Weather

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Area forecast discussion 
National Weather Service Taunton Massachusetts 
357 am EDT Monday Sep 8 2008 


Synopsis... 
high pressure builds over New England today and shifts offshore 
tonight and Tuesday. A cold front approaches from the Great Lakes 
Tuesday...crossing southern New England in the late afternoon and 
evening. Dry...seasonable weather will return Wednesday and Thursday 
before a frontal system impacts southern New England sometime 
between Friday and Sunday. 


&& 


Near term /until 6 PM this evening/... 
high pressure in place today with subsidence and dewpoints in the 
50s. Should be a pleasant day with widely scattered diurnal cumulus. 
850 mb temperatures 10-11c would support maximum temperatures in the upper 70s and 
around 80. With plenty of sunshine for mixing today...we will edge 
the warmer temperatures a little higher to better cover the lower 
80s. 


&& 


Short term /6 PM this evening through 6 PM Tuesday/... 
the high pressure settles offshore tonight but continues to maintain 
subsidence over southern New England. Look for mainly clear skies and 
light winds...resulting in radiational cooling. Dewpoints will 
continue in the 50s...but edge upward later in the night...so this 
will be a good target range for min temperatures tonight. 


Model guidance shows a weak front settling into northern New England 
overnight. With the upper flow west-southwest through the night this 
front will have little chance of reaching US. Low pressure moving up 
the front late at night will encourage warm advection into New 
England with some cirrus overnight. 


Tuesday looks like an active weather day. Low pressure moving up the 
St Lawrence Valley swings a cold front through the northeast during 
the day. Minor timing differences but all models point to cold 
frontal passage during the late afternoon/early night period. Strong 
winds across a deep layer aloft in advance of this front with 45 to 50 
knots forecast at 850 mb and 40 to 60 knots at 500 mb. Instability 
available with total totals forecast in the lower 50s and cape around 
1000 joules. Precipitable water values are expected at 1.5 to 1.75 
inches...moist enough for locally heavy downpours but not the 
torrential amounts we saw over the weekend with Hanna. The prime 
threat would appear to be wind...especially straight line wind...in 
the afternoon and evening. We will go with likely probability of precipitation...appearing 
first in the western zones early afternoon and spreading to the 
eastern zones during the afternoon and evening. This timing will be 
based on a mix of gmos...the short range ensembles...and climatology. 
We will also add extra wording in the forecast to the chance of 
thunderstorms. 


850 mb temperatures will be around 14c which would support maximum temperatures in the middle 
80s. But with increasing clouds from west to east especially in the 
afternoon we will carve maximum temperatures back to the middle and upper 70s in 
the northwest and lower 80s in the south and east. 


&& 


Long term /Tuesday night through Sunday/... 
Tuesday night...will see the cold front push through the remainder 
of the area overnight...along with the showers and thunderstorms. 
Expect the front to be stretched along the higher terrain of central 
Massachusetts and southern New Hampshire at 00z. The front should 
have cleared all of the land zones including the cape and islands by 
around 09z. With all the models spitting out quantitative precipitation forecast overnight...expect 
there will be rain through the night along and ahead of the front. 
With the loss of daytime heating...and any resultant instability am 
unsure about continuing the mention of thunder overnight. There is 
still quite a bit of shear /around 50 kts 0-6km/ which could be 
enough to keep thunder in the forecast. Will leave thunder in 
overnight but keep it as isolated. 


Wednesday and Thursday...high pressure builds back into the area 
behind the front. Dry...more autumn-like weather is expected...with 
high temperatures slightly below normal. 


Friday through Sunday...another series of fronts could move through 
southern New England. There is some discrepancy amongst the models 
on both the impact of a warm front Friday night and the timing of 
the cold front Saturday or Sunday. With high pressure remaining 
just offshore Friday...the warm front may have trouble making it to 
southern New England until later Friday evening. The cold front 
should move through between Saturday morning and Sunday afternoon. 
There is still quite a bit of difference in the models on this. At 
this point...will only make small adjustments to the grids for these 
days since the picture remains so unclear. 


&& 


Aviation /08z Monday through Friday/... 
patchy MVFR in fog through 11z this morning...otherwise VFR today. 
Continued VFR tonight except MVFR in patchy fog late at night. 


Tuesday will mainly be VFR. Showers and thunderstorms are likely in 
the afternoon and evening...with episodes of MVFR/IFR ceilings and visibilities 
at any sites they move over. The thunderstorms will have a good potential 
for producing strong straight line winds and as such should be given 
extra respect by aviation interests. 


Outlook...Tuesday night through Saturday... 


Tuesday night...MVFR in showers and thunderstorms as the front 
finishes moving through southern New England. A gradual return to 
VFR from the western terminals before midnight...to along the cape 
and islands near sunrise. 


Wednesday through Friday...VFR. 


Friday night...VFR with some MVFR possible in showers associated 
with a warm front. 


Saturday...depending on the timing of the front...possibly MVFR in 
showers and possible thunderstorms. Otherwise...VFR. 


&& 


Marine... 
still 10 foot seas off Nantucket and 5 foot seas at Montauk. So while 
winds have diminished for the while...rough seas will continue to be 
a problem today. We will continue a Small Craft Advisory for 
seas...ending from north to south during midday and the afternoon. 


All quiet tonight with light winds and seas. 


Increasing south to southwest gradient will bring winds up...with 
potential for gusts of 25 to 30 knots in the afternoon. A cold front 
will bring thunderstorms to the waters late in the day continuing 
into the evening. These thunderstorms will have a potential for 
strong straight line winds. 


Outlook...Tuesday night through Friday... 


Tuesday night...small craft criteria likely as a cold front sweeps 
across the coastal waters. 


Wednesday...winds and waves will fall below small craft criteria 
Wednesday afternoon. 


Thursday through Friday...winds and waves will remain below small 
craft criteria. 


Friday night through Saturday...winds and waves will increase to 
small craft criteria with the approach of another frontal system. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...Small Craft Advisory for hazardous seas until noon EDT today 
for anz235-254. 
Small Craft Advisory for hazardous seas until 5 PM EDT this 
afternoon for anz255. 


&& 


$$ 
Synopsis...wtb/rlg 
near term...wtb 
short term...wtb 
long term...rlg 
aviation...wtb/rlg 
marine...wtb/rlg 

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