Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
345 am EDT Tuesday Apr 28 2015

the cool conditions today give way to warmer conditions by
Wednesday. After the rain ends this morning dry weather prevails
through middle week. Coastal low pressure will pass south of New
England Friday and Saturday. This may come close enough to spread
rain into the coastal plain. High pressure then brings dry weather
to the region Sunday and Monday.


Near term /until 6 PM this evening/...
current observation suggest that backdoor cold front is draped from northwest Massachusetts
through to the southeast coastline and continuing to shift to the south-southwest
this morning. This is combined with kicker upper level shortwave
which will finally shift the cutoff vortex which has so defined
our weather lately to the east. Last of the remnant column moisture
is currently begin squeezed out with these two
mechanisms...culminating in an area of rain across east Massachusetts and Rhode Island.
These too should gradually diminish and shift to the S as the
front moves and the upper level shortwave shifts further offshore.

The north-northeast winds...with a bit of a draw off the cool waters of the
Gulf of Maine...combined with leftover clouds wrapping around the
cutoff to the east will keep conditions generally near or slightly
below normal today. Although do expect to see some clearing this
afternoon thanks to some modest mesoscale-ridging between a secondary
cutoff developing to the west. Given that 850 mb values run fairly close
to 0c...highs in the upper 50s and low 60s sound reasonable. This
same mixing will allow for some gusty winds at times. With gusts
mainly 20-25 miles per hour. This may lead to marginal fire weather
concerns...see below for details on this.


Short term /6 PM this evening through 6 PM Wednesday/...
expect some gradual clearing across the region as a weak ridge of
high pressure gains control of the region. Mass fields do show a
modest pressure gradient remains in place across the region which is
likely to mitigate radiational cooling. Dewpoints too...are likely
to rebound back into the upper 30s and low 40s without diurnal
mixing so will likely see lows only dropping into the low-middle 40s.

high pressure remains in control. Winds shift mainly northwest as the
Ridgeline shifts to the east. The caveat will be near shore locations
which are likely to experience sea breezes thanks to a weak pressure
gradient. 850 mb temperatures are likely to reach about +4c...but its
possible that some areas mix higher. Therefore...with a west
component...some highs on Wednesday could reach the low 70s in typically
warmer spots /CT valley/ to the middle and upper 60s elsewhere. The
sea breezes will keep coastal locations cooler though...mainly in
the 50s along the immediate coastline. Yet one more shortwave
associated with the cutoff to the east will be rotating through
during the afternoon...but suspect little fanfare except
increasing clouds from the north given the drier air moving in under
the west component to the flow.


Long term /Wednesday night through Monday/...
big picture... upper trough remains over the eastern USA during the
latter half of the week. Upper ridge then builds east and brings
drier more seasonable weather Sunday and Monday.

Long range guidance is similar in general pattern but differs in
detail on Friday and Saturday. The 00z GFS is slower/farther west
with the closed upper low drawing a coastal surface low up the
coast. The 12z European model (ecmwf) is faster/farther east by roughly 9 hours.
This difference brings two different projections for our area with
the GFS spreading rain and northeast wind into Rhode Island and eastern mass
while the European model (ecmwf) keeps most everything offshore. The European model (ecmwf) solution
shows a mainly Friday storm while the GFS solution shows a Friday
night/Saturday storm.

The GFS seems an outlier compared with the European model (ecmwf) op and European model (ecmwf)/GFS
ensembles. Rather than use our usual blend...we used an adjusted
blend that leans toward the European model (ecmwf).

The dailies...

Wednesday night-Thursday... weak Canada high pressure over the
region should keep the weather dry. Dewpoints will be either side
of 40 degrees. Light east flow will keep daytime temperatures coolest along
the coast with warmer temperatures inland. Mixing depths inland will reach
850-900 mb. Dew points and partial sky cover suggest min temperatures in
the 40s. Mixing temperatures suggest maximum surface temperatures 50s coast and 60-65

Friday-Saturday... surface low pressure moves out of the Gulf of Mexico
Wednesday and up the Carolina coast Thursday. The faster European model (ecmwf)
solution keeps most precipitation offshore but grazes the South Coast. Precipitation
moves offshore Friday night. We show slight chance probability of precipitation for all of
southern New England Friday but limit chance values to Rhode Island and
southeast mass. The GFS precipitation field is similar but slower and extends
a little farther north. With the faster timing...expect partial
clearing Saturday. Moisture profiles do show some lingering moisture
around 850 mb is more shallow than on previous days...but enough to
suggest some sky cover. Clouds and northeast flow should keep day
temperatures in the 50s Friday...breaks of sun and deeper mixing should
allow Saturday temperatures to reach 50s east and 60-65 west.

Sunday-Monday... high pressure builds over the region and should
trend US toward partial clearing. Building heights and a
developing southwest flow late Sunday and Monday would bring back
seasonable or seasonably mild temperatures these two days. Mixing both
days should reach at least 900 mb...which support at least 65-70
Sunday and 70s Monday.


Aviation /07z Tuesday through Saturday/...
forecaster confidence levels...

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

Through 12z...high confidence.
Mainly VFR for areas west of a line from ijd-orh-mht. A mix of
MVFR/VFR for areas east as rainfall continues through about 10z.
Winds shift to the north-northeast...with gusts increasing to around 25 knots.

Tuesday...high confidence.
Low-end VFR with some MVFR ceilings early becoming scattered. Wind gusts
drop to mainly 15-25 knots through the day.

Tonight and Wednesday...high confidence.
VFR. Increasing middle-low VFR clouds build in from the north during the
day. Low chance for a sprinkle.

Kbos taf...high confidence in taf.

Kbdl taf...high confidence in taf.

Outlook /Wednesday night through Saturday/...moderate confidence.

Friday...low-moderate confidence. VFR...except areas of MVFR in
showers in Rhode Island and southeastern mass. Northeast wind gusting 20-30
knots Cape Cod and islands...15-20 knots Boston and Providence.

Saturday...VFR. Moderate confidence. North-northeast wind below 20


forecaster confidence levels...

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

Short-term /through Wednesday/...

Today and tonight...high confidence.
Will experience north-northeast flow with gusts around 25-30 knots at times
through the morning...then diminishing this afternoon. A
developing swell in the Gulf of Maine will lead to seas building
5-8 feet mainly on the east waters...which will take into the overnight
hours and early Wednesday to subside. Therefore...will continue small
craft advisories...with the expectation that those along the S
coast can be dropped this afternoon as winds diminish.

Wednesday...high confidence.
Mainly quiet boating weather expected.

Outlook /Wednesday night through Saturday/...

Coastal low pressure moving up from the Gulf of Mexico passes south
of the waters Friday. Northeast winds on this side of the low will
bring building seas Friday and Saturday. Seas will build to at least
5 to 10 feet on the exposed waters...possibly a little higher east
and southeast of Cape Cod. Northeast winds 20-25 knots Friday and
Saturday. Uncertainty in the track and resulting effects so
confidence is lower than moderate. A Small Craft Advisory may be
needed those two days.


Fire weather...
north-northeast sustained winds will be mainly around 15 miles per hour /except stronger
on the islands/ with gusts up around 25 miles per hour. A few gusts to 30 miles per hour
possible. This will combine with min relative humidity values in the afternoon of
30-40 percent. However...the combination of some light rainfall
this morning...marginal relative humidity values and relatively cool temperatures
mitigate the risk somewhat. Therefore...marginal fire weather will
be observed today...but there are some limiting no
headlines will be issued.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory until 5 PM EDT this afternoon for anz231-
Small Craft Advisory until 2 PM EDT this afternoon for anz230-
Small Craft Advisory until 8 am EDT Wednesday for anz250-255.
Small Craft Advisory until 8 PM EDT this evening for anz251.
Small Craft Advisory until 11 am EDT Wednesday for anz254.


near term...doody
short term...doody
long term...wtb
fire weather...staff

National Weather Service Glossary of Abbreviations