Area forecast discussion
National Weather Service Taunton Massachusetts
517 PM EDT Friday may 24 2013
Synopsis...
a cold front will move slowly across eastern New England this
evening with much cooler air behind the front. Low pressure will
develop on this front...with showers lingering across the region
through Saturday night. Some improvement is likely Sunday as the
low departs into northern New England. However much nicer weather
arrives Memorial Day Monday with warm temperatures and dry
conditions as high pressure builds south of New England. A warm
front will bring even warmer temperatures by late next week.
&&
Near term /until 6 am Saturday morning/...
430 PM update...
a broken line of showers has developed along the cold front
across northwest Rhode Island into metropolitan West Boston. Not enough instability for
thunder but sufficient for a few heavy downpours early this
evening as precipitable waters remain at or above 1.4 inches across Rhode Island and eastern Massachusetts.
These showers should weaken with sunset and loss of daytime
heating.
Otherwise anomalous pattern underway with high amplitude negative
trough evolving into a closed middle level low over Long Island
tonight...inducing cyclogenesis near Nantucket. This will result in
comma head/trowal rains over New York/New Jersey and western New England to pivot
across the remainder of the region as the night progresses. Thus
categorical probability of precipitation from met and mav look reasonable. Heaviest and most
widespread rains will be focused across western CT/Massachusetts into southwest
New Hampshire...the I-91 corridor.
Strong cold air advection will continue to overspread the region in
the Post frontal airmass from west to east. Well temperatures will fall
into the 40s across much of the region tonight...model soundings
suggest there is enough blyr warmth to keep ptype all rain even
across the higher terrain.
Falling temperatures will combine with gusty northwest winds to provide a bit of a
wind chill tonight. This along with showers becoming more widespread
will yield nasty conditions for any outdoor activities. The only
positive will be temporary warmth and humidity across eastern Massachusetts.
Temperatures in the l70s along with dew points in the mu60s across this area
has resulted in sb convective available potential energy of around 500 j/kg. Despite modest deep
layer shear middle level lapse rates are weak so not expecting much in
the way of deep convection...just some heavy showers across eastern
Massachusetts/Rhode Island and eastern CT.
For the remainder of the region comma head rains will continue to
Blossom across New York/PA/NJ and NYC will continue to slowly pivot NE
into western New England later today.
Cold front will continue to ooze eastward into eastern Massachusetts late
this afternoon/early evening. Behind the front gusty west-northwest winds
with the initial surge of cool air...then relaxing a bit.
&&
Short term /6 am Saturday morning through 6 PM Saturday/...
Saturday...
not your typical start to Memorial Day weekend with coastal low
over Gulf of Maine as middle level low drifts across southern New
England. Heights aloft continue to fall which results in cooling
from top down. Very impressive synoptic scale forcing via middle
level q-vector convergence. Strongest lift will once again be
across western sections of CT/Massachusetts into southwest New Hampshire...I-91
corridor. Model soundings suggest late in the day across this area
especially the higher terrain of Massachusetts/New Hampshire that rain may mix or change
to snow at times when precipitation intensity is greatest. This will be
most common at elevations greater than 1kft as freezing levels
drop to this level. Surface and ground temperatures likely too warm for
any accumulation but minor snow accumulation possible on
trees/powerlines. Don/T expect any impact just some decorative
snow possible higher terrain.
Elsewhere showers should be widespread along with chilly temperatures in
the u40s to l50s...but will feel much cooler with gusty west-northwest wind.
Embedded heavy showers possible.
&&
Long term /Saturday night through Friday/...
highlights...
* low pressure will slowly move offshore late this weekend...
keeping showers and cool temperatures into Sunday
* fair but cool conditions for Memorial Day...with moderating
temperatures through the middle week
* warm front by end of the week will push temperatures well above average
Overview and model preferences...
medium range models appear in good agreement with the slow but
steady movement of 500 mb cutoff low and associated surface system
late this weekend into northern New England and the Maritimes by
Memorial Day. Upper level pattern evolves over time as cutoff low
remains across the eastern Maritimes into the middle of next
week...tending to flatten out across the northern tier states with
broad high pressure across the south. Will see a return to mainly dry
conditions... though a warm front may approach by middle week with a
brief period of showers possible. Then...looks like Summer warmth
will push in by late next week.
Went along with blend of previous forecast...00z European model (ecmwf)/12z GFS and
wpc guidance for this package...which showed good continuity and
consistency over the last few runs. Noted that the 00z ec /and
since then...the 12z/ op runs have come more in line with the GFS
in ejecting the surface low across the region faster than their
previous runs...and both are nearly identical in pushing system
into Maine and the Maritimes late this weekend into the Holiday.
Details...
Saturday night-Sunday...as 500 mb low moves across east Massachusetts Sat night...
the northwest flow behind combined with the cold pool aloft will bring
mighty chilly air into the region especially across S New Hampshire/west Massachusetts.
With wraparound rainfall moves in across interior areas...along
with this colder air...we have mentioned the possibility of /yes/
mixed rain/snow showers across the higher terrain of the
Monadnocks/east slopes of the Berkshires possibly down into The
Mount Wachusett region of North Worcester County Sat night.
Granted...ground has warmed up so not expecting much in the way of
accumulation... but could see some on grassy and some untreated
surfaces. Lows will drop to the middle-upper 30s even as far S of
interior southeast Massachusetts/north Rhode Island/NE Massachusetts...running 10 to 15 degrees below seasonal
norms.
As for any convection...have removed mention for now but would not
be surprised to hear a few isolated rumbles as precipitation and upper level
system start to shift NE.
On Sunday...leftover showers will end from S-north during the day.
Clouds will remain for most of the day as northwest winds pick up. Expect
gusts up to 30-35 miles per hour especially across central and western areas.
Will remain cool with highs only in the 50s to around 60...again
10-15 degrees below normal. Skies should begin to clear Sun night
and it will remain rather chilly.
Monday...looks like the Holiday weather is salvaged as high pressure
builds out of eastern Ontario and western Quebec. Will still see
some gusty west-northwest winds...up to 20-25 miles per hour...but it will be milder.
Highs are forecast to reach the middle 60s to around 70.
Tuesday-Wednesday...another nice day on Tuesday as high pressure
starts to recenter off the middle Atlantic coast. Winds start to back to
SW by late in the day. Highs mainly in the Lower-Middle 70s...though
only in the 60s along the S coast. By Tuesday night...will see
some clouds increase as a warm front approaches. Have brought in
low chance probability of precipitation for Wednesday/Wednesday night and may even see a few
thunderstorms as warm front works across.
Thursday-Friday...much warmer air works in during this timeframe.
Any leftover scattered showers/thunderstorms will push out of the region during
Thursday...with more humidity working in as well. Expect highs both
days mainly in the 80s...except cooler along the S coast.
&&
Aviation /21z Friday through Wednesday/...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Overview...moderate confidence tonight and Sat.
Through 00z...
cold front and wind shift from south-southwest to west-northwest will slowly advance
eastward into eastern Massachusetts late today. Scattered showers with
isolated heavier rains across Rhode Island and eastern Massachusetts. Risk of thunderstorms is
very low. Ceilings were an even blend of metnam and nam12 guidance while
visibilities were a 50/50 blend of met and mav guidance. IFR confined to
southeast Massachusetts with MVFR elsewhere.
After 00z...
cold front over eastern Massachusetts will drift just offshore with all
terminals having a wind shift to the west-northwest. Scattered showers
across eastern New England with more widespread rains western New
England. IFR confined to southeast Massachusetts with MVFR elsewhere.
Sat...
widespread showers over western New England pivots into eastern
New England during the afternoon. Snow may mix in with the rain
across the higher terrain of western Massachusetts and southwest New Hampshire. Northwest
winds may gusts to 25 knots. IFR confined to southeast Massachusetts with MVFR
elsewhere.
Kbos terminal...wind shift from south to west-northwest between
19z-20z. Scattered showers mainly in MVFR. Sat...showers become
more widespread during the afternoon and winds increase up to 25
knots.
Kbdl terminal...scattered showers this evening become more
widespread tonight and Saturday. Mainly MVFR conditions. West-northwest winds
up to 25 knots tonight and possibly up to 30 knots Sat with MVFR
continuing.
Outlook...Saturday night through Wednesday...
Saturday night-Sunday...low to moderate confidence. Unsettled
pattern with variable conditions from VFR to MVFR-IFR conditions
in shra/fog. Low probability of isolated thunderstorm Sat night. Precipitation tapers off
from S-north during Sunday with general VFR conditions by late Sunday
though VFR ceilings linger Sunday night. May see patchy MVFR-IFR visibilities
in patchy fog Sun night.
Monday-Tuesday...high confidence. VFR. Low confidence on sea
breeze development. May see patchy fog with MVFR-IFR visibilities late
Monday night-early Tuesday morning.
Wednesday...moderate confidence. Mainly VFR. May see clouds/scattered
showers move in ahead of warm front with local MVFR conditions.
&&
Marine...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Tonight... large S swells continue on the southern Rhode Island and Massachusetts waters.
Otherwise a slow wind shift to west with frontal passage. West-northwest winds
may gusts up to 20 knots as low pressure develops near Nantucket. Showers
become more widespread as the night progresses. Forecast confidence
moderate.
Sat...low pressure tracks from Nantucket to Gulf of Maine. Northwest winds up
to 25 knots possible along with lingering S swells south waters of Rhode Island
and Massachusetts. Showers reduce visibility as well. Outlook...Saturday night
through Wednesday...
Outlook...Saturday night through Wednesday...
Moderate confidence through the period.
Saturday night-Sunday...surface low will linger across the eastern
waters Sat night...then shift slowly NE sun. Seas remaining above
5 feet. West-northwest winds will pick up...with gusts up to gale force mainly
on the southern waters to S and east of Nantucket. Kept gale watch
going there. Winds should diminish during Sun afternoon/night.
Monday...winds diminish below small craft. Seas remain at or above 5 feet
on the outer waters.
Tuesday...winds and seas remain below small craft.
Wednesday...S-se winds may see southeast winds pick up during the day with
gusts up to 20 knots. Seas may approach 5 feet on the southern waters.
&&
Hydrology...
discounted the GFS as it appeared an outlier with up to 4 inches
of rain in western Massachusetts and southwest New Hampshire. Model consensus of 12z
NAM/European model (ecmwf) and gefs suggest widespread 0.75-1.00 inch rainfall
across the entire region. Possibly up to 1.5 inches across I-91
corridor of western CT/Massachusetts into southwest New Hampshire given proximity to
comma head/trowal. Given this is spread out into Sun morning risk
of flooding is very low. Thus no headlines.
&&
Tides/coastal flooding...
East Coast of Massachusetts this weekend...
High astronomical tides this weekend. At Boston...a high tide of
11.9 feet will occur tonight at 11:21 PM and 12.2 feet early Sunday
morning at 12:12 am. Estofs indicating up to 0.5 feet surge which
seems reasonable. Despite the lack of much wave action could see
some minor inundation especially with the Sat night high tide.
Again very minor coastal flooding possible in the typically prone
location of eastern Massachusetts...ie morrissey Blvd in Dorchester.
Confidence not high enough to issue a coastal Flood Advisory
especially given a marginal event. Later shifts will have to
reevaluate the risk.
&&
Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...gale watch from Saturday afternoon through Sunday morning
for anz235-237-254>256.
Small Craft Advisory until 2 PM EDT Saturday for anz235-237-
250-254>256.
&&
$$
Synopsis...nocera/evt
near term...nocera
short term...nocera
long term...evt
aviation...nocera/evt
marine...nocera/evt
hydrology...nocera
tides/coastal flooding...nocera
