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Area forecast discussion 
National Weather Service Taunton Massachusetts 
641 PM EST sun Nov 22 2009 


Synopsis... 
high pressure across the Saint Lawrence valley will move east of 
Nova Scotia Monday. A low pressure will approach our region Monday 
into Tuesday. Weak high pressure will briefly visit the area Tuesday 
night into Wednesday night...before another low pressure system tracks 
up the coast later Thursday and Friday bringing the chance for 
rain. Cold and blustery weather is forecast behind the low on 
Saturday...with drier weather finishing off next weekend. 


&& 


Near term /until 6 am Monday morning/... 
high pressure across the Saint Lawrence valley this afternoon will 
move to Nova Scotia overnight. This will allow northeast winds to 
become more from the east by daybreak. Currently watching an 
expansive area of marine stratus across the Gulf of Maine and Georges 
Bank. Latest visible imagery showing some of these clouds are diurnal 
in nature...and should briefly dissipate around sunset...mainly 
across the interior. 


However...the onshore flow and lowering temperatures will increase 
relative humidity as the evening wears on. Expecting these lower 
clouds to come back late this evening and linger through the night. 
Some drizzle is possible late tonight...especially along the 
immediate coast...but not overly impressed with the potential. 


A blend of the mav/met guidance looks reasonable for temperatures. 


&& 


Short term /6 am Monday morning through Monday night/... 
still some uncertainty with the track and intensity of a low pressure 
moving northeast from the middle Atlantic coast Monday night. For 
now...used a blend of the GFS and NAM to minimize forecast error. 
22/15z sref mean is even slower and weaker and slower than that 
solution. 


Most 22/12z models bring some rainfall to southern New England during 
the day Monday...especially during the afternoon. Given the 
uncertainty in the model timing...did trend the arrival of this 
precipitation faster than previous forecast. Thinking the best chance 
for the arrival of this rain will be Monday night. 


Used a blend of the mav/met guidance once more for temperatures 
during this portion of the forecast. 


&& 


Long term /Tuesday through Sunday/... 
Tuesday...low pressure center probably near/south of Nantucket 12z 
Tuesday then tracks gradually northeastward towards Nova Scotia. NAM is 
a bit weaker and further inland than the other models...taking low 
over the cape. For this package generally leaned towards the 
GFS/ECMWF/ggem. Started off with chance probability of precipitation over the 
interior...but still opted to go with likely near the coast. Low 
level moisture should keep clouds around through the day. 


Tuesday night/Wednesday...low pressure continues to move further 
North/East of the area...being replaced by weak high pressure. NAM 
indicates a layer of low level moisture just deep enough to keep 
clouds around for these 2 periods...GFS much drier. Think that at 
least some low level moisture will linger...and middle/high clouds 
possible with a short wave. So kept partly to mostly cloudy skies in 
forecast. But low level moisture layer likely too thin for measurable 
precipitation. Temperatures are a blend of MOS. Continued with previous 
thinking that Wednesday will be cool and raw during the afternoon with 
onshore flow. 


Wednesday night through Thanksgiving...mostly cloudy skies/chance 
probability of precipitation due to combination of low level moisture from easterly flow as 
high pressure departs...and as low pressure develops off the 
Carolina coast. 


Thursday night through Friday night...went with HPC guidance for 
this period with a vigorous low pressure system potentially 
affecting our area. Model discrepancies exist...as European model (ecmwf) and GFS 
show surface low tracking over southern New England but ggem keeps 
center well to the south and east. But at this time high chance to 
likely probability of precipitation seem prudent for Thursday night through Friday. Possibility that 
precipitation could end as a light rain/snow mix Friday night in interior as 
colder air spills into the area. 


Saturday...potential for blustery and chilly weather as tight 
gradient lingers while surface low pulls to the northeast. Both 
European model (ecmwf) and GFS indicate a cold pool aloft and lingering moisture 
which could potentially lend itself to some showers. 1000-500 mb 
thickness are quite low...if this scenario pans out can/T rule out a 
some snow showers in the far interior...but it would be too warm at 
the surface for any accumulation. 


Sunday...high pressure with below normal temperatures. 


&& 


Aviation /00z Monday through Friday/... 
tonight...MVFR ceilings initially over bos to pvd and southeast will spread 
northwest overnight. 


Monday...expect VFR ceilings northwest Massachusetts/far SW New Hampshire...while conditions lower to 
MVFR-IFR ceilings to the S and east. Local IFR ceilings along the S 
coast...Cape Cod and the islands during the afternoon. Patchy rain 
will approach north CT/RI/se Massachusetts during the afternoon with local MVFR 
visibilities. 


Monday night...MVFR ceilings...lowering to IFR eastern sections. Areas 
of MVFR/IFR visibilities in rain and fog...also mainly eastern sections. 


Outlook /Tuesday through Friday/... 


Tuesday...MVFR with areas of IFR in low clouds and scattered showers. 


Tuesday night through Thursday...MVFR-IFR conditions may linger in low 
clouds through this period. May have areas of drizzle and fog 
developing later Wednesday/Wednesday night. 


Thursday night and Friday...low to medium confidence of IFR ceilings and 
visibilities in showers. 


&& 


Marine... 
northeast winds should shift east overnight. The persistent onshore 
flow will continue to build seas overnight across the coastal waters 
of Massachusetts and Rhode Island. A low pressure moving northeast from the middle Atlantic 
coast Monday and Monday night will likely increase winds during this 
time as well. Small craft advisories continue for most waters. 


Outlook /Tuesday through Friday/... 


Tuesday and Tuesday night...Small Craft Advisory winds/seas linger Tuesday as low pressure tracks 
towards Nova Scotia. Winds diminish Tuesday night and Wednesday but seas will 
be slower to subside. 


Wednesday through Friday...persistent easterly winds will 
likely cause seas to remain above Small Craft Advisory thresholds across the outer waters. 
Winds and seas should increase Thanksgiving night and Friday in 
advance of the next system approaching from the south. Possibility of 
gales Friday. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...Small Craft Advisory from 5 am to 5 PM EST Monday for 
anz232>235-237. 
Small Craft Advisory until 5 PM EST Monday for anz250-254>256. 


&& 


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

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