Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 141747 

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
147 PM EDT Mon Oct 14 2019

dry and pleasant weather expected through Tuesday. Storm system
Wednesday with rain and wind threats. Blustery, cool Thursday
with chance showers. Chilly, breezy conditions Friday. Frost /
freeze conditions possible Saturday morning. Warming up into the
weekend, remaining dry. The next chance of wet weather early to
midweek the following week.


Near term /until 6 PM this evening/...

1235 PM update...

Skies have become partly sunny to the northwest of the Boston to
Providence corridor at lunch time. However, light moist southeast
flow continued to result in an abundance of clouds across
southern Rhode Island and southeast Massachusetts. We gradually should see breaks
emerge this afternoon from northwest to southeast, but this will
be a slow process given limited mixing. Little if any sunshine
expected across the cape/Nantucket for most of the afternoon.

High temps should mainly in the 60s with a few locations around
70. It will be cooler across the cape and islands given the
onshore flow and clouds.


Short term /6 PM this evening through 6 PM Tuesday/...
high pressure builds into region from plains tonight and becomes
centered S of New England Tue. Cross sections show drying through
column and subsidence so expect clear skies tonight and plenty of
sunshine Tue.

Gradient weakens enough Tue afternoon to allow for coastal sea

Lows tonight fall back into upper 30s and 40s, except near 50 on
immediate coast. Highs Tue reach 50s to lower 60s.


Long term /Tuesday night through Sunday/...
*/ highlights...

- storm system Wednesday bringing rain and wind.
- Cool, dry, blustery Thursday. Chance showers N/W.
- Cool with high pressure Friday. Frost / freeze Sat morning.
- Warm-up, dry weekend.
- Potential early to midweek storm the following week.

*/ Overview...

Near-seasonable, active weather trend. Renewed NE Atlantic cyclone
energy ahead of which mild Atlantic air funnels across north Europe. A
series of rossby wave breaks across west Russia, enough to kick east the
present siberian 500 mb cyclone energy. Rippling downstream, the pattern
transitioning across the North Pacific, a wpo / epo teleconnection role
reversal towards positive yielding a mild North Pacific jet into the west
Continental U.S.. Bering straight / alaskan 500 mb low promoting subtle 500 mb ridging
into the west Canadian Maritimes, a Hudson Bay / east Continental U.S. Trof deepens
through which energy rotates round remnant cyclone energy presently
associated with the North-Plains storm system Wednesday. Rossby wave-
train evolution into the latter October with pattern amplification,
a deep west Continental U.S. 500 mb trof upstream from anomalous east Continental U.S. Ridging. A
potential late-October warm-up. Details below.

*/ Details...

Around Wednesday...

Storm. Continued signals of potent north-stream vortlobe / pv-streamer
undergoing a negative-tilt phasing with S-stream remnant eastern North-
Pacific presently S of Cabo San Lucas. Rapid surface cyclogenesis /
bombogenesis round southeast New England / 40n-70w benchmark during energy
Transfer through a brief double-barrel low setup. Certainly strong
dynamics and associated lift / ascent. Soaking rains. Strong winds.
Another October gale / early season Nor'easter.

However uncertainty on specifics. Continued run-to-run discrepancies
and model-to-model / ensemble member spread. Synoptic wobbles with
individual features more notably the closing mid-upper level low in
respect to anticipated aforementioned cyclogenesis. Further north/west over
the interior, the surface low tucks closer to the coast, whereas the
700 mb-3 low closing over S New England as vortlobe energy bowls through
the mid-level trof yields the surface low closer the 40n-70w Bench-
Mark. Much different outcomes for our area between the 2 scenarios.
It's going to be several model runs till we can nail down with any
certainty threats and impacts for any one particular area. Potent
nevertheless with 3-4 Standard deviation anomaly.

Till then, monitoring several key features. 1.) Moderate-heavy rain.
Focus on banding / deformation as secondary cyclogenesis emerges at
or near our coastline. Trowaling sub-tropical moisture with dynamic
forcing throughout the column, expecting rain-banding with embedded
thunderstorms (some impressive +60 microbar/second Omega values per
14.0z gfs). 2.) Strong winds. Surface pressure falls 3-4 mb/second
with parent pressure fall/rise couplet. Isallobaric-gradient driven
wind. At first a conditionally unstable profile and precip-drag that
could bring faster momentum aloft down to the surface preceding the
surface low center. Then a dry slot wraps into the storm. Forecast
model relative humidity / cloud fields showing a scorpion tail feature typically
associated with a sting-jet as evaporative cooling proceeds with
isallobarically descending air but looking further downstream (e ME
into southeast Canadian provinces).

Altogether, this storm looks progressive. Not concerned much about
flooding but more about winds and their impact along the shoreline
and across the waters (wind / wave). Focus on the Wednesday PM
commute as well. Continued low confidence forecast with preference
to global models. Keep the mention of gales in the hazardous weather

Immediately behind the storm, cold air advection, steep lapse rates,
likely blustery right behind associated fronts as temperatures drop
quickly into Thursday.


Blustery, cool, showers expected north/west of the high terrain, drying and
downsloping into the CT River Valley. Typical autumn/winter pattern
is back. Chance pops. Clearing out, drying out overnight.


Crux of cooler air aloft. Will be concerned with frost / freeze head-
lines into Saturday morning as winds become light, conditions become
clear. Another breezy day. Winds subsiding along the east/southeast coast as
high pressure builds from the west overnight. Interior 30s for lows.
Frosty pumpkins.

Saturday Onward...

Continued signals of a warming trend out ahead of a suggested early
to midweek cyclone. Anomalous 850 mb temperatures aloft, the potential
for highs into the 70s Sunday through Tuesday so long as SW winds


Aviation /18z Monday through Saturday/...
forecaster confidence levels...

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

Short term /through Tuesday/...

This afternoon...moderate to high confidence. VFR conditions
will continue generally northwest of the Boston to Providence
corridor. Along and southeast of the I-95 corridor light onshore
flow was resulting in MVFR to even IFR-LIFR conditions on the
cape/islands. Gradual improvement should occur from the
northwest through late afternoon/early evening, but most of the
cape/islands will remain in the lower clouds and fog patches.

Tonight...moderate to high confidence. Mainly VFR conditions,
but along the southeast New England will have to watch out for
some patchy fog developing with sunset given lingering low
level moisture/light winds. A cold front crossing the region
overnight should scour any of that out after midnight. Winds
should become northwest behind the front, but remain light over most

Tuesday and Tuesday night...high confidence. VFR conditions
expected with light winds.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

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

Tuesday night: VFR.

Wednesday: mainly VFR, with local MVFR possible. Breezy. Rain.

Wednesday night: mainly VFR, with local IFR possible. Windy
with gusts up to 35 kt. Ra, chance rain showers.

Thursday: mainly VFR, with areas MVFR possible. Strong winds
with local gusts up to 40 kt. Chance rain showers.

Thursday night: mainly VFR, with local MVFR possible. Windy
with gusts up to 30 kt.

Friday: VFR. Breezy.


forecaster confidence levels...

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

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

Dropped small craft advisories since seas have subsided below 5 ft
per buoy observations.

Weak low pressure tracks up coast today and passes near cape/islands
early this afternoon before heading farther NE. Light S/southeast winds
shift to west/northwest behind low later in day, then give way to near shore
sea breezes Tue afternoon. Seas build slightly to 4 ft on outer southeast
waters today and tonight, then subside Tue.

Showers mainly affect S coastal waters and Cape Cod Bay through mid

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

Tuesday night: winds less than 25 kt.

Wednesday: low risk for Small Craft Advisory winds with gusts
up to 30 kt. Seas locally approaching 5 ft. Chance of rain.

Wednesday night: low risk for gale force winds with gusts up to
40 kt. Seas up to 5 ft. Rain, chance of rain showers.

Thursday: moderate risk for gale force winds with gusts up to
45 kt. Rough seas up to 10 ft. Slight chance of rain showers.

Thursday night: low risk for gale force winds with gusts up to
35 kt. Rough seas up to 10 ft.

Friday: moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Local rough seas.


Box watches/warnings/advisories...
Rhode Island...none.


near term...Frank

National Weather Service Glossary of Abbreviations