Area forecast discussion
National Weather Service Taunton Massachusetts
900 PM EDT Sat may 18 2013
Synopsis...
high pressure across northern New England will move off the coast
Sunday. A warm front will move through the region Sun
night...probably bringing a few showers. The front will lift
north of the region early next week and then stall over New York
and central New England. Weak waves of low pressure will move
along the front middle of next week bringing warmer...more humid
conditions along with scattered showers as well as possible
thunderstorms...most likely during the afternoon and evening
hours.
&&
Near term /until 6 am Sunday morning/...
9 PM update...
Plenty of middle/high clouds streaming across southern New England
tonight. Much of lower cloud cover has dissipated with loss of
daytime heating...but most model guidance suggests we will see
more low clouds reform overnight. Not sure this will be case as
there isn/T much being observed to our SW where models have it
now. As a result we will remain more optimistic and hold off on
any clouds/showers overnight.
Forecast lows in 40s/lower 50s are on track. Could see temperatures a few
degrees cooler than expected with any significant breaks in
middle/high cloud cover.
&&
Short term /6 am Sunday morning through Sunday night/...
Sunday...
high pressure moves off the New England coast as a warm front slowly
approaches from the south. This will result in middle level warm
advection and an increase in cloud cover. There still will probably
be a few peeks of sun at least in the morning...but the overall
trend will be for mostly cloudy skies. High temperatures are tricky and
will depend upon just how quickly skies become mostly cloudy. We
blended the cooler gfsmos guidance with the much milder metmos.
Best chance of the mildest readings will be across the Merrimack
valley...away from the coast and where skies will be slower to
become mostly cloudy. Will range highs from the middle 60s to around
70...but later shifts may have to make tweaks overnight.
As for precipitation chances...better focus/forcing/moisture will
remain to our south and west. Therefore...expect most of the day
will feature dry weather. Warm advection may still result in a few
spot showers at times...with the best chance in our southwest zones.
Therefore...will include some low probability of precipitation to cover this potential
across most areas.
Sunday night...
the warm front gradually lifts north across southern New England.
Middle level forcing/dynamics are not that impressive...so not
expecting a lot of rainfall. However...still expect some scattered
showers in the warm air advection pattern. Can/T rule out some
isolated thunder south of the Massachusetts Turnpike...but indices were too
marginal to insert at this Point.
May also see some patchy fog develop as higher dewpoint air
overspread the region. Low temperatures should only fall into the lower to
middle 50s given increasing low level moisture and cloud cover.
&&
Long term /Monday through Saturday/...
highlights...
* warm and humid with scattered showers through at least Thursday
Overview and model preferences...
18/12z long range guidance suite is in fair agreement through the
middle term period...but then struggles with the merging /or non-
merging/ of a split flow regime toward the end of the period.
Given the agreement that the convergent region of these two
streams will dominate through the middle term...will use a GFS/European model (ecmwf)
blend to baseline forecast. For the tail end of the long
term...will likely lean away from the European model (ecmwf) deterministic run...as
it generates a very deep meandering cutoff in northern New England
which would suggest that unsettled conditions continue well into
/and possibly beyond/ the weekend. In any case...with convergent
streams aloft through the middle term...unsettled conditions are
likely...but as was noted...it should not be a washout.
Details...
Monday into Monday night...
surface warm front shifts into northern New England with time...allowing
much of southern New England to break into the warm sector through the
period. Looks like a fair amount of moisture will combine with
diurnal heating to yield some daytime -shra...particularly over
southern New Hampshire an northern Massachusetts. Soundings look to remain fairly stable during
the day...so will keep thunder out of the forecast for now. With
high temperatures in the upper 60s to near 70 and dewpoints in the upper
50s...conditions are likely to feel muggy.
Tuesday into Wednesday...
the warm front in northern and central New England is expected to
gradually sink S of the region through the period. On Tuesday...this
frontal passage /particularly during the afternoon heat/ expect
some destabilization...especially if there are some early day
cloud breaks as some of the guidance suggests. Cooling upper levels
as high pressure noses in from the north suggest a rise in k/tt and Li/S
dipping to 0 to negative values. Shear is not
great...particularly through 850 mb...but there is enough support for
updrafts...so will continue to suggest thunder for Tuesday. On
Wednesday...weak early day ridging will likely yield a partly cloudy
start to the day until return flow develops as high pressure slides to
the NE. Given the approaching shortwave...early clearing and
increasing moisture...may see another day with the threat for
thunderstorms...especially in the west as a secondary warm front moves
through the area. A little better shear on Wednesday too possibly...so
will continue with a thunder threat on Wednesday as well.
Thursday and Friday...
tricky forecast here as it will be dependent on how quickly northern
stream jet energy sinks S from Quebec and Ontario. This will
dictate how quickly a series of shortwaves and their surface low pressure
waves will affect the region. In any case...the wet weather continues
although a bit more stable than Tuesday and Wednesday. Given the differences
between models in how the northern stream works out...exact timing for
any of these waves remains a bit of a question mark. Once
again...it will likely not rain everyday...but there is the threat
for at least -shra through the period.
The weekend...
the southern stream ridge begins to move the northern stream longwave trough
offshore through the period...so looks like a transition to more
dry weather will be likely sometime during the weekend.
&&
Aviation /01z Sunday through Thursday/...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Overview...high confidence continues tonight. Moderate confidence
Sunday and Sunday night.
Overnight...
expecting mostly VFR conditions during the overnight hours. Low
confidence in some MVFR ceilings arriving in the CT valley toward
daybreak.
Sun...
continued with optimistic forecasting suggesting the MVFR ceilings
take until middle morning to early afternoon to arrive in the
interior...holding off until evening for eastern terminals.
Therefore...mostly VFR to start...with a gradual downward trend
through the day.
Sun night...
mainly MVFR/IFR in a mix of fog and showers during the overnight
hours
Kbos terminal...high confidence in taf overnight and early in the
day tomorrow. Lower confidence in timing of MVFR by sun
evening...then IFR by overnight in fog/showers.
Kbdl terminal...moderate confidence in taf overnight...mainly in
potential for MVFR ceilings to arrive at terminal by Sun morning. It
appears best chance will be middle day Onward sun. Therefore...VFR
expected to dominate into the morning.
Outlook...Monday through Thursday...
Moderate confidence through the period.
Mainly VFR/MVFR during the days...with the best chance for MVFR in
any daytime showers or occasional thunderstorms. Expect mainly
MVFR/IFR during the overnight hours in a mix of fog and low
stratus...especially closer to the South Coast.
In sum...a period of unsettled weather is expected through the period.
&&
Marine...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Moderate to high confidence through Sunday night.
Relatively weak pressure gradient should keep winds/seas below
Small Craft Advisory thresholds tonight and Sunday. However...high pressure moving
off the coast on Sunday will begin to generate long southwest
fetch into the southern waters. This should allow seas to build to
Small Craft Advisory thresholds across our southern outer-waters Sunday night. Have
hoisted Small Craft Advisory headlines for hazardous seas in this region. Small Craft Advisory
headlines may have to be expanded into some of the southern
sounds...but since its a 3rd period event confidence was not high
enough to do at this point.
Outlook...Monday through Thursday...
Moderate confidence through the period.
Winds should remain below Small Craft Advisory thresholds through
the period. Also...a combination of showers and fog will likely
lead to reductions in visibilities through the period.
Monday into Tuesday...lingering swell along the southern waters and eastern outer
waters gradually subsides through Tuesday. Will likely need Small
Craft Advisory for seas into the day Tuesday.
Wednesday and Wednesday night...seas remain below small craft thresholds.
Thursday...as low pressure approaches from the west. Expect gradually building
seas...which may reach 5-7 feet during the day Thursday. Small craft
advisories may be needed again.
&&
Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas from 11 PM Sunday to 8
am EDT Monday for anz254-255.
Small Craft Advisory for hazardous seas from 5 PM Sunday to 8
am EDT Monday for anz256.
&&
$$
Synopsis...Frank/doody
near term...jwd
short term...Frank
long term...doody
aviation...Frank/doody
marine...Frank/doody
