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Area forecast discussion
National Weather Service Taunton Massachusetts
950 am EDT Sat may 27 2017

weak high pressure building across the region pushing east round which
onshore flow will usher slightly cooler air and an abundance of
clouds along with the possibility of drizzle. Into next week, low
pressure in the Great Lakes generates a coastal low late Monday
that passes off Nantucket on Tuesday. This will bring wet weather
on Memorial Day. Daytime clouds and scattered showers will pop
up each day Tuesday through Friday keeping seasonable temperatures.


Near term /until 6 PM this evening/...

950 am update...

A scattered to mainly broken deck of clouds covered most of the
region at mid to late morning. The exception was portions of
northeast Massachusetts where partly to mostly sunny skies have developed,
but clouds will likely fill back in this afternoon. Despite a
weak ridge of high pressure overhead, model soundings continue
to show an area of trapped low level moisture in the 2 to 5
thousand foot range. So while some peeks of sunshine will occur
at times today, expect to see clouds dominate through the
afternoon. Generally dry weather is anticipated, although the
low risk of a spot sprinkle or two can not be ruled out.

High temps are tricky this afternoon because just an hour or
two of late may sunshine can result in temps jumping quickly.
Overall though given lots of clouds, expect high temps to top
out in the 60s to lower 70s. Weak gradient will allow for
afternoon sea breezes on the immediate coast with temps in the
upper 50s to the lower 60s in those locations.


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

Turning cloudy with the possibility of drizzle. With high pressure
shifting E, will see return S onshore flow. This beneath a building
mid to upper level ridge, moisture pools beneath the dry inversion.
A weak upslope component, at minimum would expect marine stratus to
expand, but also given a sweeping weak mid-level trough and impulse
energy, can not rule out the possibility of drizzle. All aside, it
would appear to be a cool and damp night. Lows around the upper 40s.


So then the question becomes as to whether overnight marine stratus
lifts and/or breaks up or rather holds out and remains low across
the region. Subsequent temperature implications. The mid to upper
level ridge in place as high pressure remains offshore. The onshore
flow continues beneath the dry inversion. Clouds and cool conditions
not out of the question, but the magnitude even WRF-model solutions
can't agree upon. A consensus blend given the uncertainty yields
broken to overcast cloud decks that lift through the day. Would see
temperatures warm to seasonable levels, upper 60s to low 70s, the
coolest of conditions along the shores in the low to mid 60s.


Long term /Sunday night through Friday/...

* risk of rain returns Sun night into Memorial Day
* at or below normal temperatures will occur this upcoming week
* unsettled weather pattern continues with hit or miss showers
through the period

Pattern overview...

00z guidance continues to be in agreement for the extended forecast.
However there are some difference in timing and strength of each
system. Mid to upper level ridge across the region on Sunday will
begin to give way approaching trough over the Great Lakes. Potent
shortwave rounding the trough will develop a surface low over the
mid-Atlantic on Monday and track near southern New England Monday
night/Tuesday. Beyond that, broad upper level trough will take hold
over the Great Lakes and northeast through the remainder of the work
week as strong ridge builds over The Rockies. Bermuda high pressure
will keep the region in a moist southwest flow aloft resulting in a
chance of precip with each passing shortwave.


Broad upper level trough over the region will keep any Summer-like
heat at Bay through the period. Monday will be the coolest as low
pressure moves through. Otherwise anticipate generally seasonable
conditions on Tuesday and Wednesday thanks to southwest flow aloft
and thermal ridge. Resulting in high temps in the upper 60s to mid
70s. Mid-level wave and associated front on Thursday drop temps
aloft to well below average for late may. This will keep temps to
below climo with highs in the upper 60s to low 70s into Friday.
There is the potential that next Saturday may trend a bit warmer as
upper level trough begins to exit the region. However, the low could
linger a bit longer into next weekend. Overnight lows will linger in
the 50s through the period.


A spot shower and/or drizzle is possible on Sunday night despite
upper level ridge aloft. Moist east flow from passing surface high
will be trapped under an inversion as noticed in model soundings.
The Berks and Worcester Hills have the best shot for precip from
upslope flow, this is still a low risk.

The first chance for widespread rainfall will come on Memorial Day
as low pressure system tracks over the Great Lakes and towards the
northeast. A secondary low looks to develop over the mid-Atlantic
and with an increasing low level jet combined with precipitable waters near an inch,
anticipate the risk for showery weather. Timing can still change,
but appears that the later half/evening on Monday may dry out from
west to east as bulk of the precip moves in morning into early
afternoon. There continues to be a chance for some thunderstorms on
Monday as Li are below 0 and tt above 50. Why the risk is more
elevated gefs members are indicating some surface cape which could
be enough for a few thunderstorms when the bulk of the precip moves

Beyond Monday, there is a hit or miss chance for showers through
much of the period as upper level disturbance rotates through the
flow. Certainly not a washout by any means but believe that Tuesday
and Wednesday have the better shot for showers with Thursday
trending a bit drier thanks to northwest flow aloft.


Aviation /14z Saturday through Wednesday/...
forecaster confidence levels...

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

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

950 am update...


Scattered-broken ceilings should persist into the afternoon. MVFR ceilings though
should give way to mainly VFR by mid afternoon as boundary
layer warms. Sea- breezes developing around 15-16z.


Cigs becoming broken-ovc, lowering to IFR, possible LIFR, especially
across the interior. Collocated threat of -dz into the early morning
hours which may lead to visibility restrictions. Light onshore flow out of
the S/E.


Broken-overcast cigs slowly rising IFR towards MVFR / low-end VFR mix.
Continued light onshore S flow.

Kbos taf...MVFR to low-end VFR stratus will be a nuisance a
majority of the forecast timeframe. Expect a sea-breeze around
15-16z today with sustained onshore flow up around 10 kts.

Kbdl taf...IFR-LIFR mix with -dz possible overnight towards the
early morning hours Sunday.

Outlook /Sunday night through Wednesday/...moderate confidence.

Monday...deteriorating conditions to MVFR/IFR in showers and
possibly a thunderstorm. Southeast winds less than 20 kts.

Tuesday into Wednesday...

Lingering IFR/MVFR will improve to VFR for most locations. Areas of
MVFR in passing showers are still possible for Tuesday and again
Wednesday. Light east wind Tuesday becoming S in the afternoon, then
west/SW Wednesday. Speeds less than 15 kts.


forecaster confidence levels...

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

Short term /through Sunday/...high confidence.

Beneath high pressure, winds will remain light while mainly onshore
southerly throughout the forecast period. Seas subsiding, good
boating weather though cool given expected broken to overcast marine
stratus at times, along with the threat of drizzle overnight into
the early morning hours Sunday.

Outlook /Sunday night through Wednesday/...moderate confidence.

Winds less than 20 knots and seas less than 5 feet through the
period. Showers and isolated tstms possible on Monday. Drying trend
into the work week.


Tides/coastal flooding...
though astronomical tides will be high for another night in a row,
winds as well as swell and wave action will be light. Given such
conditions, do not expect there to be much in the way of impacts
along the coast in regards to vulnerable shoreline roads becoming
inundated. Thus no coastal flood statement issued with this forecast


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas until 2 PM EDT this
afternoon for anz254>256.
Small Craft Advisory for hazardous seas until 11 am EDT this
morning for anz235-237.


near term...Frank

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