Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
346 am EDT Sat Oct 10 2015

dry and cool weather is on tap today and tonight. High pressure
moving off the coast will keep our weather dry Sunday and
Monday...but with milder temperatures especially by Monday
afternoon. A cold front may bring a few showers Monday night into
Tuesday... before dry weather returns Wednesday and Thursday.


Near term /until 6 PM this evening/...
gusty northwest winds of 20 to 30 miles per hour were ushering in much cooler
air into the region behind the cold front. Should see these winds
diminish later this morning and especially this afternoon as high
pressure builds over the region. Some scattered to broken strato-
cumulus clouds very early this morning...will tend to dissipate near
daybreak as drier air moves in allowing for plenty of sunshine
today. High temperatures will still only recover into the upper 50s to near
60 in most locations in the cool air advection pattern.


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

High pressure overhead should result in rather light winds allowing
temperatures to quickly fall after sunset with the relatively dry
airmass in place. The big dilemma for tonight is the potential for
some middle/high level cloudiness...especially late across our northern
zones. This can be seen in the 300 to 500 mb relative humidity
cross sections on both the NAM and GFS.

Despite the threat for some middle/high clouds late...feel there will
be enough of an opportunity especially during the first part of the
night for low temperatures to bottom out in the middle 30s in the normally
cooler outlying locations. A few lower 30s are even possible in the
lowest lying areas such as Norwood and Orange. Therefore...have
decided to hoist a frost advisory for western Massachusetts as well as the
typically cooler spots of interior eastern Massachusetts. Patchy ground fog may
also develop in the typically prone locations late...but nothing
widespread is expected. Meanwhile...the urban heat islands of
downtown Boston/Providence will see low temperatures in the 40s.

The big caveat tonight is if middle/high level cloudiness comes in
earlier and thicker then expected. If this occurs...our low temperature
forecast will be several degrees too cool. Later shifts will have
to monitor closely.


High pressure moving off the coast will allow for a southwesterly
flow of milder air to work back into the region. Despite a rather
chilly start...plenty of sunshine should allow afternoon high
temperatures to recover into the middle to upper 60s. Its
even possible that a few locations touch 70.


Long term /Sunday night through Friday/...
* dry weather and a warming trend for Sunday and Monday
* another chance of rain Tuesday with a cold front
* cooler temperatures return for late in the week

Overview and model preferences...
latest 10.00z model guidance update not showing any significant
changes in the long term except typical uncertainty with the two
shortwaves and their interaction for Tuesday. Confidence remains
higher that the two features remain separate as they impact southern
New England...which continues to yield uncertainty in quantitative precipitation forecast totals
given the likelihood of some subsidence between the attendant cold
front and ocean low pressure. Deterministic guidance is suggesting
this as well with a min in quantitative precipitation forecast across much of interior southern New
England and ensemble probabilistic guidance is low.
Therefore...feel the deterministic blend will be a good start. The
other issue of note is the fact that guidance is likely too cool
with a digging longwave trough late in the week due to climatology
influence. Therefore...will be a bit lower than current models


Sun night into Monday...
in spite of the cool start to sun...noting fairly robust warming
aloft that will allow temperatures to increase rather quickly to near
seasonal normals by Sun night /mainly middle 40s/. By Monday...h92 temperatures
are above should be a warm day across the region with a
fair amount of sunshine. In fact some locations could make a run
at the upper 70s thanks to downsloping...with low-middle 70s
elsewhere. Dry conditions remain...thanks to influence of high
pressure moving offshore.

Monday night and Tuesday...
northern and southern stream features...a cold front and coastal low pressure
respectively will be approaching at the same time. Noting an
increase in moisture as precipitable waters near +1 Standard deviation.
Therefore...will see rain showers activity develop across both the east and west
from each of these features by early Tuesday morning. The question of
total quantitative precipitation forecast will depend on how much subsidence is observed between
the two systems and whether one ends up dynamically stronger. Do
note the modest destabilization ahead of the coastal
system...which could increase a localized risk for heavier
rain...but feel that chance probability of precipitation and blended quantitative precipitation forecast are a good start
at this point. Temperatures still above normal thanks to warm airmass
remaining in place from earlier in the week. Lows in the
50s...highs in the upper 60s and low 70s.

Wednesday and Thursday...
good cold advection regime begins with building west Continental U.S. Ridge
forcing cooler air from a cutoff low pressure near Hudson Bay into a
digging trough across the NE Continental U.S.. ensemble probs have nearly 100
percent risk of 850 mb temperatures being lower than +5c with a low risk of
temperatures near 0c. Mean h10-500 mb thickness values could make a run at
the infamous 540dm mark by Thursday as well. Still some overall
uncertainty but as mentioned above...given guidance tends toward
climatology in the is likely too warm. So will be
adjusting temperatures down. Weak shortwaves will be pushing through the
base of this trough...but with cp airmass relatively dry...feel that
leaving any probability of precipitation at slight chance is best.

Friday and the weekend...
although there is general agreement that the longwave trough
remains in place...there are differences in potential shortwave
energy and a potential shift in the pattern allowing the core of
modified Arctic air to reach the Continental U.S.. will likely lean cooler
than guidance...but not full stop given the uncertainty in any
mesoscale features.


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

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

Today...high confidence in VFR conditions other than perhaps some
brief MVFR ceilings in a few locations through 12z. Gusty northwest
winds of 20 to 30 knots early this morning should gradually diminish
later this morning and especially this afternoon.

Tonight and Sunday...high confidence in VFR conditions other than
some localized patchy ground fog in the typically prone locations
late tonight/early Sunday morning.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Sunday night through Wednesday/...

Sunday through Monday...high confidence.

Monday night and Tuesday...moderate confidence.
A cold front moves across the region with MVFR/IFR conditions
possible in any -shra that occurs ahead of the front. Expect gusty
westerly winds with the frontal passage.

Wednesday...high confidence.


forecaster confidence levels...

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

Short term /today through Sunday afternoon/...high confidence.

Today...surge of north to northwest wind gusts of 25 to 35 knots
early this morning will gradually diminish later this morning and
especially this afternoon. This a result of a weakening pressure
gradient. Will continue small craft advisories into middle to late
morning for all waters...but will maintain them for a few more hours
across our eastern outer-waters where winds/seas will be slower to

Tonight...high pressure overhead will keep winds/seas below Small
Craft Advisory thresholds.

Sunday...high pressure moving off the coast will allow for a return
southwesterly flow of air. May see some southwest wind gusts into
the lower 20 knots along with choppy seas during the afternoon. For
now kept things just below Small Craft Advisory thresholds...but
later shifts will have to re-evaluate.

Outlook /Sunday night through Wednesday/...

Sun night through Monday night...high confidence.
High pressure will be moving over the waters yielding a period of
mainly quiet boating weather. No headlines expected.

Tuesday into Wednesday...moderate confidence.
A relatively weak ocean low will pass just outside the coastal
waters Tuesday...moving north of the waters by Wednesday. Although winds should
remain low...a swell from the low pressure could impact southern and southeast
waters with seas about 5-6 feet. Therefore...a period of small craft
advisories is possible.


Box watches/warnings/advisories...
Massachusetts...frost advisory from 2 am to 8 am EDT Sunday for maz002-003-005-
Rhode Island...none.
Marine...Small Craft Advisory until 11 am EDT this morning for
Small Craft Advisory until 4 PM EDT this afternoon for anz250-


near term...Frank
short term...Frank
long term...doody

National Weather Service Glossary of Abbreviations