Area forecast discussion
National Weather Service Taunton Massachusetts
1023 PM EDT Monday may 20 2013
Synopsis...
a backdoor cold front will drop south across the region late
tonight and Tuesday resulting in briefly cooler weather across
eastern New England and chance of thunderstorms in western new
east-northeast. Warm and humid conditions return Wednesday and Thursday with
scattered showers and thunderstorms. A cooler and less humid air
mass is expected for the coming weekend.
&&
Near term /until 6 am Tuesday morning/...
1015 PM update...finally got a strong enough updraft in an
isolated convective cluster east of Chatham Massachusetts to produce a few
lightning strokes. This cell was moving southeast across the
coastal waters. Elsewhere across our region...thinking isolated
showers with areas of fog should cover the rest of tonight.
Otherwise...just tweaked forecast temperatures and dew points to
bring them back in line with observed trends. Dense fog advisory
continues.
Previous discussion...
Tonight...warm front will begin to move back S as a backdoor late
tonight and should move into NE zones by daybreak. Cant rule out a
few showers...especially north zones but most of the night should be
dry. Continued SW flow near the S coast will keep abundant low
level moisture in place and expect areas of fog to develop again
tonight. Fog bank sitting over ack to near bid and this will move
onshore tonight so we issued a dense fog advisory along the S
coast. The fog may spread further north overnight but highest
probability of visibilities 1/4sm or less will be along the S coast.
Relatively mild night with lows holding in upper 50s/lower 60s.
&&
Short term /6 am Tuesday morning through Tuesday night/...
Tuesday...
position of the backdoor front will determine temperature
variability across southern New England and where best chance of convection will be.
We followed NAM solution which typically handles the location of
these shallow fronts due to its higher resolution. This suggests
front will make it as far west as central Massachusetts to Rhode Island. Large temperature
gradient is expected across southern New England with maxes ranging from the 60s east
coastal Massachusetts through southeast New Hampshire...to the middle 80s lower CT valley.
Airmass expected to destabilize across western new eng which will
remain west of the boundary...with convective available potential energy increasing to 1000-2000
j/kg. GFS and European model (ecmwf) show very favorable middle level lapse rates
approaching 7 c/km. Best deep layer shear will be in the cooler
more stable airmass to the NE with the gradient lying across
central and western new eng...but magnitude will approach 30 knots
in the unstable air. Expect scattered thunderstorms to develop west of the
boundary and cant rule out a few strong to severe storms...closer
to CT valley and Berkshires where best instability is located.
Tuesday night...
the backdoor front will begin to move back northward as a warm front
and will approach NE zones toward daybreak. More low clouds and
areas of dense fog are expected...especially near the coast.
Strong convection may linger into the evening...otherwise models
are showing enough elevated instability to keep the threat of
a few showers or an isolated thunderstorm through the night.
&&
Long term /Wednesday through Monday/...
highlights...
* scattered showers and thunderstorms possible Wednesday-Thursday
* cooler...less humid for the weekend
Models are in decent agreement through much of the long term.
There are some timing discrepancies throughout the long term
between the European model (ecmwf) and the GFS. The GFS is about 12 hours slower
with moving a cold front through southern New England late
Thursday into Friday. However...the overall synoptic pattern is
fairly well in line throughout the period. Generally expecting a
more unsettled but warmer pattern through the end of the work
week...with quieter but cooler weather into the weekend.
Wednesday and Thursday...low pressure moving through the Great
Lakes and into southern Quebec will bring a warm front north
through southern New England Wednesday. In the warm
sector...850mb temperatures up to 15-16c will result in temperatures
around 80 degrees both days. Plenty of moisture in the region with
dewpoints in the 60s and precipitable waters more than twice that of normal.
Along with the above...there is enough instability that showers
and thunderstorms should develop during the peak heating afternoon
hours. The best instability is over the western portions of the
area Wednesday and anchored more over all of southern New England
on Thursday...so am expecting thunderstorms to be more widespread
and organized on Thursday. With the precipitable waters as high as they
are...expect heavy rain with any shower or thunderstorm that
develops.
Friday...a cold front will move through southern New England
sometime on Friday...with the European model (ecmwf) bringing it through the area
between midnight and 6 am and the GFS bringing it through about
midday. This is a change from yesterdays model runs where the GFS
was faster with the timing so theres still quite a bit of
uncertainty with the timing. This will have a large impact on the
weather as mostly cloudy skies and warmer...more humid air can be
found ahead of the front while clearing skies and cooler...less
humid air will move in behind the front. If this occurs during the
early morning...high temperatures will be lower but the area will
see more sun...while if it doesn/T occur until midday could see
warmer highs but less sun and possibly some lingering showers and
thunderstorms.
Saturday through Monday...with high pressure dominant over southern
New England...expect a pleasant period with high temperatures a few
degrees below normal and sunny skies.
&&
Aviation /02z Tuesday through Saturday/...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Overview...moderate confidence in timing and areal coverage of
stratus and fog tonight into Tuesday morning.
VFR conditions are in place across much of southern New England.
IFR conditions extending south and east from kbid-kfmh-khya-kcqx.
Still expecting these IFR conditions to spread northward across
the south coasts of Rhode Island/Massachusetts as low clouds and fog move onshore.
Eventually the clouds and fog will spread even farther inland
tonight. However...highest probability for IFR conditions is along
the South Coast.
Tuesday...conditions should improve to VFR west of kmht to korh
to kijd line /CT valley/...low clouds/fog will keep areas east of
that line in MVFR/IFR. Showers and thunderstorms are possible
across the CT valley during the afternoon.
Tuesday night...widespread IFR/LIFR in stratus and fog redevelop.
Kbos terminal...moderate confidence. Showers in the vicinity of
the terminal through 02z. Expect ceilings/visibilities to lower to IFR later
tonight. Slow improvement to MVFR Tuesday.
Kbdl terminal...moderate confidence. Expect ceilings to lower tonight
with IFR possible late tonight...improving to VFR around midday.
Outlook...Wednesday through Saturday...
Wednesday through Thursday night...low to moderate confidence.
Very unsettled pattern with variability between VFR conditions and
MVFR/IFR conditions in shra/tsra/fog.
Friday...moderate confidence. Conditions should improve to VFR
from west to east as cold front moves through region.
Saturday...high confidence. VFR.
&&
Marine...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
High confidence through Tuesday night.
Winds expected to remain below Small Craft Advisory through Tuesday night. May see
brief east/NE gusts to 20 knots late tonight over NE Massachusetts coastal waters
as the backdoor front moves through. Expect mostly easterly winds
over the eastern Massachusetts coastal waters through Tuesday night and SW winds
over the S coastal waters as the front will bisect the waters.
We followed Swan guidance for sea forecast which is handling swell
better than wnawave guidance. Expect marginal Small Craft Advisory swell to 5 feet
over the open S coastal waters tonight subsiding Tuesday.
Expect areas of dense fog tonight into Tuesday with persistent SW
flow...especially over the S coastal waters.
Outlook...Wednesday through Saturday...
Wednesday...seas increase as high pressure moves away from the
waters. Southwesterly winds gust to near 25 kts. Small Craft Advisory will be
necessary for seas if not winds as well. Visibility may be
limited at times in scattered showers and thunderstorms.
Thursday...seas remain above 5 feet as low pressure moves into
the Maritimes and a cold front approaches the waters.
Southwesterly winds gust to near 25 kts. Small Craft Advisory will be necessary
for seas if not winds as well. Visibility may be limited at times
in scattered showers and thunderstorms. Winds increase overnight
with approaching cold front.
Friday...seas begin to diminish after a cold front crosses the
waters and high pressure builds over the waters. Winds increase
to 25kts with cold frontal passage. Winds should be out of the
southwest ahead of the front...shifting to the northwest behind
the front.
Saturday...high pressure continues to build over the waters
resulting in seas remaining below 5 feet. Winds less than 10 kts
starting out of the north and then variable.
&&
Box watches/warnings/advisories...
CT...none.
Massachusetts...dense fog advisory until 10 am EDT Tuesday for maz020>023.
Dense fog advisory until 10 am EDT Tuesday for maz024.
New Hampshire...none.
Rhode Island...dense fog advisory until 10 am EDT Tuesday for riz006>008.
Marine...Small Craft Advisory for hazardous seas until 2 am EDT Tuesday
for anz235-254.
Small Craft Advisory for hazardous seas until 8 am EDT Tuesday
for anz255-256.
&&
$$
Synopsis...kjc/rlg
near term...Belk/kjc/rlg
short term...kjc
long term...rlg
aviation...kjc/rlg
marine...kjc/rlg
