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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 210739
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
339 AM EDT Sun Apr 21 2024

.SYNOPSIS...

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A ridge of high pressure will result in dry weather today through
Tuesday with mild days and chilly frost nights, along with elevated
fire weather potential. Unsettled, wet and cool on Wednesday.
Drier late in the week and heading into the weekend.
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&&

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

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330 AM Update...

* Dimming sunshine behind increasing mid level cloudiness today
* High temperatures mainly between 55 and 60 this afternoon

A wave of low pressure over the Carolinas early this morning will
move east today and stay well south of our region. This will keep
our weather dry today...although we do expect an abundance of mid-
high level cloudiness to overspread the region later this morning
and afternoon. The mid level cloudiness will result in dimming
sunshine through the day. That being said...the airmass is quite dry
which should allow for afternoon high temperatures to reach mainly
between 55 and 60. Westerly winds will gust to 20 to perhaps briefly
25 mph in spots by afternoon with good mixing.
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&&

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

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Key Points...

* Clearing tonight...lows upper 20s to the middle 30s in many spots
* Areas of frost expected to develop very late tonight
* Sunny on Monday with highs between 55 and 60

Details...

Tonight...

Low pressure well south of our region tonight will move further east
and further away from our area tonight. This will allow the mid-high
level cloudiness to move offshore and result in skies becoming
mainly clear tonight. There is some westerly flow aloft...but think
winds will decouple in many of the low lying spots for a few hours
overnight. This coupled with a very dry airmass in place will result
in a good night of radiational cooling. Overnight low temps should
drop into the upper 20s to the middle 30s across much of the region
with the coldest of those readings in the typical low-lying spots of
western MA. We did issue a Frost Advisory for CT/RI and southeast MA
now that we are into late April.

Monday...

A reinforcing dry cold front will cross the region early Monday
morning. This will result in a dry west to northwest flow of air
across the region. Model cross sections are quite dry...so expect
sunny skies. Although 850T will be between -2C/-3C...we expect a dry
super-adiabatic atmosphere on Monday with excellent mixing.
Afternoon high temperatures should recover between 55 and 60 in most
locations.
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&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...

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Highlights

* Strong radiational cooling Mon Night resulting in widespread
  frost.

* Mild and breezy on Tue with elevated fire weather concerns
  possible.

* Gusty winds and showers late Tue Night through Wed. Temps trending
  cooler.

* Windy, cool and dry on Thu.

* Still dry, but trending warmer on Fri and Sat.

Monday Night...

A ridge axis builds from the TN Valley into the Mid Atlantic/eastern
Great Lakes Mon Night. The ridge builds offshore of Mid Atlantic by
early Tue. High pressure builds overhead Mon Night, but shifts
toward Nova Scotia by early Tue.

Dry and quiet weather expected through this period with high
pressure. This brings clear skies and light winds, which will result
in strong radiational cooling. The NBM running way too warm for this
setup, so went with the 10th percentile of guidance for lows. Should
see temps ranging from the mid 20s to the mid 30s. Should see fairly
widespread frost. Frost/freeze headlines will likely be needed in
future updates.

Tuesday...

Caught under cyclonic flow. A ridge axis will be just off the Mid
Atlantic coast early on Tue, while a trough is over the Upper
Mississippi River Valley. The ridge gets shunted further to the SE,
while the trough digs into the central Great Lakes by late Tue. High
pressure nudges in from Nova Scotia, but will build further to the
northeast.

Another period of dry and quiet weather, but with gusty winds.
Anticipate there will be elevated fire weather concerns given the
well mixed boundary layer per NAM/GFS Bufkit soundings. Shows that
we mix up to roughly 800 hPa and we should see some gusts around 20
to perhaps 25 mph at times during the afternoon. In this type of
setup guidance tends to under do the temps and we typically end up
with drier dew points/RH values. Have a bit more uncertainty on the
dew points/RH values as we will be under southerly flow, which tends
to keep our moisture up a bit more than say westerly flow. For now
went with the 20th percentile of guidance for the min RH, so values
range from the mid 20s to the mid 40s. As for temps went with the
75th percentile of guidance, which results in highs ranging from the
mid 50s to the mid 60s.

Tuesday Night through Thursday...

Still stuck in cyclonic flow. The trough over the Great Lakes region
digs into the eastern Great Lakes by early Wed. A northern stream
trough digs from James Bay into Quebec. The trough may interact with
the southern stream wave over New England on Wed, though there is
uncertainty on how things evolve. The trough cuts off over northern
New England late on Wed before lifting toward Newfoundland and
Labrador on Thu. A frontal system slides in late Tue through Wed
before moving offshore on Thu. Will be stuck between a high over the
Great Lakes and a low over the Canadian Maritimes on Thu.

As was the case yesterday the PWAT plume not appearing overly
impressive with PWATs below 1 inch per EPS/GEFS and GEPS nil probs
of values AOA 1 inch. Deterministic guidance showing we generally we
be under roughly 0.75 to 0.85 inches. We do have a deeper SW/W low
level jet at 850 hPa, which could help squeeze out the moisture
available. At this point deterministic guidance shows roughly 30-40
kt jet in place. Though there is uncertainty on the interaction
between the two troughs. If they phase as some guidance indicates
this would result in a strong jet, thus a higher wind potential
especially as we turn into colder westerly flow. For now have just
stuck with the NBM with some minor tweaks for precip timing. Should
see roughly a 0.1 to around 0.4 inches of precipitation. Though
again a more intense system could squeeze out a bit more moisture
and could bring a few thunderstorms for portions of our region Wed.

High temperatures on Wed will be in the 50s. As for Thu we will be
cooler in wake of the system with highs in the low to mid 50s. Could
be quite windy due to a tightened pressure gradient. May dry out
well enough that once again there could be elevated fire weather
concerns, but this will hinge on how much precip is realized on Wed.

Friday through Saturday...

Ridge axis builds into the Great Lakes region on Fri and into Sat,
but a shortwave may ride the ridge as we head into late Sat. High
pressure generally in control through this period, but a frontal
boundary may lift toward us late on Sat.

Dry and quiet weather anticipated with temperatures rebounding as we
head into the weekend. Do have some uncertainty with the shortwave
lifting toward us. Given it is spring time there could be some
convective influences. Have just stuck with the NBM for now. Highs
around seasonable levels on Fri and slightly warmer than normal on
Sat.
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&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...

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Forecast Confidence Levels:

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

06z TAF Update...

Today...High Confidence.

VFR with just an increase in mid level cloudiness today. W winds
10 to 15 knots with gusts into the lower 20 knots at times this
afternoon in some locations.

Tonight and Monday...High Confidence.

VFR conditions continue tonight and Monday. WNW winds generally
5-10 knots. Some risk that a weak sea breeze will develop late
Monday afternoon along portions of the eastern MA coast...but
that is still uncertain at this time.

KBOS TAF...High Confidence in TAF.

KBDL TAF...High Confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: VFR. Patchy frost.

Tuesday: VFR. Breezy.

Tuesday Night: VFR. Breezy. Chance SHRA.

Wednesday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA.

Wednesday Night: VFR. Breezy. Chance SHRA.

Thursday: VFR. Breezy.
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&&

.MARINE...

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Forecaster Confidence Levels:

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

Today through Monday...High Confidence.

A relatively weak pressure gradient will keep winds/seas below small
craft advisory thresholds today through Monday. That being
said...there is enough heating over the land today to result in
westerly near shore wind gusts into the lower 20 knots for a few
hours this afternoon.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday: Winds less than 25 kt.

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

Wednesday through Wednesday Night: Moderate risk for Small
Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.
Chance of rain showers.

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft.
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&&

.FIRE WEATHER...

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Today and Monday...

There will be elevated fire weather concerns today and again on
Monday. Given that we are in a pre-greenup and dry westerly flow
will allow for minimum afternoon relative humidity values to drop to
between 20 and 30 percent both days with Monday being the slightly
drier day. Westerly winds will gust to around 20 to perhaps briefly
25 mph in some spots this afternoon. The winds will be tad lower on
Monday, but still expect WNW gusts of up to 20 mph.
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&&

.BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Frost Advisory from midnight tonight to 7 AM EDT Monday for
     CTZ002>004.
MA...Frost Advisory from midnight tonight to 7 AM EDT Monday for
     MAZ013-016>023.
RI...Frost Advisory from midnight tonight to 7 AM EDT Monday for
     RIZ001>008.
MARINE...None.
-- End Changed Discussion --

&&

$$

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