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000
FXUS61 KBOX 221506
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1106 AM EDT Mon Apr 22 2024

.SYNOPSIS...
A ridge of high pressure will result in dry weather today through
Tuesday with pleasant days and chilly frosty nights, along with
elevated fire weather potential. Unsettled with showers and
scattered thunderstorms on Wed. Winds will be gusty at times.
Cool on Thu, but temperatures rebound late in the week and
heading into the weekend with dry weather.

&&

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

Quiet weather continues. No major changes to the ongoing
forecast. Still seeing signs for a late afternoon seabreeze
along the coasts. Minor tweaks to temperatures.

325 AM Update...

* Sunny & pleasant today with highs between 55 and 60

A ridge of high pressure building over the region will result in
very pleasant late April weather across the region. After a chilly
start with areas of frost...the increasing sun angle coupled with a
very dry airmass will allow for a nice recovery in temperatures.
Afternoon high temperatures should reach between 55 and 60 degrees.
These readings are about 5 degrees below normal of this time of
year. But with lots of sunshine it will feel quite a bit milder than
yesterday did with all the mid level cloudiness.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Key Points...

* Mainly clear tonight & chilly with frost/freeze conditions
* Sunny & milder Tue, highs in the low-middle 60s away from the coast

Details...

Tonight...

A ridge of high pressure will remain in control of our weather
tonight. This will result in mainly clear skies/light-calm winds
with a dry cool airmass in place for this time of year. Overnight
low temps should bottom out in the middle to upper 20s in the
normally coldest outlying locations with mainly 30s
elsewhere...except lower 40s in the urban Heat Island of Boston. We
did issue Frost Advisories again tonight for CT/RI/SE MA where we
are passed the median date of the last freeze. Temps will probably
be a few degrees lower than early this morning...so perhaps a few
areas may need to be considered for upgrades to freeze warnings.

Tuesday...

The high pressure system will move off the southeast coast on
Tuesday. We still expect plenty of sunshine and with a milder
southerly flow of air across the region...temps will rebound to
fairly seasonable levels. After a chilly/frosty early morning
start...high temperatures should reach the lower to middle 60s away
from the cooling marine influences along parts of the immediate
coast where highs will be held in the middle to upper 50s. Southerly
winds may gust up to 20 mph or so during the afternoon.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Highlights

* Showers spreading in late Tue night through Wed as a cold front
  slides through. Scattered thunderstorms along with gusty winds and
  could perhaps see some graupel as well.

* Dry, breezy and cool on Thu.

* Trending milder late in the week into the weekend. Generally dry,
  but we could see some showers pushing in late in the weekend.

Tuesday Night through Wednesday...

Caught under cyclonic flow through this timeframe. A trough will
initially be over the central Great Lakes Tue Night. This will dig
into the eastern Great Lakes/Mid Atlantic by early Wed. There is a
northern stream trough digging toward northern New England on Wed,
which may interact with that previous trough as it is lifting
through our area on Wed. This will swing a cold front through out
region.

Main concern in the latest update is the thunderstorm risk along
with gusty winds. Appears that there is some interaction going on
between the two troughs on Wed, which given the cold pool aloft will
steepen mid level lapse rates. At this point guidance showing values
ranging from 6-8 degrees Celsius. We may even have low level lapse
rates of a similar range, but there is some discrepancy amongst
guidance. Do have some question on the instability at the NAM/GEM
show a few hundred J/kg of MUCAPE along with the GEPS. The ECMWF/GFS
along with their ensemble counterparts (EPS/GEFS respectively) are
much more muted. Despite the discrepancy we`ve got a fairly dynamic
system working its way in and a ribbon of 40-60 kts of deep layer
shear moving in. Have added more thunder to the forecast as all
guidance has good mid level lapse rates in place. Added a gusty wind
mention given the setup and also think it is not out of the question
there is a stronger storm or two. Though this may be limited by the
moisture available (0.7-0.8 inches) along with the best instability
and shear only briefly overlapping. Stay tuned for future updates.

Regardless of the thunder potential do think we will have breezy
conditions throughout the day Wed, especially during the afternoon
as flow shifts from the SW to the NW. Still some uncertainty on the
strength of the jet, but could range from 20-40 kts at 850 hPa. The
default NBM appears fine at this juncture. High temps range from the
mid 50s to the low 60s.

Thursday through Sunday...

Will initially be in cyclonic flow on Thu, but will have a ridge axis
over the Plains. The ridge will build into the Mississippi River
Valley by late Thu. The ridge builds into the TN Valley to central
Great Lakes by late Fri and the East Coast by late Sat. Confidence
high through this period. By Sun confidence lowers as the ridge may
be reinforced over the region or a shortwave may ride/shunt the
ridge offshore. High pressure nudges in from the Great Lakes Region
on Thu and overhead on Fri/Sat. The high shifts offshore on Sun.

Dry and quiet weather anticipated through the vast majority of this
timeframe. Could be a bit breezy due to a tightened pressure
gradient on Thu, but some uncertainty here as the high could build
over the region a bit quicker than the latest NBM indicates. This
would relax the gradient much fast and result in lighter winds. For
now have stuck with the higher NBM. The other risk heading into Thu
and Fri is there could be cold enough air in place where widespread
frost develops. More confident in heading into Fri with the high
overhead. For heading into Thu we may be a bit too windy for
widespread frost development. Frost/freeze headlines may be needed
in future updates.

Coldest temps of the week on Thu with a -2 to -4 degree Celsius
airmass overhead at 850 hPa. Will warm up Fri through the weekend as
flow turns W on Fri and S/SW through the weekend. High temps ranging
from the mid 50s to the mid 60s. Could be a bit warmer on Sun with
us generally being in the 60s. There is uncertainty here given
guidance is all over the place with our next shortwave lifting in.
Some still have the high dominating, so for now have stuck with the
NBM. This brings chances of showers.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

Today...High confidence.

VFR. NW winds 5 to 15 knots. Might be a brief sea breeze along
portions of the immediate coast during the late afternoon/early
evening hours.

Tonight...High confidence.

VFR. Light and variable winds.

Tuesday...High confidence.

VFR. S winds of 10 to 15 knots with some afternoon 20+ knot
possible.

KBOS TAF...High confidence through early this afternoon.
Moderate on sea breeze potential late this afternoon.

VFR with late sea breeze possible 21-23Z. Winds shift to the S
tonight and SE by Tue AM.

KBDL TAF...High Confidence in TAF.

VFR with WNW winds turning to the NW with 15-20 kt gusts. Winds
become light and variable tonight, but shift to the S by Tue AM.

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR. Breezy. Chance SHRA.

Wednesday: Mainly VFR, with local IFR possible. Breezy. SHRA
likely, isolated TSRA.

Wednesday Night: VFR. Windy with gusts up to 30 kt.

Thursday: VFR. Breezy.

Thursday Night through Friday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Tuesday...High Confidence.

A ridge of high pressure to our south today and tonight will be
in control of our weather. NW winds may gust to between 15 and
20 knots nearshore this afternoon, but this ridge of high
pressure will keep winds/seas below Small Craft Advisory
thresholds. This high shifts east of the region Tue allowing a
return southerly flow of air. Southerly winds will gust to
between 15 and 20 knots, but again expect winds/seas to remain
below Small Craft Advisory thresholds.

Outlook /Tuesday Night through Friday/...

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

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers, isolated thunderstorms.

Wednesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Seas up to 5 ft.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas.

Thursday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Friday: Winds less than 25 kt.

&&

.FIRE WEATHER...
Today and Tuesday...

There will be elevated fire weather concerns today and Tuesday.
Given that we are in a pre-greenup and a very dry atmosphere is in
control...expect minimum afternoon relative humidities to drop to
between 15 and 25 percent today and between 20 and 30 percent on
Tuesday. Winds will be NW today with some gusts of 15 to 20 mph, but
will shift to the south on Tuesday with some gusts again of 15 to 20
mph. This will all result in some elevated fire weather concerns
today and Tuesday.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for
     CTZ002>004.
MA...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for
     MAZ013-016>023.
RI...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for
     RIZ001>008.
MARINE...None.

&&

$$

SYNOPSIS...Frank/BL
NEAR TERM...Belk/Frank/BL
SHORT TERM...Frank
LONG TERM...BL
AVIATION...Frank/BL
MARINE...Frank/BL
FIRE WEATHER...Frank