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Area forecast discussion 
National Weather Service Taunton Massachusetts 
327 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure will move from the Great Lakes into southeast Canada 
tonight...then move east of Nova Scotia Monday. Low pressure will 
bring rain to the region late Monday into Tuesday. Weak high pressure 
will temporarily build into the region Wednesday night and 
Thanksgiving day...before another low pressure threatens the region 
with more rain very late Thanksgiving night and Friday. 


&& 


Near term /until 6 am Sunday morning/... 
high clouds continue to stream across southern New England...with 
the thickest clouds now across Cape Cod and the islands. Farther 
west...plenty of clouds from the Great Lakes banked up against the 
west slopes of the Berkshires. With winds shifting to the north and 
remaining fairly light...do not expect these clouds to spill over the 
Berkshires into southern New England. 


Used a blend of MOS guidance for temperatures tonight. 


&& 


Short term /6 am Sunday morning through Sunday night/... 
high pressure remains across northern New England and southeast 
Canada. This should mean another mostly sunny day...but this time 
with onshore winds by afternoon. These onshore winds could lead 
marine stratus late in the day into Sunday night...particularly south 
and east of I-95 in Massachusetts and Rhode Island. Given the expected timing of the wind 
shift though...thinking this may be more of a concern Sunday night. 


MOS temperatures look reasonable once again...so used a blend of the 
mav/met guidance. 


&& 


Long term /Monday through Saturday/... 
Monday and Tuesday... 
plenty of uncertainty remains but confidence is growing that at 
least some rain will affect the region later Monday into Tuesday. 
The main dilemma is how close to the coast a wave of low pressure 
tracks and also its intensity. However...latest models along with 
sref ensembles suggest that even if the southern and weakest 
solutions verify there will likely be at least some rain with 
persistent onshore flow. 


The main question is will a period of heavier rain effect portions 
of the region. The Gem/NAM certainly show this potential...while 
the GFS/UKMET are much further south suggesting mainly 
rain/drizzle. The European model (ecmwf) is not as extreme as the very wet Gem/NAM 
but it does lean in more of their direction. Therefore...we will 
lean in the European model (ecmwf)/S direction for now especially considering its 
track record in this timeframe. Will run with a period of likely probability of precipitation 
across the entire region Monday night/Tuesday. A period of heavy 
rain is possible depending on how close to the coast the wave of low 
pressure tracks. The best chance for heavy rain will be across the 
southern and eastern sections. In fact...later shifts may have to 
increase probability of precipitation into categorical levels for some of the region. 


Despite persistent onshore flow Monday/Tuesday...astronomical tides 
are low and the system does not appear intense enough to result in 
any coastal flooding. However...minor beach erosion certainly is 
possible. 


As for temperatures...confidence is high that it will be rather cool 
and raw during the afternoon. Highs mainly in the upper 40s and the 
lower 50s with the onshore flow. Confidence is also high that what 
ever falls will be in the liquid variety. Low temperatures should 
remain in the 40 to 45 degree range across most of the region. 


Wednesday... 
low confidence forecast over this time...but the steadiest 
precipitation will likely be over. However...will continue with the 
chance of a few showers with wave of low pressure still spinning off 
the coast. Precipitation chances may diminish later Wednesday 
afternoon and evening as drier air works into the region from the 
west and the low finally pulls away. Highs should mainly be in the 
upper 40s to middle 50s across the region. 


Wednesday night through Friday... 
although the timing can certainly change since we are still 5 to 6 
days out...at this time it appears that most of Wednesday night 
Thanksgiving day may turn out dry. A weak ridge of high pressure 
looks to temporarily build into the region Wednesday night and 
Thanksgiving day. 


However...a vigorous trough developing over the Great Lakes may 
allow another low pressure system to affect the region late 
Thanksgiving night into Friday. Again...timing and forecasts are 
subject to significant errors this far in advance. However...this may 
bring more rain to the region. Temperature profiles continue to 
look too warm support any frozen precipitation even in the distant 
interior for most of the potential event. 


Saturday... 
blustery and chilly weather looks to be filtered into the region 
behind the system. Much of the day will be dry...but can not rule 
out a few sprinkles/passing rain shower so will run with a slight 
chance. Its not out of the question that a few wet snowflakes fall 
across the interior high terrain but it does not appear to be a big 
deal. 


&& 


Aviation /20z Saturday through Thursday/... 
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 and afternoon. 


Sunday night...VFR most locations. Greater risk of MVFR ceilings along 
the East Coast and south and east of a line from kbos-kpvd. 
Confidence on this is not high at this time. 


Outlook /Monday through Thursday/... 


Monday and Tuesday...MVFR-IFR conditions in low clouds and rain will 
overspread the region from south to north sometime on Monday and 
persist into Tuesday. 


Wednesday...low confidence forecast but MVFR-IFR conditions may 
linger in low clouds/rain showers for a time. 


Wednesday night and Thanksgiving...mainly VFR but conditions may 
deteriorate late Thanksgiving night. 


&& 


Marine... 
high pressure building north of the waters tonight. Winds gradually shifting 
north tonight...then NE Sunday into Sunday night. Seas below 5 feet tonight 
into early Sunday. Do expect seas to build over 5 feet across the outer 
coastal waters Sunday afternoon into Sunday night once NE winds get 
established. There is still a question about strength of these 
winds...which will be entirely dependent upon the approach of a low 
pressure from the middle Atlantic coast. Based upon the building 
seas...will hoist a Small Craft Advisory for the outer coastal 
waters. 


Outlook /Monday through Thursday/... 


Monday through Wednesday...Canadian high pressure with low pressure 
to the south will create a persistent northeast flow and good 
gradient. This will result in Small Craft Advisory across most of our waters over this 
time. Seas may build to between 7 and 12 feet across the 
outer-waters. There is a low probability of a brief marginal gale 
at some point. 


Thanksgiving...winds should temporarily diminish as weak ridge of high 
pressure builds in during the day. However...seas will likely 
remain above Small Craft Advisory thresholds across the outer-waters. Winds and seas 
may once again increase very late Thanksgiving night in advance of 
our next possible system 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...Small Craft Advisory from 9 am Sunday to 6 am EST Monday for 
anz250-254. 
Small Craft Advisory from noon Sunday to 6 am EST Monday for 
anz255. 
Small Craft Advisory from 3 PM Sunday to 6 am EST Monday for 
anz256. 


&& 


$$ 
Synopsis...Belk/Frank 
near term...Belk 
short term...Belk 
long term...Frank 
aviation...Belk/Frank 
marine...Belk/Frank 

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