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Area forecast discussion 
National Weather Service Taunton Massachusetts
1006 PM EDT Friday Jul 29 2016

Synopsis...
low pressure will sweep south of New England during the overnight
period. A brief period of drier conditions follow for Saturday
with the slight chance of showers over southwestern New England. A
warm front will develop south of New England on Sunday with a few
waves of low pressure passing eastward along it from Sunday
through early Tuesday. Scattered showers are possible into early
Tuesday, especially in western sections. Low pressure will move
out to sea Tuesday. High pressure returns with dry and seasonable
conditions for the middle and latter portion of next week.

&&

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

10 PM update...

Showers, a few of which were very heavy, had nearly dissipated by
10 PM with what looked to be only sprinkles left over northwest
Rhode Island. Made just a few adjustments in temperatures and dewpoints to
reflect current trends. Main issue during the overnight hours will
be forecasting extent of fog areas. Some patchy fog has begun to
develop across interior valleys and an area of fog has crept south
along the Plymouth County coast with pockets of visibility below 1
mile.

715 PM update...

A few heavy showers continued across northern Worcester County and
in northern Connecticut as of 715 PM. Another heavy shower was
moving south into Middlesex County from the Nashua area. Winds
gusted to near 25 mph with one of these showers at Westfield, Massachusetts
during the past hour. The showers were shallow...below 25
kft...and were not producing lightning. The hrrr shows showers
sliding southward through central Massachusetts over the next 2 hours before
dissipating. Have updated pops to reflect this thinking. Otherwise
no changes to forecast. Will need to keep a close eye on potential
fog development in southeast Massachusetts.

Previous discussion...

Clearing continues across S New England allowing boundary layer
destabilization beneath a conditionally unstable environment.
Scattered heavy showers developing though low-topped, limited on
development with likely warmer and sinking air aloft with slightly
rising heights around 500 mb and in wake of the main mid-level vortex
parent with the surface low sweeping out to sea. Slow moving
through the rather weak 10 mph mean flow out of the NW, monitoring
for possible localized flooding impacts. Development along fine-
line convergence boundaries it would seem per observational
mesoanalysis. Diurnally driven, should see activity diminish with
sunset.

Tonight...

Clearing out with high pressure and drier air building in. With light
winds, a favorable setup for radiational cooling. Noting a somewhat
soupy airmass remaining in place with dewpoints hovering around
the low to mid 60s, and considering antecedent rains,
anticipating fog to develop. Confident within the CT River Valley,
east CT, interior southeast Massachusetts of some visibility restrictions.
Perhaps some issues along the coasts though may see more clouds
than fog with the NE onshore flow turning north through the overnight
period.

&&

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

High pressure and drier air linger lending to mostly clear conditions
and light winds. Likely sea-breezes to develop around mid to late
morning. Model forecast indications of showers developing along sea-
breezes per a measure of lift of available surface based instability
and decent low level moisture availability, that or upstream convection
from PA becomes an influence. Precipitable waters forecast up to 2
inches. But considering an unfavorable environment given confluent
mid to upper level flow and mid level height rises lending to some
measure of sinking air, feel there is a low risk of showery weather
and mainly late in the day. Thus leaning with slight chance pops
mainly for short wave New England encompassing much of the north-half of CT
into the Springfield Massachusetts Metro.

Forecast +14-16c 850 mb temperatures warrant mid to upper 80s for
highs. Already temperatures were underdone earlier today after
clouds started to break, so am going to up the forecast highs a
degree or two warmer nudging the Hartford-Metro to near 90.

Saturday night...

Approaching low to mid level warm frontal boundary parent with
the surface low over the S Great Lakes region. Continued moistening
of the low to mid levels per isentropic upslope over-running flow
out ahead of the system. Leaning that high pressure and drier air
lingers long enough to buffer the onset of wet weather into the
east-half of New England much as the 29.09z sref would suggest. There
is as well continued mid to upper level height rises.

So will go with chance pops for the W, lesser to the east. Overnight
lows slightly more mild with anticipated cloud cover and winds at
the surface slightly more ashore, though beginning to see surface
low pressure take shape short wave of New England towards Sunday morning.

&&

Long term /Sunday through Friday/...
highlights...

* unsetlled Sunday through early Tuesday with scattered showers,
mainly in western sections.
* Mainly dry and seasonable weather Tuesday afternoon through
Friday, with a warming trend.

Overview and model preferences...

Models in reasonably good agreement through the period. An upper
level trough moves from the eastern Great Lakes Sunday across New
England early Tuesday, then out to sea. A ridge of high pressure
builds aloft across the northeast states, cresting over the region
on Friday.

At the surface, a warm front will develop to our south Sunday.
Several waves of weak low pressure are forecast to move along the
front, but remaining to our south. The low finally consolidates
then moves out over Georges Bank by Tuesday. High pressure settles
over New England Tuesday afternoon through Friday. A cold front is
then poised to move through the area next Saturday.

Used a consensus blend of available model and ensemble guidance
for this portion of the forecast.

Details...

Sunday through early Tuesday...

Expect waves of low pressure to move slowly along a stalled front
just south of New England, keeping low and mid level moisture in
place with a light east-southeast flow gradually becoming
northeast.

On Sunday afternoon and evening, models have been consistently
showing instability over the Hudson Valley in southeast New York.
With upslope flow, our best chances of showers will be in the
higher terrain of western Massachusetts and perhaps also in the Worcester
Hills. The European model (ecmwf) is an outlier in showing heavy
convection/thunderstorms moving eastward from the Hudson Valley
into CT and then into southern RI, as it travels along and just
north of the warm front. For now have 50-60 percent probabilities
in western Massachusetts and northwest Hartford County, with lesser chances
as one heads east.

Generally the same reasoning continues Sunday night through early
Tuesday. During this time, low pressure consolidates and moves out
sea, southeast of Cape Cod/islands. There could be scattered
showers at any time, with the best chances in the Western Hills.
But most of the time it will be rain-free.

Temperatures will run slightly below seasonal normals with highs
Sunday in the 70s and mainly 75-80 Monday.

Tuesday afternoon through Friday...

A high amplitude 500 mb ridge moves east from the eastern Great
Lakes and crests over New England on Friday. By Wednesday, our
winds will shift to a southwesterly direction and the gradual
warming trend will begin. Maximum temperatures will rise a few
degrees each day, reaching the mid and upper 80s Thursday and
upper 80s to lower 90s on Friday. No precipitation is forecast,
although we cannot rule out an isolated shower or thunderstorm
in far northwestern sections late Friday afternoon.

A cold front is then expected to move through the area next
Saturday with a chance of showers or thunderstorms, but that's
beyond our current forecast period.

&&

Aviation /02z Saturday through Wednesday/...
forecaster confidence levels.

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

Short term /through Saturday night/...high confidence overall.

Overnight...

Main issue will be areas of MVFR-IFR in developing fog, mainly
across the CT River Valley, as well as interior east CT and southeast Massachusetts.
Pockets of dense fog are possible along the east/southeast coast of Massachusetts but
lesser confidence with respect to formation of any pocket of dense
fog.

Saturday...

Scattered-broken cigs especially towards late in the day. Light winds.
Sea-breezes developing along the shores late morning into
afternoon. Scattered rain showers/thunderstorms and rain possible across short wave New England late but
believe it to be a low risk.

Saturday night...

Broken-overcast cigs with MVFR-IFR developing along the S-coast of New
England towards Sunday morning. Increasing chance of rain from the
short wave along with visibility restrictions.

Kbos taf...high confidence. Conditions remain VFR into this
evening. Though watching closely into this evening for tempo MVFR
with NE onshore winds. Maybe even a rain showers. Believe it to be a low
risk.

Kbdl taf...high confidence. Low risk +shra towards the late
afternoon period with tempo MVFR-IFR impacts. A moderate risk.

Outlook /Sunday through Wednesday/...

Sunday through early Tuesday...moderate confidence.

Mainly VFR conditions. However, there will be scattered showers at
any time. Cannot rule out a heavier shower or thunderstorm,
especially in the slopes of the Berkshires and in northern CT on
Sunday. Brief MVFR/IFR conditions are possible in the heavier
showers. Patchy late night/early morning fog is possible,
especially along the South Coast, closer to the warm front.
IFR conditions are likely in any areas of fog.

Tuesday afternoon through Wednesday...high confidence.

VFR. Just a few areas of MVFR possible in patchy late night/early
morning valley fog and in the usual fog-prone places.

&&

Marine...
forecaster confidence levels.

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

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

715 PM update...

There is the possibility of visibility restrictions with fog
during the overnight into early morning hours. Otherwise the
majority of the forecast is comprised of winds below 25 knots and
seas below 5 feet, with increasing chances of showers mainly
Saturday night into Sunday morning.

Outlook /Sunday through Wednesday/...high confidence.

Expect easterly winds (southeast through northeast) and seas
below small craft criteria through the period. Seas may build to
4 ft Monday into Tuesday as low pressure passes through the
region and out to sea around Georges Bank. Northeast winds may
gust up to 20 kt mainly over the eastern outer waters Monday night
and Tuesday. Locally reduced visibilities in scattered showers or
an isolated thunderstorm through early Tuesday morning. Patchy
late night/early morning fog through the period.

&&

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

&&

$$
Synopsis...sipprell/gaf
near term...sipprell/gaf/Thompson
short term...sipprell
long term...gaf
aviation...sipprell/gaf/Thompson
marine...sipprell/gaf

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