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fxus61 kbox 202321 
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Area forecast discussion 
National Weather Service Taunton Massachusetts 
721 PM EDT Sat Mar 20 2010 


Synopsis... 
a cold front will bring much cooler conditions and spotty light showers 
Sunday. Coastal low pressure will bring widespread rain Monday night 
through Tuesday night...which may be heavy at times. Mainly dry weather 
with at or above normal temperatures follows Wednesday into Thursday 
before somewhat colder weather arrives next Friday into the weekend. 


&& 


Near term /until 6 am Sunday morning/... 
please see climate section referencing todays lt 100+ year lt climatology site 
Max's...reference to last time and when last time in March that we equaled 
or exceeded. Its been awhile for March. 


Cold front across upstate New York and northern New England still slowly 
moving south. Thinking arrival of this front will be a bit slower 
than previous timing...reaching I-90 late this evening. Still 
thinking this front will be well south of the South Coast by 8 am 
Sunday. 


Brief gusty wind shift to north possible late tonight. Reran gust tools 
with 18z NAM mxg...and GFS and NAM gust along and both offer a short 
prd of guts...especially over the water. 


This cold front to move through most of southern New England 
dry /trace or less/...but cannot completely rule out the possibility of 
isolated measurable showers north of I-90...especially along and 
north of Route 2 into southwest New Hampshire. 15z sref and several 12z op 
models suggest warm air advection overrunning the the southward moving surface cool front. 
This overrunning in part induced by rr1 200mb jet core in northern Maine. 


Added more cloud per a blend of 12z European model (ecmwf) relative humidity and previous 4pm kbox forecast. 


Mav/met min temperature guidance is similar...so did not stray too 
far from the consensus. 


&& 


Short term /6 am Sunday morning through Sunday night/... 
east to northeast flow dominates most of southern New England 
Sunday. So it will be quite a bit cooler than what we have 
experienced the past few days...but still above normal toward the 
South Coast and CT River Valley. Prefer the mav guidance for 
temperatures and dew points Sunday. 


Thinking the front south of New England Sunday morning washes out as 
it tries to push north during the afternoon into the evening. Left a 
chance of showers across the interior as warm air advection and the 
passage of a weak middle level shortwave may be enough to trigger 
precipitation Sunday night. 


Min temperature guidance similar once again...so used the mav/met 
consensus. 


&& 


Long term /Monday through Saturday/... 
confidence on details and this 4pm forecast package after Wednesday 
is lower than average. 


Operational models and ensembles spread apart next Thursday through 
the weekend. 


This divergence in model opinion was not easily rectified in this 
forecast and I am not satisfied with the gust output and pop/sky forecast 
issued for Thursday through Friday night. 


Monday... see large bust potential in temperatures...dependent on 
skycover and precipitation. If sky cover is thinner along with rain delayed 
until evening....the interior could see temperatures well up into the 
60s. Tried to take the middle of the Road in the blend. Obviously 
cool along the east mass coast with ocean influence. Issued probability of precipitation were 
the 09z sref. 


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. Some 
models try to keep a reflection of the Monday warmth across interior 
southern New England for tuesdays Max's...but opted for cooler than guidance due to 
increasing easterly flow off 40s SST. Any southward trend of some of 
these op models I think will result in cooler temperatures. At this time of 
year...think we need to favor the cooler side of the ensemble spread. 
Probability of precipitation near 100 percent and yes...there could be a break S of the Mass Pike 
Tuesday. For now though...09z sref probability of precipitation and overall ensemble indications 
point to low top rain or drizzle continuing even after prime lift has 
shifted into northern mass for a time. Looks a little unstable to ME in southeast 
New England with large 850-500mb lapse rates..and divergence of q. There is 
a small chance of thunder in the southeast part of our County Warning Area or waters on Tuesday. 


Ensemble probability of precipitation for 24 hour 1 inch rain ranges from around 60 percent gefs 
12z/20 vsn to 60-70 percent 09z sref. Precipitable waters  and instability similar to 
last weekend but 850-950 Ely inflow and persistence duration is 
significantly less and this reduces the potential for a high end 
event. 


Severe weather potential statement continues the theme and experimental in-house gefs/sref river 
flood potential guidance suggests renewed flooding /not necessarily or 
not as likely as severe/ for some of those same rivers that had 
moderate or major early this week in eastern mass and southeast New 
Hampshire. No action at this time...this is still 72 hours away and lots of 
room for error. 


There also is a low probability that the precipitation ends as a bit 
of snow across the interior high terrain. Bl temperatures are marginal to 
support this...too deep a layer of just above freezing but occurring 
at night makes it potentially easier. Again not a big threat and not 
severe weather potential statement material as of this writing. 


Wednesday and Thursday... 
any lingering showers should come to an end Wednesday morning. 
Otherwise...mainly dry weather with at or just above normal temperatures 
expected. GFS had a windex signal Thursday morning. It looks to ME 
like its too strong and the asstd winds Thursday morning are probably 
too strong. 


Friday/Saturday...instead...we may need to wait for a prd of northerly wind 
gusts 25-35 kts and influx of colder air. Have partially included 
12z/20 European model (ecmwf) colder temperatures/dewpoints in this forecast for Fri-Sat. Do not 
like the pop and gust forecast issued for these two days and this will 
need some work in next forecast cycle. Lots of variability and associated 
uncertainty in the weather here next Fri/Sat. 


&& 


Aviation /23z Saturday through Thursday/... 
tonight...high confidence VFR. Broken VFR 4000 to 8000 feet feet deck 
deck develops this evening from north to S behind a cold front. Deck 
mainly north of kpym-kijd-kbdl after midnight. NE wind up to 15 knots 
developing at kbos after 06z. Scattered light showers expected north of kbvy- 
korh-kbdl. Maybe only sprinkles... cant be sure but in any 
case...VFR. 


Sunday...mostly VFR ceilings in areas of stratocumulus. But low probability of 
MVFR...especially north klwm-kfit-kore-kaqw. A few showers possible 
mainly interior. 


Sunday night...medium confidence there will be patchy MVFR ceilings 
and visibility in fog. Low confidence localized IFR conditions in fog. 


Outlook...Monday through Thursday... 


Monday...VFR or MVFR ceilings through early afternoon become widespread IFR conds 
in r late day or night. Average confidence in the forecast daylight 
hours. High confidence at night. Variable winds near warm front with 
onshore flow near the coast and bays. 15z sref probs indicate quite a 
bit of low ceiling developing in the warm sector S coast. Possible LIFR 
there as surface dew point attempts to warm above sst? 


Tuesday...high confidence IFR conds rain. NE gusts of 30 to 35 knots 
on the coast....especially Boston. 


Wednesday... 
low to medium confidence that MVFR-IFR ceilings early improve to VFR 
during the afternoon. Northwest gusts 25-30 kts. 


Thursday...high confidence VFR. Average confidence northwest wind gusts 25 to 30 
kts. 


&& 


Marine... 
relatively tranquil wind and sea conditions tonight though Sunday 
night. There is a low probability of wind gusts approaching 20-25 knots 
for a brief period around daybreak Sunday across the coastal waters 
east of Massachusetts. Confidence not high enough to warrant a Small 
Craft Advisory at this point...but the situation will need to be 
monitored this evening. 


Outlook...Monday through Thursday... 


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...especially bostons North Shore seaward. 


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


Thursday...Small Craft Advisory possible in northwest flow reinforcing cold front. Confidence 
average or below average. 


&& 


Hydrology... 
most of the remaining mainstem rivers in NE Massachusetts should drop below 
flood stage overnight. 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. 


From the long term section... 


Ensemble probability of precipitation for 24 hour 1 inch rain ranges from around 60 percent gefs 
12z/20 vsn to 60-70 percent 09z sref. Precipitable waters  and instability similar to 
last weekend but 850-950 Ely inflow and persistence duration is 
significantly less and this reduces the potential for a high end 
event. 


Severe weather potential statement continues the theme and experimental in-house gefs/sref river 
flood potential guidance suggests renewed flooding /not necessarily or 
not as likely as severe/ for some of those same rivers that had 
moderate or major early this week in eastern mass and southeast New 
Hampshire. No action at this time...this is still 72 hours away and lots of 
room for error. 


&& 


Tides/coastal flooding... 
splashover and possibly some pockets of minor coastal flooding are 
only a low probability during the time/S of high tide Tuesday 
across the eastern Massachusetts coast with further beach erosion along bostons 
North Shore. Have continued this information in the severe weather potential statement...but with low 
confidence and certainly not the severity of last weekends 3 day 
15-20 feet gale noreaster. 


&& 


Climate... 
preliminary...corrected Boston last time in March this warm 


Todays highest temperature of the month so far... 
bos 72 dating back to Oct 31 2009. Last time in March this warm-31st 2006 
pvd 73 dating back to Oct 22 2009. Last time in March this warm-31st 1999 
bdl 74 dating back to Oct 22 2009. Last time in March this warm-31st 1999 
Oct 68 dating back to Oct 22 2009. Last time in March this warm-14th 2007 


And can we remember the last few days of /roughly the 27th-31st/ 
March 1998 when maximum temperatures routinely were in the 70s to upper 80s. 




On the storm of last weekend... 


Boston calendar totals...3 day 6.98 ranked 13th all time 3 day totals. 
When you break it down by events...7th wettest 3 day event. Tops were 
August 1955...Oct 1996...may 2006...June 1998...January 1939 and 
October 1962. 


&& 


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


&& 


$$ 
Synopsis...drag/Belk 
near term...Belk 720 
short term...Belk 
long term...drag 
aviation...drag/Belk 720 
marine...drag/Belk 
hydrology... 
tides/coastal flooding... 
climate... 

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