-- Discussion containing changed information from previous version are highlighted. --
353
FXUS61 KBOX 271138
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
738 AM EDT Mon May 27 2024

.SYNOPSIS...

Increasing chances for showers and thunderstorms ahead of an
approaching cold front, mainly late this afternoon into this
evening. This cold front moves offshore early Tuesday, with
decreasing clouds and drier weather conditions. Generally dry
from mid week into the weekend with more seasonable
temperatures. Cannot rule out a few hit or miss showers later
on Wednesday into Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...

Regional radar data showed that the last few runs of the HRRR
were too aggressive in triggering convection across our region
early this morning. Based the forecast for next few hours off
the 00Z HREF, as well as the latest RAP and NationalBlend runs.
Thinking there is a risk for at last some showers as a decaying
convective band approaches from eastern PA towards daybreak.
Even lower risk for thunderstorms, but not impossible.

Issued a Dense Fog Advisory for RI and the south coast of MA.

Low pressure is expected to move across the Great Lakes into
southern Canada today. The warm front associated with this low
will struggle to move much north of our region. Noticeably
cooler today, but still just as humid. Most of southern New
England should see less than one quarter inch of rainfall today,
where it rains at all. There is a risk for locally heavier
rainfall from the stronger showers and less frequent
thunderstorms.

Instability will be tough to generate today due to the stratus
and fog which will take time and energy to dissipate. Overall
MUCAPE values should remain less than 500-700 J/kg today,
meaning there is not much of a severe weather threat, other than
locally heavy rainfall.

&&

.SHORT TERM /TUESDAY/...

The cold front associated with a low pressure in southern Canada
should move into our region some time tonight into Tuesday.
Timing this front has been a challenge, as many different
possibilities have been presented over the past few days.
Consensus timing now has this front arriving after midnight
tonight, but still somewhere just east of southern New England
by Tuesday evening. We should not see the humidity diminish
until this front passes completely by our region. Looking at
another round of stratus and fog tonight.

The heaviest and most widespread rainfall is expected this
evening into tonight. Not as much forcing for Tuesday, so
thinking we can get through most of the day without rainfall.

Above normal temperatures continue.

&&

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

Highlights

* Dry for much of Wed with more seasonable temps. Could have
  spotty showers across the interior during the
  afternoon/evening.

* Shot for more widespread rain Wed Night into Thu, but there is
  a lot of uncertainty at this point.

* Overall looking pleasant Fri through the weekend with dry
  conditions. Temps near seasonable levels.

Tuesday Night through Wednesday...

Stuck in blocky cyclonic flow through this period. Will have a
trough over Upstate NY and a shortwave over the western Great
Lakes to start. The first wave lifts northeastward, while the
shortwave digs into the OH Valley. The shortwave begins
interacting with the larger trough over the eastern Great
Lakes/Mid Atlantic by late in the day. A cold front slides
through Tue Night into early Wed. Could see a secondary cold
front or surface trough sliding in late in the day.

Anticipating dry and quiet weather through the vast majority of
this period. Does appear that there will be an opportunity for
spotty showers Wed afternoon into the evening as the surface
trough/secondary cold front is sliding in. Some uncertainty on
this as winds will be W to WNW through the period. Should have a
roughly 15-30 kt LLJ sliding through. This should aid in
keeping us well mixed and drying things out as seen in the
1000-850 hPa RH. Moisture values really not that impressive with
meh PWATs at +/- 1 STD above/below NAEFS/EPS model climo. The
result are PWATs roughly of 0.75 to 0.85 inches. Dialed back our
precip chances to slight for much of the period, though western
areas could see some scattered activity push in toward the
evening.

Only other adjustment made during this timeframe was to
increase temperatures given the W/WNW flow. This should result
in downsloping with 925 hPa temps of 9-15 degrees Celsius. Opted
to bump us up to the 75th percentile of guidance. Highs will
generally be in the 70s.

Wednesday Night through Thursday...

Still in cyclonic flow. Will have that second shortwave/trough
over the Mid Atlantic lifting toward/through southern New
England by early Thu. It continues lifting toward Nova Scotia by
late Thu, though could pivot across the Cape on Thu. A cold
front will be lingering nearby. We could have an area of low
pressure ride along the front, though there is a fair amount of
uncertainty.

Big question mark during this period appears to be when the
trough lifts toward us late Wed and how negatively tilted it
becomes. Guidance is split with the GFS lifting the trough into
the Gulf of ME before it becomes negatively tilted, while the
international guidance as a whole does it as it lifts into/just
south of Long Island. This also results in the trough continuing
to slowly lift through on Thu vs the more progressive GFS. The
international guidance solutions put a baggy trough or perhaps
cutoff nearby southern New England heading into Thu at 700 hPa,
whereas the GFS does not. This cutoff solution would bring the
risk for heavier precip.

Despite these details am not overly amped up at this point
about the rain risk late Wed into Thu. NAEFS/EPS guidance show
PWATs of 1 STD below model climo. Values anticipated to be
generally around 0.75 to perhaps 1 inch. So, not a whole lot of
moisture to work with. Though if we can get the trough nearby
southern New England we could really squeeze out the moisture
available. Should also have some roughly 1.5-2.5 km warm cloud
layer depths. Despite not being amped up about it there is some
ensemble hints at more widespread QPF, especially across the
south coast. The GEFS like the GFS is the least amped up with
only low probs (10 percent) of 24 hr QPF AOA 0.5 inches. The
GEPS/EPS show low to moderate probs (10-50 percent) of 24 hr QPF
AOA 0.5 inches. Both the GEPS/EPS also showing some low probs
of 24 hr QPF AOA 1 inch. So will be something to keep an eye on.
Though at this point not anticipating to have much instability.
High temperatures on Thursday will be right around seasonable
levels.

Friday through the weekend...

Cyclonic flow continues through much of the period. A cutoff
swings through much of New England on Fri as a ridge builds into
the western/central Great Lakes. The ridge axis builds toward
the eastern Great Lakes by late Sat and Sun. High pressure
begins nudging in on Fri, but should build in for the weekend.

Generally am anticipating dry and quiet weather late in the
week and through the weekend with high pressure in control. Do
wonder if the cutoff will be close enough on Fri that we still
can see some spotty showers, but for now think NBM slight
chances suffice. Dry through the weekend with temperatures still
around seasonable levels.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...

-- Changed Discussion --
Forecast Confidence Levels:

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

Today...High confidence in trends. Moderate confidence in
timing.

IFR to VLIFR conditions today. Generally dry other than stratus
and drizzle, outside of western areas where spotty showers
developing. More robust line of rain associated with a cold
front develops after 19-21Z. Some embedded TSRA possible with
this round and have handled with PROB30 at all terminals. Winds
remain E to SE, may gust as high as 20kt this afternoon.

Tonight...Moderate Confidence.

Another round of stratus and fog. Rain will come to an end
between 05-09Z, yielding improving conditions with improvement
from IFR to MVFR/VFR around sunrise. Winds shift from the SE to
the S/SW, gusting to 20kt, behind a frontal passage.

Tuesday...Moderate Confidence.

A cold front continues to move across our region, but likely
stalls some where just offshore. Improving to VFR toward mid to
late AM. Winds out of the SW/W at 5-10 kts and could have some
15-20 kt gusts during the afternoon.

KBOS TAF...High confidence in TAF trends, moderate in timing.

VLIFR to start with stratus/fog. Thinking we see improvement
roughly 14-17Z to MVFR visby, but IFR stratus persists. Dry for
much of the day other than spotty drizzle. Will see steadier
showers moving in approx 23-01Z. Could have some embedded
thunder and have handled with a PROB30 for tonight. Should
rapidly improve to MVFR/VFR Tue AM and wind shift to the SW.

KBDL TAF...High confidence in TAF trends, moderate in timing.

Will have IFR conditions today with SE winds increasing. Should
see gusty 20-25 kt winds toward this evening as showers spread
in. Rainfall may be heavy at times tonight along with embedded
thunder. Have handled the embedded thunder with a PROB30. Winds
turning S/SW late and rapidly improving to MVFR/VFR toward Tue
AM.

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR. Breezy.

Wednesday: VFR. Slight chance SHRA.

Wednesday Night through Thursday: VFR. Chance SHRA.

Thursday Night through Friday: VFR. Slight chance SHRA.
-- End Changed Discussion --

&&

.MARINE...

-- Changed Discussion --
Forecaster Confidence Levels:

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

Through Tuesday...Moderate Confidence.

Dense marine fog expected as winds prevail from the east.
Increased shower activity late today before a cold front brings
the chance for more potent rain and embedded thunderstorms to
the waters late this evening and early Tuesday morning. Winds
increase, gusting between 25-30kt from the east before turning
south behind this front. Waves climb in excess of 5 feet across
the outer waters. Small Craft Advisories remain in effect for
the eastern outer, and southern waters, including Nantucket
Sound late today into tonight.

Outlook /Tuesday Night through Friday/...

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Patchy fog.

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft.

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft.

Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft. Chance of rain showers.

Thursday: Winds less than 25 kt. Chance of rain showers.

Thursday Night through Friday: Winds less than 25 kt. Slight
chance of rain showers.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Dense Fog Advisory until 8 AM EDT this morning for MAZ020>024.
RI...Dense Fog Advisory until 8 AM EDT this morning for RIZ001>008.
MARINE...Small Craft Advisory from 9 PM this evening to 11 AM EDT
     Tuesday for ANZ232-233-235-237.
     Small Craft Advisory from 6 PM this evening to 5 AM EDT
     Wednesday for ANZ250-254.
     Small Craft Advisory from 9 PM this evening to 5 AM EDT
     Wednesday for ANZ255-256.

&&

$$

SYNOPSIS...Belk/BL
NEAR TERM...Belk/BL
SHORT TERM...Belk
LONG TERM...BL
AVIATION...Belk/BL
MARINE...Belk/BL