Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
344 am EDT Sat Jul 26 2014

high pressure south of New England will provide dry and warm weather
today. Low pressure developing over southeast Canada will result in
scattered showers and thunderstorms at times late tonight into
Sunday as its attending warm front approaches. A cold front then
swings across the region Monday bringing more showers and
thunderstorms. The front then lingers east of the Massachusetts
coast through Friday.


Near term /until 6 PM this evening/...
a low amplitude short wave ejects southeast from the Great Lakes
into New England today. Moisture and instability are limited with
this feature so just expected some cloudiness given the weakly
cyclonic middle level flow. Thus a mix of sun and clouds today. BUFKIT
soundings indicate mixing layer will extend up to 800 mb along with
850 temperatures around +12c. Therefore highs in the low to middle 80s seems
reasonable. A few degrees cooler along the South Coast with south-southwest wind
trajectory off the ocean. However with tide gages and buoys
indicating water temperatures in the l70s even south coastal beaches will
be near 80 degrees despite onshore winds.

Despite the warm temperatures it will be somewhat comfortable with dew points
in the u50s to l60s. In addition a modest SW breeze of 15 to 20 miles per hour
will help take some of the edge off the warm temperatures. Overall nice
weather for any/all outdoor activities.


Short term /6 PM this evening through 6 PM Sunday/...


Quiet/dry weather prevails much of the night. However low pressure exits
the Great Lakes and reorganizes over southeast Canada. Its attending
warm front approaches the region from the southwest toward morning.
Patchy fog and low clouds will likely develop before sunrise Sunday
ahead of the front across portions of southern New England. Greatest
risk of showers and T-storms will be over western portions of CT/Massachusetts
and toward daybreak Sunday. It will be a mild night given south-southwest winds
advecting higher dew pt air into the area.


Models struggling with location and timing of warm sector Sunday.
00z European model (ecmwf) and 00z gefs indicating better instability/warm sector
airmass across eastern New York and western New England with less
instability over Rhode Island and eastern Massachusetts. This is likely due to warm
frontal clouds and precipitation lingering across this region. At this
time range looks like a period of warm frontal convection during the
morning followed by a risk of strong thunderstorms later in the day across
western New England given magnitude of instability and deep layer
shear. Of course this is pending partial clearing across western New

As for the morning and early afternoon could be an active warm
frontal passage as models suggest modest synoptic scale lift
/mid and upper level q-vector convergence/ combined with deep layer
moisture and instability. Qg forcing will be enhanced as lfq of
upper level jet streak moves across southern New England. Too early
for more details given model spread here on handling warm frontal

Nevertheless noticeably more humid as dew points climb into the 60s.


Long term /Sunday night through Friday/...

Big picture...

One thing can be said about the upcoming week: any Pacific weather
will be reaching the Atlantic via the Scenic Route. Deep troughs
over the Gulf of Alaska and eastern North America. Meanwhile upper
ridges rebuild over western North America and the west Atlantic. A
shortwave moving through this flow merges with the eastern no-am
trough Sunday and swings its energy across New England Monday.
Another shortwave over the Canadian Arctic drops south into the
trough and maintains its position to our west through midweek. The
trough ejects north through Quebec late in the week...but less well
defined low pressure remains over eastern North America at week/S
end. This means that the upper flow along the East Coast
will remain S-SW to north-NE through the week.

The mass fields and thermal fields of the GFS and European model (ecmwf) look similar
in overview. Some differences in details emerge Thursday-Friday. The
similarity builds confidence in the overall flow of the forecast.
The longer range differences in detail support using a blend of the
forecast data.

The dailies...

Sunday night-Monday... shortwave moves through the Great Lakes
Sunday night with supporting 100-knot jet. This approaches the coast
overnight supporting increased upper venting/lift. Meanwhile 30-40
knot southwest low level jet feeds moisture up the coast along with
low level isentropic lift. Will build probability of precipitation overnight across all of
the forecast area with peak values in the likely range. On Monday
with upper jet nose over the region and cooling temperatures aloft as the
trough moves into New England...expect sufficient destabilization
for a second round of precipitation/convection especially in the afternoon
north and west of I-95.

Precipitable water values reach 1.75-2 inches Sunday night...and
should linger near 1.5 inches Monday. Potential for locally heavy
downpours/poor drainage flooding.

Shortwave lifts north Monday night. Surface reflection of this
feature also pulls north/northeast. Models show this surface low
pulling the cold front through our area Monday afternoon/early
night. So precipitation should diminish Monday night.

Tuesday... second shortwave deepens the main upper trough to our
west. This will also hold the upper jet in place with entrance
region over New England. Continued cooling aloft. Low
confidence...but enough factors in favor of showers/thunderstorms to
maintain chance probability of precipitation in southern New Hampshire/eastern mass where the upper dynamics
are best.

Wednesday through Friday... with the trough and Atlantic ridge
remaining in position...expect the cold front to linger east of our
area with showers over the ocean. On Friday as the bulk of the
trough lifts north through Canada leaving a much weaker upper flow
over eastern North America...expect the Ocean Ridge to nudge
westward and shift the upper flow west. This will bring the stalled
front closer to the coast and bring an increased chance of showers
to the cape and islands...possibly to the coastal plain. Will show
chance probability of precipitation in these areas on Friday.


Aviation /08z Saturday through Wednesday/...
forecaster confidence levels...

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

2 am update...

Ceilings and visibilities mainly a blend of GFS and its mavmos output.

Short term /today through Sunday/...high confidence through
this evening then lowering confidence late tonight into Sunday on
specific timing of lower ceilings/visibilities associated with

Through 12z...dry weather along with VFR conditions. Exception will
be in a few spots inland where patchy ground fog possible.

After 12z...dry weather continues along with VFR conditions. SW
winds 15-20 knots with a few gusts up to 25 knots possible over
southeast Massachusetts this afternoon.

Tonight...dry with VFR to start then lowering to marginal VFR/MVFR
toward morning along with a low probability of IFR ceilings well inland.
Scattered showers and T-storms enter western New England late.

Sunday...marginal MVFR/VFR in scattered showers and T-storms...
most numerous in the morning.

Kbos taf...high confidence through this evening then lower
confidence on exact timing of showers/T-storms late tonight into
Sunday. Modest SW wind today with speeds of 15-20 knots.

Kbdl taf...high confidence through this evening then lower confidence
on exact timing of showers/T-storms late tonight into Sunday.

Outlook...Sunday night through Wednesday...moderate confidence.

Sunday night-Monday... VFR but with areas of MVFR in showers/tstms.
Areas of IFR/LIFR in late night/early morning fog especially along
the South Coast.

Tuesday...VFR but with scattered MVFR in showers/thunderstorms mainly southern
New Hampshire and eastern mass.



forecaster confidence levels...

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

Short term /today through Sunday...high confidence today into
this evening and then diminishing later tonight into Sunday
regarding timing and areal coverage of showers/T-storms.

Today...another nice boating day with dry weather and good visibility.
Only wrinkle will be modest SW winds 15-20 knots with a few gusts
near shore possibly approaching 25 knots. Held off on a Small Craft
Advisory as most locations will have winds less than 25 knots.

Tonight...quiet to start but an approaching warm front will lead to
patchy fog/low clouds reducing visibility toward daybreak Sunday. Low risk
of showers/T-storms toward sunrise Sunday.

Sunday...SW winds 15-20 knots with a low risk of gusts to 25 knots. Scattered
showers/T-storms possible as well. Today definitely the better of
the two weekend days.

Outlook...Sunday night through Wednesday...moderate confidence.

Sunday night-Monday...increasing southwest winds especially on
Monday as a cold front approaches. Winds may reach 25 knots at
times. The steady southwest flow should build seas with 5-8 feet on
the exposed waters. Warm humid air over the waters will lead to low
visibilities in areas of fog. Showers and thunderstorms possible with gusty
winds and locally heavy rain. A Small Craft Advisory may be needed
during this period.

Tuesday...the cold front moves across the eastern waters with a
continued chance of a shower/thunderstorm. Winds will be lighter
than Monday...staring southwest and eventually shifting to
northwest. Continued 5-6 foot seas on the outer waters. A Small
Craft Advisory may be needed on some of the waters.

Wednesday...lighter winds and seas as high pressure builds over the


Box watches/warnings/advisories...
New Hampshire...none.
Rhode Island...none.


near term...nocera
short term...nocera
long term...wtb

National Weather Service Glossary of Abbreviations