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Area forecast discussion 
National Weather Service Taunton Massachusetts 
1035 am EST Sat Nov 21 2009 


Synopsis... 
dry and pleasant weather will continue through this weekend with 
high pressure in place. A weak low pressure system will approach 
southern New England from the south Monday night and Tuesday. Weak 
high pressure will probably result in a dry Thanksgiving before a 
possible coastal storm on Friday. 


&& 


Near term /until 6 PM this evening/... 
high clouds continue to stream across southern New England...with 
more sunshine filtering through. Temperatures are on track with 
existing forecast...so no major changes there. Light west winds will 
gradually shift to north during the day...but should not be much of a 
factor. 


&& 


Short term /6 PM this evening through 6 PM Sunday/... 
tonight...feel that the middle-high clouds will shift NE as the center 
of the high builds into northern New England. With the ridge axis north 
of the region...will see light winds with some NE component along 
the coast. May see a few clouds lingering...along with some patchy 
valley fog developing late at night. Overnight lows will bottom out 
in the 30s to near 40...which is still around 5 degrees above 
normal. 


Sunday...high pressure remains across northern New England...meaning 
another mostly sunny day. May see some clouds develop across southeast 
Massachusetts/Rhode Island with the NE flow. Models are hinting at an increase in pressure 
gradient across southern areas and especially over the coastal 
waters. This may help bring low level moisture onshore with some 
cloud development. With the cooler onshore flow in place...expect 
daytime highs to run cooler than today but still several degrees 
above normal...with the coolest readings along the coast. 


&& 


Long term /Sunday night through Friday/... 
confidence is below average during this period due to spread in 
model solutions as well as some run to run discontinuity. 


Seeing tendency for various medium range models to project 
measurable rain for Monday night through Tuesday...and this is supported by 
sref probabilities. Noticed that 00z European model (ecmwf) is wetter than its prior 
run. There are timing and quantitative precipitation forecast variations among the models. 
Thus...have not tried to be too precise on timing of onset and 
ending of probability of precipitation and have capped at high chance for now. Suspect most 
locations will get measurable sometime in the Monday night to Tuesday night 
time frame but cannot pin the timing down any better. The global Gem 
still looks too robust given that this system is associated with a 
dampening short wave trough moving into the long wave ridge position. 
However...as weak as system is...does look like decent overrunning 
with a subtropical moisture source. As far as timing...am suspicious 
that dry low level air associated with moderately strong high pressure 
centered over Nova Scotia at the outset may delay the spread of rain 
into southwest New Hampshire and northeast Massachusetts Monday night. 


Wednesday is a little complicated with vigorous negative tilt short wave 
trough rotating through the Great Lakes. Southern New England is 
fairly well east of significant dynamics. GFS depicts southeast flow that 
could in itself contribute to low clouds and drizzle whereas the 
European model (ecmwf) shows less relative humidity and flat gradient amidst weak surface ridge. 
Have gone with slight chance to chance probability of precipitation. Temperatures may be 
tricky for Wednesday given warm air mass aloft with 8+c 850 mb 
temperatures but inversion may prevent realizing the relative warmth 
at the surface. If get enough sun...then Wednesday maximum temperatures may 
end up considerably higher than currently forecast. 


Thanksgiving day currently looks dry with perhaps a sunny start 
before increasing clouds during the afternoon ahead of the next 
system. A vigorous short wave trough helps initiate a coastal low but 
again medium models not in good agreement in handling this system 
with regard to intensity and track. Have gone with chance probability of precipitation Thursday 
night and Friday. Air mass may cool sufficiently toward back part of 
storm to cause ptype uncertainty. Potential for rain to mix with or 
change to snow over the higher elevations of our northwest zones on Friday but 
confidence of this actually occurring is currently low. 


&& 


Aviation /16z Saturday through Wednesday/... 
today...VFR. 


Tonight...VFR. Patchy fog with brief MVFR ceilings/visibilities late at night 
in the normally susceptible valleys. 


Sunday...VFR. May see patchy VFR to local MVFR ceilings along the coast 
during the late morning/afternoon. 


Outlook /Sunday night through Wednesday/... 


Monday through Wednesday...VFR Monday becoming MVFR with areas IFR in rain and fog 
Monday night through Tuesday night. MVFR ceilings may persist into Wednesday. 


&& 


Marine... 
today...Small Craft Advisory will likely be dropped at 11 am. Want to 
get one more round of buoy reports to be sure. Winds are not the 
concern at this point...but the lingering rough seas across the outer 
coastal waters. 


Tonight...high pressure building north of the waters. Expect north-NE winds at 
15 knots or less with seas 4 feet or less. 


Sunday...NE flow slowly increases...with gusts up to 20 knots. Expect 
highest winds east and S of Nantucket. For now...have forecasted seas 
at 4 feet or less...but may build with the NE flow on the open outer 
waters. 


Outlook /Monday through Wednesday/... 


Persistent east gradient with considerable fetch will likely keep seas 
near or above 5 feet exposed coastal waters Monday night through Wednesday morning and 
may be strong enough to meet Small Craft Advisory wind thresholds over most of waters. 
Respite likely late Wednesday through Thursday before risk of potent coastal low pressure 
system toward end of week. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...Small Craft Advisory until 11 am EST this morning for anz250- 
254>256. 


&& 


$$ 
Synopsis...evt/Thompson 
near term...Belk/evt 
short term...evt 
long term...Thompson 
aviation...Belk/evt/Thompson 
marine...evt/rlg/Thompson 

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