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Area forecast discussion 
National Weather Service Taunton Massachusetts 
1028 am EST Monday Nov 23 2009 


Synopsis... 
low pressure along the Carolina coasts today will pass east of Cape Cod 
late Tuesday...possibly as a gale noreaster. Weak high pressure covers 
New England Wednesday. A large gale will be centered near the New 
England coast Friday then move into the Maritimes this weekend. 


&& 


Near term /until 6 PM this evening/... 
showers moving up in a zone across Rhode Island and eastern CT but not farther 
east. Most reports so far are of trace level showers/sprinkles but 
this should change over the next few hours as lift generates more 
precipitation and the lower airmass moistens. We have bumped probability of precipitation up to 
likely a little earlier along the Rhode Island coast and around Buzzards 
Bay...and blended this into the original timing for onset. 


Temperatures and dewpoints are mostly in agreement with forecast...a 
few scattered minor differences. Winds are a few knots 
stronger...this update bumps sustained winds into the middle 20s on the 
southern waters based in part on observations. 


&& 


Short term /6 PM this evening through 6 PM Tuesday/... 
short range models still having trouble locking in on track and 
intensity of the approaching low. Appears the GFS and rgem were 
outliers as compared to most of the other model solutions...so 
leaned toward a blend of the non-GFS ensembles with a little 
contribution from the sref. Appears the low will pass southeast of 
Nantucket Tuesday morning. Have continued with likely-categorical 
probability of precipitation tonight...then will shift offshore on Tuesday. Right now... 
feel the heaviest precipitation will remain offshore...but some heavier 
rains may clip the cape and islands overnight. 


Models did not handle lows for tonight well at all considering the 
onshore flow as well as precipitation and cloud cover...so leaned toward a 
blend of the previous forecast with the MOS guidance with 
adjustments to account for somewhat milder readings. Kept temperatures 
above freezing at all locations...and still may be a bit too cold 
over S New Hampshire /mid-upper 30s forecast for now/. As for Monday...leaned 
toward previous forecast along with the 2m NAM/GFS temperatures which tend 
to remove the MOS seasonal effects. Went with readings in the 
Lower-Middle 50s. 


Only other problem could be a brief wind increase late tonight into 
Tuesday morning. Have kept winds below advisory criteria for Cape 
Cod and the islands for now...but will need to monitor this in case 
the low is a bit stronger than currently forecast...as well as moves 
a bit closer to the coast. 


&& 


Long term /Tuesday night through Sunday/... 
model uncertainty Tuesday night-Thursday morning leads to a below average confidence 
on forecast details this period then high confidence for combined Great 
Lakes coastal merger Thursday night or Friday followed by high confidence on 
a developing blustery weekend. 


Tuesday night-Thu...maintained considerable continuity with the 4pm Sunday 
kbox forecast due to the various model outputs. Overall..leftover r or 
drizzle Tuesday night. Probably dry Wednesday into early Thursday but am uncertain 
due the resultant surface weather being dependent on subtle bl wind 
direction/associated terrain lift. The 00z GFS MOS was not heavily 
weighted...due to uncertainty regarding clearing and the output of 
the NAM and ggem temperature fields. 


Late Thursday into the weekend...blv model consensus favors some sort of low pressure 
moving to New England with a period of showers. Thunder is possible 
but did not forecast in the grids or write into the severe weather potential statement as its day 5. 
For the coast this could be either or both a brief Ely gale Friday 
followed by a blustery weekend with pockets of westerly gale force gusts. 
Temperatures were modified at night...upward due to expected mixing and the 
00z/23 GFS MOS. 


Erosion...constancy of onshore flow and large Ely ocean swells of 10 
feet Tuesday into Wednesday and possibly again Friday. We cant forecast the extent of 
erosion but it could be significant. 


&& 


Aviation /15z Monday through Friday/... 
today...generally MVFR midday except an area of higher ceilings over the 
cape and islands. Expect flight conditions to lower to MVFR/IFR during 
the afternoon and evening in developing showers and fog. 


Tonight...MVFR-IFR ceilings expected...with local LIFR ceilings possible on 
Cape Cod and the islands. Areas of MVFR-IFR visibilities in rain and fog. 


Tuesday...MVFR ceilings/visibilities in rain mainly central and eastern areas. 
May see improving conditions during the afternoon across the CT 
valley. 


Outlook /Tuesday night through Friday/... 


Tuesday night through Thursday...considerable uncertainty. Low confidence. 


Generally VFR interior though with a period of IFR St/fog early Wednesday 
and early Thursday. 


Along the coast-especially Cape Cod and the islands...generally MVFR or IFR 
ceilings outlooked. Leftover rain/drizzle Tuesday night. 




Thursday night and Friday...high confidence of IFR conds in rain with a period 
of gusty east 25 to 35 knots coast...possibly shifting to west Friday afternoon along 
with improving conds. 


&& 


Marine... 
today...E-NE winds with sustained values around 25 knots over the 
southern waters and gusts around 30 knots. Updated the forecast to 
reflect these values better. The 00z wna wavewatch model was running 
a foot or so too low this morning. Buoy 008 well southeast of Nantucket up 
to 10 feet already at 09z and buoy 018 up to 7 feet. Have increased 
the seas on the outer coastal waters. 


Tonight and Tuesday...with the low passing southeast of Nantucket late 
tonight...may see a brief period of gale force gusts on the outer 
waters as well as Nantucket Sound and Cape Cod Bay. Have put up a 
gale watch for late tonight into Tuesday morning for this 
possibility. Wavewatch has also forecasted seas up to 13 feet on the 
eastern outer waters. 


Outlook /Tuesday night through Friday/... 
leftover Small Craft Advisory conds Tuesday evening shift to hazardous seas Small Craft Advisory Wednesday and Thursday 
in the outer waters then another gale condition possible Friday. 


&& 


Equipment... 
National Weather Service Boston-Taunton point and click has delays in updating by about 45 
minutes- a continuing recent problem. 


Tdwr in the Boston area continues ots ufn. 


44020...any problem with this Nantucket Sound buoy will probably be 
updated on its maintenance link by ndbc later today. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...gale watch from late tonight through Tuesday afternoon for 
anz232-254-255. 
Small Craft Advisory until 1 am EST Tuesday for anz232-254>256. 
Small Craft Advisory until 1 PM EST Tuesday for anz233>235-237. 
Small Craft Advisory from 7 am to 1 PM EST Tuesday for anz230- 
236. 
Gale watch from Tuesday morning through Tuesday afternoon for 
anz231-250. 
Small Craft Advisory from 1 am to 7 am EST Tuesday for anz231. 
Small Craft Advisory until 7 am EST Tuesday for anz250. 
Small Craft Advisory from 1 am to 1 PM EST Tuesday for anz251. 
Gale watch from late tonight through Tuesday morning for 
anz256. 


&& 


$$ 
Synopsis...drag/evt 
near term...wtb 
short term...evt 
long term...drag 
aviation...drag/evt/wtb 
marine...drag/evt/wtb 
equipment...drag 

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