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Area forecast discussion 
National Weather Service Taunton Massachusetts
700 am EDT Tuesday Jul 22 2014

Synopsis...
southwest flow will bring an increase in heat and humidity
today...which will persist into Wednesday. Showers and
thunderstorms will likely move across the region late Wednesday
afternoon and evening ahead of a cold front. A few strong to
severe thunderstorms will be possible. Cold front slowly moves offshore
Thursday with a trend to improving weather. High pressure builds
over the region Friday and Saturday...then makes way for unsettled
weather approaching from the southwest Sunday and Monday.

&&

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

7 am update...
fog lingers across the Outer Cape and the islands. Also some
patchy fog in places such as Norwood and Westfield. This should
burn off shortly this morning. We have made only minor changes to
the earlier timing. Hourly temperatures and dewpoints were adjusted a
little lower based on observed conditions...but no change to
expected values this afternoon.

Previous discussion...
the two main issues today involve burning off of low clouds and
fog and risk of any late afternoon convection in the west.

With regard to low clouds and fog...expect gradual improvement through
middle/late morning. Have a strong sun angle at this time of
year...but developing SW flow and gradually increasing dewpoints
will likely slow the pace at which the low clouds and fog burn off
over the cape and Nantucket.

Convection chances appear to be very limited this afternoon as
models depict middle level cap becoming established.
Nevertheless...will retain a slight chance over the east slopes of
the Berkshires where showalter index drops to near zero and the k
index rises to near 30 for a period. Also...isolated showers/thunderstorms
developed Monday afternoon across New York state in an air mass that
is sliding in our direction.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
tonight...expecting temperatures to be 2 or 3 degrees milder
tonight in most locations with dewpoints rising from the low to
middle 60s. Also expecting areas of low clouds and fog along S
coastal areas and possibly in a few interior valleys.

Wednesday...weather becomes more interesting as a cold front
approaches from the west. Initially a middle level cap is expected to
inhibit convection but that cap should erode as the front
approaches in the late afternoon. SBCAPE projected to be 1200 to
2000 j/kg and middle level lapse rates 6.0 to 6.5 c/km. A fairly
notable bump of the k indices into the middle to upper 30s takes
place late Wednesday afternoon/evening while the showalter indices drop
to around -2 to -3. The 0 to 6 km wind shear is fairly marginal at
around or just stronger than 30 knots with stronger wind shear
indicated north of the forecast area per the 00z GFS and European model (ecmwf).
The 00z NAM run projected closer to 40 knots shear across the
northern zones but not quite ready to buy that. At any
rate...shear still looks strong enough combined with the
instability to support some strong to severe thunderstorms to perhaps as
far east as an ash-lwm-bed-ijd line. Precipitable waters are expected to rise to
between 1.7 and 2 inches and so the risk for localized flash
flooding needs to be considered as well. Have put in mild enhanced
wording for gusty winds and heavy rainfall. Will mention the risk
of strong to severe thunderstorms and localized flash flood risk in the
severe weather potential statement.

&&

Long term /Wednesday night through Monday/...
big picture... big ridge builds over The Rockies and plains while
troughs dig into the northeast and the Pacific northwest. Upper
ridge lingers over the western Atlantic. For US...this will bring
falling heights/cooling temperatures aloft Thursday and Friday...then
rising heights/warming temperatures over the weekend. The Pacific northwest
trough ejects over the top of The Rockies ridge and moves east.
Over the weekend it will merge with the northeast trough and pull
the trough axis back to our west. The Atlantic ridge remains in
place to our east. This will bring a moist southwest flow up over
New England Sunday-Monday.

Good agreement among most of the long range models...allowing US to
use a consensus.

The dailies...

Wednesday night-Thursday... the cold front crosses much of our
region while the right entrance region of the upper jet moves into
position overhead. Winds at 500 mb will be 35-40 knots. Totals near
50/Li -4 and lower during the early part of the night. The
combination of dynamics and instability and shear suggest a
potential for strong wind gusts. Precipitable water values will be
near 2 inches...so heavy downpours also possible.

The cold front will be just off the South Coast at 12z. The right
entrance of the upper jet will still be in position overhead. This
may cause a wave to form on the front and keep showers over
southern/eastern parts of southern New England through the morning.
But the trend during the day will be for improvement from northwest
to southeast with at least partial clearing in southern New Hampshire and the
CT valley. Temperatures in the mixed layer will support maximum surface temperatures
in the middle 70s to around 80.

Friday-Saturday... high pressure builds overhead. Some concern that
Friday would feature more clouds during the day. The upper trough
axis and cooler temperatures aloft will move overhead at this time with
some increase in cloud level moisture. With this in mind we have
increase Friday sky cover. Then on Saturday the upper flow starts to
shift to southwest with an increasing in high clouds. Overall a
couple of fair days with temperatures at seasonable levels or a little
below.

Sunday-Monday... as the upper flow re-establishes as southwest and
aimed up the coast...a shortwave moves into the flow. This has the
potential to develop a coastal low that moves our way and spreads
clouds and rain our way especially for Sunday night/Monday. Given
how far out this is...day 6/day 7...we will show chance probability of precipitation
developing Sunday and continuing Monday.

&&

Aviation /12z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through Wednesday night/...

Generally moderate confidence on forecast.

Areas of IFR ceilings/visibilities cape and Nantucket and patchy IFR visibilities
in fog across the interior. The low clouds and fog should
gradually burn off this morning and then reappear along the South
Coast again tonight. Otherwise...VFR conditions are expected
through Wednesday middle afternoon.

During late Wednesday afternoon...MVFR ceilings and visibilities in vicinity of scattered
thunderstorms ahead of a cold front. A few thunderstorms may briefly lower
ceilings/visibilities to IFR levels. Also...a few thunderstorms may produce strong
wind gusts...especially northwest of an ash-lwm-bed-ijd line.

Kbos taf...moderate to high confidence. Generally VFR conditions
expected through most of Wednesday...althoug areas of fog could reduce
visibility to 5 to 6 Michigan for a short time tonight. There will be a risk
of thunderstorms approaching the field after about 23z Wednesday.

Kbdl taf...high confidence in taf. VFR conditions expected to at
least middle afternoon Wednesday...except for a low probability of MVFR
ceilings/visibilities in stratus/fog tonight. There will be a risk of thunderstorms
in the vicinity of the airfield sometime after about 20z Wednesday.

Outlook...Wednesday night through Saturday...moderate confidence

Wednesday night-Thursday... mainly VFR. Cold front crosses the
region with period of MVFR ceilings/visibilities in showers/tstms. Patchy IFR
in fog...mainly South Coast and islands.

Friday-Saturday...VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday/...moderate confidence.

Winds and seas are expected to remain below Small Craft Advisory
levels through tonight. The SW flow will strengthen ahead of a
cold front on Wednesday with a risk of gusts approaching 25 knots. Areas of
fog will gradually burn off this morning but may redevelop along
the south coastal waters tonight.

Outlook...Wednesday night through Saturday...moderate confidence.

Wednesday night-Thursday... a cold front crosses the waters late at
night and during Thursday. Gusty southwest winds leading the front
may approach 25 knots at times Wednesday night. Winds shift to north
and northeast on Thursday. Showers and scattered thunderstorms with
strong wind gusts and briefly heavy rain. Seas remain below 5
feet...but briefly higher seas possible in any thunderstorms.

Friday-Saturday... north winds shift to southwest with speeds 15
knots or less. Seas remain less than 5 feet.

&&

Equipment...
kbox radar is in standby Mode today while construction takes
place nearby. The radar will return to service when construction
ends for the day.

&&

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

&&

$$
Synopsis...wtb/Thompson
near term...wtb/Thompson
short term...Thompson
long term...wtb
aviation...wtb/Thompson
marine...wtb/Thompson
equipment...

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