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Area forecast discussion 
National Weather Service Taunton Massachusetts
705 am EDT Tuesday Mar 31 2015

Synopsis...
a quiet weather day is followed by a chance for rain/snow across
the South Coast overnight. Warmer temperatures Thursday and
especially Friday ahead a cold front. Low pressure develops along
the cold front Friday night and moves across the region by early
Saturday bringing locally heavy rain showers. Mainly dry and much
colder Sunday. Still cool with a chance of a rain or snow shower
on Monday.

&&

Near term /until 3 PM this afternoon/...
7 am update...

Made minor upward adjustments to temperatures based on current
observations and sped up the onset of increasing clouds. Otherwise
current forecast is right on track. A few low and middle clouds
continued across the northwest portion of the region early this morning
in association with a cold front that was passing through. Dry
weather will prevail into the middle-afternoon hours. The cold
advection associated with the front will lead to falling 850 mb
temperatures...preventing daytime highs from reaching seasonal normals.
Mainly the middle-upper 40s across the region. Clouds increase from
the west later this morning and early afternoon.

&&

Short term /3 PM this afternoon through 6 PM Wednesday/...
this evening and overnight...
a fast moving clipper with cp origins will be riding stalled
baroclinic zone S of the southern New England waters during the early
overnight hours. At odds in the last couple of days is how far north
the precipitation shield associated with this clipper will reach.
Yesterday/S runs were offshore. Tonight...a shift back to the
north...even in available mesoscale-scale guidance. Note a modest low-middle
level f-general axis which is supported by BUFKIT profiles as a channel
of negative Omega between 800 mb and h6. Dry air will be entraining
into the low-levels from the north through the same period.

Given these factors...looks like a light precipitation shield will slowly
move across the region from SW then due east through the evening-
overnight. At this time...it looks like the dry air wins anywhere
S of a line drawn across the CT/Rhode Island border with Massachusetts and southeast Massachusetts. The
closer to the coast that one gets...the better chance for more
steady precipitation...so it/S likely some areas toward the edge of the
shield receive sprinkles/flurries at best.

Regarding p-type...low-lvl temperature profiles suggest mainly a rainy
start in CT this evening...gradually transitioning to a mix of
rain/snow as the precipitation shield shifts east. There is some moderate
lift within the dendrite zone aloft...so it/S possible the change
over to snow could occur faster in areas of heavier precipitation thanks
to dynamic cooling. Otherwise...expect a change to light snow
before ending. Accums will be light to none...and mainly on grassy
sfcs.

Wednesday...
cold advection and high pressure follows the developing clipper
offshore. Skies clear...but with 850 mb temperatures falling back to -8c to
-10c suspect another day where high temperatures remain below seasonal
normals. Mainly low-middle 40s expected...breezy with wind gusts
around 20 miles per hour at times.

&&

Long term /Wednesday night through Monday/...
highlights...

* temperatures rising to near normal Thursday and above normal Friday
* storm system brings showers Thursday night into early Sat...

Wednesday night...high pressure centered off the middle Atlantic
coast will ridge northward across southern New England providing
clear skies and cold temperatures. Lows in the 20s.

Thursday...temperatures begin to moderate as high pressure moves
offshore and low pressure moves across Ontario. Southwest flow
will boost temperatures to near normal levels...in the lower 50s
except cooler on the cape and islands. Low level jet will increase
late in the afternoon...reaching 50 knots at 925 mb. At the
surface...expect winds to gust to 20-25 miles per hour toward evening.

Thursday night and Friday...a cold front moves eastward into
southern New England and stalls somewhere across the interior.
There are timing differences in the models...with the GFS fastest
and European model (ecmwf) slowest. Nevertheless...it will be a cloudy period with
a good chance of showers. The showalter index drops to below zero
Thursday night but other parameters are not favorable for convection...
so will not mention any elevated thunder at this time.
Temperatures will hold in the 40s Thursday night...and despite
cloudiness..should rise to actual springlike readings...in the
lower 60s Friday (upper 40s to middle 50s cape and islands) as 850 mb
temperatures rise to near +10c. GFS mex guidance actually gives 66 for
bdl Friday but with cloudy skies and scattered showers...have held
close to previous forecast of lower 60s.

Friday night into Saturday...a low pressure storm system is
forecast to move eastward from the Ohio Valley and intensify along
the stalled front as it reaches southern New England. The main
impact will be a widespread rainfall of about 0.5 inches...but
there is the potential for pockets of 1 inch of rain. The GFS
strengthens the low to 995 mb and has it moving into the Gulf of
Maine with enough precipitation wrapping around to cause a
changeover to snow in northwest portions of Massachusetts. The European model (ecmwf) has
trended colder...but not that cold. Yesterday it had an intense
storm over northern Vermont and this morning/S run has it over
southeast New Hampshire...closer to the GFS solution. However...
any leftover snow would be confined to areas north and west of our
forecast area. That is how we currently played this. The
precipitation clears out by about noon on Saturday. Highs mainly
in the 40s.

Sunday...mainly sunny and dry but much colder with highs only in
the lower to middle 40s...below normal again. Cannot rule out a brief
passing flurry in the morning as a weak upper disturbance passes
through.

Monday...a warm front approaches the region in association with
low pressure moving through the upper Midwest and lower Great
Lakes region. This could bring another chance of rain...or
possibly mixed precipitation in northern Massachusetts...by late Monday.
The European model (ecmwf) implies that this could be a long duration event into
the middle of next week because strong high pressure builds into
northern New England from Canada. A lot will depend on the
orientation of that high. Anyway...that is a whole week away.

&&

Aviation /12z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through Wednesday/...

Through today...high confidence.
Mainly VFR. Expect increasing clouds late this morning and early
this afternoon with some west winds gusting to 20+ knots at times
especially east Massachusetts.

This evening and overnight...moderate confidence.
A mix of MVFR/VFR conditions in light rain/snow especially S of an
hfd-ijd-pym line. VFR to the north. Conditions improve during early
morning hours. Any snow accums will be light...and mainly on grass
rather than runways.

Wednesday...high confidence.
Mainly VFR.

Kbos taf...high confidence in taf.

Kbdl taf...moderate confidence in taf...at issue is the chance for
a window of MVFR conditions this evening.

Outlook...Wednesday night through Saturday...

Wednesday and Thursday...high confidence. VFR. Gusty southwesterly
winds are possible Thursday.

Thursday night and Friday...moderate confidence. VFR becoming
MVFR ceilings and visibilities in showers. Low level wind shear expected
throughout the region with southerly surface winds 10-20 knots
increasing to southwesterly at 55-65 knots at 5000 feet.

Friday night into Sat morning...high confidence. MVFR and IFR
conditions in widespread showers. Areas of fog.

Saturday afternoon...high confidence. VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /today through Tuesday/...high confidence.

7 am update...
have lowered small craft advisories for mass Bay...Ipswich
Bay...Cape Cod Bay...and Nantucket Sound as winds have diminished
to about 20 knots or less. As seas gradually diminish offshore
today...the remaining small craft advisories will likely be
allowed to expire.

Tonight into tomorrow...
low pressure will slide S of the waters. Winds will shift from the west
to north early Wednesday morning with gusts increasing as they shift with
gusts around 25 knots possible. Seas also increase such that 5-7 feet
seas are possible during the day on Wednesday. Therefore...after a
brief lull today...small craft advisories are likely needed late
tonight...but with ongoing headline will hold off for now

Outlook...Wednesday night through Saturday...

Wednesday night and Thursday...seas diminish as high pressure
builds over the waters. Northwesterly winds shift to the southwest
diminishing through the period. Occasional 25 knots gusts are
possible on the outer waters at times.

Thursday night through Saturday...seas increase ahead of a cold
front which stalls over southern New England...and then as a
storm system develops along the front and moves into the Gulf of
Maine. Southwesterly winds 15 to 25 kts with gusts to 30 kts
throughout the period...shifting to the to the northwest Saturday
morning. Small craft advisories are likely for both winds and
seas at least on the outer waters...if not on the interior bays
and sounds at times. Low probability of a gale force gust or two
over the outer waters.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 2 PM EDT this afternoon for anz235-
237.
Small Craft Advisory until 8 PM EDT this evening for anz250-
254-255.
Small Craft Advisory until 5 PM EDT this afternoon for anz256.

&&

$$
Synopsis...doody/gaf
near term...doody/gaf
short term...doody
long term...gaf
aviation...doody/gaf
marine...doody/gaf

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