BOX issues Area Forecast Discussion (AFD) at Aug 7, 7:09 PM EDT592
FXUS61 KBOX 072309
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
709 PM EDT Wed Aug 7 2024
.SYNOPSIS...
Mainly dry conditions expected into Thursday with below normal
temperatures. The remnants of Debby will begin to approach
Southern New England Thursday night into Friday, but make its
closest approach to our north and west Friday evening into early
Saturday. This will bring showers with pockets of heavy
rainfall focused across the interior. That being said...it
appears the threat for significant flooding has shifted west of
the region. Dry and warm weather should arrive for most
locations Saturday afternoon. The first half of next should
feature very pleasant and mainly dry weather.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
High pres builds over Maine with surface ridging extending south
into SNE will keep dry conditions across SNE tonight. Clouds will
decrease this evening as drier air spills south, but may hang on to
more clouds near the south coast as higher moisture axis remains
along the coast. With any clearing, will have to watch for
development of late night patchy radiation fog and stratus as winds
will be light to calm. Lows will be mostly in the 50s, except lower
60s Cape/Islands.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Thursday...
While surface ridging persists across SNE, column moisture will
begin to increase from the south. Some of the global and hi-re
guidance is suggesting a few showers may develop during the
afternoon. This appears to be in response to a modest instability
burst as reflected by increase in KI and lowering of SI values from
SW to NE. Best chance of a few showers will be across western MA and
northern CT where moisture is greatest, but much of the day will be
dry. Otherwise, sunshine to start the day will give way increasing
clouds. Highs will be in the 70s.
Thursday night...
Backing flow aloft will result in tropical moisture plume ahead of
Debby to spread northward into SNE as PWATs increase to around 2
inches. The increasing moisture combined with marginal elevated
instability will lead to scattered showers developing and moving
northward across the region. A few embedded t-storms are also
possible. However, heavier rainfall will be confined well to the SW
where best forcing assocd with remnants of Debby is located. Cloud
cover and increasing dewpoints will result in a milder and more
humid night with lows in the 60s.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Key Points...
* Showers with heavy rainfall and a low risk for severe weather Fri
into early Sat with the focus across interior southern New England
* Threat for Significant Flash Flooding & River Flooding continues
to shift west of the region with the latest model guidance
* Dry & Warm weather may return for Sat afternoon
* Pleasant/Mainly dry weather for the first half of next week
Details...
Friday into Early Saturday...
Confidence continues to increase that the remnants of Debby will
track further west and also faster than guidance depicted 36 hours
ago. The remnants of Debby will lift rapidly northward across
interior PA and NY State Fri/Fri night and then into northern New
England/Quebec region Sat morning.
It is quite common for the main threat of significant
flooding/heaviest rain to setup west of the track of tropical
remnants. Given we are on the east side of the remnants and
that it also picks up speed...the threat for Significant River
Flooding and Flash Flooding has shifted west of the region.
Still expect periods of showers with locally heavy rainfall Fri
into early Sat...the focus of the heaviest rain should be Fri
night into early Sat when the remnants pass closest to our
region. The ECMWF/RGEM are on the heavier side indicating the
potential for 2-3 inches of rain across parts of western MA/CT.
This appears to be a result of some sort of secondary re-
development near the Long Island/southern CT border.
Meanwhile...the NAM/GFS does not show this secondary feature as
well with rainfall generally under 1-1.5 inches.
Regardless...the threat for significant flooding appears to have
shifted west of the region. If the higher amounts depicted by
the ECMWF/RGEM occur...there might be some minor flooding issues
but that appears to be the reasonable worst case scenario at
this point.
We should also mention that we can not rule out a low risk of severe
weather/brief tornado risk. This would mainly be late Fri into early
Sat. Keep in mind this is a low probability as many mesoscale
ingredients have to come together for severe weather. That being
said...there is at least a low probability including a tornado risk.
This is supported by the CSU Machine learning probs with our
interior zones most at risk given they will be closest to the
passage of the remnants.
Saturday Afternoon...
Given the faster movement of Debby/s remnants...Sat afternoon looks
to be mainly dry with sunshine emerging on southwest flow. A mild
start and 850T near +16C should result in highs well into the 80s.
Sunday through Wednesday...
Upper trough sets up across the northeast bringing very pleasant
late summer weather to the region. Highs will be well into the 70s
to the lower 80s with comfortable humidity levels for August
standards. Overnight lows will be very pleasant in the 50s to
the lower-middle 60s. Dry weather should dominate...but can not
rule out a spot shower or two.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update...
Tonight...Moderate Confidence.
Mainly VFR through midnight except for some MVFR conditions
towards the Cape and Islands. Stratus and fog develop in some
of the typically prone spots after midnight...especially
interior northeast MA as well as portions of southeast MA/RI.
However...areal coverage of the stratus and fog remains
uncertain. Calm to mainly light NE Winds.
Thursday...Moderate Confidence.
Low clouds and fog patches will scatter out Thu morning...but
may linger a bit longer towards the south coast and especially
Nantucket. A few spot showers possible during the afternoon with
the greatest risk across the interior. E-SE wind 5-15 kt.
Thursday night...Moderate confidence.
Conditions lowering to MVFR-IFR from S to N. A few showers
spreading north across the region. Light E-SE wind.
KBOS TAF... High confidence in TAF. Patchy MVFR cigs possible
til 19z.
KBDL TAF... High confidence in TAF.
Outlook /Friday through Monday/...
Friday: Mainly MVFR, with areas IFR possible. Breezy. Chance
SHRA, slight chance TSRA.
Friday Night: Mainly MVFR, with areas IFR possible. Windy with
areas of gusts up to 30 kt. SHRA, slight chance TSRA.
Saturday: Mainly VFR, with areas MVFR possible. Windy with
local gusts up to 30 kt. Chance SHRA.
Saturday Night through Sunday: VFR. Breezy.
Sunday Night: VFR.
Monday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Thursday night...High Confidence.
Lingering 5+ ft seas over southern waters will subside this evening,
otherwise winds and seas will remain below SCA thresholds through
the period. E-NE winds 10-20 kt through Thu veering to SE Thu night.
Outlook /Friday through Monday/...
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.
Friday Night: Strong winds with gusts up to 30 kt. Rough seas
up to 11 ft. Rain showers likely, slight chance of
thunderstorms.
Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain
showers.
Saturday Night: Winds less than 25 kt. Areas of rough seas.
Sunday through Sunday Night: Winds less than 25 kt. Areas of
seas approaching 5 ft.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 10 PM EDT this evening for
ANZ254>256.
&&
$$
SYNOPSIS...KJC/Frank
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...Frank
AVIATION...KJC/Frank
MARINE...KJC/Frank
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 7, 7:09 PM EDT----------------
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