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Area forecast discussion 
National Weather Service Taunton Massachusetts 
1021 PM EDT sun Mar 21 2010 


Synopsis... 
coastal low pressure will bring rain starting Monday...but the 
heaviest rainfall will be Monday night into Tuesday morning. Mainly 
dry and somewhat cool weather is in store for Wednesday and Thursday. 
A strong cold front could cross southern New England Thursday night. 
Chances of rain or snow with this feature will depend on if the front 
slows and a wave develops on it just south of southern New England 
late Thursday night and Friday. Fair and unseasonably cold weather 
looks to follow in the wake of the front for the weekend. 


&& 


Near term /until 6 am Monday morning/... 
lower clouds beginning to develop across eastern new eng as easterly 
flow moistening the low levels. NAM is capturing this fairly well 
and suggests low clouds will overspread much of the region 06-12z. 


Otherwise...it should remain mostly dry tonight. Exception is along 
the S coast where a few showers possible late tonight associated with 
weak instability burst. Radar is showing these showers developing 
from southeast PA to New Jersey coast. Have a slight chance probability of precipitation late tonight along 
the coast. 


&& 


Short term /6 am Monday morning through Monday night/... 
warm air advection and moisture in the column increases during the 
day on Monday. Therefore...we expect much more in the way of 
cloudiness than what we experienced Sunday. Went with high chance to 
likely probability of precipitation for rain. However...the rain will probably be light and 
of the on-and-off variety. Cooler temperatures than Sunday with easterly 
winds...clouds...and precipitation. We blended the mosguide with the NAM 2m 
temperatures for highs to get the highs colder than straight MOS. 


Strong closed low over the middle Atlantic will lift northeast Monday night. 
This will aid in a strengthening southerly low level jet across a 
strengthening baroclinic zone. This along with decreasing stability 
will allow for heavier rain to develop during the night that will 
last into Tuesday morning. 


As of now...we are forecasting a widespread 1 to 2 inches of rain to 
fall Monday night and Tuesday. However...we do think there very well 
could be areas of 2+ inches given +2 to +3 South Dakota precipitable water anomalies. The 
good thing is that the low level jet anomalies are quite a bit weaker 
with this event than they were with the last one. In addition...this 
system will be much more progressive. Therefore...flooding will not 
be as big as a problem as it was a week ago. Nonetheless...area 
rivers are still running quite high with a couple still in flood. 1 
to 2 inches of rain will allow for a rekindling of minor flooding. 
Since any flooding probably won't start to occur until the 4th period 
of the forecast /Tuesday/ we opted to not issue a Flood Watch at this 
time. However...we suspect one will have to be issued tonight. The 
middle shift will be able to get another look at the model forecast quantitative precipitation forecast 
amounts and where any axes of heaviest rain may set up. 


&& 


Long term /Tuesday through Sunday/... 
after a period of heavy rain as low pressure moves through southern 
New England Tuesday...quiet weather expected for the rest of the 
week. A cold front late Thursday will result in colder weather 
Friday into the weekend. 


The models are in good agreement that low pressure moving across 
southern New England Tuesday while the middle level low moves across or 
near the 40/70 benchmark. 


This will result in a period of widespread rain beginning 
Monday/Monday night /refer to short term discussion above for more 
information on this time period/ and extending through Tuesday 
night. All the models indicate that the heaviest rainfall will be 
across eastern Massachusetts...Rhode Island...and southeast New 
Hampshire. Total rainfall amounts from Monday night through 
Wednesday morning are modeled to be about 1 to 2 inches...with 
isolated higher amounts to 2.5 inches. Most of the rain is expected 
to fall through Tuesday evening. However...expect some lingering 
rain through Wednesday morning. May see a brief period of snow or 
rain mixed with snow early Wednesday morning. However...do not 
anticipate any problems as it is such a brief period /a few hours/. 
This one to two inches of rain may result in another period of 
flooding for some of the rivers/streams that flooded last week 
across eastern Massachusetts/southeastern New Hampshire/Rhode Island. This flooding does 
not look as significant as what occurred last week. However...a 
Flood Watch will likely be needed. Have opted to delay any watch 
issuance to later shifts as the onset of flooding is likely at least 
36 to 48 hours from now. 


Surface and middle level lows move into the Maritimes Wednesday 
bringing any lingering showers in southern New England to an end. 
Good mixing will result in breezy conditions both days with westerly 
to southwesterly gusts generally in the 25 to 35 miles per hour range. 
Temperatures will be right around or slightly above normal. 


Low pressure moving across southeastern Canada will pull a cold 
front through southern New England Thursday evening or Thursday 
night. While the frontal passage remains dry...much colder air 
moves in behind the front with high pressure. Temperatures will be 
roughly 5 to 10 degrees below normal for this time of year. But 
given we spent most of last week 15 to 20 degrees above normal... 
Friday and Saturday will feel much colder. Keep in mind though that 
this is still 5 to 7 days out and things will likely change. There 
are some discrepancies in the models as to how quickly the high 
pressure will move out of the area but overall at this point...the 
weekend looks dry and cold. 


&& 


Aviation /02z Monday through Friday/... 
tonight...MVFR ceilings have developed from bos-mht and southward along the 
coast as of 02z. Even some IFR ceilings coastal pym County as easterly 
flow moistens low levels. These lower clouds should expand across 
the region 06-12z with widespread MVFR and areas of IFR. Patchy fog 
possible toward daybreak. 


Monday...widespread MVFR/IFR in St and patchy fog and developing 
showers...moderate to high confidence. 


Monday night...high confidence in MVFR conditions...with IFR 
conditions becoming increasingly likely in developing heavy rain. 


Outlook...Tuesday through Friday... 


Tuesday...high confidence in MVFR/IFR conditions in rain/low 
clouds/fog. 


Wednesday...low confidence MVFR/IFR early improving to VFR by 
afternoon. Northwesterly wind gusts to 35 kts likely. 


Thursday...high confidence VFR. Southwesterly wind gusts to 35 kts 
likely. 


Thursday night and Friday...low confidence. Likely VFR...but if more 
moisture available during frontal passage...could see MVFR/IFR 
conditions in -ra/-sn. 


&& 


Marine... 
winds will mainly be east/southeast tonight through Monday and light. 
Winds may increase to Small Craft Advisory levels Monday night as low pressure 
approaches. Seas will build to Small Craft Advisory level by late Monday 
night...especially on the outer waters south and southeast of New 
England. 


Outlook...Tuesday through Friday... 


Tuesday...seas increase to 5 to 10 feet on the outer waters. Winds 
diminish becoming westerly late. Small Craft Advisory will be 
necessary for seas. 


Wednesday...high confidence in high end Small Craft Advisory 
northwesterly winds. Low to moderate confidence northwesterly gales 
on the northeast coastal waters. Seas remain 5 to 10 feet on the 
outer waters. 


Thursday...seas and winds diminish through the day then increase 
again late in the evening. High confidence Small Craft Advisory. 
Low to moderate confidence in a brief period of gale force winds. 


Friday...winds and seas diminish through the day. High confidence in 
a Small Craft Advisory for most of the day and at least a portion of 
the evening. 


&& 


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


As of now...we are forecasting a widespread 1 to 2 inches of rain to 
fall Monday night and Tuesday. However...we do think there very well 
could be areas of 2+ inches given +2 to +3 South Dakota precipitable water anomalies. The 
good thing is that the low level jet anomalies are quite a bit weaker 
with this event than they were with the last one. In addition...this 
system will be much more progressive. Therefore...flooding will not 
be as big as a problem as it was a week ago. Nonetheless...area 
rivers are still running quite high with a couple still in flood. 1 
to 2 inches of rain will allow for a rekindling of minor flooding. 
Since any flooding probably won't start to occur until the 4th period 
of the forecast /Tuesday/ we opted to not issue a Flood Watch at this 
time. However...we suspect one will have to be issued tonight. The 
middle shift will be able to get another look at the model forecast quantitative precipitation forecast 
amounts and where any axes of heaviest rain may set up. 


&& 


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


&& 


$$ 
Synopsis...ekster 
near term...kjc 
short term...ekster 
long term...rlg 
aviation...kjc/ekster/rlg 
marine...ekster/rlg 
hydrology... 

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