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Area forecast discussion 
National Weather Service Taunton Massachusetts 
946 am EDT Sat Mar 20 2010 


Synopsis... 
one more day of dry and unseasonably mild weather today...then a cold 
front will bring much cooler conditions and spotty light showers 
Sunday. Coastal low pressure will bring rain Monday night through 
Tuesday night...which may be heavy at times. This will be followed by 
mainly dry weather with at or above normal temperatures Wednesday 
into Thursday. 


&& 


Near term /until 6 PM this evening/... 
plenty of sunshine this morning helping to boost temperatures 
quickly. A cold front remain located near the U.S./Canadian border at 
9 am...with a pre-frontal trough along the New England coast and middle 
Atlantic coast. Made some adjustments to temperature and dew point 
trends per latest observations...but not maximum temperatures which still 
look on target at the moment. 


Still expecting this cold front to push south this afternoon... 
possibly reaching I-90 by 8 PM. Latest visible pictures showing 
fair-weather cumulus clouds developing across the higher terrain. 
Current forecast had this handled well...so no changes here. Sunny 
skies expected for most locations this afternoon. 


Light southwest to west flow continues per metars and mesonet 
observations. Not a great synoptic pattern for sea-breezes...but 
cannot rule out the possibility with such a weak pressure gradient. 
Will continue to monitor trends for temperatures and aviation 
concerns. 


No records should be set today as record highs are in the upper 70s 
and lower 80s. 


&& 


Short term /6 PM this evening through 6 PM Sunday/... 
cold front will move south of the coast by late tonight with 
increasing clouds expected from north to S behind the front. There may 
be a few showers developing across north zones as SW flow at 850 mb 
overruns the shallow cool air mass. We have low chance probability of precipitation northwest Massachusetts and S 
New Hampshire. 


Sunday will be a much cooler day as Ely flow encompasses the region 
but still above normal. Coolest temperatures will be across east coastal Massachusetts 
and portions of northern high terrain where temperatures may not get out of 
the 40s. Elsewhere...mainly 50s to around 60 lower CT valley. 


The front may try to move back northward into southern New England but think it will get 
hung up S of the coast through sun. Overrunning of shallow 
boundary may result in a few showers in the interior where best 
moisture and have chance probability of precipitation here...but relative humidity time sections suggest 
there could be some sunshine along the South Coast. 


&& 


Long term /Sunday night through Friday/... 
Sunday night... 
backdoor cold front will probably remain south of our region through 
most of Sunday night. Shallow cool air is tough to erode 
sometimes...especially this time of year. While much of the night 
will likely be dry...weak warm advection in the middle levels should 
result in a few rain showers mainly across our northern/western 
zones. Will run with mainly chance probability of precipitation across our region and show 
the highest in our northern/western zones. In addition...there may 
also be areas of fog with the onshore flow. Lows should mainly be in 
the upper 30s to the lower 40s. 


Monday... 
closed low pressure system over the southeast will begin to lift 
northeast into the Middle Atlantic States. In response...southwest 
flow aloft will increase. The best forcing will remain to our west 
but enough lift is available with southwest flow aloft for scattered 
rain showers. Will run with chance probability of precipitation for now. 


Confidence in high temperatures is below normal on Monday. The GFS 
model appears too aggressive in lifting out the backdoor cold front across 
our entire region. The NAM appears more realistic with its Superior 
low level resolution and also has agreement from the European model (ecmwf). Feel 
the backdoor cold front will likely get hung up south of the Massachusetts 
Turnpike. Therefore...leaned temperatures towards the cooler met 
MOS. Highs north of the Pike should only reach into the upper 40s 
to lower 50s. South of the Massachusetts Pike...there may be some upper 50s 
and lower 60s depending how far the front ends up lifting. 


Monday night through Tuesday night... 
the models are in very good agreement in showing a deep closed upper 
level low and its surface reflection lifting northeast somewhere 
near the benchmark. 


We have high confidence in widespread rain developing sometime 
Monday night and continuing Tuesday/Tuesday night in association 
with low pressure passing near the benchmark. Will go with 
categorical probability of precipitation over much of this time and do expect the rain to be 
heavy at times. Easterly inflow is good for a time...but certainly 
not to the magnitude of what was observed last weekend. While 
rainfall amounts will not compare to what fell last weekend...still 
expect to see 1 to 2.50 amounts across the region. River levels 
remain quite high and several are still in flood across our region. 
With that said...there certainly is the potential for renewed river 
and stream flooding with this rainfall and will need to watch this 
closely. 


There also is a low probability that the precipitation ends as a bit 
of snow across the interior high terrain. This is only supported by 
the GFS model and our other long range models are a bit too warm for 
that to happen. Therefore...think its a low probability at this 
point. 


Wednesday and Thursday... 
any lingering showers should come to an end Wednesday morning. 
Otherwise...mainly dry weather with at or just above normal 
temperatures are expected over this time. 


Friday... 
a wave of low pressure could threaten the region with a bit of rain 
or even wet snow if it tracks close enough to the coast. That is 
highly uncertain at this time so will just include some low chance 
probability of precipitation Friday afternoon and night. It does looking like the weather 
will finally be turning a bit chillier. 


&& 


Aviation /14z Saturday through Wednesday/... 
today...high confidence VFR. Some cumulus will develop this afternoon 
especially toward northern New England. 


Kbos...there is a low probability of a brief sea-breeze developing...but 
more likely occurrence is west wind around 10 knots during the day 


Tonight...high confidence VFR but broken SC will develop overnight from 
north to S behind a cold front. NE wind up to 10 knots developing at bos after 
06z. A few showers possible north of the Pike. 


Sunday...mostly VFR ceilings in areas of SC...but low probability of MVFR 
especially north of the Pike. A few showers possible mainly 
interior. 


Outlook...Sunday night through Wednesday... 


Sunday night and Monday...medium confidence that there will be times 
of MVFR ceilings and possibly localized IFR conditions in fog 
patches. 


Monday night and Tuesday...medium to high confidence that MVFR-IFR 
conditions develop in low clouds/rain and northeast wind gusts of 30 
to 35 knots on the coast. 


Wednesday... 
low to medium confidence that MVFR-IFR ceilings early improve to VFR 
during the afternoon. 


&& 


Marine... 
fairly tranquil conditions today with SW winds 10-15 kts and flat 
seas. SW winds become NE later tonight into Sunday behind the 
front. NAM shows 975 mb winds increasing to 20-25 knots behind the 
front which may bring a brief pulse of near Small Craft Advisory gusts late tonight 
or early sun...especially mass Bay and eastern outer waters. 
Otherwise east/NE winds 10-15 kts sun with seas building to 3-4 feet 
eastern waters. 


Outlook...Sunday night through Wednesday... 


Sunday night and Monday...stalled backdoor cold front will likely be 
draped across our waters. Winds and seas though should generally 
remain below Small Craft Advisory thresholds. However...areas of fog may affect the 
waters resulting in reduced visibilities. 


Monday night and Tuesday...low pressure passing near the benchmark 
will result in increasing northeast winds and seas. Medium to high 
confidence in gale force northeast wind gust developing along with 
seas building to at least 15 feet over the eastern outer-waters. 


Wednesday...low pressure pulls away and winds shift to the 
northwest. However...gale force wind gusts remain possible behind 
the storm system. 


&& 


Hydrology... 
a few of the main Stem rivers in NE Massachusetts should drop below flood stage 
today. The Charles River at Dover and Concord River at Lowell 
will remain in flood into early next week. 


Please see flood warnings and statements for more specific 
information about the status of individual rivers. 


&& 


Tides/coastal flooding... 
splashover and possibly some pockets of minor coastal flooding are 
possible during the time/S of high tide Tuesday/Wednesday across the 
eastern Massachusetts coast. In addition...further beach erosion is certainly 
possible on north and east facing beaches. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...none. 


&& 


$$ 
Synopsis...kjc/Frank 
near term...Belk/kjc 
short term...kjc 
long term...Frank 
aviation...Belk/kjc/Frank 
marine...kjc/Frank 
hydrology...staff 
tides/coastal flooding...Frank 

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