NWS Technical Forecast Discussion


Observed at
Lowell, Massachusetts
22-Jan-2019 03:50 PM

Temperature

24.8°F

Hour Change

0.5°F

Humidity

37%

Hour Change

1%

Dewpoint

2.3°F

Hour Change

1.0°F

Wind

5 mph from 315° (NW)

Wind Gust

12 mph

Barometer

30.528 inHg

3 Hour Trend

0.031 inHg

Today's Rain

0.02 in

Rain Rate

0.00 in/hr

Rain Last Hour

0.00 in

Monthly Rain

0.98 in

Yearly Rain

0.98 in

Wind Chill

18.6°F

Heat Index

24.8°F

Est. Cumulus Base

5300 feet

Today Highs / Lows

High Temperature

Low Temperature

24.8°F at 02:28 PM

3.5°F at 12:00 AM

High Humidity

Low Humidity

74% at 12:00 AM

36% at 02:40 PM

High Dewpoint

Low Dewpoint

5.9°F at 11:48 AM

-3.2°F at 12:05 AM

High Barometer

Low Barometer

30.528 inHg at 03:46 PM

30.145 inHg at 12:07 AM

High Wind Gust

26 mph from 319° at 02:25 AM

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

-18.2°F at 02:25 AM

High Heat Index

24.8°F at 02:28 PM

Yesterday's Statistics

High Temperature

Low Temperature

4.6°F at 12:00 AM

0.9°F at 08:56 AM

High Humidity

Low Humidity

85% at 06:37 PM

74% at 02:00 PM

High Dewpoint

Low Dewpoint

0.1°F at 12:00 AM

-4.5°F at 08:43 AM

High Barometer

Low Barometer

30.152 inHg at 11:57 PM

29.535 inHg at 12:05 AM

High Wind Gust

27 mph from 300° at 08:53 AM

Rain

0.00 in

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

-23.5°F at 08:53 AM

High Heat Index

4.6°F at 12:00 AM

000
FXUS61 KBOX 222042
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
342 PM EST Tue Jan 22 2019

.SYNOPSIS...
Low pressure lifting across the Great Lakes into Quebec will
result in considerably milder temperatures Wednesday. The risk
for showers will increase later Wednesday into Wednesday night.
Heavy rainfall and possible flooding, strong coastal winds and
unseasonably mild temperatures expected on Thursday ahead of a
cold front. Mainly dry and more seasonable temperatures Friday
then turning colder Saturday. Snow showers are possible Sunday
then another frontal system may impact the region Tuesday.

&&

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

340 pm update...

High pressure will continue to move off the mid Atlantic coast
tonight. The pressure gradient will be quite weak, so light
winds and snow cover would result in a good night of radiational
cooling. The issue is model cross sections indicate a fair
amount of mid/high level cloudiness overspreading the region.
Therefore...a rather tricky forecast in regards to overnight low
temps. Given the uncertainty...have low temps falling well down
into the teens in many locations with some single digits across
western MA.

&&

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

Intensifying low pressure will be lifting towards the Great
Lakes as high pressure continues to move east of the mid
Atlantic states. This will result in an abundance of mid level
cloudiness and significantly milder temperatures. Despite a lot
of clouds, expect high temperatures to top out in the lower to
middle 40s in most locations with some upper 30s in the highest
terrain. A developing strong southwest low level jet should also
result in 20 to 30 mph wind gusts by Wed afternoon, perhaps up
to 35 mph along the southeast New England coast.

Dry weather should prevail through early afternoon.  The
strengthening low level jet will increase the forcing for
ascent...so some light rain showers may develop by mid-late
afternoon across the interior. It may be just cold enough to
support a bit of light sleet/freezing rain at the onset across
the interior high terrain. Greatest risk the east slopes of the
Berks and northern Worcester Hills. Confidence not high enough
to issue an advisory at this time...but will highlight the
potential in a special weather statement. It is one of those
cases, where there could be some icing with temperature a few
degrees above freezing given the very cold ground from the past
two days.

Wednesday night...

The low level jet/Pwat axis will continue to increase across
southern New England Wednesday night.  This a result of low pressure
lifting northeast from the Great Lakes into Quebec.  Therefore...the
forcing for ascent will increase and expect rain to increase in
areal coverage/intensity from west to east, particularly after
midnight.  In addition...also expect areas of fog to develop as
anomalously high dewpoint air advects in over the snowpack.

Temperatures should rise overnight and probably be 50+ degrees
across portions of RI/SE MA by daybreak Thu.  Even across most of
the interior, there is not any mechanism to hold the cold air in
place so expect temps may be at or above 40 by daybreak.  The strong
low level jet should also result in southwest wind gusts of 30 to 40
mph across the Cape/Islands by daybreak.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highlights...

* Heavy rainfall/possible flooding Thu and strong winds SE New Eng
* Mainly dry and turning colder Fri into Sat
* Snow showers possible Sunday
* Another round of snow/rain showers possible next Tue

Thursday...

Heavy rain:
Strong heavy rainfall and wind signal for Thu. Approaching mid level
shortwave and sharp frontal boundary with anomalous low level jet 80-
90 kts advecting high PWATs into SNE. PWAT anomalies are 3-4 SD
above normal with wind anomalies +4SD across SE New Eng. This will
result in a period of heavy rain, which will be focused along and
just ahead of the frontal boundary within the low level jet axis.
Given strong forcing and some elevated instability, cant rule out
isolated t-storms which may organize into a fine line of convection
along the front. Additional rainfall on Thu 0.75-1.50" with locally
2+" possible across RI and SE MA especially with any convection.
This rainfall combined with Wed night`s rain will likely lead to
areas of urban and poor drainage flooding and flood watches may be
needed for portions of SNE. In additions, some river flooding is
possible across portions of RI and SE MA.

Strong winds:
80-90 kt low level jet moves across SE New Eng and especially
Cape/Islands around midday into early afternoon. Soundings show an
inverted profile, but temps may soar well into the 50s across
portions of RI and SE MA which will weaken inversion and enhance
mixing potential, especially with any convective elements.
Fairly high confidence that at least wind advisories for 50 mph
gusts will be needed for SE New Eng with a lower risk for high wind
warnings. If fine line does develop, high wind risk will
significantly increase with strongest winds focused along the fine
line.

Tides/Coastal Flooding:
Astronomical tides are elevated Tue, which is cause for concern
along the south coast, but strongest winds and surge expected to
occur after the Thu morning high tides which will minimize risk.

Friday into Sunday...

Turning colder as piece of polar vortex drops south to Hudson Bay
with series of shortwaves reinforcing Gt Lakes to New Eng trough.
Mainly seasonable temps Fri and Sun with coldest day on Sat with
intrusion of modified arctic air. Dry weather Fri/Sat, then
increasing risk for snow showers Sun as warm advection and onshore
easterly flow develops.

Monday into Tuesday...

High uncertainty. Additional shortwave energy rotates around the
vortex to the north but timing, amplitude and location uncertain.
May be dealing with an inverted trough sometime Monday/Mon night but
location uncertain, then a possible clipper tracking to the north
Tue with secondary development to the south. Something to watch.

&&

.AVIATION /21Z 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/...

Tonight...High confidence. VFR despite an increase in some
mid/high level cloudiness. A light SSW will develop.

Wednesday...Moderate to high confidence. VFR conditions through
early afternoon but with plenty of mid level cloudiness. Some
MVFR conditions may develop across western MA/northern CT
by late afternoon/early evening. Scattered light rain showers
are also expected to develop by late afternoon/early evening
across the interior, which may begin as a brief period of light
sleet/freezing rain in a few locations. Greatest risk for that
will be along the east slopes of the Berkshires. SW wind gusts
of 20 to 30 mph develop during the afternoon, perhaps up to 35
mph across the southeast New England coast.

Wednesday night...Moderate to high confidence. Widespread low
end MVFR to IFR conditions develop from west to east as the
night progresses. Rain along with areas of fog will also become
more widespread from west to east. Southwest wind gusts of 25 to
35 knots expected across the southeast New England coast.
Lastly...LLWS will become a concern across much of the region by
daybreak Thursday.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF

Outlook /Thursday through Sunday/...

Thursday: Mainly MVFR, with areas IFR possible. Strong winds
with gusts to 45 kt SE New Eng. RA.

Thursday Night through Saturday: VFR. Breezy.

Saturday Night: VFR.

Sunday: MVFR/IFR conditions possible. Breezy. Chance SHSN.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

Tonight...High confidence.  High pressure sliding off the mid
Atlantic coast will result in winds/seas continuing to diminish.
Will need to small craft headlines for a time this evening for left
over seas across the outer-waters, but these should diminish by mid
to late evening.

Wednesday...Moderate to high confidence.  Increasing low level jet
should result in southwest wind gusts of 25 to 35 knots across the
waters during the day Wed.  Strongest of those winds look to be
across our northern waters, where a Gale Watch goes into effect
during the afternoon.

Wednesday night...Moderate confidence.  Strong southwest low level
jet will be fighting a growing inversion over the waters.
Nonetheless...the low level jet is strong enough to support 30 to 35
knot wind gusts. It is always uncertain how much of that mixes down
in these cases, given its magnitude certainly worth a watch
especially approaching 12z.  The long southwest fetch should also
build seas to between 6 and 12 feet across our open waters.  Areas
of fog may also develop too, given the high dewpoint air
overspreading the colder ocean.

Outlook /Thursday through Sunday/...

Thursday: Moderate risk for gale force winds with gusts up to
45 kt. Rough seas up to 17 ft. Rain, isolated thunderstorms.
Local visibility 1 nm or less.

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 14 ft. Slight chance
of rain showers.

Friday: Moderate risk for Small Craft Advisory winds with local
gusts up to 30 kt. Rough seas up to 11 ft.

Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft.

Saturday: Winds less than 25 kt. Local rough seas.

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

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain showers, chance of
snow showers. Visibility 1 to 3 nm.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from late Wednesday night through Thursday
     afternoon for ANZ231>237-251-254>256.
     Gale Watch from Thursday morning through Thursday afternoon
     for ANZ230.
     Gale Watch from Wednesday afternoon through Thursday afternoon
     for ANZ250.
     Small Craft Advisory until 7 PM EST this evening for ANZ250-
     255.
     Small Craft Advisory until 10 PM EST this evening for ANZ254.

&&

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

NWS BOX Office Area Forecast Discussion