BOX issues Area Forecast Discussion (AFD) at Aug 6, 1:35 AM EDT160
FXUS61 KBOX 060535
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
135 AM EDT Tue Aug 6 2024
.SYNOPSIS...
Hot and humid conditions end today with a more comfortable
airmass settling in for the rest of the week. Showers expected
to form overnight and last into tomorrow morning. Another round
of moderate to heavy rain likely Tuesday night into Wednesday. Driest
period of the week occurs late Wednesday into Thursday. Impacts
from Debby will begin Friday and persist through Sunday.
&&
.NEAR TERM /THROUGH TODAY/...
Highlights:
* A raw feeling with morning showers and a somewhat drier afternoon.
* Afternoon temperatures struggle to reach the middle and upper 70s.
Decaying mid-level shortwave and cold front will bring another round
of light to moderate rainfall this morning, not out of the question
there could be a few heavier downpours or rubles of thunder. Not
concerned with anything severe, but there is sufficient moisture as
PWATs are 1.8 to 2.2 inches and the warm cloud layer is between 12
and 14 thousand feet. Showers should wind down by late morning and
followed by drier conditions this afternoon. As the cold front sags
south and stalls over the southern waters, this boundary will be a
source of convergence where showers may develop this afternoon with
our greatest confidence for the Islands; Block Island, Nantucket,
and Martha's Vineyard. It is here were there is the greatest chance
for thunder as well this afternoon. In terms of rainfall, which is
only through 00z/8pm is between 0.25 and 0.75 inch, and around an
inch on the Islands. As the front is expected to remain off shore
the flash flood potential has diminished, though not eliminated.
There is a MARGINAL ERO for all of southern New England for Tuesday.
It is a mostly cloudy day, although there could be some breaks in
the clouds for areas north of Route 2. Given the cloud cover and
onshore east to east/northeast winds we expect below normal
afternoon highs in the 70s. Lower 70s for eastern MA with the warmer
spot being the CT River Valley in the upper 70s.
&&
.SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/...
Tonight:
Still some uncertainty with how far south the cold front stalls.
Guidance seems to want to stall the front along or south of Long
Island stretching to Nantucket. A weak surface low looks to ride up
the stalled front overnight which will bring a widespread soaking
rain to much of the region. PWATS range from 1.0 north of the
MA Pike to 2.0 near the stalled front over the southern waters.
With strong forcing from a shortwave aloft and warm cloud depth
in excess of 10-12 kft, expecting moderate to heavy rain
showers. The best chance for seeing 1-2 inches of rain appears
to be across CT, RI, and SE MA. Further north, QPF totals will
likely fall off quickly ranging from 0.25-0.75 inches.
Overnight lows finally drop to a more comfortable level into the
low 60s and even some upper 50s.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
* Potential for heavy rain to linger through Wednesday morning
associated with a stalled frontal boundary to our south
* Longest stretch of dry weather this week will occur Wednesday
evening through early Friday
* Impacts from Debby will begin late Friday, potentially lasting
through Sunday
Wednesday and Thursday...
There remains uncertainty in the location of a cold frontal boundary
come Wednesday morning, with the threat for the heaviest rain
occurring prior to 12Z. Still, cannot rule out some shower and
downpours persisting through the first half of the day. Shortwave
trough moves east of the region by Wednesday evening with weak mid
level ridging and surface high pressure building in for Thursday. Do
anticipate the period of Wednesday afternoon to late Thursday
evening will be the driest 36 hour period of the week. With frontal
boundary still south of the region, do anticipate much more
temperate highs for the mid week period, generally in the 70s with
much cooler dewpoints. Many locations will drop into the 50s
overnight Wednesday/Thursday, the coolest temperatures we have seen
in several weeks.
Friday through Sunday...
There appears to be some moderate consensus in that the impacts from
Debby will begin on Friday, and will likely persist through Sunday;
generally in the form of heavy rain and potential flash flooding.
The impacts felt here in southern New England will be highly
dependent on the exact track of the system, with a more coastal
track shifting the heaviest rain potential across our entire region
and a more inland track, like the GFS portrays, isolating the
heaviest rain threat to our western zones. It is much too early,
given mesoscale models have yet to include the period, to deduce the
exact location of heavy rain banding and rainfall totals, but will
note that ensemble probabilities continue to be quite notable for 24
hour QPF above 2" (up to 40% in the GEFS), and greater than 4" (up
to 20%) for portions of SNE, for the period of late Friday through
Saturday evening.
While ensemble probabilities are beginning to hint at a considerable
rainfall event for our region, there remains substantial spread
between ensemble members with the 10th and 90th percentile GEFS
painting very different scenarios; with as low as 2" (10th) and as
high as 6-7" (90th) of QPF through the next 7 days. 50th percentile
guidance settles around 3-4" for the region. So, while it is quite
possible that portions of our region see upwards of 5"+ of rain,
uncertainty remains too high to place much confidence in our QPF
forecast this far in advance. In collaboration with WPC and other
northeastern forecast offices, elected to keep the Day 5 ERO in the
Slight category, holding off on any upgrades to Moderate until
if/when confidence increases in our forecast.
In any case, do expect trough digging south across the Great Lakes
and eventually southern New England to sweep the remnants of Debby
to our east by late Sunday evening and Monday morning, setting up
for what looks like a much drier period next week.
&&
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z Update:
Through 12z...Moderate Confidence.
VFR to MVFR, with IFR/LIFR over the Cape and Islands. Winds stay out
of the SE at 5-10 knots, gusting 20 knots over the Cape and Islands.
Light to moderate showers move from west to east late overnight with
showers starting around 09z/10z.
Today...Moderate Confidence.
MVFR/IFR with light to moderate rain showers. Showers may linger
across eastern MA into 18z to 20z along with MVFR/IFR conditions.
Elsewhere should have slight improvements to low-end VFR 18z/20z to
around 00z. Winds are east/northeast around 10 knots.
Tonight...Moderate Confidence.
MVFR north to IFR south with periods of heavy rain and low risk for
embedded thunder. Winds are east less than 10 knots.
Wednesday...Moderate Confidence.
MVFR/IFR with periods of rain early in the day, drying with
improving conditions to VFR/MVFR early afternoon. Winds are
east/northeast around 10 to 15 knots.
KBOS TAF... Moderate confidence in TAF.
Light to moderate rain return early this morning with light to
moderate rain showers possible between 10z-17z, possibly even
lingering into 19z. MVFR conditions after 10z through mush of today,
could have slight improvements to VFR late afternoon. Another round
of moderate to heavy rain late tonight into Wednesday morning with
MVFR/IFR conditions.
KBDL TAF... Moderate confidence in TAF.
VFR early, becoming MVFR this morning with light to moderate rain
showers between 07z-14z, but could linger as late as 16z. Lull for
the afternoon but another around of rain arrives overnight into
Wednesday morning.
Outlook /Wednesday Night through Saturday/...
Wednesday: Mainly VFR, with areas MVFR possible. Chance SHRA,
isolated TSRA.
Wednesday Night through Thursday: VFR. Slight chance SHRA.
Thursday Night: MVFR/IFR conditions possible. Chance SHRA,
isolated TSRA.
Friday: Mainly MVFR, with areas IFR possible. SHRA, isolated
TSRA.
Friday Night: Mainly MVFR, with areas IFR possible. Breezy.
SHRA, isolated TSRA.
Saturday: Mainly IFR, with areas MVFR possible. Breezy. SHRA
likely, isolated TSRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Tuesday night...Moderate Confidence.
Persistent southwest flow results in marginal small craft seas
across the southern outer-waters right into Tuesday. Showers and
possibly some thunderstorms move over the southern waters
Tuesday morning and linger into Tuesday afternoon. Widespread
moderate to heavy rain expected Tuesday night into Wednesday.
Outlook /Wednesday Night through Saturday/...
Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. Rain showers likely, isolated thunderstorms.
Wednesday Night through Thursday: Winds less than 25 kt. Seas
locally approaching 5 ft. Chance of rain showers.
Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers, isolated
thunderstorms. Local visibility 1 to 3 nm.
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Rain showers likely, isolated thunderstorms.
Friday Night: Winds less than 25 kt. Local rough seas. Rain
showers likely, isolated thunderstorms.
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Rain showers likely, isolated
thunderstorms. Areas of visibility 1 to 3 nm.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ254.
Small Craft Advisory until 8 PM EDT this evening for ANZ255-
256.
&&
$$
SYNOPSIS...KP/KS
NEAR TERM...Dooley
SHORT TERM...KP
LONG TERM...KS
AVIATION...Dooley/KS
MARINE...KP/KS
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 6, 1:35 AM EDT----------------
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