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Area forecast discussion 
National Weather Service Taunton Massachusetts
706 am EDT Wednesday Jul 29 2015

Synopsis...
hot and humid conditions today through Thursday. A cold front will
bring scattered thunderstorms late Thursday and Thursday night. Not
as warm and less humid weather is expected Friday into the weekend
and probably into early next week. While Friday through early next
week will be mainly dry...can/T rule out an afternoon and evening
thunderstorm each day.

&&

Near term /until 7 PM this evening/...

*** heat advisory Hartford/Springfield metropolitan regions today ***

7am update...

Only change to previous forecast was to discontinue the dense fog
advisory for the islands as visibilities have improved. Off to a
very warm start already with Boston at 76...Worcester and
Providence 73. As mentioned below near record highs today with bdl
most vunerable of tying or breaking the record. Earlier discussion
below.

====================================================================

Today...

Middle-level ridge axis will crest over the region. This will allow for
the muggy airmass to remain in place. 850mb temperatures warm to 18-20c
this afternoon which is several degrees warmer then yesterday.
Therefore have high confidence that temperatures will be several
degrees warmer then yesterday...with highs in the low to middle 90s
with upper 90s across the CT valley. Dewpoints will be in the middle
60s and with light winds. This humidity combined with near record
temperatures will lead to heat indices in the low to middle 90s.
However across the CT valley region...especially in the
Hartford/Springfield metropolitan regions heat indices will reach between
98 and 101. Therefore have issued a heat advisory for this region.
There is the potential that the day shift may expand if temperatures and/or
dewpoints increase more than forecasted.

Aside from the heat...forecast should remain dry for much of the
day. Cannot rule out a spot shower today if locations reach their
convective temperatures...especially across the higher terrain. However
because it will be a rogue shower have kept the forecast dry.

&&

Short term /7 PM this evening through 6 PM Thursday/...
tonight...

Dry weather will resume tonight. However there could be another
round of fog especially for the South Coast...cape and islands where
dewpoints will be highest. Otherwise a muggy and mild night will be
on tap with temperatures dropping into the low 70s.

Tomorrow...

Descent shortwave will move through the flow on Thursday pushing a
cold front across the area. Warm...humid airmass with southerly
flow will be in place ahead of this approaching front. The
southerly flow will allow for much of the region to have 70+
dewpoints. This will help keep temperatures slightly lower...in the upper
80s to low 90s. Heat indices will still be high...reaching into the
low to middle 90s.

00z guidance is in good agreement on timing of the front. In fact
most models have sped this system up by about 6+ hours. Showers
and thunderstorms will begin to move into the region around 18z and
push across the area by Thursday night. A few strong to a severe
storm is possible as instability will be quite high with marginal
middle-level lapse rates. Shear values look to be along or behind the
front...which could limit strong/severe potential. Biggest threat
with these storms appears to be heavy downpours leading to nuisance
flooding as precipitable water values are about 2+ inches. Gusty winds/localized
downburst also cannot be rule out due to the inverted-v soundings.

&&

Long term /Thursday night through Tuesday/...
highlights...

* pattern change to more seasonable temperatures is accompanied by showers
and thunderstorms Thursday night

* not as warm and humid Friday and beyond

* mainly dry weather prevails Friday through Tuesday

Synoptic overview and model preferences...

Impressive and anomalous vortex currently over southern Manitoba as
seen on the latest water vapor imagery will become the main weather
feature this period...as it evolves into a much broader circulation
over James and Hudson Bay this weekend and next week. This results
in a broad mean long wave trough setting up across the Great Lakes
and the northeast. This will suppress excessive heat and humidity
airmass currently over the area southward beginning Friday and
lasting through the weekend into early next week. Given good multi
model agreement among deterministic and ensemble guidance regarding
the large scale flow this period...forecast confidence is above
average.

Daily sensible weather details...

Thursday night...

Northern stream short wave and attending cold front move across the
area. Modest synoptic scale forcing associated with this feature.
While instability and shear is marginal in the prefrontal
environment...precipitable waters climb to 2+ inches /+2 Standard deviations above
climo/. Thus greater risk of heavy downpours and localized flooding.
Warm and muggy conditions prevail as Post frontal airmass doesn/T
arrive until Friday.

Friday through Tuesday...

Trend toward more seasonable temperatures and lower humidity arrives
Friday behind departing cold front with highs in the 80s and lows in
the 60s. Too difficult at this time range to time individual short
waves embedded in the cyclonic flow. So best wording would be many
hours of dry weather this period but cyclonic flow and cooler temperatures
aloft will result in the risk of a thunderstorm during peak heating
hours each day.

&&

Aviation /12z Wednesday through Sunday/...
forecaster confidence levels...

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

Short term /through Thursday/...

7 am update...

No major changes from 06z and 09z tafs. Earlier discussion below.

=================================================================

Tonight...moderate confidence. VFR for many sites...however
anticipate patchy dense fog has dropped some sites down to IFR or
even LIFR. Best locations is across the cape...islands and South
Coast where dewpoints are in the 70s.

Today into tonight...high confidence in VFR conditions. May see
patchy fog overnight dropping conditions to IFR.

Thursday...VFR to start conditions dropping to MVFR in -shra/thunderstorms and rain
between 18-00z. A few strong storms are possible.

Kbos terminal...high confidence. Sea breeze develops between
14-15z.

Kbdl terminal...high confidence.

Outlook /Thursday night through Sunday/...

Thursday night...MVFR and IFR in scattered showers/T-storms and fog.
Moderate to high forecast confidence.

Friday and Saturday...moderate to high confidence in VFR conditions.
Very low risk for an afternoon T-storm Saturday.

Sunday...moderate confidence for mainly VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Thursday/...high confidence.

Winds and seas below Small Craft Advisory today and tonight has high pressure will
be in place. Approaching cold front on Thursday will increase
winds along the southern waters. Could see some gusty near 25 kts.
Persisent southerly swell will increase seas between 4-6 feet. A
Small Craft Advisory may be needed on Thursday.

Outlook /Thursday night through Saturday/...

Thursday night...SW winds 15 to 20 knots with gusts up to 25 knots
possible. Rough seas on south ocean waters with wind waves of 3 to 6
feet possible. Visibility reduced in scattered showers/thunderstorms and fog.
Moderate to high forecast confidence.

Friday/Saturday and Sunday...cold front slowly moves offshore with
wind shift from south-southwest to west-southwest. Dry weather and good visibility. High forecast
confidence. Leftover southerly swells on south ocean waters from Thursday
night linger Friday but slowly diminish.

&&

Climate...
record highs for 7/29:

Boston97 on 1933 & 1931

Providence95 on 2002 & 1949

Bradley96 on 1933

Worcester94 on 1892

&&

Box watches/warnings/advisories...
CT...heat advisory from noon today to 7 PM EDT this evening for
ctz002.
Massachusetts...air quality alert from 11 am this morning to 11 PM EDT this
evening for maz017>024.
Heat advisory from noon today to 7 PM EDT this evening for
maz011.
Rhode Island...air quality alert from 11 am this morning to 11 PM EDT this
evening for riz005>008.
Marine...none.

&&

$$
Synopsis...nocera/dunten
near term...dunten
short term...dunten
long term...nocera
aviation...nocera/dunten
marine...nocera/dunten
climate...

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