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Area forecast discussion 
National Weather Service Taunton Massachusetts 
448 PM EDT Sat Jul 5 2008 


Synopsis... 
a Bermuda high pressure system will bring increasingly warm and 
humid air into southern New England through Wednesday. Temperatures 
may exceed 90 on Tuesday and Wednesday across much of the region 
with high humidity levels. In addition...isolated to scattered 
strong afternoon and evening thunderstorms are expected at times 
through the middle of the week until drier and somewhat cooler air 
arrives by Thursday or Friday. 


&& 


Near term /until 6 am Sunday morning/... 
water vapor imagery suggests a weak short wave trough moving along 
frontal boundary this evening. This may help initiate isolated to scattered 
elevated convection through late evening...mainly lower CT River Valley and S 
coastal areas. Location of nearly stationary frontal boundary just S 
of New England sets the stage for considerable low clouds and areas 
of fog late tonight. There is a risk of dense fog forming near the S 
coast of Rhode Island and Massachusetts...and that region will need to be monitored 
closely this evening for need of a dense fog advisory. 


&& 


Short term /6 am Sunday morning through 6 PM Sunday/... 
short wave passage tonight would appear to bring in drier air at middle 
and upper levels for Sunday. Expect breaks/thin spots in cloud cover to 
allow for warmer temperatures. Warm air advection may set off isolated to scattered 
thunderstorms Sun afternoon...with greatest instability across CT River Valley 
of Massachusetts and CT. Wind fields are relatively weak and do not expect 
organized thunderstorms. Precipitable waters  around 1.5 in expected SW zones and so heavy 
downpours possible. 


Temperatures are tricky Sunday due to uncertainties in cloud cover. Have 
gone close to mav values but suspicious that mav temperatures may be too 
high for Rhode Island and eastern Massachusetts points. 


&& 


Long term /Sunday night through Saturday/... 
Sunday night... 
scattered diurnal showers/thunderstorms should diminish 
during the evening hours with the loss of daytime heating. 
However...a shortwave will be moving along the South Coast may cause 
additional scattered showers/thunderstorms to form into the night 
across the southern sections of our region. Therefore...will keep probability of precipitation 
going south of the Massachusetts Pike with the highest near the South Coast. 
Lows should mainly be in the upper 60s and lower 70s and areas of 
fog should also develop late. 


Monday... 
any left over precipitation along the southeast New England coast 
should have exited the region by early morning as the shortwave 
departs. Otherwise...fog patches burnoff by middle morning and a 
southwest flow of air will result in a very warm and humid day. 
Partly sunny skies with 850 mb temperatures around +16c should yield 
highs the upper 80s away from the marine influence of the South 
Coast/cape/islands. It will also feel quite humid as surface 
dewpoints will be climbing into the upper 60s to around 70. 


Although skies will be partly sunny...we expect scattered 
showers/thunderstorms to develop during the afternoon mainly along 
and northwest of a Boston to Providence line and particularly across 
the interior. This will be result of an approaching weak shortwave 
combining with mean layer convective available potential energy on the order or 1000 to 1500 j/kg. 
Wind fields are not great with 0 to 6 km shear values of 20 to 25 
knots. However...plenty of low level instability and 70+ dewpoints 
will bring the potential for isolated to scattered severe 
thunderstorms. The main threat with any severe thunderstorm will be 
damaging straight line wind gusts from wet microbursts. The Fly in 
the ointment to this is that the 12z European model (ecmwf)/Canadian are both completely 
dry and show no precipitation at all Monday afternoon. These 
shortwaves this time of year can be so subtle that a slight 
difference in timing can make all the difference. Our feeling is 
that with the amount of cape and support from the ensembles that we 
will have scattered convection Monday afternoon...but this is not 
written in stone and subject to change. Southeast of a Boston to 
Providence line...a stabilizing marine influence will likely prevent 
thunderstorm development. 


Monday night... 
scattered showers/thunderstorms should come to an end during the 
evening with the loss of daytime heating. We should see areas of 
fog develop with high dewpoints...particularly in locations that see 
precipitation. Lows should again only fall into the upper 60s and 
lower 70s. 


Tuesday... 
a hot and humid day is on tap for southern New England. Warming middle 
level temperatures should support highs mainly in the lower 90s away 
from the South Coast/cape/islands. Surface dewpoints at or just 
above 70 will make it feel quite uncomfortable outside with heat 
index values possibly in the middle to upper 90s. It will also be a 
bit breezy during the afternoon. 


Confidence in the amount of convection we see during the afternoon 
is uncertain. Nonetheless...plenty of instability will be available 
with another weak shortwave will be approaching from the west. Will 
go with some chance probability of precipitation for afternoon/evening thunderstorms with 
the best chance across the interior. 


Wednesday... 
an approaching cold front and 850 mb temperatures warming to around 
+18c should yield another hot and humid afternoon. We raised mex 
guidance and expect high temperatures to be mainly between 90 and 95 
away from the South Coast/cape/islands. Heat index values will 
probably be in the 95 to 100 degree range as high dewpoints will 
remain in place. It should also be quite breezy and would not be 
surprised to see some 35 miles per hour wind gusts ahead of the cold front. 


Otherwise...the main concern will be for showers/thunderstorms 
during the afternoon and evening as the cold front drops into the 
region. The 12z GFS is dry but its ensembles along with the 
European model (ecmwf)/Canadian show showers/thunderstorms developing along the 
front. With the amount of instability and good middle level wind 
fields would expect showers/thunderstorms to develop. Its 
early...but would expect at least some severe weather with this 
front giving the amount of instability and strength of the middle level 
wind fields. The main threat would be damaging straight line wind 
gusts. 


Thursday and Friday... 
drier air follows behind the front. Kept some low chance probability of precipitation 
Thursday afternoon mainly along and southeast of I-95 as 
showers/thunderstorms could refire if the front has not cleared our 
region. Highs should be mainly in the 80s over this time and 
humidity levels should not be as oppressive as drier air works into 
the region. 


Saturday... 
its a long way off and plenty of uncertainty. GFS has US dry but 
European model (ecmwf) hints at northwest flow and tries to bring a complex of 
showers/thunderstorms into our region. Just went with a slight 
chance for now as confidence is very low this far out. 


&& 


Aviation /21z Saturday through Thursday/... 
tonight...expect lowering ceilings and visibilities with nightfall due to moist S/southeast 
flow under inversion just north of frontal boundary. Anticipating 
widespread IFR ceilings with areas of LIFR...especially S coastal areas. 
Visibilities also expected to lower to MVFR range much of area north of Massachusetts Route 
2 and mainly IFR after 04z S of Route 2. S coast airports may 
experience LIFR visibilities below 1/2 Michigan in fog between 07z and 11z. 
Sunday...ceilings and visibilities should begin to lift after 13z or 14z Sunday. 
By middle afternoon expect mainly VFR ceilings and visibilities except locally 
lower in widely scattered thunderstorms...mainly CT River Valley...and along S coast 
where ceilings may persist bkn015-020 and visibilities near 6 Michigan in haze. 


Outlook...Sunday night through Thursday... 


Sunday night through Wednesday...we are mainly looking at VFR 
conditions from the late morning through the early evening hours 
during this time. However...rounds of scattered 
showers/thunderstorms will result in time of MVFR/IFR conditions. 
In addition...MVFR/IFR conditions expected overnight as areas of low 
clouds and fog patches develop in the very humid airmass. 


Thursday...mainly VFR. 


&& 


Marine... 
tonight and Sunday...quiet in the short term for marine with respect to winds 
and seas below Small Craft Advisory criteria. Widespread fog expected tonight...however...with 
locally dense fog possibly lowering visibilities to or below 1/2 Michigan 
S coastal areas. 


Outlook...Sunday night through Thursday... 


Persistent south to southwest flow through the middle of the week 
will allow for Small Craft Advisory seas in the Monday through at least Wednesday 
time frame across our southern outer-waters. In addition...wind 
gusts to near Small Craft Advisory conditions are expected Monday and Tuesday with a 
good chance of 25 to 30 knot wind gusts by Wednesday out ahead of an 
approaching cold front. Areas of dense fog will affect the waters 
at times during the overnight and early morning hours as very high 
dewpoint moves over the relatively cool ocean waters. 


&& 


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


&& 


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

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