Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 231918

Area Forecast Discussion
National Weather Service Taunton MA
318 PM EDT Sun Jul 23 2017

Cooler, damp conditions are forecast for Monday and Tuesday.
High pressure Wednesday will bring dry and pleasant weather,
probably through much of Thursday, too. Another low pressure
will likely bring showers/isolated thunderstorms to the region
Thursday night and/or Friday, perhaps lingering into Saturday.
Temperatures will be below normal for most, if not all, of the
coming week.


Rather tranquil weather continues into the early evening. Band
of low clouds from this morning continued to slowly dissipate
this afternoon. Elsewhere, mid and high level clouds associated
with our next weather-maker had already started to move in from
the west. Minor tweaks to bring the afternoon forecast back in
line with observed trends.

Increasing clouds tonight, with rain arriving from west to east,
most likely after midnight and especially toward daybreak
Monday. 23/12z guidance has rather good agreement on the track
and timing of a low pressure passing by to our south, so have
high confidence in this timing.

Continuing onshore flow and increasing clouds should prevent
temperatures from lowering too far below normal.


Impressive 5 to 6 standard deviation easterly flow at 925 mb
Monday. Very rare event for late July. Precipitable water values
also about 2 standard deviations above normal. Thinking a
widespread rain will result, despite the strongest lift staying
over the south coast of New England during the morning. Locally
heavy rain will be possible at times, especially toward the
south coast of New England. Generally thinking one half to one
inch of rainfall, with locally higher amounts.

The steadier rain should taper off to showers Monday afternoon
into Monday night. This should be forced mainly by a cold pool
aloft and a trailing mid level shortwave. Rainfall amounts
expected to be quite a bit less that what happens Monday morning
and early afternoon.

With our region remaining on the north side of this low
pressure, expecting temperatures to remain generally below



* Dry and pleasant Wed and probably into much of Thu afternoon
* Unsettled/wet weather likely returns by Thu night and/or Fri
* Temps will remain below normal through the end of the week


Tuesday through Tuesday Night...

Cool and damp Tuesday as the mid-level dynamics sweep the
region with stronger mid-level forcing acting upon remnant,
available moisture, though more continental rather than sub-
tropical. Light showery weather is to be expected along with an
abundance of low clouds, perhaps some patchy fog.

Clearing out Tuesday night in wake of the H5 trough. Subsidence
prevailing as cooler, drier air settles S brought in by N flow
becoming light with increasing high pressure up to around 1025.

As model solutions vary, especially with respect to the magnitude
of low level convergent forcing along the frontal profile from the
NE with the GEFS suggesting +3-4 standard deviation above normal
and both the EC/NAM hinting at least a 30 mph inflow, will keep it
conservative and keep close to the latest SREF output. Upstream
convective elements transitioning along the quasi-stationary boundary
S at the start of the forecast period late Sunday into Sunday night,
indications of mesoscale convective systems across PA and NY, but
then it would appear the pattern across the NE CONUS becomes more
synoptic with energy pinwheeling.

Chance to likely PoPs, highest Monday. Will hint at the chance of
thunder towards SW CT Monday. No special wording just yet on heavy
rain given the uncertainty and low confidence spatially as to where
heavy rain will occur.

Wednesday into Thursday afternoon...

High pressure will build across the region Wed and slide east of our
area by Thu. The result will be dry weather Wed and probably into
most of Thu afternoon. Temperatures should rebound from early in
the week, but still average a bit below normal for late July. Highs
should mainly be in the middle 70s to lower 80s Wed and Thu afternoons
with comfortable humidity.

Thursday night through Saturday...

A rather impressive shortwave for late July will dive southeastward
from the Great Lakes and carve out another Northeast trough. The
approaching shortwave will likely bring a period of showers and
perhaps isolated thunderstorms to the region. Specific timing is
uncertain with most guidance currently focused on Thu night/Fri,
but it is possible some activity lingers into Sat. Temps should
remain below normal with highs mainly in the 70s to the lower 80s.


Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Through 00Z...VFR. east to northeast winds continue.

Tonight...High confidence. CIGs lowering SW to NE towards MVFR-
IFR as -RA begins to spread across the region. Continued E flow
with gusts up to 25 kts towards the south coast.

Monday...Moderate confidence. MVFR-IFR CIGs. Impacts to the AM
push possible with RA/+RA. VSBY restrictions expected.
Continued breezy NE flow with gusts up to 25 kts.

Monday Night...Moderate confidence. MVFR-IFR CIGs linger with
-SHRA/DZ. LIFR conditions possible towards the Cape and islands.
 NE winds continue with gusts up to 25 kts possible during the
 evening, especially across E MA.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Thursday/...

Tuesday...Moderate confidence.

MVFR-IFR CIGs linger with -SHRA/DZ.

Tuesday Night...Moderate confidence.

Improving towards VFR. Winds backing N remaining breezy.

KBOS Terminal...VFR. NE wind gusts of 20 to 30 knots diminish
this morning, but gusts to between 15 and 20 knots will be
possible into early afternoon.

Wednesday and Thursday...Moderate confidence.

Mainly VFR conditions into Thursday afternoon. Potential for
deteriorating cigs/vsbys Thursday night but timing of showers,
low clouds, and fog patches are uncertain at this time.



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

Short Term /through Monday Night/...

A more winter-like low pressure is expected to travel south of
New England Monday morning. This will result in an increasing
easterly flow with gusts up to 30 kt at times. Its possible for
a brief period of gale force gusts around the Cape and islands
Monday morning, but have low confidence it will persist long
enough to warrant a Gale Watch or Warning at this time. Will be
issuing a Small Craft Advisory for some of the waters, soon.

Outlook /Tuesday through Thursday/...

Tuesday and Tuesday Night...

Winds diminish some, but rough seas continue across the outer
coastal waters.




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