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Area forecast discussion 
National Weather Service Taunton Massachusetts
219 PM EDT Tuesday Sep 2 2014

Synopsis...
hot and humid across the region today...although a cold front will
cross the region overnight. A few showers and thunderstorms are
possible this afternoon and this evening ahead of this front. Drier
but warm weather follows the front Wednesday and Thursday. Humidity
will once again increase by the end of the week...as the next cold
front brings the risk for more scattered showers/thunderstorms by
Saturday. Cooler and less humid weather follows by next Sunday and
Monday.

&&

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

230 PM update...

Showers and thunderstorms have been developing in a region with
high k index values. This convection appears to be developing
along a pre frontal trough that is passing through alb region
currently per msas observation. Surface cape values are up to 3000 j/kg
showing enough instability for convection to continue through the
afternoon. Shear values are very weak but with dewpoints in the
70s cannot rule out a possible spin up as there could be mesoscale
shear. There is some rotation with a few of these storms. Biggest
concern is the heavy rain potential as precipitable water values are well above
2 inches. Small hail could be possible but with the high surface
temperatures...the hail will melt as it falls to the surface. Still
cannot rule out the potential for a wet microburst as well.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
tonight...
surface cold front will be rapidly approaching from the west...with
timing generally agreed upon by guidance. Expect it to be in
East New York by 00z...central box County Warning Area by 06z and then offshore between 09z
and 12z. Suspect there will be ongoing convection /potentially
strong/ across eastern New York by about 00z this evening. Initially...the
best low level jet energy will be shifting north-northeast suggesting slow east
progression...so suspect it may take until as late as 03z for any
of this convection to arrive in west Massachusetts/CT and SW New Hampshire. The key is how
much of this holds together into the box County Warning Area given that by
03z...almost 3 hours without significant surface heating will have
elapsed. Do note that as it approaches with the cold front...there
is an increase low level jet energy to about 35-40 knots at 850 mb. Therefore...30
knots of 0-3 km shear and nearly 40 knots of 0-6km are possible as this
convection approaches. Regarding surface conditions...do note a
pocket of helicity near 100 as well. However...will be gradually
losing the near 1000-1200j/kg of surface cape with diurnal
stabilization. Therefore...it/S a balancing act between the
stabilization of the column and the increase in localized shear.
Do feel that the guidance shifting quantitative precipitation forecast out of the region is likely
too dry especially in the west half of the region. Feel that
maintaining the threat for T-storms into at least 03-06z is
warranted. Not out of the question that an isolated severe storm
is noted given the shear...but not confident enough to include
enhanced wording with this update given stabilization. Will
however maintain wording for heavy rain...as high precipitable waters could
still promote an isolated flash flood threat. All this thinking
coincides nicely with latest Storm Prediction Center day 1.

Outside of the heavy rain/thunder potential...may need to watch
especially east areas for the return of some overnight fog and
stratus thanks to dewpoints holding near 70 for much of the night.
Mins are likely to remain warm as the cooler air will lag the
front until mainly around or after sunrise.

Wednesday...
rapid improvement following the front thanks to dry air moving in.
Will likely see dewpoints fall back into the 50s during the day. The
column as a whole is dry also...so after leftover debris clouds
diminish during the morning expect a mainly sunny day. 850 mb temperatures
still remain close to +13c...so highs are likely still to reach
the middle to upper 80s.

&&

Long term /Wednesday night through Monday/...
highlights:

* dry Thursday/Friday with very warm afternoon/S
* humid with scattered showers/storms possible Sat
* cooler and less humid sun into Monday

Details:

Wednesday night...

High pressure overhead will result in mainly clear skies and light
winds. This will allow low temperatures to bottom out mainly in the
50s...to lower 60s. Patchy fog may develop late in the typically
prone locations.

Thursday and Friday...

High pressure in control will keep the weather dry with warm
afternoon/S...particularly by Friday. High temperatures should be well up
into the 80s on Thursday...but humidity will be in check. As the
high moves further off the coast by Friday...850 mb temperatures reach +16c
as southwest flow aloft increases. This should allow highs well up
into the 80s to near 90. Humidity will also increase on
Friday...although it will not be oppressive.

Saturday...

A cold front will approach the region and likely trigger scattered
showers/thunderstorms during the day Saturday. Not expecting the
entire day to be a washout...but appears enough instability/moisture
and forcing available for convection. Precipitable waters approaching 2 inches
will make heavy rain and very localized flooding the main concern.
While more clouds will likely keep temperatures a few degrees lower than
Friday...it will be quite humid ahead of the cold front with
dewpoints near 70.

Sunday and Monday...

The cold front should have exited the southeast New England coast
early Sunday. This will allow cooler and less humid air to work
into the region Sunday and Monday. Will also have to watch a couple
waves of low pressure off the middle Atlantic coast. For now most of
the models keep them far enough away to result in mainly dry weather
and that will be shown in our deterministic forecast. However...
there certainly is at least a low probability that one of them ends
up further north and we end up with a period of showers.

&&

Aviation /18z Tuesday through Sunday/...
forecaster confidence levels...

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

Short term /through Wednesday night/...high confidence in
trends.

Through 00z...scattered thunderstorms and rain north of the Pike with isolated thunderstorms and rain south of
the Pike. Anticipate brief localized lower conditions until about
22z.

Tonight...a lull in activity after 00z. Before another round of
showers with isolated thunder moves through after 03/04z. This
convection is associated with an approaching cold front which
will pass through the region overnight. Expect convection to
weaken as it moves through with brief lowering in ceiling heights.
Patchy fog is expect ahead of the front and should dissipate as
it passes through.

Wednesday into Wednesday night...VFR. Patchy fog in CT valley Wednesday night.

Kbos terminal...high confidence in trends. May be a shower or
thundershower in the afternoon.

Kbdl terminal...high confidence. An afternoon shower or thunderstorm
is possible.

Outlook...Thursday through Saturday...

Wednesday night through Friday...high confidence. Mainly VFR
conditions other than late night/early morning patchy ground fog in
the typically prone locations.

Friday night and Saturday...moderate confidence. A period of MVFR-
IFR conditions expected in low clouds/fog patches and scattered
showers/thunderstorms. Timing highly uncertain at this point.

&&

Marine...
forecaster confidence levels...

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

High confidence through the period Wednesday.

SW flow continues today...and a few gusts to around 20 knots are
possible mainly near the shorelines of Cape Cod and the islands.
By tonight...winds will shift to the west-northwest and continue in this
direction into Wednesday following a cold frontal passage. Low chance
for some showers or thundershowers this evening. Seas may approach
5 feet on the S ocean waters this evening...but should remain below
Small Craft Advisory thresholds through the day on Wednesday.
Otherwise...some fog may lead to visibility reductions early this
morning and again tonight.

Outlook...Wednesday night through Saturday...

Moderate confidence through this period.

Wednesday night and Thursday...high confidence. Weak pressure
gradient should keep winds/seas below Small Craft Advisory thresholds. Good
visibilities should make for nice boating weather.

Friday...moderate to high confidence. Near shore southwest wind
gusts of 20 to 25 knots may develop in the afternoon with good
mixing over the land. Seas should remain below Small Craft Advisory thresholds...but
may become choppy especially near shore.

Friday night and Saturday...moderate confidence. Areas of fog may
affect the southern waters. Southwest wind gusts around 20 knots
are expected ahead of an approaching cold front. There will be the
risk of scattered showers and thunderstorms during the day Saturday.

&&

Equipment...
the Bourne/Hyannis National oceanic and atmospheric administration weather radio transmitter...kec-73...
broadcasting on 162.550 mhz...continues to experience occasional
outages. The technical issues are being worked on presently. We
apologize for the inconvenience.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...Frank/doody
near term...dunten
short term...doody
long term...Frank
aviation...Frank/dunten
marine...Frank/doody
equipment...

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