Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
420 am EDT Thursday Jul 24 2014

Synopsis...
a cold front slowly exits the coastal waters today. High pressure
centered over the Ohio Valley will build eastward and provide
sunny skies Friday. The high shifts offshore Saturday. Then
unsettled conditions late in the weekend and into next week. A warm
front approaches Sunday bringing warm humid air. A cold front then
swings across the region Monday and Tuesday...and lingers off the
East Coast the middle of next week.

&&

Near term /until 6 PM this evening/...
4 am update...

Water vapor imagery shows a weak short wave moving through central
Massachusetts at 4 am. Ahead of it there was a batch of showers racing
northeast through southern New Hampshire. These showers will be long gone by
daybreak. Fog and low cloudiness has not been as widespread as the
models indicated. So far...only Nantucket has visibility of 1/2
mile in fog. In fact...most other portions of southern New England
had only partial cloud cover...so many areas may start out partly
sunny at daybreak.

At the surface...the cold front is already along the coast. The
upper trough axis is still to our west and an upper level jet
maximum is forecast to strengthen as it moves across our region
this afternoon. This is likely to keep it on the cloudy side
through the morning and early afternoon especially in Rhode Island and
southeast Massachusetts. The front will be slow to exit the coastal waters
since a weak wave of low pressure will be moving along it. We are
watching a batch of showers in eastern PA but with drier dewpoints
filtering in from the northwest...already down to 57 at Keene...thinking
that these will erode. All models restrict any chance of showers
to mainly the cape and islands into the early afternoon hours...so
have cut back on probability of precipitation for today. The northwest two-thirds of the
region should become mostly sunny and pleasant in the afternoon.
Highs today mainly upper 70s to lower 80s.

&&

Short term /6 PM this evening through 6 PM Friday/...
a mostly clear night is expected tonight. The only exception may
be on the islands where models are quite emphatic about the return
of low cloudiness and fog with light northeasterly wind flow and
dewpoint temperatures hanging in the lower 60s. The possibility
exists for low visibilities on Nantucket. Lows will be much more
comfortable...in the middle 50s to lower 60s except lower to middle 60s
on the islands.

High pressure centered over the Ohio Valley will build eastward on
Friday and provide sunny skies to southern New England with highs
reaching into the lower 80s...cooler on the islands.

&&

Long term /Friday night through Wednesday/...

Big picture...

Much of the upper flow remains unchanged through the forecast
period. Deep ridges will extend across western North America and the
western Atlantic. Closed low over northern Quebec anchors a trough
over eastern North America. Shortwave ejecting from the Pacific
northwest will plow over the top of the western ridge...then merge
with the eastern North America trough over the weekend. This will
deepen the trough and pull its features farther south. The depth of
the trough and the extent of the ridges on either side will make
straight west-to-east movement difficult next week.

The mass fields and thermal fields of the GFS and European model (ecmwf) look similar
in overview. Some differences in details emerge during the first
half of next week. The similarity builds confidence in the overall
flow of the forecast. The longer range differences in detail support
using a blend of the forecast data.

The dailies...

Friday night and Saturday...

This should be a fair period but with signs of changes to come. High
pressure shifts offshore and the surface flow turns southwest. Also
increasing southwest flow aloft with increasing moisture at the
cirrus Level. Cross sections do show some increasing moisture toward
Saturday evening around 5000 feet as well. Expect mostly clear
skies and light winds Friday night. Sky cover increases Saturday
but mostly high thin clouds until late in the day. Temperatures in the
mixed layer will be 12-14c which supports maximum surface temperatures low to middle
80s.

Saturday night-Sunday... as the shortwave phases with the eastern
upper trough...the supporting upper jet extends east toward New
England. Meanwhile west to southwest low level winds will bring
increasing humidity. This will mean increasing clouds and an
increasing chance of showers/thunder overnight into Sunday as the
resulting warm front approaches. Expect dewpoints to increasing
during this time and reach 65-70.

Monday-Tuesday-Wednesday... surface low associated with the
shortwave pivots over the Great Lakes Sunday night/Monday and swings
a cold front toward the East Coast. At this same time...the upper
trough deepens and turns the upper flow over the East Coast more
south-southwest. As a result of this...the cold front will slow its
eastward progress Monday as it becomes parallel to the upper flow.
We will be in the warm sector leading the cold front Monday and
probably Tuesday. This should support a chance of showers/thunderstorms each
day...although less confidence in the areal coverage of chance probability of precipitation
Tuesday. Long range guidence suggests dry weather Wednesday even
with the upper low over the lakes and broad cyclonic flow over New
England. We went along with this idea for now...but with low
confidence.

&&

Aviation /08z Thursday through Monday/...
forecaster confidence levels...

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

Short term /through Friday/...moderate confidence.

MVFR ceilings were scattered throughout southern New England shortly
before daybreak except low IFR on Nantucket with locally dense
fog. Expect skies to dawn partly sunny. There is a slight chance
of showers today in southeasternmost Massachusetts including Cape Cod and the
islands. Skies should become VFR across the northwest two-thirds
of the region by middle afternoon.

VFR with mostly clear skies expected most areas tonight. The only
exception may be on the islands where models are quite emphatic
about the return of low cloudiness and fog with light northeasterly
wind flow and dewpoint temperatures hanging in the lower 60s. The
possibility exists for low visibilities on Nantucket.

VFR with abundant sunshine expected region-wide on Friday. Local sea
breezes in the afternoon.

Kbos taf...moderate confidence.

Kbdl taf...moderate confidence.

Outlook...Friday night through Monday...moderate confidence.

Friday night through Saturday...VFR. Local IFR possible in early
morning fog/low clouds.

Saturday night-Sunday-Monday... VFR but with areas of MVFR in
showers/tstms.

&&

Marine...
forecaster confidence levels...

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

Short term /through Friday/...moderate confidence.

Winds and seas are forecast to be below Small Craft Advisory
thresholds through Friday. Northwest to northeast winds are
forecast for today...gradually shifting to the southwest by Friday
afternoon. Local sea breezes are expected on Friday. Locally dense
fog at times today and tonight...especially over the waters
southeast of Massachusetts with visibilities 1 mile or less at times.

Outlook...Friday night through Monday...moderate confidence.

Friday night-Saturday... light southwest winds Friday night increase
on Saturday but should remain below 25 knots. Seas also build but
should remain below 5 feet.

Saturday night-Sunday...a warm front approaches the waters with
warmer more humid air and with clouds/showers/tstms. Increasing
southwest winds with gusts near 25 knotsd Sunday afternoon and seas
build to 5-6 feet on the exposed waters. A Small Craft Advisory may
be needed.

Monday...warm humid air over the waters with southwest winds gusting
20-22 knots. This should keep seas at 5-7 feet on the exposed
waters. The potential for Small Craft Advisory will continue.

&&

Equipment...
the Blue Hill National oceanic and atmospheric administration weather radio transmitter is temporarily out of
service due to a phone company issue. This is being worked on and
is expected to be resolved today.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...gaf/wtb
near term...gaf
short term...gaf
long term...wtb
aviation...gaf/wtb
marine...gaf/wtb
equipment...gaf

National Weather Service Glossary of Abbreviations