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Area forecast discussion 
National Weather Service Taunton Massachusetts
938 am EDT Mon Oct 24 2016

a wave of low pressure tracking along the coast will move offshore
this morning with rain quickly exiting the region. Otherwise,
winds become blustery out of the west/northwest beneath a cool, dry airmass
which continues through midweek. A period of rain is likely
Thursday into Friday as low pressure crosses the region.
Seasonable temperatures are expected for next weekend.


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

No major changes to the forecast this morning. Rain has moved well
away from southern New England, already. Will need to keep an eye
out for some stray lake-effect showers spilling east of The Spine
of the Berkshires in the northwest flow. Still expecting mainly
clouds, though.

Tweaked temperatures and sky cover this morning to reflect
observed trends.

Previous discussion...

Rain is quickly moving into southern New England south of the Pike. Hi-res
guidance and NAM/GFS/rgem are in good agreement and are targeting
CT/Rhode Island and southeast Massachusetts for a brief burst of rain through 6-8 am. Open
wave at the surface tracks near the South Coast. However, robust
mid level shortwave with with area of mid level frontogenesis
producing a narrow band of strong mid level Omega which quickly
moves near the South Coast early this morning within an area of
deep moisture. In addition, tt 50+ and swi near zero moves near
and south of the coast so low risk of an isold T-storm. System
is quick moving and rain will exit northern CT around 6 am and
cape/islands 8-9 am.

Excellent mid level drying moves in this morning with clouds
quickly giving way to mosunny skies from west to east through the
morning hours. However, a secondary shortwave moves in later today
with 500 mb temps dropping to near -30c by 00z. The column is dry
but some low level moisture will lead to sct-bkn strato-cu
developing during the afternoon, and cant rule out an isold
sprinkle in the interior.

High temps mid/upper 50s except closer to 50 over higher
elevations. Good cold advection will lead to gusty northwest winds
developing with gusts 25-30 mph.


Short term /6 PM this evening through 6 PM Tuesday/...
tonight into Tuesday...
series of shortwaves rotating through the flow will reinforce the
mid level trof across new eng with cold mid level temps and
cyclonic flow aloft. Generally partly cloudy skies tonight, then
increasing diurnal clouds developing late morning into the
afternoon on Tue. Mainly dry conditions as the column is quite
dry. Below normal temps.

Regarding temps, expect lows tonight in the low/mid 30s across
much of the region, milder Outer Cape/islands. For those areas
where the growing season is still active, temps will remain above
freezing and frost is not a concern given large enough T/TD
spreads with dewpoints falling into the 20s and modest wind. So no
frost/freeze headlines. Chilly day on Tue with 850 mb temps
around -6c and 925 mb temps 0-1c. Highs upper 40s to near 50
coastal plain and lower 40s higher terrain. Gusty northwest winds to
25-30 mph Tue.


Long term /Tuesday night through Sunday/...

* unseasonably chilly but mainly dry Wed other than a few ocean
effect rain showers across Plymouth County/cape/islands

* lows should drop well down into the 20s Wed night/Thu am

* period of rain likely sometime Thu into Fri, low risk for
wintry mix early Thu if several conditions are met

* confidence in weekend forecast low

Overview and model preferences...
Labrador trof will continue to impact the region as ridging
builds from the Great Lakes through early Thu. Clipper system,
which looks to be undergoing an occlusion process as it approaches
S New England then brings more wet/unsettled wx for Fri,
especially as the trof takes on a slight negative tilt. Models are
in good agreement through this point, enough such that a general
blend of deterministic guidance can be used as a baseline.
However, into the weekend there are disagreements at the handling
of a secondary trof which may/may not phase with the hudson's Bay
vortex. GFS appears like the biggest outlier, with a much deeper
trof than both its own ensemble mean, European model (ecmwf) and some of the ecens
members. Now it is too early to tell how this phasing will occur,
but given the fact that the GFS solution seems far different from
many of the others, will lean more heavily on the ecens/gefs and
European model (ecmwf) beyond Fri.


Tue night through Wed night...
the coolest portion of the period. 850 mb temps dive well below 0c
(as low as -7c by Wed morning to be exact) while h92 near -2c.
This, combined with continued northwest unmodified flow, should yield
highs mainly in the 40s and low 50s. Overnight mins Tue night will
dip into the 30s, but not expecting widespread frost as the pres
gradient should mitigate its development. However, good
radiational cooling ahead of cirrus deck on Wed night should yield
several locations below freezing (and in the 20s). This suggests
frost in locations where the growing season continues, so stay
tuned if you continue to have growing interests. Otherwise, ocean
effect rain showers likely for the cape/islands and immediate
coastal Plymouth County Massachusetts thanks to north flow and Delta-T values
between 850 mb and the sea sfc exceed 20c.

Thu into Fri...
clipper low pres undergoing slow cold occlusion process will be
approaching on Thu as the attendant trof gradually shifts toward a
negative tilt. Precip shield out ahead of the occlusion may take
until late Thu to initiate across the west as soundings show a fair
amount of moisture in the lowest lvls that will need to be
overcome. By Fri night, as the initial low pres shifts north toward
Canada, secondary (triple-point) low may form and traverse
directly over S New England into Fri, enhancing the rainfall
process. Precipitable waters are modest, mainly around or even below 1.00 inch,
so it will take this secondary low for moderate-heavy rainfall.
Quantitative precipitation forecast values around 0.5-1.00 inches are possible should this occur.
Otherwise, temps closer to seasonal normals thanks to warmer
nights under cloud cover (mainly 40s and low 50s. Highs in the 50s
and low 60s.

One other minor note here, there is a slight chance for wintry
mixed precip at the onset early Thu. This is highly dependent on
timing, how efficiently the veering winds are able to scour out
the low valleys, and dynamic cooling potential. It would really
need all these things to line up right (or wrong depending on your
perspective) for this to occur. However, feel it is at least Worth
noting here given the cool airmass and low dwpts (wetbulb process)
in place before the precip shield arrives.

Sat and sun...
removing the GFS with this update, and using thermal wind (mean-
jet) arguments, noting steering should be mainly S of New England
with any additional vort-maxes and/or mid lvl f-gen. Therefore,
will allow for the high pres to the north to dominate the pattern
across the region, with the primary focus for additional rainfall
well to the S. Will yield none pops for now, but maintain that this
remains an uncertain forecast as the wave in question has yet to
be even sampled. Temps will be very close to seasonal normals, as
h92 temps average +4 to +6c. Although overnight mins would be
colder with the crest of high pres and radiational cooling.

Early next week...
low confidence. Even using the blends for the weekend yields
different results as the upper flow pattern suggests zonal flow
and fast moving (albeit weak) shortwaves moving through.
Therefore, will suggest seasonable conditions with a low risk for
occasional shra, but at least at this point, it does not look like
a true washout.


Aviation /14z Monday through Friday/...
forecaster confidence levels.

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

Short term /through Tuesday/...

Today...west to northwest winds pick up through the late morning and
afternoon, with gusts 20-25kt, at times, expected.

Tonight and Tuesday...high confidence. Sct-bkn VFR cigs.
Occasional northwest gusts 20-25 kt, although diminishing wind tonight,
except over higher terrain and along the immediate coast.

Kbos taf...high confidence in taf.

Kbdl taf...high confidence in taf.

Outlook /Tuesday night through Friday/...

Tuesday night into Thursday morning...high confidence.
Mainly VFR. 20-25 kt winds out of the northwest near shore continue Tue
night into early Wed.

Thursday into Friday...moderate confidence.
Low risk for some wintry mix when precip starts on Thu. Otherwise
expect rain lingering into Fri with IFR/MVFR conditions. Winds
veer from NE to southeast and finally to S by Fri.

Sat...moderate confidence.
Mainly VFR with some improvement.


forecaster confidence levels.

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

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

Small craft advisories in effect through Tue.

Today...winds turn northwest today and stay blustery with gusts to 25 kt.

Tonight into Tuesday...persistent northwest winds with gusts 25-30 kt.
Seas 5-7 ft over the outer waters.

Outlook /Tuesday night through Friday/...

Tue night into Wed...high confidence.
Last day of continued Small Craft Advisory conditions. Winds out
of the north-northwest will continue to gust to around 25 kt into the morning
hours on Wed. Seas will gradually recede form 5-7ft, dropping
below 5 ft by Wed evening.

Wed night into Thu...high confidence.
Mainly quiet boating weather regarding seas (which should only
top out at 3-5 ft), while winds will gradually shift from NE to southeast
through the day. Some rain overspread the water by evening Thu.

Thu night into Fri...moderate confidence.
As areas of rain overspread the waters, winds out of the east-southeast
will increase, gusting 25-35 kt at times, this suggests a risk for
gales, although at the very least small craft advisories will be
needed. Seas build to 8-10 ft potentially, if low pres passes
directly over the waters. The winds shift to the S on Fri, but
remain elevated.

Sat...low confidence.
It's possible conditions subside through the overnight hours Fri
night, such that mainly quiet boating weather is experienced by
Saturday. However, there is also a risk for winds and seas to
remain at low end Small Craft Advisory thresholds.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory until 8 PM EDT Tuesday for anz231>235-237-
Small Craft Advisory until 8 PM EDT Tuesday for anz230-236.


near term...Belk/kjc/doody
short term...kjc
long term...doody

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