Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 251711
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
111 PM EDT Sun Sep 25 2016

.SYNOPSIS...
Cool and dry weather continues into Monday. Low pressure may
bring showers to southern New England some time late Monday night
into Wednesday morning. Otherwise, seasonable and mostly dry
weather is expected much of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

1 PM Update...

No significant changes in near term forecast. Temperatures are
running a tad above forecast in a few spots. Winds are a tad
higher in gusts in a few eastern zones but not enough to change
Small Craft Advisory headlines. Will be considering whether an
expansion of the Frost Advisory for tonight might be necessary for
the 4 PM update.

10 AM Update...

Clear skies dominated the southern New England sky at 10 AM and is
expected to continue to do so today. Patches of radiational fog
appear to have dissipated. Have only made very minor tweaks in
temperatures as they recover from the chilly lows. Sufficient NW
gradient to preclude any sea breeze issues.

730 AM update...

Overall trend in the forecast remains on track for today. Clear
skies overhead as temps radiate out this morning. Frost Adv
appears to be in a good location so will keep it going. Will have
to issue a new one for tonight but will wait until temps warm
above 38F this morning. Otherwise radiational fog has developed
over valley locations, this will dissipate over the next hour or
two.

Previous Discussion...

Otherwise, it`s going to be a beautiful SKC start to the day,
refreshing and sunny. With this cooler than normal start, H85 and
H92 temps dropping to the lower 10th percentile of climatology,
not expecting a warm day, as temps will likely hold in the low-mid
60s at most locations. Could see a few sites overachieve thanks to
it only being early in the fall period, and continued dry
conditions.

Otherwise, a light 10-20 mph NW breeze will add to the fall-feel
especially through the afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Tonight...
With H92 temps dipping as low as +5C, clear skies and a very weak
pres gradient, expect better inversion development overnight
tonight than even last night. Guidance that has handled temps will
early this morning (MET especially) are as much as 2-4F cooler
early Mon morning. Agree with previous forecaster that more
widespread frost is likely across the region, with several
locations in NW MA and even portions of CT and the interior
coastal plain dropping to the mid-upper 30s. A few sites may
approach freezing, in the normally coldest valleys. Therefore,
expect another round of frost headlines to be coming through the
day today, but with current ongoing headline, will allow day-shift
to issue. For now, will have an SPS highlighting the risk to allow
as much lead-time as possible.

Mon...
Core of high pres moves E allowing for slight return flow. This
suggests both weak warm advection and increase in column moisture.
So instead of the steady SKC conditions, expect more clouds
building over the region through the day. Even though column is
moistening ahead of an occluding low pres, expect any actual
precip to hold off until the fronts arrive by the overnight hours.
POPs will reflect this.

Temperatures a bit closer to seasonable normals. H85 temps
increase from near 0C Sun to an average around +5C on Mon. With
full mixing, looking at highs more the upper 60s and low 70s. The
good news, is the humidity should remain low most of the day, in
spite of the increase in moisture, mixing should keep sfc dwpts
mainly in the 30s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
HIGHLIGHTS...

* Seasonable temperatures expected much of the long term
* Frontal system will bring showers to the area Tuesday
* Quite a bit of uncertainty in the pattern for mid to late week

Overview/confidence...

High confidence in widespread rain fall late Monday into Tuesday as
frontal system pass through. Thereafter models show low
predictability and thus high uncertainty in regards to the cut-off
low over the eastern half of the CONUS. GFS continues to be the more
progressive solution opening up the low by late Friday into Saturday
while the EC keeps the cut-off low around through the upcoming
weekend. The UKMET seems to be more inline with the EC whereas the
GEFS are inbetween the solutions. For now, continued with model
blend until guidance becomes more inline.

Monday night into Tuesday...Moderate Confidence.

Upper level ridge will move overhead Monday night as WAA spills into
the region. Overnight temps will begin to fall during the evening
hours before remaining steady or even rising by the early morning
hours. A few showers are possible after midnight, within the higher
theta-e plume, but the bulk of the rain will move through on
Tuesday.

Ahead of the FROPA, temperatures will warm into low 70s across the
area. Dewpoints will be on the rise as well making it feel a bit
more humid. Appears the best timing for precip will be Tuesday
morning which could make way to a rough morning commute. GEFS
continue to show 70-80 percent probs of over a half of an inch of
rain, so confidence is increasing in widespread rainfall. Went ahead
and bumped pops to categorical as all guidance is signally for rain
across the area. A good pressure gradient develops behind the
passing frontal system which could result in gusty winds near 25
mph. A few higher gusts are possible within the heavier rain showers
as 40 kt LLJ develops over the region. Cannot rule out a rumble of
thunder across the immediate south coast as there is some elevated
instability. But because potential is still uncertain kept it out of
the forecast for now.

Wednesday and Beyond...Low Confidence.

Again low confidence with this forecast as models seem to always
struggle with cut-off lows. Depending on the guidance, passing
frontal system on Tuesday could stall the front close enough to
southern New England that passing waves rotating around cut-off
could keep showers in the vicinity through the remainder of the week.
Biggest question is the high pressure to the north of the region. If
it will build in enough to keep the front and precip far enough
south to keep the region dry. The EC thinks it will for Wed into
Thursday while the GFS is more progressive keeping the high too far
north bringing precip in as early as Wed. Because of the large
spread in guidance will keep a slight chc of pop through the week
until details and timing can be distinguished. Seasonable
temperatures can be expected for this period.

&&

.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels.

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

Short Term /through Monday/...High confidence.

VFR. Still expect mostly clear skies this afternoon through
tonight. Some 15-20 kt NW winds early to mid afternoon hours,
diminishing by sunset.

Mon...VFR expected again. Sea breeze potential on the coastlines.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday night thru Tuesday...Moderate confidence.
VFR through the period with localized MVFR in rain on Tuesday. Gusty
southerly winds near 30 kts across East coastal terminals.

Wednesday into Thursday...Low confidence. Most likely VFR for much
of this time, but model uncertainty could mean periods of MVFR in
lower clouds and scattered showers.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Monday/...High confidence.

Through 15Z (11Am local)...
A resurgence of winds will allow some gusts to reach 25-30 kt out
of the NW, particularly on the ocean waters before they begin to
subside. Seas build during this period as well, 5-6 ft thanks to a
combination of this wind and a southerly swell from Karl.

After 15Z into tonight...
Winds remain NW but generally below 20 kt. They shift slowly to
the S tonight, but stay light. Seas will begin to decline, but
take until overnight for the ocean waters to fully dissipate below
5 ft. Therefore some small craft advisories will linger into the
overnight hours.

Tomorrow...
Mainly quiet boating weather as high pres slips over, then east of
the waters.

Outlook /Monday Night through Thursday/...

Tuesday...High confidence. Strong cold frontal system will approach
the waters on Tuesday increasing both seas and winds. Ahead of the
front southerly winds will increase close to gales with seas
building near 7-8 feet as a response. Vsbys will drop within any
heavy rain showers as the front passes. Low risk for a rumble of
thunder across the southern waters.

Wednesday and Thursday...spread in the guidance has resulted in a
low confidence forecast. Could see small craft conditions on the
outer waters for a time as front stalls across the waters. Passing
waves could increase both seas and winds each day. Again low
confidence forecast.

&&

.CLIMATE...
Record low temperatures...

September 25th / 26th (last set in...)

Boston ....... 38 (1950) / 34 (1879)
Hartford ..... 30 (1963) / 33 (1978)
Providence ... 36 (1963) / 37 (1967)
Worcester .... 31 (1944) / 28 (1925)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Frost Advisory from 2 AM to 8 AM EDT Monday for MAZ002>004-
     008>010-017-018.
RI...None.
MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ235-
     237.
     Small Craft Advisory until 3 AM EDT Monday for ANZ250-254-255.
     Small Craft Advisory until 5 PM EDT this afternoon for ANZ256.

&&

$$
SYNOPSIS...Doody/Dunten
NEAR TERM...Doody/Dunten/Thompson
SHORT TERM...Doody
LONG TERM...Dunten
AVIATION...Doody/Dunten/Thompson
MARINE...Doody/Dunten
CLIMATE...



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