Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
1000 PM EDT sun Sep 21 2014

a period of steady rain will affect the far southeast New England
coast this evening. Otherwise...drier and less humid weather is
on tap for Monday as a dry cold front sweeps across the region.
Strong high pressure will bring sunny days and clear nights to the
region from Tuesday through next weekend with a warming trend. We
could approach record warmth on Saturday.


Near term /until 6 am Monday morning/...
10 PM update...

A band of steady rain has generally diminished across portions of
east Massachusetts this evening as low pressure developing offshore begins to shift
NE. A few more showers are likely to remain from this but just
over the next couple of hours. Otherwise...have been watching a
downward trend in convective activity in New York associated with the
cold front...still a bit of -shra activity left...but not much
convection. Looks like mainly western Massachusetts and SW New Hampshire will be have this
rain in the cards but generally after 03z. After that...the rapid
entrainment of dry air...long since loss of diurnal heating and
shift of best dynamics into northern New England should allow for most
of these to dissipate such that very little activity...aside from
a brief gust of wind and wind seen elsewhere with this
frontal passage.

Otherwise...a pocket of very dense fog has developed from the North
Shore of Massachusetts into coastal Maine. This will likely continue into the
morning hours. Have issued a dense fog advisory for this area.
Otherwise...only other locations reporting under half a mile are
orh and tan...but feel these are likely more colocated with the

Previous discussion...

Marginal instability with deep low level moisture has allowed
isolated to scattered showers to continued to affect southern New
England. We should see this activity diminish early this evening
with the loss of daytime heating.

The main concern will be the surface low pressure system off the middle
Atlantic coast which will be tracking northeast and passing near the
benchmark this evening. The main question is how far northwest
the rain shield will get. Latest near term guidance has been
trending further northwest. Therefore...expect a period of steady
rain across the cape/islands and probably further northwest into
interior southeast Massachusetts/Rhode Island for at least a time. In
fact...latest hrrr showing the potential for a brief period of
rain across the northeast Massachusetts coast including Boston. Not sure if
it will get that far northwest...but its certainly possible.
Regardless...the heaviest rainfall will occur across Nantucket...
where between 0.50 to perhaps up to 1 inch of rain may occur.
The rain may persist through much of the evening across the cape
and islands...but should wind down near or just after midnight.

Meanwhile...once the isolated to scattered diurnally driven
scattered showers wind down early this evening...the rest of the
region will mainly be dry tonight. However...a cold front will be
approaching our western zones toward midnight. While shear is quite
impressive...very little instability will be left. So while we may
see a few spot showers affect our western zones...they will be in
the process of weakening and not expecting much more than that. Low
temperatures will only bottom out in the upper 50s and the lower 60s by
daybreak Monday.


Short term /6 am Monday morning through Monday night/...

A much drier airmass will work into the region behind
the cold front on Monday. While partly to mostly sunny skies are
expected early...may see a scattered to broken deck of strato-
cumulus clouds work into at least the interior by afternoon. Highs
should mainly be in the 60s across the interior...but still will
reach between 70 and 75 along he coastal plain. Gusty west winds
of 20 to 30 miles per hour are expected as BUFKIT soundings showing very good

High surf...given large south to southeast swell from departing
coastal low pressure system have issued a high surf advisory for the
South Coast on Monday. We issue high surf products through the end
of September if conditions warrant.

Monday night...

High pressure will be building in from the west. This will allow
for diminishing winds and skies to become mostly clear. Looks like
a pretty good night of radiational cooling...with lows bottoming out
in the upper 30s to the middle 40s in most locales. The urban heat
island of Boston will be the mild spot with the low bottoming out
near 50.


Long term /Tuesday through Sunday/...

* high pressure and dry weather through the period
* near record warmth possible next Saturday

very good agreement amongst model guidance the entire forecast
period. An upper level trough departs the northeast states on
Tuesday. Then...much ado about building high pressure...both at
the surface and aloft the remainder of the week. The upper ridge
is very strong as it is parked from the Great Lakes to southern
New England by next weekend.

Details... Tuesday will feature mostly sunny skies except only
partly sunny northwest Massachusetts and SW New Hampshire closer to some higher 925 mb
humidity. Otherwise...expect sunny days and clear nights through
next weekend. Have gone a few degrees lower than model consensus
temperature minimums through Thursday due to excellent radiational
cooling expected along with very dry dewpoints. As the center of
the upper high expecting a dramatic warmup Friday
and especially Sat. The 12z European model (ecmwf) run is even warmer than the
previous run with 925 mb temperatures warming from +12c
+17c Friday... to +19c or +20c on Sat... with warm temperatures
likely continuing into early the following week. Have gone several
degrees above model consensus maximums for next Saturday...with
highs soaring to 80 to 85 across interior southern New England.
Records for that day include 85 at Worcester and 86 at both Boston
and Providence.

Light winds are expected for the although it will be
dry we are not expecting fire weather concerns. Local sea breezes
will occur...especially Friday through next Sunday. It should be
noted that the GFS has a hint of a potential backdoor front/trough
over northeast Massachusetts on Sat but this was not enough to detract from
the very warm yet.

An upper low over Virginia and an associated inverted trough is
likely to be causing precipitation in the middle Atlantic region
middle to late in the work week that tries to work its way northward.
There is excellent model agreement that this area only gets as
far northward as off the New Jersey coast by Friday...before retreating
southward as strong high pressure becomes established over the
northeast on the weekend.


Aviation /02z Monday through Friday/...
forecaster confidence levels...

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

Short term /through Monday night/...

Tonight...low to moderate confidence. IFR conditions with some
low IFR conditions across far southeast Massachusetts including the cape and
islands with visibilities below 1/2 mile at times in locally dense
fog. Most of the rest of the region will be MVFR ceilings...with
many areas becoming IFR ceilings between 02z and 06z. Best
confidence for IFR is from about a Jaffrey-Worcester-Willimantic
line eastward. Steady rain with embedded showers will affect the
far southeast New England coast this evening. The rain will likely
reach into Rhode Island/interior southeast Massachusetts for a short time and
perhaps even into northeast Massachusetts.

Monday and Monday night...high confidence in VFR conditions.
Just a low risk for brief MVFR ceilings across the interior on Monday
as a deck of stratocumulus clouds moves into the region.
Otherwise...gusty west to northwest winds of 20 to 25 knots
expected during the day Monday.

Kbos terminal...moderate confidence tonight with high confidence on

Kbdl terminal...moderate confidence tonight with high confidence on

Outlook...Tuesday through Friday...

High confidence.


forecaster confidence levels...

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

Short term /tonight through Monday night/...

Tonight...moderate to high confidence. Low pressure passing near
the benchmark will result in enough south to southeast swell for
Small Craft Advisory seas to develop across the outer-waters and western sounds.
Southeast winds should become southwest tonight at 10 to 15 knots
later tonight. Areas of fog...some locally dense...will occur
across the waters...especially south of Boston Harbor.

Monday and Monday night...moderate to high confidence. Small Craft Advisory seas
on the western sounds and outer-waters will continue through
Monday night. In addition...a period of west to northwest wind
gusts near 25 knots is possible for a time on Monday. is possible we may need to expand Small Craft Advisory for a time
during the day Monday into some of the nearshore sounds and
waters. Confidence not quite high enough to do this right now...
so will defer to the next shift.

Outlook...Tuesday through Friday...

High confidence...

Tuesday and Wednesday...seas near 5 feet may linger at times Tuesday and Wednesday over
the waters S and east of Nantucket. Otherwise winds and seas should
be below Small Craft Advisory criteria. A northeast wind gradient
will increase over the southern coastal waters Tuesday night into Wednesday
as strong high pressure pushes into northern New England. But
gusts are expected to only reach 20 knots.

Wednesday night through Friday...quiet boating weather with high pressure
dominating the weather. Winds and seas below Small Craft Advisory thresholds.


Box watches/warnings/advisories...
Massachusetts...high surf advisory from 8 am to 5 PM EDT Monday for maz020>024.
Dense fog advisory until 5 am EDT Monday for maz006-007-014.
New Hampshire...none.
Rhode Island...high surf advisory from 8 am to 5 PM EDT Monday for riz006>008.
Marine...Small Craft Advisory until 5 am EDT Tuesday for anz235-237.
Small Craft Advisory until 8 am EDT Tuesday for anz250-254>256.
Small Craft Advisory from 6 am to 4 PM EDT Monday for anz251.


near term...Frank/doody/gaf
short term...Frank
long term...gaf

National Weather Service Glossary of Abbreviations