Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 250309
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1109 PM EDT TUE MAY 24 2016

.SYNOPSIS...
A few leftover showers may fall across western MA and north
central Conn., as well as south coastal MA and RI through the
pre dawn hours of Wednesday as low pressure slowly moves
northeast out of southeastern New England overnight. An upper
level high pressure ridge will then bring very warm to hot
weather to most of the region Wednesday through Saturday, except
for cooler temperatures at times on the immediate coast. A few
showers and thunderstorms are possible Thursday night into Friday,
but a better chance exists Saturday afternoon and evening ahead of
a backdoor cold front.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

1030 PM Update...

Upper level whirlpool continues to spin across eastern MA and RI
at 02Z as seen on water vapor satellite imagery and NE regional
88D radar mosaic imagery. Noting some thunderstorms across
portions of the Gulf of Maine, but the showers bands across W New
England and south coastal MA/RI have been slowly but steadily
weakening as they spin around the upper level low. Can not
totally rule out a quick shower across central and eastern areas,
as well as the eastern slopes of the Berkshires through around 1
or 2 AM, and maybe some brief patchy mist along the immediate east
coast with continued light N-NE winds. Drying air aloft finally
working S across the Hudson valley of NY on the WV satellite,
which should work E as the low begins to exit the E coast of MA
over the next few hours.

With light winds across the region, along with lowering
temp/dewpoint spreads, will still see patchy fog develop along
with lingering low clouds from around Worcester and Windham
counties eastward through around midnight, but trends continue to
indicate that this should slowly push E during the early morning
hours as the low exits, but will be slowest across E coastal MA.
Partial clearing should begin moving into the CT valley after
midnight as winds back to light NW, then will slowly shift E
overnight. Clouds will linger along the E coast through daybreak.

Temps were running a few degrees above forecast, mainly in the
50s with a couple of 60 degree readings at 02Z. Have adjusted
temps just a bit to reflect this trend.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
*** Summer-like Temperatures Arrive Wednesday ***

4 pm update ...

Wednesday ...

Vertically stacked low just east of Cape Cod at 12z/8am but ejects
seaward quickly with rising heights and northwest flow aloft by
midday. Thus any cloudiness across Eastern MA at sunrise quickly
erodes and/or moves offshore with abundant sunshine for the
afternoon. Warming temps aloft to +14c at 850 mb and +21c at 925 mb
yields surface temps at least 30C/86F. Although with boundary layer
mixing beyond 850 mb highs will make a run at 90 in many locations.
However humidity will be low with dew pts only in the mid to upper
40s. Not as warm along the South Coast including Cape Cod and the
Islands...where winds will bend to the southwest off the cooler
ocean waters.

Wed night ...

Dry, tranquil weather with mid level ridge and associated
anticyclonic flow continuing to build across the region from the
west.  Dry airmass in place along with diminishing winds and mostly
clear skies will allow temps to fall into the 50s...except 60-65 in
the urban areas.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
HIGHLIGHTS...

* Well above average temperatures for Thu and Fri with the potential
  for a spot thunderstorm
* Hazy, Hot and Humid for Saturday with locations reaching 90+F
* Scattered showers and thunderstorms are possible on Saturday
* Back door cold front on Sunday will keep conditions cool into
  Monday

OVERVIEW...

Large scale pattern is in agreement with both determinisic and
ensemble guidance. Upper level trough will move eastward towards the
Maritimes as Midwest ridge builds into the Northeast. Anomalous
high pressure over the western Atlantic will continue to build this
ridge through Saturday. Anticipate summer-like warmth and humidity
to return to the region as ensembles show both the 700 and 500
heights nearly 1-2 standard deviations above normal. Several waves
will move through the flow keeping a chance of showers and
thunderstorms in the forecast for Late Thursday and again on
Saturday. Because of the mesoscale differences in the guidance
trended the forecast towards an overall blend. Back door cold front
will swing through by Sunday cooling the area down. However, on
Monday, still some discrepancies with offshore high pressure. The
GFS keeps it closer to the coast keeping temps on Monday cooler
while the EC is weaker and more offshore. Continued with a model
blend for now.

DAILIES...

Thursday into Friday...High Confidence.

Upper level ridge will build into the region on each day. Anticipate
the warm weather to continue into Thursday as 925 mb temps are
generally around 20C. This warm airmass combined with westerly flow
and the warm May sun will help aid in high temps reaching into the
mid to upper 80s with a few 90s near the CT valley. Conditions look
to be cooler along the MA coastline as a sea breeze will develop
from weak winds aloft. A spot shower or thunderstorm may develop in
the afternoon, but most of the region will remain dry.

Weak shortwave will pass through the flow Thursday night. Due to
building heights across the region and weak southwesterly flow,
appears that the better forcing will be north of southern New
England. However, cannot rule out the potential for precip Thursday
night into Friday morning across the north and northwest portion of
the region. Guidance continues to highlight the potential for
elevated convection so continued the mention for thunder in the
forecast for now.

Temperatures on Friday look to be similar as they will be on
Thursday with heights in the mid to upper 80s with a few 90F across
the CT valley. Still a large spread in the guidance on if Boston
will reach 80F as there is question in the sea breeze development.
However 925 mb winds appear to be strong enough to allow for good SW
flow to warm the immediate eastern coastline. This southwest flow
will keep the south coast cooler thanks to onshore flow and the
cooler ocean waters.

Once again a spot shower looks to be possible in the afternoon, but
better forcing and instability appears to remain west of the region.
So another dry weather day is expected.

Saturday...Moderate Confidence

Upper level ridge will strengthen across the the eastern Great Lakes
as warm front lifts northward. A very warm day will be on tap as 925
mb temps will warm to 23-24C. Ensembles continue to show
probabilities that many locations could reach above 90F. This hazy,
hot and humid day does have some caveats. Approaching surface trough
looks to trigger afternoon convection for the region. Some storms
could be strong or severe, but a bit to early to tell.

Sunday into Monday...Moderate Confidence.

Back door cold front will swing through the region late Saturday
night into Sunday. This will cool temperatures down across the
region. The front does look to push and stall across the Hudson.
However, could still see upper 70s or low 80s across the CT river
valley as 925 mb temps are between 18-20C. Otherwise anticipate a
cooler weather day.

Still large spread for surface temps on Monday. GFS and EC have
about a 15 degree difference amongst each other. The GFS is cooler
with highs in the low 70s while the EC is warmer with highs in the
low 80s. Continued with a model blend for now to split the
difference. May see a few sct showers on Monday depending on the
location of the southeast low pressure system and how quickly it
moves northwards towards the region.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels.

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

Overnight...Moderate confidence with uncertainty on timing of
improving conditions.

Mainly MVFR-IFR conditions from Worcester and Windham counties
eastward, but will improve from W-E overnight. Low clouds and fog
may linger through daybreak along the immediate E coastal
terminals. Isolated showers may linger along S coastal areas
through 06Z, as well as near the E slopes of the Berkshires.

Wednesday...High confidence.

Any leftover MVFR cigs at sunrise will be across Eastern MA but
quickly lifting to VFR by 15z or sooner. Dry weather and west
winds except southwest along the coast.

Wednesday night...High confidence.

VFR/DRY and light sw winds becoming west.

KBOS TAF...Moderate confidence. Uncertainty remains on exact
timing of improvement, but should take place from 08Z to 10Z.

KBDL TAF...Moderate confidence. Will still see some MVFR-low end
IFR CIGS/VSBYS through 05Z, otherwise VFR.

Outlook /Thursday through Sunday/...

Thursday...High confidence. VFR.

Thursday night and Friday...Moderate confidence.  VFR conditions
likely dominate but some brief MVFR conditions possible in a few
showers/t-storms mainly across the interior.

Saturday...Moderate confidence. Mainly VFR conditions but brief
MVFR- IFR conditions possible Saturday afternoon/evening in
scattered showers and thunderstorms.

Sunday...Low confidence. MVFR conditions to start with some
improvements on Sunday as a back door front swings through.

&&

.MARINE...
Forecaster Confidence Levels.

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

Overnight...High confidence.

Upper level low will slowly move into Massachusetts Bay during
the early morning hours. Light E-NE winds across the eastern
waters will back to N-NW, becoming mainly W of all waters toward
daybreak. Leftover SE swells will linger on the outer waters E
and S of Cape Cod, but should subside below 5 ft by around 08Z-
09Z. Visibility restrictions in patchy fog, locally dense in some
locations, should improve from W-E.

Wednesday...High confidence on all weather parameters.

Low pressure near Cape Cod at sunrise moves east/offshore by
midday with a drying trend and vsby improving to the horizon.
Winds become southwest by midday.

Wednesday night...High confidence.

Light southwest winds become westerly. Dry weather and vsby
continue.

Outlook /Thursday through Sunday/...High Confidence.

Winds and seas will remain below Small Craft Advisory thresholds
the majority of the period. Could see some brief near shore
southwest wind gusts of 15 to 20 knots are possible Friday and
Saturday...which will result in some choppy seas. Otherwise could
see some afternoon convection on Saturday as a back door cold
front swings through.

&&

.FIRE WEATHER...

Wednesday...High temperatures soaring well into the 80s to near
90 in most locations will result in minimum afternoon RH values
dropping to between 20 and 30 percent. A few hours of westerly
wind gusts of 20 to 25 mph are anticipated. Given today`s rainfall
and marginal criteria, will probably fall short on the need for
fire weather headlines especially given many locations are near
full green-up.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Air Quality Alert from 11 AM to 11 PM EDT Wednesday for
     MAZ020>024.
RI...Air Quality Alert from 11 AM to 11 PM EDT Wednesday for RIZ003-
     004-006>008.
MARINE...Small Craft Advisory for hazardous seas until 4 AM EDT
     Wednesday for ANZ254-255.

&&

$$
SYNOPSIS...Nocera/Dunten
NEAR TERM...EVT
SHORT TERM...Nocera
LONG TERM...Dunten
AVIATION...Nocera/Dunten/EVT
MARINE...Nocera/Dunten/EVT
FIRE WEATHER...Staff


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