NWS Technical Forecast Discussion


Observed at
Lowell, Massachusetts
06-25-2019 08:00 PM

Temperature

69.0°F

Hour Change

-0.7°F

Humidity

93%

Hour Change

2%

Dewpoint

66.9°F

Hour Change

-0.1°F

Wind

2 mph from 158° (SSE)

Wind Gust

4 mph

Barometer

29.864 inHg

3 Hour Trend

0.020 inHg

Today's Rain

0.05 in

Rain Rate

0.00 in/hr

Rain Last Hour

0.01 in

Monthly Rain

4.35 in

Yearly Rain

19.55 in

Wind Chill

69.0°F

Heat Index

69.0°F

Est. Cumulus Base

658 feet

Today Highs / Lows

High Temperature

Low Temperature

71.0°F at 03:52 PM

56.7°F at 05:33 AM

High Humidity

Low Humidity

95% at 02:52 PM

74% at 12:00 AM

High Dewpoint

Low Dewpoint

69.2°F at 03:52 PM

53.3°F at 05:18 AM

High Barometer

Low Barometer

29.901 inHg at 06:52 AM

29.831 inHg at 05:21 PM

High Wind Gust

17 mph from 161° at 05:34 PM

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

56.7°F at 05:33 AM

High Heat Index

71.0°F at 03:52 PM

Yesterday's Statistics

High Temperature

Low Temperature

87.6°F at 03:11 PM

60.3°F at 05:35 AM

High Humidity

Low Humidity

82% at 05:54 AM

30% at 02:25 PM

High Dewpoint

Low Dewpoint

59.2°F at 09:55 AM

49.4°F at 07:35 PM

High Barometer

Low Barometer

29.854 inHg at 11:52 PM

29.778 inHg at 03:24 AM

High Wind Gust

16 mph from 29° at 11:47 AM

Rain

0.00 in

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

60.3°F at 05:35 AM

High Heat Index

87.6°F at 03:11 PM

000
FXUS61 KBOX 252251
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
651 PM EDT Tue Jun 25 2019

.SYNOPSIS...
A frontal boundary will bring a period of showers early in the
night, followed a drying trend later tonight. Summer like
warmth is expected Wednesday through Friday with a few showers
and thunderstorms at times, but should be mainly dry. A cold
front sweeps south through Southern New England Saturday
bringing another chance of showers and thunderstorms. Cooler
weather then moves in Sunday, followed by warming Tuesday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

650 PM Update...

Radar showed two areas of showers at 7 PM. One was along a line
from near Lowell to Sturbridge, the second was along the South
Coast from Narragansett Bay to the Mid Cape and Nantucket.
Rainfall estimates in this area showed Westerly at 1.63 inches
and Newport at 0.48. Marthas Vineyard was at 0.33, but with most
of the rain still to the west.

Surface analysis placed the front in the Hudson Valley with
partial clearing already advancing into Western New England. But
no change in the airmass with dew points behind the front still
in the 60s. Winds change direction behind the boundary, but
remain light. Expect clouds to slowly advance east, but RI/East
MA may have difficulty clearing before morning due to the
humidity and light wind. Where there has been a lot of rain
during the day, expect fog to develop or thicken. Washington Co.
RI and the Islands are most vulnerable to this.

We adjusted timing of clouds and POPs a little, but no other
changes to the forecast.

Previous discussion ...

Frontal boundary moving across the region late this afternoon and
early evening and will be accompanied by scattered showers with
locally heavy rain given PWATs over 2 inches and some elevated
instability. Ahead of this boundary warm/humid airmass advecting
northward across the region with dew pts 65-70. So partial clearing
possible before sunset across CT River Valley. Otherwise clouds hang
tough and with warm/moist airmass in place patchy fog is likely
later this evening. Greatest risk likely along the south coast with
onshore winds and moderate to heavy rain late this afternoon
saturating the low levels. Patchy fog possible inland as well just
thinking more widespread along/near the coast. Given moist airmass
temps only bottom out 60-65 for overnight mins.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Wednesday ...

Low pres SE of New Eng will gradually pull away, but the northerly
flow along the coast and lingering low level moisutre may keep areas
of lower clouds persisting through the morning across eastern MA.
Thereafter subtle height rises over the region should provide some
subsidence and column drying as evident by PWATs falling to about an
inch along with K indices really dropping off. Thus partly to mostly
sunny conditions and warm with mixing to 850 mb and temps at this
level around +14C, supporting highs in the mid to upper 80s. It will
feel warm with dew pts in the 60s. Afternoon seabreezes will take
the edge off the heat along and near the coast.

Late in the day short wave trough moves across northern NY state.
Convection from this feature may hold together and spill into
western MA/CT late in the day before dissipating per 12z CAMs.

Wednesday night ...

Other than possible early evening convection weakening across
western MA/CT, column begins to dry supporting quiet weather
overnight. Remaining warm and humid with dew pts in the 60s. Patchy
fog possible as well.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Big Picture...

Zonal flow over the Northeast USA through Friday. Broad upper ridge
over the Southern USA builds north through the Plains late in the
week, then shifts east early next week. Large closed low lingers
over the Pacific Coast through Friday, then ejects northeast into
Canada over the weekend. This ejecting low kicks another low away
from Hudsons Bay. The Hudsons Bay upper low sweeps southeast to New
England by Sunday and to our east Monday. The remnants of the
Pacific upper low moving southeast out of Ontario Tuesday.

Contour heights from 500 mb will be above normal through Saturday.
Heights then lower to the low side of normal Sunday-Monday as the
Hudsons Bay upper low sweeps across New England. Heights return to
seasonable levels Tuesday-Wednesday. Expect above normal
temperatures Thursday to Saturday, cooler Sunday-Monday, then
warming again Tuesday-Wednesday.

Forecast confidence is moderate-high. The various model mass fields
are similar through Sunday morning. They agree on the general
pattern after that through Wednesday, but with differences in
handling the departing upper low Sunday and the following shortwave
over Ontario Tuesday.

Concerns...

Thursday-Friday...

Two shortwaves move through the flow during this period. The GFS
brings them through Thursday night and Friday night while the ECMWF
shows just one passage on Thursday night. Moisture is limited to the
700-850 mb layer with plenty of dry air above. This would suggest
shallow clouds. The supporting upper jets with the shortwaves mostly
aim their favorable dynamics north of the Mass border, directing
most cloud development there. PW values top out 1.0 to 1.25 inches
Thursday, drop back, then resurge to 1.5 inches Friday night.

Expect mainly dry weather Thursday, but with diurnal clouds
developing, either cumulus or alto-cu. SBCAPES are forecast around
500 mb along the NH border. Total-totals show a similar favoring of
VT/NH. Scattered or widely scattered afternoon showers should form,
with placement favoring northern Mass. Could be isolated thunder as
well. Mixing will reach between 800-850 mb, which will tap equiv 850
temps of 14-16C. This supports max sfc temps in the 80s.

Friday should be dry during the day, but expect scattered showers
with the Friday night shortwave. Most of these should develop in
Upstate NY in the afternoon and move into our area Friday evening or
Friday night. The SREF shows a 50 pct chance of CAPE over 1000 in CT
and Western MA Friday evening, so we will mention some thunder as
well. Temps aloft support 80s again, possibly around 90 in some
spots.

Saturday...

Upper low from Hudsons Bay drives southeast, aided by a 100-kt upper
jet. This drives a cold front southeast across New England Saturday
afternoon and night. The cold front provides a source of low-level
convergence, the upper jet provides dynamic support, and daytime
heating generates instability. CAPE of 1000-1500 J/Kg and totals
near 50 are forecast. So we expect showers/thunder to develop.
Mixing is not expected to go as deep as previous days, but should
still reach 850 mb, where temps will be around 15C. So max temps
will again be well into the 80s.

Sunday...

Surface cold front moves south of New England, while the upper
low/cold pool/cold pool moisture move south across Southern New
England Sunday. With the colder air moving in aloft, expect to
around 850 mb and possibly near 800 mb. The cold pool moisture
should be enough to generate clouds, and stability parameters
support showers and scattered thunder. Temperatures at 850 mb will
be 10-11C, supporting max sfc temps 75 to 80.

Monday-Tuesday...

The uppper low pulls east Monday, taking much of the cloud cover and
showers. Another cold front may dive out of Canada Tuesday night,
bringing another chance of showers.

&&

.AVIATION /00Z WEDNESDAY 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/...Moderate confidence.

Tonight... High confidence on trends, lower on exact details.

Any heavy showers will diminish as they move east. This will
leave an area of low ceilings over Eastern Mass and RI, while
Northern CT/Western MA will have slow lifting/clearing. The
lingering humidity will lead to lowering vsbys in fog. This will
be especially true along the South Coast where heavier rain took
place during the day...areas of dense fog may form in those
areas.

Wednesday ... high confidence.

Patchy MVFR/IFR cigs/vsbys in the morning across portions of
east coastal MA, otherwise VFR. Chance of a late day
shower/t-storm across western MA/CT.

Wednesday night ...

Scattered showers and T-storms over eastern NY at 00z may hold
together and enter western-central portions of MA/CT but slowly
weaken as well.

KBOS Terminal...heavy showers and embedded thunder over
southeast CT at 18z may stay mainly south of Logan but will be a
close call through 21z/22z

KBDL Terminal... High confidence in trends. Lower confidence in
specific details and timing.

Outlook /Thursday through Sunday/...Moderate confidence.

Thursday through Friday: VFR.

Friday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA, isolated TSRA.

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

Saturday Night: Mainly VFR, with local IFR possible. Chance
SHRA, slight chance TSRA.

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

&&

.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.

Tonight ... S-SE winds becoming light north toward morning.
Vsby reduced in scattered showers and areas of dense fog.

Wednesday ... light and variable winds with weak low pressure
meandering east of Nantucket. Areas of morning fog may reduce vsby
but improving trend for the afternoon.

Wednesday night ... Weak low east of Nantucket exits east with light
and variable winds over the waters of MA/RI.

Outlook /Thursday through Sunday/...Moderate confidence.

Thursday through Thursday Night: Winds less than 25 kt. Local
visibility 1 to 3 nm. Seas less than 5 ft.

Friday: Winds less than 25 kt. Seas less than 5 ft.

Friday Night: Winds less than 25 kt. Seas less than 5 ft. Slight
chance of rain showers.

Saturday: Winds less than 25 kt. Seas less than 5 ft. Slight
chance of rain showers, slight chance of thunderstorms.

Saturday Night: Winds less than 25 kt. Seas less than 5 ft. Chance
of rain showers, slight chance of thunderstorms.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, chance of thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...WTB/Nocera
NEAR TERM...WTB/Nocera
SHORT TERM...Nocera
LONG TERM...WTB
AVIATION...WTB/Nocera
MARINE...WTB/Nocera

NWS BOX Office Area Forecast Discussion