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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

                            
000
FXUS61 KBOX 140907
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
507 AM EDT Sat Sep 14 2019

.SYNOPSIS...
An approaching cold front will bring increasing clouds across 
the region today. Expect scattered showers to push into northern
areas around midday, then move southeast tonight into Sunday 
morning. Dry weather returns behind the front by late Sunday 
morning from west to east, bringing warm afternoon temperatures.
Canadian high pressure then builds southward from Quebec into 
New England next week, providing very pleasant weather with dry 
conditions, low humidity, mild days and cool nights. By late in 
the week a gradual warming trend develops.

&&

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

Temps have fallen quickly since around midnight across the
normally susceptible inland valley locations thanks for mostly
clear skies and calm winds. Lowest temps so far reported at the
usual suspects, down to 38 degrees at both KTAN and KOWD, while
most other locations have fallen to the lower-mid 40s except up
to the lower 50s across the lower CT valley where a veil of mid
level clouds have moved in.

Some lower clouds have also pushed in well ahead of the
approaching cold front across western areas at 08Z. Ridging from
the exiting high pressure passing near Nova Scotia extends
across S coastal areas down to the mid Atlc coast. Have kept dry
conditions across the region through 12Z, as it will take some
time for the precip and front to shift E. 

For today, the front will push into the region, with scattered
showers arriving across N central and NW Mass by mid morning,
then will shift slowly SE through the day. Instability
parameters remain well below thresholds ahead of this front with
limited heating as clouds move across and thicken during the
day. Have left mention of thunder out of this portion of the
forecast. 

Noting a 20-25 SW get moving across through H925 with low
level lapse rates at around 9C/km, though limited above that.
Have mentioned gusts up to around 20 kt as the showers move in
around midday through the afternoon. Can't rule out a few gusts
to 25 kt later in the day, but should be few and far between.

Expect temps to top off in the upper 60s to lower 70s this
afternoon. One thing to keep an eye on would be some marginal
instability that may approach late in the day. Most parameters
remain below criteria, as mentioned above, but may get close
around or after 22Z. 

&&

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

Tonight...

Mid level short wave steadily crosses the region tonight,
bringing the front with it. Several high res short range models
signaling bands of heavier showers moving across southern areas,
mainly near the S coast. May see some QPF totals around 0.5 to
0.9 inches overnight across central/S RI into SE Mass. Also
noting some instability parameters close to or just above
thresholds, including Showalters at or just below zero and K
indices in the lower 30s. So, can not rule out a few
thunderstorms may develop along the S coast with the heavier
downpours. Have mentioned thunder in these areas from about 06Z
to 12Z. 

Some question whether the front will clear the S coast by 
daybreak on Sunday as it becomes parallel to the mid level 
steering flow. Best chance for showers will remain there through
12Z. 

Expect lows in the lower-mid 50s across the E slopes of the
Berkshires to the CT valley, ranging to the lower-mid 60s at the
coast. 

Sunday...

Big question at this point will be how quickly the front and
showers move off the S coast. Looks like the best instability
shifts offshore, as winds shift from SW to W during the morning.
Most of the 00Z model suite indicating the drier air working in
and the precip ending. At this point, have pushed the last of
the precip offshore by midday, with skies becoming partly to
mostly sunny during the afternoon. 

Cooler air lingers N and W of the region through the day, so 
expect temps to rebound to the 70s, mildest across the coastal 
plain and southern CT valley.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

355 AM Update ...

Highlights ...

* Very pleasant stretch of weather featuring mainly dry conditions, 
  mild days (70s) and cool nights (50s)
* Core of cool air settles over the area Tue night into Wed night 
  with highs only in the 60s and lows in the 40s inland
* Warming trend late next week with highs near 80 possible 

Temperatures ...

Normal daytime high/low this time of year is 70-75 and 54-59. Much 
of next week will feature temperatures in this range, thus very 
pleasant conditions. However anomalous mid level low over 
Newfoundland mid week will advect a chilly airmass into eastern New 
England. Both deterministic and ensemble guidance only 
supporting highs in the 60s mid week along with lows in the 40s!
Therefore much cooler than normal mid week. Given the negative 
temp anomalies here will blend in some of the cooler guidance to
derive maxes and mins. As mid level low ejects out to sea, OH 
valley ridge builds into New England late next week supporting a
warming trend with highs near 80 possible by Friday. 

Precipitation ...

Other than a very low risk of a brief isolated shower from Sunday 
evening into Monday afternoon/evening from multiple short waves and 
attending cold pools aloft, dry weather prevails much if not all of 
next week.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

Through 12Z...
Continued VFR conditions through the night as mid to high 
clouds move in overnight. May see some local MVFR CIGS mainly 
along the S coastal terminals, possibly as far N as KPVD to KGHG
with S-SE winds increasing to around 5-10 kt by daybreak. 

Today... 
Mainly VFR conditions, but may MVFR CIGS/VSBYS in any scattered
showers moving in from NW-SE from about 17Z-18Z through the 
remainder of the afternoon. Low risk for isolated thunder around
or after 21Z. SE winds becoming S-SW 10-15 kt with gusts to
around 20 kt by around midday.

Tonight... 
VFR-MVFR CIGS lowering to IFR mainly across interior terminals 
with local LIFR by around 04Z-06Z. MVFR VSBYS may lower to IFR 
at times after 04Z along the S coast in locally heavy rainfall. 
Conditions improve to VFR across across NE and N central Mass 
toward daybreak. SW winds around 10 kt shift to W around or 
after 06Z as cold front passes. 

Sunday...
Local IFR CIGS/VSBYS mainly across the CT valley and southern
areas early will improve to VFR by mid to late morning. W wind
5-10 kt. 

KBOS Terminal...High confidence in TAF trends. 
VFR conditions through today, then may see brief MVFR 
CIGS/VSBYS in any showers this afternoon. CIGS/VSBYS lower to 
MVFR in better chance for -SHRA and patchy fog around or after 
03Z. S-SE winds 5-10 kt this morning, then S around 10 kt with 
gusts up to 20 kt this afternoon. 

KBDL Terminal...High confidence in TAF trends. 
Mainly VFR conditions through early tonight. May see MVFR CIGS 
from mid morning to midday. MVFR-IFR CIGS/MVFR VSBYS in 
scattered showers push in by around 03Z-04Z. S-SW wind 5-10 kt,
shifting to W toward daybreak Sunday.

Outlook /Sunday Night through Wednesday/...High confidence.

Sunday Night: VFR. 

Monday: Mainly VFR, with areas MVFR possible. Slight chance
SHRA.

Monday Night through Tuesday: VFR. 

Tuesday Night: Mainly VFR, with local MVFR possible. Slight
chance SHRA.

Wednesday: Mainly VFR, with local MVFR possible.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

Through 12Z... 
Expect S winds around 10-15 kt, with gusts to around 20 kt 
across the southern outer waters. Seas will linger to around 5 
ft on the southern outer waters, so have kept Small Craft 
Advisories in effect. 

Today...
S-SW winds around 10 kts early will increase to 10-15 kt with
gusts to around 20 kts. Expect gusts to reach around 25 kt on 
the eastern waters by mid to late morning and continue through
the day, so have hoisted Small Craft Advisories there. a few
showers may bring visibility restrictions off the Cape Ann coast
late this afternoon.

Tonight...
SW winds 10-15 kt with gusts to around 20 kt, expect up to near 25
kt this evening on the eastern outer waters, then will shift to
W on the eastern waters after 07Z-09Z. Seas briefly near 5 ft on
the eastern outer waters this evening, otherwise 4 ft or less.
Visibility restrictions in showers and patchy fog. Chance for
thunderstorms across the southern waters from around 06Z until
daybreak. 

Sunday...
SW winds at around 10 kt will be slow to shift to W during the 
day. Visibility restrictions in scattered showers lingering on 
the southern waters through early afternoon, then should 
improve.

Outlook /Sunday Night through Wednesday/...Moderate confidence.

Sunday Night: Winds less than 25 kt. 

Monday: Winds less than 25 kt. Slight chance of rain showers. 

Monday Night: Winds less than 25 kt. 

Tuesday through Wednesday: Winds less than 25 kt. Seas locally
approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 11 AM this morning to 10 PM EDT this 
     evening for ANZ250.
     Small Craft Advisory from 11 AM this morning to 6 PM EDT this 
     evening for ANZ251.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ256.

&&

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