NWS Technical Forecast Discussion


Observed at
Lowell, Massachusetts
17-Oct-2018 07:50 AM

Temperature

38.4°F

Hour Change

0.6°F

Humidity

92%

Hour Change

-1%

Dewpoint

36.3°F

Hour Change

0.3°F

Wind

1 mph from 180° (S)

Wind Gust

4 mph

Barometer

29.889 inHg

3 Hour Trend

-0.042 inHg

Today's Rain

0.00 in

Rain Rate

0.00 in/hr

Rain Last Hour

0.00 in

Monthly Rain

2.23 in

Yearly Rain

34.00 in

Wind Chill

38.4°F

Heat Index

38.4°F

Est. Cumulus Base

659 feet

Today Highs / Lows

High Temperature

Low Temperature

41.4°F at 12:00 AM

36.8°F at 05:13 AM

High Humidity

Low Humidity

93% at 05:29 AM

83% at 12:00 AM

High Dewpoint

Low Dewpoint

36.9°F at 12:01 AM

34.7°F at 05:13 AM

High Barometer

Low Barometer

29.993 inHg at 12:00 AM

29.885 inHg at 07:30 AM

High Wind Gust

6 mph from 138° at 06:42 AM

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

33.1°F at 06:42 AM

High Heat Index

41.4°F at 12:00 AM

Yesterday's Statistics

High Temperature

Low Temperature

58.3°F at 12:00 AM

41.4°F at 11:55 PM

High Humidity

Low Humidity

92% at 12:00 AM

42% at 02:50 PM

High Dewpoint

Low Dewpoint

55.9°F at 12:00 AM

29.3°F at 05:31 AM

High Barometer

Low Barometer

30.016 inHg at 10:17 AM

29.722 inHg at 12:00 AM

High Wind Gust

27 mph from 287° at 03:28 AM

Rain

0.03 in

High Rain Rate

0.18 in/hr at 12:56 AM

Low Wind Chill

36.4°F at 07:16 AM

High Heat Index

58.3°F at 12:00 AM

000
FXUS61 KBOX 171101
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
701 AM EDT Wed Oct 17 2018

.SYNOPSIS...

A cold front moves across the region this afternoon with some
brief scattered showers and gusty winds...followed by the coldest
air of this young fall season tonight and Thursday along with windy
conditions. Cooler than average temperatures persist through the end
of the week into the weekend. A shot of some showery weather ahead
of a sweeping cold front Saturday. Breezy conditions at times.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

7 am update (no major changes to the prior forecast)...

*/ Highlights...

 - Brief period of 35-45 mph wind gusts may result in a few
   downed trees/isolated power outages between 2 and 8 pm today

*/ Discussion...

A chilly start early this morning with temperatures down into
the 30s and lower 40s across the region. Plenty of sunshine this
morning along with gusty west to southwest winds developing by
afternoon will allow for a nice recovery. Afternoon high
temperatures should reach the middle to upper 50s across the
high terrain, while the rest of the region should see high
temperatures reach between 60 and 65.

A strong shortwave/cold front will approach from the west this
afternoon. The result will be a scattered to broken deck of
cloudiness overspreading the region. While moisture is rather
limited...there should be enough forcing for a brief band of
scattered showers. A pretty quick drop in temperatures will
also occur behind this cold front. That combination and decent
pressure rises behind the front may result in a brief period of
35 to 45 mph wind gusts. Given fully leafed trees...the risk for
a few downed tree limbs and isolated power outages. Opted to
issue a special weather statement to highlight this potential.
Greatest time of concern is between 2 and 8 pm this evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...

* Unseasonably cold tonight and Thursday
* Wind Headlines possible later tonight into Thu AM

Tonight...

An unseasonably cold airmass will be ushered into the region on
gusty northwest winds tonight. A few left over sprinkles or
perhaps even a few high terrain snow flurries will be possible
this evening. Otherwise...850T dropping to between -8C and -10C
will result in a cold night. Low temperatures by daybreak will
range from the upper 20s across the high terrain...to the lower
to middle 30s elsewhere. While the wind will stay up to prevent
the need for any frost headlines...we have issued a Freeze
Watch for areas expected to drop near or just below freezing
where the growing season has not officially ended. Opted to go
with the watch as opposed to a warning given temperatures will
be marginal and wanted to let the next shift get a look.

As for winds...expect northwest wind gusts of 25 to 40 mph at times.
Some guidance shows these winds diminishing a bit this evening
behind the cold front...but picking back up after midnight. We did
issue a wind advisory for the Cape/Nantucket...where confidence was
highest in criteria being met with NW winds blowing over the
relatively mild waters. Will need to watch the Worcester Hills too
and even the lower elevations as 850 mb winds increase to between
40 and 50 knots. These strong winds can sometimes mix down in these
setups...so an expansion to the headlines might be needed. Concern
is greater this time of year given fully leafed trees. Regardless...
the gusty winds will make it feel quite cold with wind chills in
the upper teens to middle 20s by daybreak Thursday.

Thursday...

A blustery and unseasonably chilly day is on tap for the region.
Despite plenty of sunshine...an anomalously chilly airmass will
hold highs in the lower 40s across the higher terrain with upper
40s elsewhere. It will remain rather windy with northwest wind gusts
of 25 to 40 mph and perhaps up to 45 mph in some locations during
the morning.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...

*/ Highlights...

 - Touch of winter at times into the weekend, sub-freezing lows
 - Breezy conditions possible throughout warranting wind headlines
 - Average temperatures throughout below seasonable

*/ Overview...

Shots of colder air ahead. NE Atlantic anti-cyclonic wave break that
evolves into an omega block. Progressive N hemispheric pattern other-
wise. Through a preferred reloading NE N America H5 trof, individual
impulses develop into deep storms as they obtain greater curvature /
angular momentum across Greenland into Iceland. +AO, the Arctic door
is open. Behind aforementioned deepening lows, expecting equatorward
cold air shots ushered by anomalously strong isallobaric / pressure-
gradient forced low-level surface-H925 cold air advection, dropping
S roughly -1 to -2 standard deviation H85 temperature airmasses. Do
agree with the prior forecaster, the -EPO / +PNA trend only aids in
the downstream H5 trof preference through which cross-polar flow and
+AO gives us our first touch of Winter.

*/ Discussion...

So watching closely for frost / freezing conditions, as well as any
conditions that would warrant wind-headlines. Thursday night and
Sunday night especially with respect to cold-weather related head-
lines, watching for wind threats and impacts Saturday into Sunday.
Any outcomes associated with sweeping frontal boundaries, Saturday
especially, along which airmasses are more continental-polar, void
of deeper moisture. Cold, showery outcomes, mainly Saturday, that
are scattered to broken, hardly a washout. Otherwise the remainder
of the forecast is mostly dry with some warm rebounds in-between.
Preference to MOS guidance for 2m temperatures.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...

Forecaster Confidence Levels...

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

Short Term /through Thursday/...High confidence.

Today...
VFR, but briefly localized lower conditions are possible this
afternoon and early evening in a brief band of SCT SHRA. W wind
gusts of 25 to 35 knots develop this after, perhaps even briefly
a bit stronger in any SHRA.

Tonight...
VFR. NW wind gusts of 20 to 30 knots persist, but between 35 and
40 knots across portions of the high terrain as well as the
outer-Cape/Nantucket.

Thursday...
VFR. NW wind gusts of 25 to 30 knots, but up to 35 knots along
portions of the coast and high terrain during the first part of
the day.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...Moderate-High confidence.

Thursday: VFR. Strong winds with gusts to 40 kt.

Thursday Night: VFR. Windy with local gusts to 30 kt.

Friday: VFR. Breezy.

Friday Night: VFR. Windy with gusts to 30 kt. Slight chance
SHRA.

Saturday: Mainly VFR, with local MVFR possible. Windy with
gusts to 30 kt. Chance SHRA.

Saturday Night through Sunday: VFR. Breezy.

&&

.MARINE...

Forecaster Confidence Levels...

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

Short Term /through Thursday/...High confidence.

A cold front cross the waters late today. The result will be
west winds increasing to between 30 and 40 knots this afternoon.
Gale force NW wind gusts tonight into Thursday afternoon as
strong cold air advection over the relatively mild ocean will
support excellent mixing. Gale headlines remain posted for all
waters...except strong small craft headlines for Narragansett
Bay. Later shifts may have to consider upgrading this zone too
given the amount of mixing that will be generated over the very
mild waters.

Outlook /Thursday Night through Sunday/...Moderate to High

Thursday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 13 ft.

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas.

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Slight chance of rain
showers.

Saturday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Chance of rain showers.

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Slight chance of rain
showers.

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of rough seas.

&&

.CLIMATE...

Record Low Maximum Temperatures for Thursday October 18

BOS   45 in 1898
ORH   36 in 1989
BDL   44 in 2009
PVD   46 in 1939

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...Freeze Watch from late tonight through Thursday morning for
     CTZ002>004.
MA...Freeze Watch from late tonight through Thursday morning for
     MAZ005-006-009>013.
     Wind Advisory from 5 PM this afternoon to 11 AM EDT Thursday
     for MAZ022-024.
RI...Freeze Watch from late tonight through Thursday morning for
     RIZ001.
MARINE...Gale Warning from 2 PM this afternoon to 4 PM EDT Thursday for
     ANZ230>235-237-250-251-254>256.
     Small Craft Advisory from 10 AM this morning to 8 PM EDT
     Thursday for ANZ236.

&&

$$

SYNOPSIS...Frank/Sipprell
NEAR TERM...Frank/Sipprell
SHORT TERM...Frank
LONG TERM...Sipprell
AVIATION...Frank/Sipprell
MARINE...Frank/Sipprell
CLIMATE...WFO BOX Staff

NWS BOX Office Area Forecast Discussion