Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 270147 
afdbox

Area forecast discussion
National Weather Service Taunton Massachusetts
947 PM EDT Mon Jun 26 2017

Synopsis...
an active/strong jet stream will move across New England
tonight and Tuesday, bringing a few showers and isolated
thunderstorms. The greater threat will be on Tuesday. A warming
trend begins for the latter half of the week with a return to
Summer heat and humidity Friday and Saturday. A warm front may
bring some showers and some thunderstorms Thursday night, with
more showers and thunderstorms possible Friday through the
weekend.

&&

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

945 PM update...

Scattered showers with isolated thunder across northern Massachusetts into
New York state continue to show a weakening trend given the loss of
daytime heating. However modest mid level lapse rates of 6-6.5
c/km combined with 40-50 kt 0-6km deep layer shear will maintain
showers and T-storms over New York and likely clip northwest Massachusetts later
this evening and early overnight hours. Farther to the southeast
into CT/Rhode Island and southeast Massachusetts weaker lapse rates and less jet
support precluding shower/T-storm development. Thus dry weather
prevails. Previous forecast capturing these trends nicely so no
major changes with this forecast update.



&&

Short term /6 am Tuesday morning through Tuesday night/...
sharp shortwave over the Great Lakes today moves through the
cyclonic flow. One part ejects across New York and northern New
England Tuesday afternoon/evening, while the main portion
crosses our area late Tuesday night or Wednesday morning.

We remain on the edge of the cold pool Tuesday, but close enough
to expect mid level lapse rates of 6.5 to 7c/km during the
afternoon and early night. Going along with this will be totals
in the lower 50s and Li values below zero, as well as SBCAPE
values of 500-1000 j/kg. Theta-east values show a ridge over CT
during the afternoon/evening. Expect scattered showers/tstms
during the afternoon and early night.

Winds aloft show some support for a few strong or damaging
storms. Winds at 850 mb will be 20-30 knots during Tuesday
afternoon, although this is forecast to move offshore by
evening. Winds at 500 mb are forecast at 50-60 knots during
Tuesday afternoon, but also move offshore by evening. Timing of
this wind and of the shower/tstm development may be the
determining factor in how strong these storms may get. The mixed
layer is expected to reach near 850 mb, where winds as noted
above will be 20 to 30 knots. Our forecast includes gusts on the
lower half of that range, but slightly higher values are
possible.

With the main shortwave moving through during Tuesday night, and
with the upper cold pool moving overhead, expect a continued
chance of showers/storms Tuesday night.

If mixing reaches 850 mb it will work on temps of 8-10c, which
suggests Max sfc temps of 75 to 80. If mixing GOES a little
higher, such as to 800 mb, then Max sfc temps would be more
centered around 80. No change in the airmass Tuesday night
compared with tonight, so expect similar min temps.

&&

Long term /Wednesday through Monday/...

Highlights...

* pleasant Wednesday with low risk of a shower
* heat and humidity return Friday thru Sunday
* thunderstorm chances increase Thursday night through Sunday

Details...

Wednesday...

An area of high pressure passes to our south, and model soundings
show quite dry airmass in place with precipitable water around 0.75
inch. Models show a short wave moving thru the area, then modest mid
level ridging develops later in the day. Anticipating development of
diurnal cumulus clouds, overall partly to mostly sunny skies.
Guidance continues to show very little quantitative precipitation forecast on Wednesday. Can't rule
out a few pop-up showers during the afternoon since low level lapse
rates are steep, however for much of the area, the day should stay
dry. Highs mainly in the 70s with dew points dropping to 45-50 in
the afternoon.

Dry conditions expected Wednesday night with any isolated diurnal
showers coming to an end early. Winds aloft will begin to turn more
to the southwest by Wednesday night with warm air advection, which
should bring some increase in clouds. Overnight lows mainly upper
50s to low 60s.

Thursday...

Surface high pressure slides offshore, meanwhile low pressure
tracking east thru the Great Lakes region pushes a warm front
northeastward across southern New England. As we end up in the warm
sector, increasing heat and humidity will occur. Increasing moisture
will result in more clouds, and the potential for showers and
thunderstorms. Highest probability for precipitation would be across
the northern half of our area, continuing with likely pops there.
Chance pops further to the south. Could see gusty winds with any
thunderstorms and/or if sun breaks out for awhile and allows good
mixing, potential gusts 25 to 30 mph or so.

With zonal flow and both 850mb isotherms and winds becoming
parallel, appears that any convection that generates across upstate
New York could track eastward into southern New England. Will continue the
chance for showers/thunderstorms into Thursday night. More abundant
cloud cover coupled with high surface dew points will keep lows in
the 60s.

Friday thru Sunday...

Continue to anticipate an unsettled weather pattern for this
timeframe, influenced by broad upper trough to near zonal flow, with
periodic short waves passing thru our area, and areas of surface low
pressure moving thru the flow and to our north. Southern New England
remains in the warm sector until later Sunday, with heat and
humidity. Models continue to indicate during Fri night/Saturday that
a back door cold front should remain to our north. Thus the
potential for 90 degree high temps returns for both Friday and
Saturday. Chance for showers and thunderstorms each day. Difficult
to place the exact timing and location of any strong storms during
Friday and Saturday.

During Sunday models indicate a cold front pushing thru the area,
which would be a trigger additional showers and thunderstorms.

The potential for strong thunderstorms appears possible each day
during this period. One caveat to watch is the subtropical ridge. If
this ridge moves closer, it may keep portions of the area dry.

Monday...

With cold front possibly to the east, drier airmass should build
into the area. Some uncertainty here whether the day is dry or
whether a short wave can bring some diurnal showers to the area.
Will have slight chance to low chance pops.

&&

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

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

945 am update...

Showers and isolated thunderstorms will continue to weaken late
this evening across northern Massachusetts into New York state. Previous
discussion below.

=============================================================

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

Tonight...

VFR. Scattered to broken cumulus with bases 6000-7000 feet this
evening, then diminishing cloud cover. Scattered showers and
isold T-storms in the interior, mainly along/north of the Mass
Pike. Showers and tstms should diminish during this evening, but
can't rule out isolated showers past 04z.

Tuesday...

VFR. Scattered to broken cumulus with bases 5000-6000 feet.
Scattered showers and thunderstorms expected from midday through
the first part of Tuesday night. Showers and storms may bring
briefly lower conditions, mainly vsbys 3-5 miles in heavier
showers. Southwest winds will gust to at least 20 knots and
possibly as high as 30 knots.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Wednesday through Saturday/...

Thursday...moderate confidence. Mainly VFR. Afternoon showers
possible in the interior with showers/T-storms possible all southern New England Thu
night. Gusty SW winds to 25-30 kt developing.

Friday...moderate confidence. Patchy early morning stratus and fog,
especially south coastal Massachusetts/RI, with local MVFR. Then VFR, except
local IFR in possible thunderstorms, mainly during the afternoon and
evening hours.

Saturday...moderate confidence. VFR, except local IFR in possible
thunderstorms, mainly during the afternoon and evening hours. Also
IFR ceilings/fog possible south coastal MA/RI.

&&

Marine...
forecaster confidence levels...

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

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

Winds and seas mostly below Small Craft Advisory thresholds
through the period with SW flow. A few gusts to 20 knots
expected with potential for a few gusts to 25 knots especially
nearshore.

Outlook /Wednesday through Saturday/...

Wednesday...high confidence. Winds and seas below Small Craft Advisory. Gusts to 20
kt possible nearshore waters and along southern outer coastal
waters.

Thursday...moderate confidence. Small craft advisories will likely
be needed. Increasing and persistent SW winds with gusts around 25
kt probable, and gusts 30 kt possible, especially over nearshore
waters. Building seas may reach 5 to 7 ft over southern outer
coastal waters Thu night.

Friday...moderate confidence. Persistent SW winds continue, with
potential gusts 25-30 kt. Seas of 5 to 7 feet may linger on the
southern outer coastal waters. Scattered thunderstorms, some with
reduced visibilities and strong gusty winds.

Saturday...moderate confidence. SW/S winds continue, with gusts 20-
25 kts. Seas 4-6 feet may linger on outer coastal waters.

&&

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

&&

$$
Synopsis...wtb/nmb
near term...wtb/nocera/nmb

National Weather Service Glossary of Abbreviations