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fxus61 kbox 032110 
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Area forecast discussion 
National Weather Service Taunton Massachusetts 
510 PM EDT Friday Jul 3 2009 


Synopsis... 
low pressure over the northeast moves to Quebec Sat forcing a cold 
front across our area. Drier weather arrives Sunday into Monday. 
The middle of next week may become unsettled as very warm air tries 
to invade the northeast USA for a day or 2. 


&& 


Near term /until 6 am Saturday morning/... 
scattered showers and thunderstorms were affecting portions of the 
region late this afternoon. This in response to a cold pool aloft 
and marginal instability. Despite rather weak wind fields...500 mb 
temperatures will continue to bring the potential for some hail with 
the strongest storms into the early evening hours. Mainly pea size 
hail is expected...but a few of the storms may become severe and 
produce penny to nickel size hail. The best chance for this will be 
just northwest of the I-95 corridor where there is a bit better 
surface convergence based on the latest surface observations. 
Otherwise...any storms that go up may produce heavy rainfall and 
localized flooding. With the saturated ground from the heavy rains 
of the last few days...will continue the Flood Watch into the early 
evening hours for localized flooding. However...widespread flooding 
is not expected. 


Otherwise...expect the scattered showers and thunderstorms should come to 
an end by middle to late evening with the loss of daytime heating. 
Otherwise...expect quiet weather during the overnight hours with 
lows mainly in the lower 60s. 


&& 


Short term /6 am Saturday morning through Saturday night/... 
Saturday... 
a strong shortwave will drop down in northwest flow aloft. This 
will bring an area of very cold air aloft into the northern and 
eastern sections of our region...with 500 mb temperatures dropping 
to between -15c and -17c. Middle level lapse rates are expected to 
increase to between 6.5 and 7 c/km across southern New Hampshire/northeast Massachusetts. 
At the same time though...drier air will be working in from the 
northwest. 


There looks to be a small window from middle to late morning into the 
early afternoon...where marginal instability may combine with 
increasing wind fields and cold air aloft. This may bring a few strong 
thunderstorms into our northern and eastern sections of the County Warning Area. 
Both the GFS and sref ensembles indicate the potential for around 500 
j/kg of cape across southern New Hampshire/northeast Massachusetts. Therefore...will 
include a few hours of chance probability of precipitation in this region and quickly taper 
probability of precipitation down southwestward. Either way the most of the day should be 
dry...other than the risk for a brief shower or thunderstorm. 


Uncertainty revolves around this forecast since there is a 
relatively small window...before the dry air comes rushing into the 
region. However...the potential exists for a few strong 
thunderstorms across southern New Hampshire/northeast Massachusetts from middle morning into 
the early afternoon. What ever happens...any risk for convection 
should come to an end by late afternoon. 


High temperatures should reach into the lower 80s with partly sunny 
skies and a westerly flow of air. In fact...we expect wind gusts to 
around 25 miles per hour in the late morning and afternoon. 


Saturday night... 
a dry night is expected across southern New England but is may be a 
bit breezy into the early evening. The dry airmass should allow low 
temperatures to fall mainly into the 50s...with lower 60s in the 
urban heat islands of Boston. 


&& 


Long term /Sunday through Friday/... 
Sunday...dry with Maritimes low pressure the primary influence resulting 
in a gusty west wind. A very nice Sunday. Another area of low pressure 
should remain far enough south to barely threaten the S coast at 
night. Temperatures are 12z GFS MOS blended with the 4am kbox forecast. Wind 
gusts are 12z NAM mxg heights and gust along. 


Monday-Tuesday...continuity with sort of an in between transition. Could 
be a late Monday afternoon thunderstorm in the interior. Lots of uncertainty. 


Wed-Thu...model disparity prevails but it seems as Wednesday is vulnerable 
to a shower or thunderstorm. Then on Thursday we have a probable dry forecast as 
high pressure moves overhead. 


Next Friday...warm air advection from the west. Gefs is cooler than the ec and even the 
12z GFS op run so have 50 50 blended the 12z GFS mosguide with the 
4am kbox forecast. If anything...we think next Friday could be warmer than 
normal but confidence on this solution is less than normal. 


Forecast winds this Sunday/Monday are 50 50 blend GFS mosguide and NAM through 84 
hours then 50/50 12z GFS MOS and 4am EDT kbox forecast for the next Tuesday-Friday 
time frame. 


Forecast sky...50 50 blend of the 12z GFS MOS guide and the 4am EDT kbox 
forecast Sunday-Friday though I added 20-30 percent skycvr next Friday...this due 
to the warm air advection pattern as the hot produce in the nations middle section tries 
to intrude under west-northwest flow aloft-NE periphery of the middle USA ridge. 


&& 


Aviation /21z Friday through Wednesday/... 
scattered showers/thunderstorms are developing under cold pool aloft. Main 
concentration at 18z is from bdl-pvd and sref probs for cape>500 j/kg 
is capturing this area very well. Sref suggests greatest coverage of 
convection through this afternoon will be near or just west of i95 
corridor. Brief MVFR/IFR conditions with brief downpours and possible 
hail will accompany any thunderstorms...otherwise VFR ceilings expected. 
Meanwhile...stratus deck south of the cape is eroding so mainly VFR 
expected this afternoon fmh-hya-ack. 


Tonight...widely scattered MVFR showers and thunderstorms possible 
early...otherwise VFR. IFR St/fog may develop at ack by 00z...and 
over interior terminals and hya/fmh after 06z. 


Saturday...local IFR possible early...otherwise VFR. Scattered showers/thunderstorms 
associated with next shortwave may bring brief MVFR conditions 
14-18z...primarily mht-orh-bos. Rapid drying occurring after 18z with 
west wind gusts to 25 knots possible. 


Outlook /Sunday through Wednesday/... 


Generally VFR. West wind gusts to 25 kts possible Sunday 17z-23z. 


&& 


Marine... 
tonight...a few thunderstorms will affect the waters this evening. 
The strongest storms may contain brief gusty winds and hail. 
Otherwise...seas over the outer waters will generally be between 2 
and 4 feet. However...5 foot seas may flirt with the outer-waters. 


Saturday...enough westerly flow expected to bring seas to 5 feet 
across our southern outer-waters...so will hoist a Small Craft Advisory in this 
region. In addition...westerly flow and good mixing support 20 to 
25 knot wind gusts especially near shore. Later shifts will have to 
consider a Small Craft Advisory for the rest of our region...but confidence not high 
enough to hoist at this time. 


Saturday night...winds and seas should drop below Small Craft Advisory thresholds. 


Outlook /Sunday through Wednesday/... 


No headlines at this time though westerly wind gusts to 25 knots Sun afternoon may prompt a 
partial east Massachusetts coast short term Small Craft Advisory. 


&& 


Box watches/warnings/advisories... 
CT...Flash Flood Watch until 8 PM EDT this evening for ctz002>004. 
Massachusetts...Flash Flood Watch until 8 PM EDT this evening for maz002>021- 
026. 
New Hampshire...Flash Flood Watch until 8 PM EDT this evening for nhz011-012- 
015. 
Rhode Island...Flash Flood Watch until 8 PM EDT this evening for riz001>007. 
Marine...Small Craft Advisory from 9 am to 6 PM EDT Saturday for anz254- 
255. 


&& 


$$ 
Synopsis...wtb/drag/Strauss 
near term...Frank 
short term...Frank 
long term...drag 509 
aviation...kjc/drag 509 
marine...drag/Frank 

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