Area forecast discussion
National Weather Service Taunton Massachusetts
503 PM EDT Thursday may 23 2013
Synopsis...
a cold front will move slowly into New England Friday. Low
pressure will develop on this front...causing the system to linger
across the region through the weekend. This will bring showers and
cooler conditions...with a few thunderstorms possible. Some of the
rainfall will be heavy at times. Conditions should improve on
Monday. Dry weather and seasonable temperatures are expected into the
middle of next week.
&&
Near term /until 6 am Friday morning/...
numerous showers and isolated thunderstorms with locally heavy rainfall
moving NE across western new eng. Environment is marginally
unstable with MLCAPES around 500 j/kg while middle level lapse rates
are less than 6 c/km. Instability is a limiting factor for severe weather
despite 30-40 knots 0-6km shear. Near term forecast of significant
severe parameter also supports limited severe potential. Still cant
rule out an isolated severe storm...but heavy rainfall is primary
concern into this evening across the interior with precipitable waters near
1.7".
Tonight...cold front moves slowly east from central New York and
will approach western new eng toward daybreak as middle level trough
amplifies over the Great Lakes. Southern New England will be under the right entrance
region of the upper jet which will provide good forcing acting on
high precipitable water airmass to bring locally heavy rainfall to southern New England. Showers
and isolated thunderstorms will be ongoing across the interior in the
evening...then focus will shift to the coastal plain after
midnight as low level jet strengthens across southeast new eng.
Instability will be weakening overnight and even elevated
instability parameters are marginal. Still cant rule out isolated
thunderstorms given deep synoptic forcing...but lack of instability
should limit rainfall rates. Areas of urban and poor drainage
flooding likely overnight in eastern new eng.
&&
Short term /6 am Friday morning through 6 PM Friday/...
high amplitude trough forecast to close off over the middle Atlantic
region on Friday with southerly flow aloft. Surface low develops on
the front which will slow its eastward progress across southern New England. Low level
jet will be situated just east of Cape Cod in the morning with axis
of heavy rainfall confined to the cape/islands...before moving east
in the afternoon. However...showers will persist all day across
much of the region with deep moisture axis in place and surface wave
moving along frontal boundary. In fact...this has a winter look
to it with decent low level frontogenesis and deformation axis
setting up across western new eng northwest of surface low. Temperatures will
likely fall into the 50s over northwest higher terrain as front moves to
the east...but should reach well into 60s to around 70 across southeast
new eng which will remain east of the boundary for most of the day.
The front should reach the i95 corridor by late afternoon.
&&
Long term /Friday night through Thursday/...
highlights...
* slow moving upper level system will keep showers and cooler
temperatures for the weekend
* improvements begin on Monday...with drier but cool conditions
* moderating temperatures arrive by late next week
Overview and model preferences...
all operational models now on board with developing amplified
upper level pattern across the lower 48...with digging troughs on
the east and west coasts with building ridge across the central
U.S. Through a good portion of this period. 500 mb cutoff low develops
across the middle Atlantic then slowly moves into the region this
weekend...with surface low developing along slowly moving cold
front. Lowered confidence on timing the exit of the low...
however. By early next week...though...should see improving
conditions but cool temperatures. Temperatures start to moderate by middle week.
Went along with 12z GFS/00z European model (ecmwf) and their ensembles...which is
pretty close to the wpc guidance.
Details...
Friday night through Sunday...continued cloudy skies with showers
and cool temperatures will continue through most of the Holiday weekend.
Surface low pressure trapped with its upper level cutoff low will
slowly move across the region...with periods of heavy rainfall
anytime during this timeframe. Current quantitative precipitation forecast forecast suggests
possibility of 1-2 inches of general rain with the highest amounts
across the CT valley and SW New Hampshire. However...with the chance of
thunder...could see localized flooding especially across central
and western areas with good low level moisture inflow. Will
continue to monitor for potential of flooding along rivers and low
lying areas.
Temperatures will become rather chilly across S New Hampshire/west Massachusetts Sat night as low
pressure spins across east Massachusetts...with north-northwest winds in place. MOS guidance
suggests readings falling back to the middle-upper 30s across the
higher terrain. Can not rule out the remote possibility of some
mixing over the highest terrain of SW New Hampshire.
For now...looks like the low and upper level system will slowly
move NE during Sunday...but precipitation will linger into Sun night
before tapering off from SW-NE overnight sun. Daytime highs will
only be in the 50s through the weekend.
Monday...transition day as high pressure builds out of central Canada.
May still see some widely scattered showers across S New Hampshire/NE Massachusetts early but
will push NE. Will continue cool...but readings should reach the
60s.
Tuesday-Thursday...high pressure will shift to the middle Atlantic coast then
offshore during this timeframe. Expect a dry forecast with slowly
moderating temperatures.
&&
Aviation /20z Thursday through Tuesday/...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Overview...moderate confidence.
Variable MVFR/IFR ceilings this afternoon will trend to widespread
IFR/LIFR tonight into Friday with areas of fog developing. Showers
and scattered thunderstorms CT valley and western new eng this afternoon will
expand east across rest of southern New England tonight into Friday...with focus for
heavy rainfall shifting to the coastal plain late tonight and Friday
morning. Localized low level wind shear possible late tonight cape/islands as low level jet
strengthens across the region.
Kbos terminal...moderate confidence. Expect lowering ceilings to IFR
tonight with showers increasing. Scattered thunderstorms possible.
Kbdl terminal...high confidence. Widespread showers and a few
thunderstorms this afternoon and evening.
Outlook...Friday night through Tuesday...
Friday night through Sunday...low to moderate confidence. Very
unsettled pattern with variability between VFR conditions and
MVFR/IFR conditions in rain showers/scattered tsra/fog. Improving conditions
during Sunday night from SW to NE.
Monday-Tuesday...moderate to high confidence. VFR. Low probability of
MVFR ceilings across S New Hampshire/north Massachusetts early Monday then improving. Low
confidence on sea breeze development.
&&
Marine...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
High confidence through Friday.
Low level jet will bring near Small Craft Advisory gusts on the waters through
tonight...diminishing west of the canal later tonight as the low level jet
moves to the east. Strong low level inversion will limit gusts so
gales not expected. Persistent SW flow will result in building
seas through Friday. Winds will diminish on Friday as the low level jet
moves east of the waters. Expect low visibilities in fog and locally heavy
showers. Isolated thunderstorms are also possible.
Outlook...Friday night through Tuesday...
Friday night...low to moderate confidence. Low pressure and cold front
will slowly cross the waters...then stall along the eastern near
shore waters. Expect SW gusts up to 20 knots early...then will
diminish. Low probability for thunder. Areas of low visibilities in heavier
showers and patchy fog. Seas will remain at or above 5 feet mainly over the
open waters.
Saturday-Sunday...low confidence mainly for timing. As low pressure
stalls across east Massachusetts/mass Bay...will see light/variable winds except
north-northwest over the western waters later Sat...which will shift toward
the eastern waters during sun. Seas remain high. Low chance of
thunderstorms Sat-Sat night. Low probability of gusts up to 25 knots sun.
Monday-Tuesday...low to moderate confidence. Winds become west with
gusts up to 20 knots Monday...then diminish Monday night-Tue. Seas around 5
feet on the outer waters Monday...then subsiding.
&&
Tides/coastal flooding...
Rhode Island South Coast this evening...
a moderately strong southerly fetch of surface wind and increasing
low level jet is expected to drive enough water into Narragansett
Bay for a surge around or even just above a foot at the time of
the evening high tide...about 2330z. This will be on top of a
particularly high Spring tide. Both the estofs and etss surge
guidance depict essentially no surge this evening but seems like
too much of a S to SW wind to avoid some surge...and at 15z pvd
was already showing a .4 feet surge and climbing. In addition...
shoreline flooding could be exacerbated some by any heavy rain
producing fresh water runoff that struggles to drain at the
shoreline during high tide.
East Coast of Massachusetts this weekend...
astronomical high tides will occur this weekend into early next week.
With surface low wobbling over southern New England Saturday and
into Sunday...expect gusty northerly to northwest winds especially
during the daytimes hours. At Boston...a high tide of 11.9ft will
occur on Friday night at 11:21 PM and 12.2 feet early Sunday
morning at 12:12 am. Expect a light southerly winds during the
Friday high tide so this is less than a concern. Looking at the
Sunday morning high tide...northerly to northwesterly winds may
help increase the surge especially for Cape Cod Bay. Right now
only expect minor splashover across north facing beaches. Will
need to continue to monitor and update with the latest forecast
guidance.
&&
Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...coastal Flood Advisory until 9 PM EDT this evening for riz002-
004>007.
Marine...Small Craft Advisory until 10 am EDT Friday for anz232.
Small Craft Advisory until 6 am EDT Friday for anz233-234.
Small Craft Advisory until 10 PM EDT this evening for anz230-
236.
Small Craft Advisory until 4 am EDT Friday for anz231-251.
Small Craft Advisory until 6 PM EDT Friday for anz235-237.
Small Craft Advisory until 8 PM EDT Friday for anz250.
Small Craft Advisory until 6 am EDT Saturday for anz254>256.
&&
$$
Synopsis...kjc/evt
near term...kjc
short term...kjc
long term...evt
aviation...kjc/evt
marine...kjc/evt
tides/coastal flooding...Thompson
