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Area forecast discussion 
National Weather Service Taunton Massachusetts 
940 am EDT sun Jul 20 2008 


Synopsis... 
a very warm humid and unstable pattern continues into early next 
week. A frontal boundary oscillating across New England will yield 
nearly daily rounds of scattered showers and thunderstorms into middle 
week...generally strongest and most widespread during the afternoon 
and evening. A trend toward seasonable temperatures and lower 
humidity is expected the middle and end of the work week. Tropical 
Storm Cristobal will likely pass southeast of Nantucket Monday night...and 
could contribute to high swells and surf across portions of the New 
England S and southeast coast. 


&& 


Near term /until 6 PM this evening/... 
at middle morning...a decent deck of middle level cloudiness covered the 
region especially north of the Massachusetts Turnpike. There were 
also a few very light rain showers scattered about southern New Hampshire/far 
northern Massachusetts. 


The main question that needs to be answered is will we see enough 
destabilization across portions of our region for any severe 
weather? The area of concern is mainly to the north of the Massachusetts 
Turnpike...especially southern New Hampshire/far northern Massachusetts as a strong 
shortwave and its associated lift moves into this region. 0 to 6 km 
shear is expected to be on the order of 30 to 40 knots in this 
region which is pretty good. However...middle level lapse rates are rather 
weak so we are going to need heating at the surface to provide most 
of the instability. The problem is that there looks to be a fair 
amount of middle level cloudiness in this region for much of the day 
although we will see peeks of sun at times. 


All in all...as is typically the case in southern New England its 
not a clear cut scenario. We will just have to monitor cloud trends 
in this region. However...given the 30 to 40 knots of shear we have 
the potential for a few severe thunderstorms mainly north of the Massachusetts 
Turnpike with the best chances north of Route 2 and into southern 
New Hampshire. This again will depend upon the amount of destabilization we 
receive which remains uncertain. The main threat would be damaging 
straight line wind gusts but an isolated report of large hail can 
not be ruled out. In addition...fairly high precipitable water values will bring 
the potential for heavy rainfall and brief/localized flooding with 
any thunderstorm. To the south of the Massachusetts Pike...we still will have 
the threat of an isolated strong thunderstorm later this 
afternoon/evening but the best dynamics will be to the north. 


As for precipitation chances...will run with likely probability of precipitation across the 
interior this afternoon/early evening based on model quantitative precipitation forecast and Omega 
fields. Will taper just to slight chances across far southeast 
Massachusetts/cape/islands as the better dynamics will pass to the northwest of 
the region. 


High temperatures will still be very warm but more clouds will keep 
them lower than the past few days. Highs should be in the middle to 
upper 80s north of the Massachusetts Pike...with upper 80s and lower 90s south 
of the Massachusetts Pike and away from the coast. 


Surf zone: upgraded to moderate risk of rip currents along south 
facing beaches of the South Coast/islands based on latest guidance 
and reports. 


&& 


Short term /6 PM this evening through 6 am Monday/... 
model consensus has precipitable waters  approaching 2 inches late today and 
tonight. Thus...have added wording for possible locally heavy rain 
northwest of bos-sfz-ijd line this evening and tonight. One or two impulses may 
also enhance rafl this eve/tonight. Have not opted to issue Flash 
Flood Watch since too much uncertainty as to greatest focus of 
convection later. 


Have stayed close to mavmosguide values. No break in the humidity 
expected through tonight. 


&& 


Long term /Monday through Saturday/... 
good model agreement on a long wave trough setting up across the Great 
Lakes and the northeast next week. However models differ on the 
evolution of the long wave trough...specifically the timing of it 
departing New England middle to late week. The 00z GFS appeared to be 
in the middle of the pack regarding these details...along with 
support from the 00z gefs and the 00z hi resolution European model (ecmwf). 
Therefore this portion of the forecast was weighted heavily toward 
the 00z GFS and its MOS output. 


This pattern favors multiple days of convection along with a trend 
toward seasonable temperatures and lower humidity middle to late week. 


Monday and Monday night... 


Widespread showers likely given deep layer cyclonic flow across the 
northeast combined with fairly robust baroclinic/thermal gradient 
trough-frontal boundary sweeping across the region. In addition...deep 
layer moisture in place with precipitable waters  at or above 2.0 inches combined 
with dew points in the low to middle 70s! Thus...showers will likely 
contain heavy downpours. Very warm and humid conditions /almost 
tropical-like/ expected. 


As for ts Cristobal...all of the 00z guidance tracks this tropical 
cyclone southeast of the 40n/70w benchmark Monday night-Tue. This is 
consistent with the latest TPC latest forecast. This seems 
reasonable given the middle level flow doesn/T back sufficiently to the 
S-SW to steer Cristobal more northerly and closer to New England. In 
addition...it is expected to remain a minimal tropical storm. 
Therefore...at the moment the most likely scenario is for Cristobal 
to remain offshore with little if any direct impact to southern New 
England. The main concern with Cristobal will be its wave field 
which will likely result in increased surf along the Rhode Island and 
southeast Massachusetts beaches this upcoming week. This will yield an 
increased risk of strong rip currents. 


Tuesday... 
there are indications that Tuesday may turn out to be a mainly dry day 
as lead short wave trough and Cristobal move east of the area... 
followed by some short wave ridging ahead of the next trough to impact 
the region middle week. Therefore any shower/thunderstorm activity should be 
isolated in coverage at most. 


Wednesday through Saturday... 


Next bundle of jet energy approaches the region Wednesday and will result 
in an increased risk of showers and thunderstorms. As mentioned 
above models differ on the timing of middle level trough exiting the 
region. However...the bulk of the guidance suggest a drying trend 
later Thursday into Friday...as middle level trough moves offshore. This will 
also usher in an airmass across the region that is not as hot and 
less humid. 


&& 


Aviation /13z Sunday through Thursday/... 


Today and tonight... 
marginal MVFR/VFR conditions across most of the region by middle 
morning in haze. The exception was the cape and islands where IFR 
conditions in low clouds were observed. These may break up a bit 
for a time late this morning/early afternoon but should reform again 
toward evening. 


Across the rest of the region...marginal MVFR/VFR conditions in haze 
should continue into the afternoon. Scattered strong thunderstorms 
with the potential for 40 knot wind gusts are expected mainly north 
of the Massachusetts Turnpike after 18z or 19z this afternoon into the 
evening. 


Outlook...Monday through Thursday... 


Mainly VFR...with conditions lowering to MVFR in scattered showers 
and thunderstorms each day. MVFR will be most common Monday with VFR 
prevailing Tuesday. 


&& 


Marine... 


Today and tonight... 
Small Craft Advisory seas continue this afternoon for portions of our southern 
waters. This is mainly for marginal 5 foot seas...but should see 
southwest wind gusts in the low 20 knots develop in this region 
during the afternoon with mixing. A few strong thunderstorms with 
gusty winds may impact the waters late this afternoon/evening but 
the bulk of this activity should be across the waters north of 
Boston Harbor. 


We will likely need to extend Small Craft Advisory for left over swell across our 
southern outer-waters for tonight. 


Outlook...Monday through Thursday... 


Monday/Monday night...S-SW winds 15-20 knots along with building seas. 
Scattered thunderstorms with cold front moving across the waters. 


Tuesday...front moves offshore with improving weather. However ocean 
waters remain rough as a combination of leftover S wind waves from 
Monday combine with S swells from Cristobal. 


Wednesday and Thursday...another cold front enters New England yielding 
scattered showers and thunderstorms. Modest S swells will persist 
across the south ocean waters. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...Small Craft Advisory for hazardous seas until 6 PM EDT this 
afternoon for anz235-237-254-255. 


&& 


$$ 
Synopsis...nocera/Thompson 
near term...Frank 
short term...Thompson 
long term...nocera 
aviation...Frank/Thompson/nocera 
marine...Frank/Thompson/nocera 

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