BOX issues Area Forecast Discussion (AFD) at May 2, 8:19 PM EDT
263
FXUS61 KBOX 030019
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
819 PM EDT Fri May 2 2025
.SYNOPSIS...
Low chance for an isolated thunderstorm this evening, then mild
tonight with low clouds and fog once again. Summer-like
temperatures tomorrow near 80F with dewpoints near 60F.
Scattered thunderstorms with isolated severe wind gusts and
small hail are possible across interior Southern New England
Saturday afternoon. Mild again Saturday night with another
chance of showers. The weather pattern will remain unsettled at
times for the first half of next week but with cooler
temperatures.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Tonight:
Southerly moist flow continues tonight, keeping temperatures mild in
the upper 50s and low 60s with dewpoints in the mid to upper 50s.
Low cloud cover and fog will again form overnight near the south
coast and Cape/Islands, with warm air advecting over cold ocean
waters in the upper 40s to low 50s. A weak impulse of shortwave
energy progressing through the SW flow aloft may pop off some light
showers tonight, but not expecting any thunder as instability
remains under 100 J/kg.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Saturday:
Key Point
* Marginal risk for severe thunderstorms between 2-8 pm
A strong shortwave trough stalls over the Ohio River Valley, keeping
the region under moist SW flow. A summer-like feel to the air
tomorrow with highs around 80F and dewpoints around 60F will
allow instability to build to around 500-800 J/kg. However,
light rising heights and warming 500mb temperatures are less
than favorable conditions to promote convection. With 0-6km
bulk shear around 35-45 knots, this will set the stage for
scatted organized thunderstorms with some isolated severe wind
gusts and small hail possible. Hi-res guidance is pretty
consistent with thunderstorms firing along a stalled convergence
boundary across eastern NY into Western MA and southern VT
between 2-4 pm. As thunderstorms progress east through the
evening, they will run into the stable marine layer before
reaching the I-95 corridor, thus dissipating sometime between
6-8 pm. The best chance for any severe thunderstorms appears to
be across West Central MA, where the HREF shows the greatest
updraft helicity probs.
Saturday night:
Not much change in the weather pattern as the stalled, now cut off
500mb trough remains to the east with southerly flow still at
the surface. More low clouds and fog move in for the South Coast
and Islands again, with dewpoints still in the mid-50s.
Overnight lows will be bound by dewpoints again, only dropping
into the mid to upper 50s. A weak cold front actually approaches
from the south overnight, which could bring another round of
showers and embedded thunder depending on how much instability
is left over from the previous day.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Messages:
* Frontal boundary likely staying N of the region Sunday.
* Closed mid-level low slowly moves to the northeast next week and
promotes periods of rainfall through midweek.
* Ridging and a break from unsettled weather later next week.
Sunday and Sunday Night:
Latest guidance continues to make adjustments with respect to the
location of the quasi-stationary boundary Sunday. The trend has been
to shift the boundary and the bulk of the QPF to the north of the
CWA. Still thinking that we will at least see some areas of showers,
especially across northern areas. The latest NBM has trended a good
5-10 degrees warmer for Sunday's highs across the interior with the
northward jump in the location of the boundary. Increasing POPs
Sunday night as an mid-level low pressure approaches from the Great
Lakes. Guidance places the region in the right entrance region of
the 250 mb jet. At the same time, the NAEFS suggests PWAT anomalies
climb to +2-2.25 STD Sunday night into Monday. This favorable
combination of high moisture and favorable dynamics should result in
periods of showers and steadier rainfall beginning Sunday night.
Monday through Wednesday:
Vertically stacked low over the southern Great Lakes region will be
slow to move northeast through the week. The slow movement will keep
the region under the most favorable upper-level divergence allowing
ample opportunities for soaking rain, and perhaps even a limited
flood risk across western areas. Ensembles currently keep the best
forcing and heaviest rainfall to the southwest, but subtle changes
in the track of the mid-level low center could move the axis of
heavier rainfall closer to our forecast area. Maintaining chances for
thunder through early next week with elevated instability in place
under the upper-low. Upper-low center moves over the region
Wednesday, and so there could be more widespread thunderstorm
activity as lapse rates steepen Wednesday afternoon. Temperatures
should remain in the mid to upper 60s for Tuesday, with a decent
chance (roughly 50 percent on the ensembles) the interior could rise
above 70F for Wednesday.
Later Next Week:
Better news for the later part of the extended forecast as a broad
upper-level ridge builds over the north central CONUS beginning
later Wednesday night. A few lingering showers early Thurs could
give way to improving conditions in time for the start of the
weekend.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update:
Tonight: Moderate confidence.
Mainly VFR for most airports south and east of I-95; a low
chance of patchy fog in the interior, especially where hit-or-
miss showers which developed today popped up. For south
coastal/Cape and Islands airports, early VFR then gives away to
expanding stratus and areas of fog, starting over the waters
00-01z then expanding landward to I-95. Reduced confidence on
visbys in any foggy areas given persistent SW winds around 10 kt
overnight (indicated 2-3 SM BR but wouldn't rule out locally
dense fog); IFR-LIFR categories in stratus is likely though.
Saturday...High confidence.
Stratus and patchy fog along the south coast and Cape/Islands
improving to VFR by midday but low clouds may linger at ACK.
Otherwise VFR, but expect scattered showers/t-storms developing
NW of I-95 in the afternoon. A few of these storms may be
strong and produce brief heavy rainfall & localized strong wind
gusts. The marine layer should result in little if any
convection making it SE of the I-95 corridor. SW wind 10-20 kt
with a few higher gusts may shift to NW late in the day across
NW MA.
Saturday night...Moderate confidence.
Stratus and patchy fog expected to redevelop with IFR-LIFR
conditions, but uncertain how widespread low conditions will
be. Highest probability will be along the south coast but
stratus may develop in the interior as well. Scattered showers
and isolated thunder in the interior. SW wind 5-10 kt near the
south coast, with wind shift to NW possible along and north of
the MA Pike as a front stalls across the region.
KBOS TAF...High confidence in TAF. Should remain VFR through
the period as stratus and fog expected to remain to the south.
KBDL TAF...Moderate Confidence in TAF.
Outlook /Sunday through Wednesday/...
Sunday: Mainly VFR, with local IFR possible. Chance SHRA.
Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely.
Monday: MVFR/IFR conditions possible. Breezy. Chance SHRA.
Monday Night: MVFR/IFR conditions possible. Chance SHRA.
Tuesday: MVFR/IFR conditions possible. Breezy. SHRA likely.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Saturday night
Continued southerly winds through Saturday night around 15-20
knots. Seas increase to 4-6 feet in the open waters Saturday
afternoon. Low clouds and fog likely form tonight and again
Saturday night. Cold front move north Saturday night may bring
some showers over the waters.
Outlook /Sunday through Wednesday/...
Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers. Local visibility 1 to 3 nm.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.
Sunday Night: Winds less than 25 kt. Chance of rain showers.
Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.
Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.
Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 1 PM Saturday to 11 AM EDT Sunday
for ANZ254>256.
&&
$$
SYNOPSIS...KP/FT
NEAR TERM...KP
SHORT TERM...KP
LONG TERM...FT
AVIATION...KJC/Loconto
MARINE...KP/FT
Source: BOX issues Area Forecast Discussion (AFD) at May 2, 8:19 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202505030019-KBOX-FXUS61-AFDBOX)
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