.

Will take a blended guidance approach to the forecast for this
period given the larger variability in model solutions.

&&

Aviation /03z Friday through Tuesday/...
forecaster confidence levels...

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

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

VFR conditions continue. Diminishing northeast winds on the
cape and islands through tonight, with winds turning light
westerly (under 10 kts) into Friday.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Saturday through Tuesday/...

Saturday through sunday: VFR.

Sunday night: VFR. Breezy.

Monday: mainly VFR, with areas MVFR possible. Breezy. Chance
rain showers.

Monday night: mainly MVFR, with areas VFR possible. Breezy.
Chance rain showers.

Tuesday: mainly VFR, with areas MVFR possible. Slight chance
rain showers.

&&

Marine...
forecaster confidence levels...

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

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

Recent observations from buoys indicate seas around 3-5 feet,
though still expect to see building easterly swell from
Humberto contributing to waves rising into the 5 to 8 foot range
tonight into early Friday on outer waters. Seas then gradually
subsiding into Friday night. Scas continue in effect for most of
the outer waters. Winds offshore and light (10 kts or less).

Outlook /Saturday through Tuesday/...moderate confidence.

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

Saturday night through sunday: winds less than 25 kt.

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

Monday: winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.

Monday night: winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.

Tuesday: winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...high surf advisory until 6 PM EDT Friday for maz020-022>024.
High surf advisory until 6 PM EDT Friday for maz007-019.
Rhode Island...high surf advisory until 6 PM EDT Friday for riz006>008.
Marine...Small Craft Advisory until 8 am EDT Saturday for anz250-
254>256.
Small Craft Advisory from 6 am Friday to 8 am EDT Saturday for
anz251.

&&

$$
Synopsis...kjc/loconto

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