Area forecast discussion
National Weather Service Taunton Massachusetts
701 am EDT Monday may 20 2013
Synopsis...
a warm front lifting through the region will bring a few showers
or thunderstorms today as it heads into central New England. The
front will drop back south on Tuesday resulting in briefly cooler
weather...before warm and humid conditions return Wednesday and
Thursday with scattered showers and thunderstorms. It will turn
cooler and less humid next weekend.
&&
Near term /until 7 PM this evening/...
7 am update...
Warm front progressing northward and will move through the region
by late morning or midday at the latest. Temperatures already off to a
mild start with readings in the u50s and l60s at 7 am. Temperatures will
soar throught the 70s to around 80 this afternoon away from the
shore. Once boundary lifts north of the area not much of a focus
for convection. In addition 0-6km wind field drops below 30 knots
this afternoon. Thus any convection would not be organized or
widespread. Previous forecast captures this well so no major
changes with this update.
===================================================================
Last of showers were exiting Cape Cod and islands early this
morning. Clouds remain locked in with patchy fog and drizzle...
which will persist through middle morning. Thereafter model cross
sections show some drying through column as weak warm front lifts
to our north. This should allow for breaks of sunshine to develop
later this morning and this afternoon for much of southern New
England. Exception will be near S coast...Cape Cod and islands
where marine layer should hold strong given SW flow.
Potential for convection this afternoon is limited by lack of
instability as sb convective available potential energy only forecast to be as high as 500
j/kg...weak middle level lapse rates of less than 5c/km...and
marginal 0-6km shear of 30kt. That said we do expect to see at
least widely scattered showers/storms develop across interior.
Maintained chance probability of precipitation away from S coast...although best chance
looks to be across SW New Hampshire and northwest Massachusetts. Hrrr shows scattered activity
developing in those areas after 18z.
Certainly looks like a warmer and somewhat more humid day with
highs ranging from 60s along S coast to 70s and lower 80s
elsewhere. Used a blend of NAM/GFS MOS.
&&
Short term /7 PM this evening through 6 PM Tuesday/...
warm front stalls across central New England tonight. This will
maintain light S/SW flow across region and with plenty of low
level moisture...confidence is high on seeing low clouds/fog and
possibly drizzle spread inland from coast. Potential is there for
areas of dense fog...especially around Cape Cod and islands.
Otherwise no significant rainfall is expected as best dynamics
stay to our north and west. Relatively mild night with lows holding in
50s/lower 60s...which is closer to NAM MOS.
Weak upper ridge building across New York state will force front
back southward Tuesday as a backdoor cold front. Models in good
agreement in dropping front through Tuesday afternoon...but GFS seems
to overdo convection riding east along boundary from Great Lakes. NAM
seems much more reasonable in stabilizing airmass over southern
New England as flow turns more east/southeast and focuses any convection to
our west/north where it becomes more unstable. We are not thinking we
will see much in way of showers/storms develop...although it is
possible a few showers make it into western New England by end of
day.
Should be wide range in temperatures Tuesday due to onshore flow...
from lower 60s along east Massachusetts coastline including Cape Cod to upper
70s across CT River Valley. Leaned more toward NAM MOS which
captures this well.
&&
Long term /Tuesday night through Sunday/...
highlights...
* warm and muggy Wednesday/Thursday then turning cooler and less humid Friday
* scattered showers and thunderstorms Wednesday and Thursday
* dry but cooler than normal for Memorial Day weekend
Good overall agreement on the large scale flow including frontal
positions from the 12z/19 gefs and ecens. Both of these ensemble
data sets have a backdoor front sagging southward through the
southern New England Tuesday night then lifting north of the region Wednesday
and Thursday with true warm sector overspreading the area. Both ensembles
offer +16c airmass at 850 mb and +20c at 925 mb over the region
Wednesday. Thus potential for temperatures to soar into the 80s both days if
sunshine develops. It will be muggy as well with dew points in the 60s.
This will result in warm nights /Wed and Thursday/ along with patchy fog.
Scattered showers and thunderstorms likely both Wednesday and Thursday given
warm sector over the area both days. Also models in good agreement
on convection along or near the warm front Tuesday evening/night.
Convection will be more widespread during peak heating hours of the
afternoon and lingering into the early evening both days. Ensembles
suggest instability greater Wednesday (mean cape about 1000j/kg) than Thursday.
However approaching cold front will yield greater frontal
convergence Thursday along with stronger jet dynamics /0-6km deep layer
shear/...so convection may be more organized/numerous Thursday than Wednesday.
In addition gefs suggest instability ridge across New York/PA and New Jersey.
Therefore western New England has greatest risk for strong to
perhaps severe thunderstorms Wednesday and Thursday. Given instability and precipitable waters of +1
to +2 Standard heavy downpours are possible with any convection.
Good model agreement that frontal passage will occur sometime late
Thursday or Friday. 00z GFS slower with frontal passage as it develops a wave along
the front. At this time range prefer not to Chase a single
deterministic solution so will follow pressure pattern from gefs and
ecens. This suggest Friday will be our transition day from warm and
muggy to a dry...much cooler and less humid airmass for Memorial Day
weekend. In fact by Sat both gefs and ecens have a 1030mb high
settling over the Great Lakes with core of this anomalous cool
airmass /850 temperatures 0c to +2c/ across northern Massachusetts/southwest New Hampshire...then
slowly moderating by Monday. Hence mild days but cool nights. In fact
there could be some patchy frost across northwest Massachusetts into southwest
New Hampshire with temperatures dipping into the mu30s Sat and Sun morning!
&&
Aviation /12z Monday through Friday/...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
7 am update...
no change to previous forecast. Forecast remains on track.
Moderate confidence through Tuesday.
Widespread IFR/LIFR through 12z in low clouds/fog/drizzle. Gradual
improvement to MVFR expected 12z-15z and eventually VFR by 18z
except around Cape Cod and islands where IFR likely to persist all
day. Scattered showers will reform across interior after 18z with
isolated thunder also possible.
Should see rapid deterioration this evening to IFR/LIFR 23z-03z
as low clouds/fog/drizzle return in light onshore flow. Will be
harder for IFR to erode Tuesday with persistent east/southeast wind...but expect
all but cape/islands to improve to MVFR ceilings by 18z.
Kbos terminal...moderate confidence. Confident on timing of
improvement this morning...but ceilings may only lift to 025 through
18z.
Kbdl terminal...moderate confidence. May be 2-3 hours too fast on
improvement to MVFR ceilings this morning.
Outlook...Tuesday night through Friday...
Tuesday through Thursday night...moderate confidence. Very
unsettled pattern with variability between VFR conditions and
MVFR/IFR conditions in shra/tsra/fog. A few strong to severe thunderstorms
possible Wednesday and Thursday.
Friday...moderate confidence. Conditions should improve along with
a wind shift from west to east as cold front moves through region.
&&
Marine...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
High confidence through Tuesday.
Warm front lifts north of coastal waters today and stalls over central
New England. Light S/SW flow develops across waters but seas
slowly build in southerly swell...most notably across S coastal
waters where Small Craft Advisory remains posted. Although SW flow is modest at
best it should still create steep waves on Buzzards Bay and
Vineyard Sound during outgoing tide this afternoon...so maintained
Small Craft Advisory for those areas as well.
Expect areas of dense fog tonight into Tuesday with persistent SW
flow...especially around Cape Cod and islands. Front drops back S
Tuesday and shifts winds to E/se...so visibilities should improve Tuesday
afternoon. Seas should begin to subside as well due to decaying
southerly swell.
Outlook...Tuesday through Friday...
Tuesday night... backdoor front slips across the area with NE winds
likely over the northern waters and SW winds across southern waters.
Rain and fog will reduce visibility. Modest wind at best with marginal
swell.
Wednesday and Thursday... warm front lifts north of the area with modest south-southwest
winds developing across the waters. South-southwest winds may increase to 20-25
knots from late Wednesday into Thursday ahead of approaching cold front. Showers
and thunderstorms should be most numerous Thursday with approaching cold front.
Friday...cold front along with wind shift from south-southwest to west-northwest should
commence. Visibility will improve with the wind.
&&
Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas until 2 am EDT Tuesday
for anz233>235-237.
Small Craft Advisory for hazardous seas until 8 am EDT Tuesday
for anz254>256.
&&
$$
Synopsis...nocera/jwd
near term...nocera/jwd
short term...jwd
long term...nocera
aviation...nocera/jwd
marine...nocera/jwd
