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Area forecast discussion 
National Weather Service Taunton Massachusetts
220 PM EDT Sat Jul 4 2015

Synopsis...
low pressure races south of New England this afternoon and evening
bringing scattered pockets of light rain. High pressure returns
Sunday and lingers through Monday. A transition period is likely
middle next week...with a chance for showers and thunderstorms.

&&

Near term /through tonight/...

Through 8 PM...main area of concern is over western
mass/Connecticut. Radar shows patchy yellows and oranges while
observations show visibilities around 10 miles...except 4-5 miles in the
Berkshires. With cloud bases 9-10 thousand feet...expect much of
the rain on radar is evaporating on the way down. We will continue
with light showers through the afternoon in our western and
central areas...scattered sprinkles in the east.

Early afternoon observed temperatures show a range of 65 to 75.
Upper 60s and 70s should cover the afternoon maximum temperatures.

Tonight...
coastal low pressure moves out to sea. Upper shortwave swings over
New England. Right entrance region of the supporting upper jet
will be right over US at 00z/8 PM creating upper venting. If
sufficient moisture lingers then we may continue to see widely
scattered light showers/sprinkles for a couple of hours. But the
amount of evaporation in progress suggests a factor counteracting
any lingering showers.

We will make our final call on evening probability of precipitation based on the radar
display between 3 and 4 PM. But the trend on the forecast is for
diminishing chance of showers. The uncertainty is whether it will
be starting at 70 percent or 20 percent or 5 percent.

The upper shortwave axis sweeps east of our area by morning...so
expect a trend to clearing skies after midnight. Dew points
upstream are in the 50s...this should allow min surface temperatures in the
50s and lower 60s.

&&

Short term /Sunday through Sunday night/...

High pressure from the plains builds east over New England Sunday.
Cross sections of relative humidity show dry air above 800 mb...and a moist layer
at 800-850 mb. Mixing should reach above 850 mb. This suggests
some diurnal cumulus developing Sunday and dissipating Sunday
evening. Tempertures at the top of the mixed layer would support
maximum surface temperatures of 80-85.

Fair skies Sunday night with light winds and radiational cooling.
Dew points rise a little to around 60. Expect min surface temperatures in
the upper 50s and lower 60s. This may support patches of fog
developing late at night...especially in western mass.

&&

Long term /Monday through Saturday/...
highlights...

* high pressure and warming conditions into early next week.
* Unsettled conditions return middle-late next week.

Overview and model preferences...with 04.00z model guidance
coming in...there is better agreement with the middle and long term
than previous runs...although typical uncertainty remains in the
long term. Strong ridging early in the week will give way to
mainly zonal flow on the SW quadrant of a strong northern stream vortex
developing across north central Canada. The flattening wave will
arrive middle week...with high precipitable waters and instability in Tow which may
need to be watched. There are timing issues...especially regarding
the influence of the ridge of high pressure for Tuesday...but with better
agreement in this round of guidance a blend of operational models
will work well as a baseline.

Details...

Monday into Monday night...warm ridging builds across southern New England
with high pressure at the surface. Mainly dry weather prevails with moderating
highs/lows as 850 mb temperatures increase to between +12c and +14c by late
Monday. This suggests highs mainly in 80s across the region.

Tuesday...upper level wave will be approaching from the west. Models
indicate increasing moisture as precipitable waters approach 2 Standard deviations
above normal with k-values over 30. A warm front will be the
initial surface reflection of this wave. However...soundings support
the possibility of high pressure remaining in control through much of
Tuesday. Therefore...chance for afternoon rain showers/T-storm with the warm
frontal approach may be quite low to near zero the further east one
GOES. In fact...the best axis of surface cape/Theta-E ridge is mainly
west of the Massachusetts/New York border. Therefore...chance probability of precipitation west will be lowered
to slight chance to none probability of precipitation further east. Will include thunder with
this forecast given the favorable parameters.

Wednesday...as previous forecaster noted...this is where the model
solution divergence begins to show more significantly. Mainly with
the timing of a cold frontal passage. GFS remains progressive
while European model (ecmwf)/CMC continues to linger as the front begins to
parallel the zonal flow developing aloft. Will continue with the
chance and slight chance probability of precipitation from the the previous forecast since
the convergent boundary remains in place. Soundings do support
some surface based cape exceeding 1000j/kg and high k-values...so will
continue to include ts...but given the lacking shear...remain
somewhat dubious of severe chances at this time.

Thursday...the uncertainty remains as the cold front continues to push
further southeast...albeit slowly. Will gradually reduce probability of precipitation from
north-S during the day...but will have to wait before we can nail down
timing for the late week.

Friday and Sat...uncertainty remains but with zonal flow...a series
of ridge/trough Couplets is likely to yield periods of
dry/potentially wet periods are likely. Interestingly...with southern
New England on the ridge periphery may need to monitor for mesoscale convective system
steering flow as well. Still way too many variables to nail
anything down...but seasonable temperatures and low to none probability of precipitation should
cover the spread.

&&

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

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

Short-term /through Friday night/...

Through 8 PM...moderate to high confidence. Large area of rain on
radar but only light amounts reaching the ground. Expect
conditions to remain VFR through evening. There is some potential
for MVFR ceilings/visibilities but mainly in northwest Massachusetts where
1000-1500 foot ceilings and 4-5 mile visibilities are possible in any heavier
showers.

Tonight...high confidence. Any lingering rain tapers off early in
the night. Patches of MVFR ceilings/visibilities are possible...but we think
dry air below 5000 feet will overcome most of the potential for
MVFR. Drier air moving in after midnight will bring clearing skies
by morning. Light winds trend to west/northwest toward morning.

Sunday...high confidence. VFR

Sunday night...high confidence. VFR. Patches of IFR in late night
fog possible in the CT valley of Massachusetts.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Monday through Wednesday/...

Monday...high confidence. VFR with high pressure. Sea breezes likely.

Tuesday and Wednesday...moderate confidence. First a warm front Tuesday...then a
cold front Wednesday may provide a focus for occasional showers and
thunderstorms each day with periodic MVFR or lower conditions.
Otherwise VFR. Some fog possible during the overnights.

&&

Marine...
forecaster confidence levels...

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

Tonight...high confidence. Low pressure passes south of the
waters and moves off south of Nova Scotia tonight. Winds shift
from east to north after the passage of the low...but will remain
below 25 knots. Expect seas to build a little with heights around
5 feet on the southern outer waters. Timing on the advisory has
been adjusted to a later start time but otherwise the headline
remains the same.

Sunday and Sunday night...high confidence. High pressure builds
over the waters with light wind and diminishing swell. The Small
Craft Advisory will end around midday.

Outlook /Monday through Wednesday/...

Monday...high confidence. Any lingering swell recedes below 5 feet Sun
night. High pressure then brings quiet boating weather to the waters
through Monday.

Tuesday and Wednesday...moderate confidence. A warm front on Tuesday...then a cold
front on Wednesday will be approaching from the west. While winds should
generally remain out of the S-se...wind speeds should remain below
Small Craft Advisory thresholds. Seas is also likely to remain
below small craft thresholds. Some showers/thunderstorms and/or
fog are possible over the waters.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas from 2 am to 4 PM
EDT Sunday for anz255-256.

&&

$$
Synopsis...wtb/doody
near term...wtb/doody
short term...wtb
long term...doody
aviation...wtb/doody
marine...wtb/doody

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