NWS Technical Forecast Discussion


Observed at
Lowell, Massachusetts
16-Aug-2018 03:40 AM

Temperature

71.8°F

Hour Change

-0.8°F

Humidity

89%

Hour Change

2%

Dewpoint

68.4°F

Hour Change

-0.1°F

Wind

0 mph from 223° (SW)

Wind Gust

1 mph

Barometer

29.896 inHg

3 Hour Trend

0.007 inHg

Today's Rain

0.00 in

Rain Rate

0.00 in/hr

Rain Last Hour

0.00 in

Monthly Rain

4.11 in

Yearly Rain

24.10 in

Wind Chill

71.8°F

Heat Index

71.8°F

Today Highs / Lows

High Temperature

Low Temperature

75.2°F at 12:00 AM

71.8°F at 03:39 AM

High Humidity

Low Humidity

89% at 03:36 AM

83% at 12:00 AM

High Dewpoint

Low Dewpoint

69.8°F at 12:11 AM

68.1°F at 03:30 AM

High Barometer

Low Barometer

29.900 inHg at 03:19 AM

29.883 inHg at 12:00 AM

High Wind Gust

3 mph from 220° at 12:49 AM

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

71.8°F at 03:39 AM

High Heat Index

75.2°F at 12:00 AM

Yesterday's Statistics

High Temperature

Low Temperature

88.6°F at 02:59 PM

66.8°F at 02:10 AM

High Humidity

Low Humidity

98% at 03:46 AM

54% at 03:01 PM

High Dewpoint

Low Dewpoint

72.9°F at 12:08 PM

65.9°F at 02:10 AM

High Barometer

Low Barometer

29.883 inHg at 11:59 PM

29.784 inHg at 04:32 AM

High Wind Gust

9 mph from 24° at 12:08 PM

Rain

0.00 in

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

66.8°F at 02:10 AM

High Heat Index

95.3°F at 02:59 PM

000
FXUS61 KBOX 160707
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
307 AM EDT Thu Aug 16 2018

.SYNOPSIS...
More heat and humidity today, then increasing risk of showers and
thunderstorms with locally heavy rain Friday afternoon into Saturday
as a cold front approaches. This front moves through later Saturday,
followed by mainly dry and cooler weather Sunday into Tuesday as
high pressure builds in from the north. The humidity will return by
Wednesday leading to the risk of more showers and thunderstorms.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1010 PM Update...

Area of showers/thunderstorms across central and N NH/VT moving
just a bit S of due E as seen on latest NE regional 88D radar
imagery. Noted a few showers earlier this evening, but they
dissipated as they pushed out of E central NY into S VT, as near
term model data had signaled.

High clouds associated with the convection has spread E-SE
across most of the region, as seen on GOES-East RGB Nighttime
Microphysics composite imagery through around 02Z, but noting
the higher clouds tending to dissipate as drier air works in
aloft from southern NY state.

Will still see low T/Td spreads especially across the CT valley
into the E slopes of the Berkshires overnight, so have kept
mention of patchy fog there. Temps bottom out in the 70-75
degree range.

Have updated overnight forecast to bring conditions current.

Previous Discussion...

Convection across upstate NY into Ontario should remain north
of the region as subtle height rises and backing mid level flow
should steer this activity into central and northern New
England overnight. This subtle height rises are also
accompanied by mid level dry air via subsidence and is
supported by decreasing K index values on the SPC mesoanalysis
across mid to lower Hudson Valley of NY into southern New
England.

Might see some patchy fog late tonight across central and
western areas, as well as near Nantucket, as somewhat higher
dewpoints will linger.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
A light sea breeze may develop along E coastal areas with the
light pressure gradient. This may be a trigger for a few showers
that may develop around midday Thursday. Expecting temperatures
just a few degrees higher than today. Given the fairly high
dewpoints, may need to consider a Heat Advisory if we can use
the lower threshold for consecutive days. Looking rather
marginal at this time, so will let the next shift take another
look. Regardless, it will be hot and humid for most Thursday
afternoon.

For Thursday night, a weak cold front will try to push south
through our region. This would mean at least a low risk for
some showers or thunderstorms. Given the timing, thinking
showers would be more likely than thunderstorms. Greatest risk
will be towards NW MA.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...

Highlights...

* Showers/t-storms likely Fri night into Saturday
* Locally heavy rainfall possible along with the potential for
  a few strong to severe storms Fri evening and again Saturday
* Mild to warm days and cool nights Sun/Mon/Tue
* More humid with increasing risk of showers/t-storms Tue night/Wed

Friday night into Saturday...

Warm front may be in the vicinity of northern MA Fri evening before
lifting north. Warm sector airmass will be firmly entrenched across
SNE with PWATs exceeding 2 inches and dewpoints in the 70s.
Scattered showers and t-storms will likely be ongoing in the
evening, especially interior, and expect convective activity to
persist through the night and move east across SNE as mid level
trough approaches and instability is maintained. Models indicate a
strengthening low level jet Fri evening which will increase low level
shear and helicity so a few strong to severe storms possible with
potential for rotation. Given high dewpoints in the 70s and low LCLs
this will have to be watched closely. In addition, heavy rainfall
and localized flash flooding will be a threat with high PWAT airmass
and +2SD low level jet.

On Saturday, there is still some uncertainty with timing of fropa
but consensus of model guidance favors slower timing with cold front
moving south across SNE during the afternoon. This will keep
tropical airmass across the region with threat of showers/t-storms
continuing. Deep layer shear is marginal but enough instability for
a few strong to marginally severe storms with heavy rainfall threat
as well. Some of the guidance doesn`t push the front to the south
coast until Sat evening. Drying trend possible across northern MA in
the afternoon depending on exact timing of fropa. If front is
delayed, temps will reach well into the 80s, especially south of the
Pike. Some showers may linger near the south coast in the evening,
otherwise, cooler and drier conditions will filter into the region
from north to south Sat night with gusty NE winds developing,
especially along eastern MA coast.

Sunday into Monday...

Uncertainty with location of frontal boundary south of New Eng leads
to a lower confidence forecast for Sun/Mon. ECMWF trended further
north with boundary and surface wave track closer to New Eng which
keeps it unsettled Sun into Mon. GFS and ensembles are further south
and drier and have support from UKMET so we leaned toward drier
solution. Cooler and drier airmass overspreads SNE Sunday and Monday
as high pres builds to the north. Looks mainly dry during this
period although will have to watch moisture to the south Sun into
Mon. Coolest day will be Sunday, especially SE coastal MA where
temps may struggle to reach 70 with gusty NE winds, but ranging
through the 70s elsewhere. Clouds may linger through the day Sunday
near the south coast. Gradual airmass moderation Mon.

Tuesday into Wednesday...

Model differences with timing and amplitude of next upstream trough,
but it appears humidity and risk of showers/t-storms return by Tue
night or Wed. It is possible showers could impact region as early as
Tue, but more likely Tue night into Wed.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Friday/...

1020 PM update...

Overnight...High confidence. VFR. Local MVFR in patchy fog
around or after 06Z across CT valley into the E slopes of the
Berkshires. Otherwise, dry weather prevails.

Thursday...High confidence. VFR. Mainly dry conditions. Patchy
fog with MVFR-IFR VSBYS across central and W areas through
around 13Z. May see isolated showers/thunderstorms develop
across E Mass around midday Thursday.

Thursday Night...VFR.

KBOS Terminal...Sea breeze may impact the terminal at times late
this afternoon. Moderate confidence.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: MVFR/IFR conditions possible. Breezy. Chance
SHRA, chance TSRA, patchy FG.

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

Saturday Night: Mainly VFR, with local MVFR possible. Breezy.

Sunday through Sunday Night: VFR. Breezy.

Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

A weak front will push to near or just off the S coast tonight
before stalling. W winds will prevail, with some leftover gusts
up to 20 kt this evening, then will back to during Thu. Seas up
to 5 feet through tonight across the southern outermost coastal
waters, then should remain less than 5 feet. Good visibility.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, chance of thunderstorms, patchy
fog.

Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, chance of thunderstorms.

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

Sunday through Monday: Winds less than 25 kt. Seas up to 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Air Quality Alert from 11 AM this morning to 11 PM EDT this
     evening for MAZ020-022>024.
RI...Air Quality Alert from 11 AM this morning to 11 PM EDT this
     evening for RIZ006>008.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for
     ANZ255-256.

&&

$$
SYNOPSIS...KJC
NEAR TERM...Nocera/EVT
SHORT TERM...Belk
LONG TERM...KJC
AVIATION...Belk/KJC/EVT
MARINE...Belk/KJC/EVT

NWS BOX Office Area Forecast Discussion