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Area forecast discussion 
National Weather Service Taunton Massachusetts 
830 PM EST Monday Nov 23 2009 


Synopsis... 
low pressure near Cape Hatteras NC at 8 PM will move NE passing east of 
Nantucket Tuesday. Weak high pressure will move across New England 
Wednesday. A large gale should be centered near the New England coast 
Friday...then move into the Maritimes this weekend. Another low 
pressure is expected to approach from the Great Lakes early next 
week. 


&& 


Near term /until 6 am Tuesday morning/... 
radar stp is much too high Buzzards Bay southward...otherwise OK in southern New England. 
Going forecast as of 0120z looks decent. 


Northeast winds pick up a little especially over the cape and 
islands as coastal low pressure approaches...but should stay below 
advisory level. 


Temperatures/dew points are a blend of MOS. 


&& 


Short term /6 am Tuesday morning through Tuesday night/... 
low pressure passes well east of Nantucket Tuesday. This moves the 
isentropic lift north and northeast of our area...with lingering 
showers Tuesday morning and early afternoon as the supporting upper 
trough moves across. The GFS dries out the sub-850 mb layer fast...but 
the NAM holds onto this moisture through the day...the global starts 
drying out this layer after 18z. We have agreed with the slow 
clearing mostly late Tuesday into Tuesday night. 


Stiff gusty northeast winds across the cape and islands Tuesday 
morning and midday as the offshore low makes its closest approach. 
GFS forecasts 950 mb winds at 40-45 knots 12z Tuesday while the NAM 
has 35 knots and much less favorable thermal profile to bring the 
wind to the surface. Will bring cape/ids winds up to around 20 knots 
but keep below advisory level. 


Skies clear Tuesday night as the air mass dries out. 


Temperatures Tuesday and Tuesday night are a blend of MOS. 


&& 


Long term /Wednesday through Monday/... 
still some uncertainty Wednesday and Thursday with a weak high 
pressure expected to be across New England. Leaning more toward an 
optimistic forecast with better agreement amongst the 23/12z models. 
The uncertainty comes in from the exact location of this high 
pressure. If we get too much of an onshore flow with this high 
pressure shifted north...could see quite a bit of marine stratus 
instead. 


Thinking Wednesday...and at least Thursday morning should be dry. A low 
pressure expected to start moving north from the middle Atlantic coast 
Thursday...so thinking an increase in clouds and risk for rainfall 
as the day progresses. 


Thursday night into Friday poses another problem...with the GFS 
merging the coastal low pressure with another low pressure across the 
upper Great Lakes. This merger results in a significant storm south 
of New England for Friday. Do not have enough confidence in the 
details at this point to say much more than that is the most likely 
day for precipitation during this portion of the forecast. As noted 
by previous shifts...thunderstorms are possible given the energetic 
dynamics in place...but at this point remain a low probability. 


Thinking the GFS may be a bit overdone...but the 23/12z European model (ecmwf) has a 
stronger low pressure at the surface. Stayed conservative with the 
winds for now since a lot of things have to happen for this solution 
to play out. 


This storm modeled to depart Friday night into Saturday...followed by 
a weak surface ridge for Sunday. Another low pressure could impact US 
early next week. 


Constancy of onshore flow and large easterly ocean swells of 10 feet 
Tuesday into Wednesday...and possibly again Friday...could lead to 
significant beach erosion. 


&& 


Aviation /02z Tuesday through Saturday/... 
tonight...MVFR ceilings/visibilities early on...then ceilings deteriorate to IFR 
this evening and remain so overnight. Some gusts to 30 kts 
anticipated hya/fmh/ack late tonight. 


Tuesday...lingering IFR ceilings improve to MVFR in the morning. MVFR 
visibilities in light rain and fog early. Some gusts to 30 kts early at 
hya/fmh/ack. 


Tuesday night...sky conditions improving to VFR from west to east over the 
course of the night. Local IFR visibilities in patchy fog. 


Outlook /Wednesday through Saturday/... 


Wednesday...VFR expected...especially across the interior. Patchy 
IFR in stratus and fog possible at night...particularly in the river 
valleys. 


Thursday...VFR to start. Conditions lowering to MVFR though the 
day...but mainly at night. Timing of this change is still uncertain. 


Thursday night and Friday...increasing confidence of IFR conds. Brief east-northeast 
g25 kts possible Massachusetts coast. 


Saturday...IFR conditions slowly improving to VFR from southwest to 
northeast. West wind gusts 25-35 kts across all of southern New England...possibly higher 
vicinity kack. 


&& 


Marine... 
tonight...Carolina low pressure moves up the coast. Surface pressure 
gradient increases a little. Models show 30-35 knots /ECMWF and NAM/ 
or 40-45 knots /GFS/ at 950 mb...within range of being brought to the 
surface in a heavier burst of rain. This should carry enough 
potential for gale force winds...so we will issue a Gale Warning for 
overnight and Tuesday for the southeast and southern outer waters and 
Nantucket Sound...the areas closest to the track of the offshore low. 
All other zones show potential for 25 knot winds and/or 5 foot 
seas...so small craft advisories for all other waters. 


Winds diminish Tuesday night but seas remain above 5 feet on the outer 
waters. The Small Craft Advisory will be extended through Tuesday night. 


Outlook /Wednesday through Saturday/... 


Rough seas expected to linger across the outer coastal waters of Massachusetts 
and Rhode Island Wednesday through Thursday. A low pressure is expected to 
develop south of New England Thursday night into Friday. This low 
should move into the Maritimes Saturday. Gale force winds are more 
likely at this point...but storm force wind gusts cannot yet be ruled 
out. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...Gale Warning until 10 am EST Tuesday for anz232-254>256. 
Small Craft Advisory until 5 am EST Wednesday for anz231- 
233>235-237-250-251. 
Small Craft Advisory until 5 PM EST Tuesday for anz230-236. 


&& 


$$ 
Synopsis...wtb/Belk 829p 
near term...wtb/drag 829p 
short term...wtb 
long term...Belk 
aviation...wtb/drag/Belk/nmb 829p 
marine...wtb/Belk