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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
402 PM EDT Tue Jul 23 2019

Synopsis...
another round of showers expected tonight into early Wednesday
across the southeast New England coast as another low pressure
tracks to the south. Mostly dry, seasonable weather later
Wednesday into the weekend, with a return to warmer and more
humid weather early next week.

&&

Near term /until 6 am Wednesday morning/...
anomalous mid level trough for late July over eastern US with
500 mb heights 2-3sd below normal. Another shortwave rotating
around the base of the trough will result in coastal low pres
developing tonight and tracking near the 40n/70w benchmark.
Right entrance region of robust upper jet remains across the
region. The uncertainty is how far deep moisture plume will
extend into new eng. Highest confidence in a period of showers
will be across the cape/islands where we will have likely to
categorical pops. Deep moisture and pwats 1.5-1.75 inches across
far southeast new eng. Some shower activity may extend into Rhode Island and southeast
Massachusetts but expect less coverage further inland from the cape.
Potential for locally heavy rainfall probably confined to
Nantucket. Not expecting any thunder as instability will remain
well to the south.

&&

Short term /6 am Wednesday morning through Wednesday night/...
Wednesday...
mid level trough remains to the west but deep moisture is moving
out with decent drying developing. So any lingering showers over
the cape/islands will exit early followed by increasing sunshine
from west to east through the morning and into the afternoon.
Sunshine will be slow to develop over the cape/islands. Temps
will be a few degrees below normal with highs upper 70s to lower
80s, but cooler east coastal Massachusetts and cape/islands where sea
breezes develop.

Wednesday night..
de-amplifying trough axis and shortwave moves into the region
late Wed night, but column is rather dry. So expecting dry
weather with just some high clouds. Cool night with lows
dropping into the 50s in most locations, except lower 60s in the
urban centers.

&&

Long term /Thursday through Tuesday/...

Highlights ...

* dry stretch of weather thru the weekend & possibly early next week
* seasonably warm & comfortable humidity Thu & Fri
* gradually warmer and more humid Sat & sun but tolerable
* highs upper 80s/lower 90s Mon/Tue and dew pts approaching 70

Thursday ...

Upper trough and cold pool (-14c at 500 mb) overhead along with
cyclonic flow lingering. Thus could be some diurnal clouds but the
column probably too dry for any showers. Overall very pleasant with
seasonable highs of 80-85, 75-80 along/near the coast with afternoon
seabreezes. Dew pts in the 50s so very comfortable.

Friday ...

Cold pool and upper trough offshore with rising heights over the
region. Thus plenty of sunshine and temps a few degs warmer with
highs in the low to mid 80s. 1024 mb high over the region will
promote afternoon seabreezes, so cooler along/near the coast. Very
comfortable with dew pts in the mu50s but lower to to mid 60s along
the coast with seabreezes.

The weekend ...

Remaining pleasant Sat with 1020+ mb high anchored across southern
New England. Seasonable heat and humidity with highs in the 80s and
dew pts in the 60s. By Sunday slightly warmer and more humid with
ridge axis moving offshore, so highs pushing 85-90 inland and dew
pts climbing into the mu60s.

Next weekend ...

Northern stream mid level trough and attending cold front enters
Great Lakes with increasing low level warm air advection into southern New England.
Ensembles and deterministic guidance advecting +17c 850 mb temps
across the region. This combined with SW winds will support highs in
the upper 80s to lower 90s away from the South Coast. Also
noticeably more humid with dew pts at or above 70.

&&

Aviation /20z Tuesday through Sunday/...
forecaster confidence levels...

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

Short term /through Wednesday night/ ...

Through 00z...
MVFR/IFR cigs improving to VFR from west to east. Brief north wind
gusts to 25 kt over the cape/islands.

Tonight... moderate confidence.
Mainly VFR cigs but another round of showers expected around or
after midnight over cape/islands which will lower conditions to
MVFR/IFR. Showers may extend into southeast Massachusetts but lower confidence.

Wednesday... high confidence.
Areas of MVFR/IFR conditions early over cape/islands with a few
lingering showers possible. Otherwise VFR. Coastal sea breezes
developing.

Wednesday night... high confidence. VFR.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Thursday through Saturday/ ... high confidence.

VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday night/...high confidence.

Gusty northerly winds eastern Massachusetts waters diminish by late
afternoon. Small Craft Advisory will linger tonight over outer waters due to
hazardous seas but subsiding late tonight.

Light winds this evening, then a period of NE winds up to 20 kt
possible over southern waters late tonight and early Wed as low
pres tracks to the south. Light winds Wed night. Seas
approaching 5 ft over southern outer waters Wed/Wed night.

Outlook /Thursday through Sunday/...high confidence.

Thursday: winds less than 25 kt. Seas locally approaching 5 ft.

Thursday night through Saturday night: winds less than 25 kt.

Sunday: winds less than 25 kt. Seas locally approaching 5 ft.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 6 PM EDT this evening for anz231-
232.
Small Craft Advisory until 4 PM EDT this afternoon for anz230-
233-234-251.
Small Craft Advisory until 2 am EDT Wednesday for anz235-237-
254.
Small Craft Advisory until 8 PM EDT this evening for anz250.
Small Craft Advisory until 8 am EDT Wednesday for anz255-256.

&&

$$
Synopsis...kjc/nocera

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