Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 261955

Area Forecast Discussion
National Weather Service Boston/Norton MA
355 PM EDT Thu Apr 26 2018


A weak high pressure ridge will bring a return to mainly dry
weather later this morning through tonight with seasonable
temperatures. Another fast moving low pressure system will bring
a period of widespread showers to the region Friday afternoon
and evening. Milder temperatures return Saturday, but a cold
front will bring a brief shot of cooler air to the region Sunday
into Monday. A significant warming trend will occur Tuesday
into Thursday with dry weather expected.



4 pm update...

Quiet, pleasant afternoon into evening. Mix of sun and clouds to
close out the day, W winds still driving with gusts up around 20
to 25 mph. Low to mid 60 highs topping out with 66 observed here
at our office, will begin the downward trend into this evening,
faster more so to the W with lower dewpoints in the low 40s central
and W.


Scattered cloud decks linger, especially N/E, otherwise mostly clear
with light winds. Opportunity for boundary layer decoupling, given
recent abundant rain, can`t rule out shallow ground fog in spots.
Higher confidence in sheltered regions such as interior valleys and
dense forests. Parent temperatures bottoming out shortly after
midnight, stable afterwards with SW increasing mid-high clouds and
beginning onshore S flow by morning. Lows in the 40s, some isolated
upper 30s.



Friday into Friday night...

Late day into evening moderate, possibly heavy rain at times. S-
stream shortwave through a broad mid-level trof pattern with high
pressure situated E. Capturing sub-tropical, anomalous moist pwat
plume in excess of 1-inch into S New England fetched via strong
southerlies. Forced ascent beneath broader diffluence, focus along a
low-level warm front parent to a weak surface low reflection. Both
convergent and isentropic upsloping low-level jet into the boundary,
frontogenesis and lift, both deep column moisture and lift apparent.
Indications of steep lapse rates, moist adiabatic, conditionally
unstable environment with negative showalter indications.

Altogether a moderate to possibly heavy rain event with a potential
rumble of thunder. Greatest concern for PM commute over SE New
England with reduced visibility, ponding of water on roadways.

Some divergence on axis of heavy rainfall from high-res models as
well as timing, centering around 2p (18z), GFS faster than other
available guidance. Will lean with HREF trends with bullseye on
SE New England of generally 0.50 to 0.75 inches, locally heavier
amounts at or in excess of 1-inch, especially those areas observing

Follow-up weak frontal boundary as the surface low passes overnight.
Becoming diffuse beneath increasing subsidence, mid-level ridging,
hardly much airmass change, low level moisture becomes trapped below
the inversion. Diurnal cooling, visibility issues look certain thru
Saturday morning with some light shower activity lingering.




* Scattered showers Sunday and Monday
* Dry and warmer Tuesday through Thursday

SW flow prevails Saturday ahead of cold front. After morning
fog/low clouds burn off, especially near coast, partial sunshine
should help temperatures reach 60s to around 70 away from South
Coast. May see few showers near Berkshires Sat afternoon/evening,
otherwise dry weather expected.

On larger scale, cutoff low over Great Lakes gradually heads
east and crosses New England Sunday and Monday, which should
bring diurnal clouds and scattered showers to much of SNE.
Colder air aloft means highs will remain in 50s to near 60 both

Warming trend gets underway Tuesday through Thursday as upper
ridge builds over Gulf of Mexico and off southeast coast. Looks
like typical summertime pattern with prevailing SW flow and dry
weather. Good agreement among GFS and EC ensembles with rather
high probabilities of 80 degree temperatures Wednesday and
Thursday. Showers/possible thunderstorms with next cold front
should hold off until after Thursday.



Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Friday Night/...High confidence.

Rest of today...

VFR, MVFR/IFR lingering an hour or two over the immediate E/SE
coast. Breezy W winds with gusts around 20 kts. SCT-BKN 4-5 kft


VFR. W winds, gradually diminishing, becoming light. Watching
interior sheltered valleys, dense forests, whether shallow IFR
fog will develop. Isolated. Otherwise mid-high CIGs increasing
after midnight.

Friday into Friday Night...

Rain in by 16-18z, conditions deteriorating towards IFR-LIFR.
Heaviest around 21z with a risk TSRA over E/SE coastal New
England terminals. S/SE winds, potential gusts up to 20 kts,
especially SE coast with an additional risk of SW LLWS at 40
kts. Areas of FG developing into evening continuing overnight
with light winds. Potential beginning trend by early Saturday
morning of conditions improving.

KBOS Terminal...VFR with W winds, gusts up to 20 kts, becoming
light overnight. Mid-upper CIGs increasing towards Friday
morning. -RA/RA in by 18-19z.

KBDL Terminal...VFR with W winds, gusts up to 20 kts, becoming
light overnight. Mid-upper CIGs increasing towards Friday
morning. -RA/RA in by 17-18z.

Outlook /Saturday through Tuesday/...Moderate to High confidence.

Saturday: VFR. Slight chance SHRA.

Saturday Night: VFR. Chance SHRA.

Sunday: VFR. Breezy. Slight chance SHRA.

Sunday Night through Monday: VFR. Breezy.

Monday Night through Tuesday: VFR.



Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Friday Night/...High confidence.

Rest of today...
SW winds shifting W towards late, last of fog / low visibility
pushing out. Gusts up to 25 kts possible with improving conditions.

W winds gusting to 25 kt early then diminishing. Seas will
slowly subside but remain at or above 5 ft. Good visibility.

Friday into Friday Night...
Rain moving in towards noon, lower visibility with moderate,
possibly heavy outcomes in addition to a low risk of thunder.
Increasing S winds, peaking around late afternoon into evening,
waves building 5 to 7 feet with low visibility that`ll likely
continue with areas of fog into Saturday morning.

Outlook /Saturday through Tuesday/...Moderate confidence.

Saturday: Winds less than 25 kt. Seas up to 5 ft.

Saturday Night through Sunday: Winds less than 25 kt. Areas of
seas approaching 5 ft. Slight chance of rain showers.

Sunday Night through Monday: Winds less than 25 kt. Areas of
seas approaching 5 ft.

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Tuesday: Winds less than 25 kt.



The NOAA Weather Radio transmitter serving Providence is out of
service due to phone line problems. The phone company has prioritized
the issues and is working to get the weather broadcast back on the
air as soon as possible. The transmitter serving Hyannis is back
in service.



MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ232.
     Small Craft Advisory until 1 AM EDT Friday for ANZ233-234.
     Small Craft Advisory until 6 AM EDT Saturday for ANZ235-237-
     Small Craft Advisory until 8 AM EDT Friday for ANZ251.



NEAR TERM...Sipprell
SHORT TERM...Sipprell
EQUIPMENT...WFO BOX Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.