NWS Technical Forecast Discussion


Observed at
Lowell, Massachusetts
22-Jul-2018 09:40 PM

Temperature

73.0°F

Hour Change

-0.7°F

Humidity

94%

Hour Change

2%

Dewpoint

71.2°F

Hour Change

-0.1°F

Wind

1 mph from 85° (E)

Wind Gust

5 mph

Barometer

30.137 inHg

3 Hour Trend

0.043 inHg

Today's Rain

0.25 in

Rain Rate

0.00 in/hr

Rain Last Hour

0.01 in

Monthly Rain

2.31 in

Yearly Rain

18.81 in

Wind Chill

73.0°F

Heat Index

73.0°F

Today Highs / Lows

High Temperature

Low Temperature

79.2°F at 04:26 PM

63.8°F at 12:39 AM

High Humidity

Low Humidity

97% at 09:42 AM

76% at 04:36 PM

High Dewpoint

Low Dewpoint

73.6°F at 02:14 PM

59.4°F at 12:22 AM

High Barometer

Low Barometer

30.137 inHg at 09:39 PM

30.037 inHg at 09:30 AM

High Wind Gust

14 mph from 148° at 04:06 PM

High Rain Rate

0.82 in/hr at 08:51 AM

Low Wind Chill

63.8°F at 12:39 AM

High Heat Index

79.2°F at 04:26 PM

Yesterday's Statistics

High Temperature

Low Temperature

78.7°F at 01:09 PM

59.1°F at 06:08 AM

High Humidity

Low Humidity

94% at 06:40 AM

45% at 12:14 PM

High Dewpoint

Low Dewpoint

62.1°F at 06:06 PM

53.7°F at 09:01 AM

High Barometer

Low Barometer

30.156 inHg at 08:49 AM

30.087 inHg at 04:36 PM

High Wind Gust

14 mph from 177° at 12:57 PM

Rain

0.00 in

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

59.1°F at 06:08 AM

High Heat Index

78.7°F at 01:09 PM

000
FXUS61 KBOX 222309
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
709 PM EDT Sun Jul 22 2018

.SYNOPSIS...
A tropical airmass will remain entrenched across southern New
England for most of the upcoming work week. Showers and a few
thunderstorms are likely Monday. Tuesday and Wednesday will be
mainly dry, but there is a chance of showers or thunderstorms in
western sections. A cold front will be in the vicinity Wednesday
night through Friday, bringing better chances of showers and
storms. Slightly lower humidity possible next Saturday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
710 PM update...

Note...have let the High Surf Advisory expire. We are no longer
expecting 7 ft seas. That said, we still do expect a moderate
risk for rip currents on Monday, so beachgoers should be aware
of this threat!

Shower activity has increased from the south during the past few
hours. The heaviest were over Cape Cod. High resolution guidance
indicates scattered showers and a few embedded thunderstorms
continuing to increase overnight, mainly in a north-south line
somewhere in central or east central sections. This seems
plausible given magnitude of the low level jet and Pwats over 2
inches. However...the big limiting factor is that despite the
anomalous low level jet/Pwat axis there is a lack of synoptic
scale forcing. So while we do expect an uptick in activity...
uncertain on the areal coverage and intensity of any showers or
embedded t-storms.

The overall severe weather threat remains low through tonight
given lack of synoptic scale forcing/poor mid level lapse rates.
However...when ever your dealing with a southerly 25 to 35 knot
low level jet this time of year and 70+ dewpoints...the low
risk for an isolated severe thunderstorm/very localized flash
flood event exists. So while a low probability...something that
will have to be monitored through the night.

Most locations will only see overnight low temperatures in the
70 to 75 degree range given high dewpoints in place. Enough
mixing in the boundary layer should prevent widespread/dense
fog...although a bit of patchy fog is certainly possible.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Monday...

A tropical environment remains in place across southern New
England with the southerly LLJ/Pwats both 2+ standard deviations
above normal. The models indicate a bit better instability on
Monday with Capes probably near 1000 J/KG. Therefore...we expect
scattered showers and embedded t-storms with locally heavy
rainfall. Appears most of the activity will be near or northwest
of the Boston to Providence corridor as upper level ridge over
the Atlantic begins to retrograde to the west.

The overall severe weather threat will remain low on Monday
given poor mid level lapse rates and lack of deep layer shear.
However...given impressive low level jet and 70+ dewpoints an
isolated severe thunderstorm/very localized flash flood event
can not be completely ruled out. High temperatures on Monday
will be well up into the 70s to the lower 80s...but it will be
very humid.

Monday night...

Upper level ridge over the Atlantic continues to retrograde west
Monday evening. This should bring an end to any
convection...except perhaps for a few left over spot showers
across the interior. It will remain quite muggy though and
overnight lows will likely remain above 70 in most locations.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Tuesday...
Strong high pressure ridge builds westward from the western
Atlantic. Deep upper trough in the Tennessee Valley will
continue. The axis of rich, tropical moisture will be pushed to
our west with very dry air moving in above the moist surface
air. While this leads to some instability, the air should be too
dry through the column to procuce more than a stray shower in
central and eastern sections. But a scattered thunderstorm is
possible in western MA and a portion of northern CT, closest to
the moist axis. Expecting morning clouds giving way to partial
sunshine and highs in the mid 80s with sultry dewpoints of 72-75.

Wednesday...
Not much change in the upper pattern, although the Atlantic
ridge retreats slightly and the moist axis heads slighltly
farther east, extending into western MA and northern CT.
Expecting a partly cloudy day, with increasing clouds late.
Scattered showers and thunderstorm are possible, mainly in the
western half of southern New England. Still warm and very humid.

Wednesday night and Thursday...
The upper flow becomes more southwesterly, instead of
meridional. This allows a cold front to move slowly eastward
into southern New England. There is a high likelihood of showers
and some thunderstorms. Have added wording of locally heavy
rainfall during this time frame, since the axis of precipitable
waters above 2 inches will be over us again. There is some
potential for localized urban flooding, especially with any
repeat storms. High temperatures on Thursday may be held to the
upper 70s and lower 80s due to the cloud cover and
precipitation.

Thursday night and Friday...
A brief period of drying aloft moves in late Thursday night and
early Friday. But, the low levels remain very moist, with
dewpoints still in the lower 70s. Both the GFS and ECMWF show
a second frontal boundary...the real one...approaching from the
west Friday afternoon. Skies should be partly sunny, allowing
temperatures to climb into the upper 80s. Both models predict
the atmosphere to be very unstable, with high CAPEs and an axis
of high K indices approaching from the west. GFS is 6-12 hours
faster than the ECMWF. Unlike previous days, the mid-level lapse
rates may be favorable for convection. If the axis approaches
at the time of maximum heating Friday afternoon, scattered
strong/isolated severe thunderstorms would be possible, despite
relatively weak wind fields aloft.

Saturday...
Possibly some lowering humidity values, especially in western
sections. Otherwise, southwest flow aloft and at the surface
continues. Expecting partly sunny skies a just a slight chance
of a shower. Highs in the 80s.

&&

.AVIATION /23Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Tonight into Monday...Moderate confidence. MVFR conditions
should dominate tonight into Monday with scattered showers and a
few embedded thunderstorms. Localized IFR conditions will also
be possible and some areas will improve to VFR at times.
Overall...expect a wide variety of conditions possible over this
time with MVFR conditions dominating.

Monday night...Moderate confidence. Mainly dry weather expected
with MVFR conditions likely dominating.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: Mainly VFR, with areas MVFR possible. Chance SHRA,
slight chance TSRA.

Tuesday Night: MVFR/IFR conditions possible. Slight chance
SHRA, isolated TSRA.

Wednesday: Mainly MVFR, with areas VFR possible. Breezy. Chance
SHRA, slight chance TSRA.

Wednesday Night: Mainly MVFR, with local VFR possible. Breezy.
SHRA likely, chance TSRA.

Thursday: Mainly MVFR, with local VFR possible. Breezy. Chance
SHRA, slight chance TSRA. Locally heavy rainfall.

Thursday Night: Mainly MVFR, with local IFR possible. Breezy.
Chance SHRA, slight chance TSRA.

Friday: MVFR/IFR conditions possible. Chance SHRA, slight
chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Tonight through Monday night...High confidence. Persistent south
to southeast flow will result in wind gusts around or just over
20 knots at times. Seas will slowly diminish through Monday
night but remain at or above small craft thresholds for most of
our outer-waters. Scattered showers and patches of fog will also
reduce visibility for mariners at times.

Outlook /Tuesday through Friday/...

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

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers, isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Local rough seas.
Chance of rain showers, slight chance of thunderstorms.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of rain showers, slight
chance of thunderstorms.

Thursday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain showers, slight chance of thunderstorms.

Friday: Winds less than 25 kt. Local rough seas. Slight chance
of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 AM EDT Tuesday for ANZ235-237-250-
     254>256.

&&

$$
SYNOPSIS...Frank/Field
NEAR TERM...Field/Frank
SHORT TERM...Frank
LONG TERM...Field
AVIATION...Frank/Field
MARINE...Frank/Field

NWS BOX Office Area Forecast Discussion