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Area forecast discussion 
National Weather Service Taunton Massachusetts
102 PM EDT Sat Aug 1 2015

Synopsis...
seasonably warm this weekend with a risk of scattered showers and
thunderstorms middle to late this afternoon. Warm conditions will
continue into early next week. There will be the threat of showers
and thunderstorms Monday into Tuesday. Pattern change by middle-week will
keep temperatures below average into the weekend.

&&

Near term /until 6 PM this evening/...
1 PM update...scattered showers with some embedded thunder are
already starting to develop across parts of southern New England
and eastern New York state. There is a decent amount of
instability...500-1000 j/kg of cape per Storm Prediction Center/S mesoanalysis Page.
However...lapse rates are still very marginal. Given that...expect
these to remain showers for the most part. Brief heavy rain and
perhaps some small hail are the greatest threats from these
showers.

This afternoon...

Trailing short wave energy currently moving across the Great Lakes
advects through New England later today. This results in cooling temperatures
aloft with 500 mb temperatures going from -9c this morning to about -12c by
days end. This will result in steepening lapse rates. Modest forcing
for ascent associated with this short wave trough as it crosses the
region. Limiting factor for convection with this feature is column
is fairly dry along with surface dew points in the 50s. This will
likely limit areal coverage to isolated or widely scattered.

Convection may be more numerous with stronger updrafts along the
South Coast as dew points here will be higher...in the 60s due to SW
wind. This greater instability will provide a low risk of one or two
stronger T-storms in this area. The combination of deep layer shear
of 30-40 knots and inverted /\ sounding signature suggest one or two
stronger storms may yield gusty winds and possibly small hail.
Overall most if not all storms will be sub-severe and should be
short in duration.

Otherwise a fairly typical Summer day with temperatures climbing into the
80s along with a few showers/T-storms.

Beach forecast...

Increasing south-southwest winds this afternoon may be sufficient to
kick up the surf to 3 to 4 feet on south facing ocean beaches. This
may support moderate rips.

&&

Short term /6 PM this evening through 6 PM Sunday/...
tonight...

Any lingering convection early this evening should be confined to
the South Coast and will dissipate shortly after sunset given
cooling blyr. Thereafter subsidence behind departing short wave
overspreads the region. This will support dry weather 2nd half of
the night. Seasonably cool with mins in the 60s /u50s northwest Massachusetts/
and comfortable humidity with dew points in the 50s.

Sunday...

Nice day with short wave ridging and associated subsidence providing
dry weather and abundant sunshine. Highs in the 80s but tolerable
humidity with dew points in the 50s.

&&

Long term /Sunday night through Saturday/...
highlights...

* showers and thunderstorms Monday into Tuesday
* pattern change by middle week bringing below average temperatures

Overview...

00z guidance is in decent agreement until middle-week when models
diverge. Appears guidance is having an issue handling the upper
level low over the Hudson Bay as well as the potent northwest low
and how it will respond downstream. The GFS is the most
progressive while the ec is more amplified in the extended. Latest
gefs appear to side towards the ec as well as the eps. Because of
the discrepancies trended the forecast closer to the ensembles.
Overall upper level low over Hudson Bay will keep the region in
southwesterly flow. Several waves through the flow will kick off
showers and thunderstorms Monday into Tuesday. Pattern change by
middle-week as low moves eastward dropping temperatures and heights for New
England. Several fronts will keep reinforcing the cooler airmass
for southern New England through the remainder of the period.

Dailies...

Monday into Tuesday...moderate confidence.

Upper level low over Hudson Bay will begin its eastward trajectory.
Shortwave will round the low pushing a cold front across the Great
Lakes and into New England. Significant timing issues with the front
as the GFS is quicker than the NAM/ec. Ec is also less amplified
than the GFS and hardly has any quantitative precipitation forecast over the region on Monday.
Therefore have moderate confidence in this portion of the
forecast until details can be settled...hopefully over the next
model run or two.

As cold front approaches the region late Monday...could see scattered
showers and thunderstorms develop out ahead as Theta-E values
increase as well as instability. Dewpoints will also be increasing
as southerly low level jet strengthens. Decent instability values amongst
guidance...with 1000-2000 j/kg and steepening middle-level lapse
rates. A dual jet appears to be in place putting the region in
favorable lift. So with all of the above believe that
thunderstorms will develop with some being strong late Monday.
Best region looks to be across western mass and CT as shear values
are strongest in that region...30-40 kts. However most of the
region has the potential for thunderstorms. Although this is 3
days out...if everything lines up could be a severe storm or
two...but low confidence at the moment.

Front will slowly slide through the region overnight. Appears that
there is still enough instability...high Theta-E and k values over
32c...to keep the thunderstorm potential going into the night.

Tuesday will still have cyclonic flow over the region and depending
on where the front is set-up could still see some showers over the
region. Because of the cyclonic flow...temperatures on Tuesday will be
cooler than Monday as there will be more clouds around. It wont be
until late Tuesday into early Wednesday when cooler temperatures and lower
humidity takes hold over the region.

Wednesday and beyond...moderate confidence.

Closed low aloft will move eastward as ridge builds over the
central Continental U.S.. potent shortwave will move through the flow
dropping temperatures and heights over the region. The lowering heights
overhead will keep temperatures below average and it will be somewhat
less humid as well. Temperatures will mainly be in the 70s into the 80s
for Wednesday through Saturday. No 90s in the near future.
Overnight lows will mainly be in the upper 50s to 60s.

Additionally...potent shortwave from the upper low appears to
develop a southern stream surface low. The lows placement has a
large spread amongst guidance with the GFS over the middle-Atlantic
and the ec over the Carolinas. Because of the spread and looking
at the ensembles kept slight chance of precipitation with higher confidence
across the South Coast thurs-Fri. But this can change as it is 6
to 7 days out.

&&

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

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

This afternoon...high confidence. VFR but isolated to widely
scattered showers and T-storms likely this afternoon and early
evening. One or two storms may contain small hail and gusty
winds...however most if not all of the activity will be sub-
severe.

Tonight...high confidence. VFR with any lingering evening
T-storms rapidly diminishing with sunset.

Sunday and Sunday night...high confidence. VFR/dry weather and
good visibility.

Kbos terminal...high confidence in taf. Widely scattered thunderstorms
should develop across Logan/S airspace this afternoon and early
evening but not enough confidence to reflect in taf at this time.

Kbdl terminal...high confidence in taf. Isolated to widely
scattered thunderstorms possible this afternoon and early evening.

Outlook /Monday through Wednesday/...

Monday into Tuesday...moderate confidence. VFR much of the time with
a low risk for scattered showers and thunderstorms through the
period.

Wednesday...moderate confidence. VFR.

&&

Marine...
forecaster confidence levels...

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

Short-term /through Sunday/...moderate confidence.

Today...south-southwest wind increase to 15-20 knots this afternoon. This long
fetch will likely increase seas to 3 to 6 feet across the south
coastal waters. Thus Small Craft Advisory remains in effect and also included Rhode Island
Sound. Scattered showers and T-storms likely this afternoon.

Tonight...south-southwest winds 15 to 20 knots ease and become west late. Thus seas
will subside. Any early evening showers and T-storms will dissipate
with sunset.

Sunday...light west winds in the morning becomes SW in the
afternoon. Dry and tranquil boating weather Sunday.

Outlook /Monday through Wednesday/...moderate confidence.

Monday into Tuesday...approaching cold front will increase showers
and thunderstorms for the waters. SW winds will increase ahead of
the front building seas up to 5-6 feet. Winds could be gusty
requiring Small Craft Advisory.

Wednesday...seas will slowly relax however westerly winds will still
be gusty. Could still need Small Craft Advisory for the waters.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas until 2 am EDT Sunday
for anz235-255-256.

&&

$$
Synopsis...nocera/dunten
near term...nocera/rlg
short term...nocera
long term...dunten
aviation...dunten/rlg
marine...nocera/dunten

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