BOX issues Area Forecast Discussion (AFD) at May 8, 1:38 PM EDT787
FXUS61 KBOX 081738
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
Issued by National Weather Service New York NY
138 PM EDT Thu May 8 2025
.SYNOPSIS...
A very slow frontal boundary will be moving within the region
through early Friday. Then, associated low pressure moves in
Friday into early Saturday. High pressure returns for the
latter half of the weekend into early next week. High pressure
however is forecast to move offshore towards middle of next week
with another frontal system approaching.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Point
* Scattered to numerous showers develop this afternoon mainly
across western parts of the region. A few thunderstorms are
possible as well this afternoon.
Approaching upper level trough with positive vorticity advection
will help enhance synoptic lift this afternoon. CAMs depicting
multicells and areas of convection developing across portions
of the region. Increased POPs after incorporating the HRRR,
NAMNest into the forecast.
The convective potential will be present due to increasing CAPE,
up to almost 600 J/kg possible this afternoon. This seems to be
focused more in the Connecticut River Valley. Interior CT and
Western MA are likely to get rain showers this afternoon.
Heavy downpours can be expected with any thunderstorm activity
but not expecting severe weather.
Temperatures adjusted slightly warmer per latest NBM. Highs
still in the upper 60s to lower 70s across much of the region.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
Upper-level shortwave deepens into the Ohio River Valley,
strengthening a surface low-pressure system over PA. WAA begins
to kick in ahead of the low pres, which will help maintain the
showers that formed in the afternoon even as instability wanes.
Better forcing from the short wave arrives overnight, allowing
more widespread moderate to heavy rain to move in from west to
east. With the WAA and rain, another mild night with lows only
dropping into the upper 40s to low 50s.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Key Points:
* Soaking rains Friday into Friday night with below normal
temperatures. Heavy rainfall with possible hydro concerns across
western MA/CT
* Rain gradually exits during Saturday morning with improving
conditions in the afternoon
* Drying with a warming trend Sunday through Tue. Showers may return
by Tuesday night or Wed
Details:
Friday into Saturday:
Slow moving upper low across the Gt Lakes gradually moves into New
Eng late Fri night before lifting to the NE Sat afternoon. Deep
southerly flow ahead of this upper low will transport elevated PWATs
1.25 to 1.5" northward into SNE Fri into Fri night. Meanwhile,
surface low pres will move across interior SNE with area of enhanced
low level frontogenesis along a warm front acting on deep moisture
to bring widespread rain to the region Fri into Fri night. Heaviest
rainfall will likely be focused across central/W MA and northern CT
near the axis of low level frontogenesis. Across eastern New Eng,
steadier rainfall may be delayed until later Fri and especially
Fri night as low level forcing and deep moisture moves east.
Despite cool low level airmass, cooling temps aloft as upper low
moves overhead may lead to some elevated thunder Fri night
which could add to the rainfall amounts.
Modest E-SE low level jet should enhance rainfall along east slopes
of the higher elevations. EPS ensembles are most bullish on heavy
rainfall with 60-80% probs of greater than 1 inch of rainfall and 20-
40% probs of greater than 2 inches focused in western MA/CT. GEFS
ensembles shift the axis of heavy rain probs (greater than 1 inch) a
bit further north and west but the Berkshires are within the axis of
highest probs. Generally looking at total rainfall amounts of 1-2
inches, heaviest in western MA/CT where localized amounts greater
than 2 inches possible, while rainfall amounts may be less than 1
inch across portions of eastern MA. This is not really a flash flood
scenario as rainfall rates will be somewhat muted. However, we may
see renewed flooding on the CT river at Hartford and Middle Haddam
with rainfall approaching 2 inches. NAEFS and GEFS ensembles
indicate about a 40 percent prob of renewed minor flooding along CT
river at Hartford and Middle Haddam with lower probs at other points
along the CT river.
It will be a chilly day on Fri with temps well below rainfall.
Easterly flow and rainfall will keep highs mostly in the 50s but
possibly remaining in the upper 40s across portions of northern MA.
Looking ahead to Sat, the dry slot will be overspreading SNE during
the morning with steadier rainfall tapering off, but lingering
showers in the comma head may continue in the morning before
gradually drying out in the afternoon. Increasing NW winds in the
afternoon as low pres pulls away. Temps remain below normal.
Sunday through Wednesday:
Mainly dry weather for much of the period as high pres builds into
the region before moving offshore early next week which will lead to
a gradual warming trend with above normal temps returning. Next
upper trough will be approaching from the west beyond Tue so
depending on timing of this system the risk of showers will
increase Tue night into Wed.
&&
.AVIATION /18Z THURSDAY THROUGH MONDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update:
Thursday: High confidence.
VFR. MVFR in SHRA/TSRA. Scattered showers and possibly a
thunderstorm through early evening. Have maintained PROB30s for
most terminals, but added TSRA save for the coastal sites. TSRA
chances should wane after 00Z.
Thursday Night: Moderate confidence.
MVFR/IFR conditions. Left over rain from the afternoon
convection may continue through 04z, then the rain from the next
system reaches western MA and CT after 06z, and moves east
through the night. Rain may become moderate to heavy at times.
Friday: High Confidence
Continued IFR conditions with rain. East winds at 10-15 knots.
KBOS TAF...High confidence.
KBDL TAF...High confidence.
Outlook /Friday through Monday/...
Friday: Mainly IFR, with areas MVFR possible. RA, slight chance
TSRA.
Friday Night: MVFR/IFR conditions possible. RA, slight chance
TSRA.
Saturday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA.
Saturday Night through Monday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Friday: High Confidence.
Calm conditions today with light winds and calm seas due to
weak high pressure. Low pressure system will bring rain and
increasing southerly winds to the waters Friday. Seas begin to
increase to 3-5 feet in the open waters.
Outlook /Friday through Monday/...
Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain,
slight chance of thunderstorms.
Friday Night: Winds less than 25 kt. Seas up to 5 ft. Rain,
slight chance of thunderstorms.
Saturday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.
Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Sunday Night through Monday: Winds less than 25 kt.
&&
.HYDROLOGY...
A flood watch remains in effect for the CT river valley into
the Berkshires. Latest 00z HREF brings impressive rain totals to
the CT river valley into the east slopes of the Berkshires. the
24 LPMM shows a widespread 1.5-2.5 inches of rain with
localized spots up to 3 inches. Given the antecedent wet
conditions from the previous system earlier this week, there
will be a renewed threat for river flooding esspically in the
southern portion of the CT river. Not expecting flash flooding
given the stratiform nature of this event, but minor street and
nuisance flooding are likely with several hours with rain rates
around 0.1 inches/hr.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from late tonight through Saturday morning for
CTZ002-003.
MA...Flood Watch from late tonight through Saturday morning for
MAZ002-003-008>011.
RI...None.
MARINE...Small Craft Advisory from 5 AM to 8 PM EDT Friday for ANZ250.
&&
$$
UPDATE...JM/DBR
Source:
BOX issues Area Forecast Discussion (AFD) at May 8, 1:38 PM EDT----------------
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