BOX issues Area Forecast Discussion (AFD) at Aug 7, 1:58 AM EDT077
FXUS61 KBOX 070558
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
158 AM EDT Wed Aug 7 2024
.SYNOPSIS...
Low pressure tracking along a stalled front south of New England
will bring widespread showers and embedded thunderstorms tonight
into Wednesday morning. Locally heavy rainfall is possible. Drier
conditions develop from north to south during Wednesday afternoon,
with dry weather persisting into Thursday with below normal
temperatures. The remnants of what is currently Debby will
impact our region Thu night into Saturday with the potential for
Heavy Rain & Flooding...although the greatest risk may end up
west of our region. Pleasant weather looks to return Sunday into
early next week with temperatures slightly below normal.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Update: 10:30PM
No major changes to the forecast since the last issuance. Rain
has become widespread with locally heavy downpours along the
Mass Pike. Rainfall has been fairly light up until this point,
around 10th of an inch an hour. But there is locally moderate
rain with KBOX depicting isolated pockets of 1-2 inch per hour
rates.
See previous discussion below.
8 PM Update...
* Widespread Showers with a few embedded t-storms develop later
this evening and into the overnight hours
Quite the active evening to our southwest in the NYC to PHL
region...where numerous showers and t-storms with torrential
rainfall has resulted in Flash Flooding. The northern edge of
this activity was grazing the south coast...but not to nearly
the extent of what is going on across the mid-Atlantic States.
However...mid level trough and shortwave tracking east from NY
State will allow widespread showers with a few embedded t-storms
to develop. This activity was just starting to develop in
western New Eng and will quickly spread east through midnight.
Best chance of a few t-storms will be south of the MA Pike where
there will be marginal elevated instability, with decreasing
chances further N. We have a pseudo PRE set up tonight as SNE is
within the right entrance region of the upper jet and east of
mid level trough axis with northern extent of tropical PWATs 2+
inches streaming north into SNE. As a result we expect locally
heavy rainfall, with heaviest along the south coast and Islands
near the low level boundary which will enhance convergence as
wave of low pres tracks along the boundary. Generally expecting
0.50 to 1.5 inches of rainfall tonight with locally 2+ inches
near the south coast. Not expecting any significant flood issues
with low risk of typical minor urban and poor drainage flood
issues. Lows will drop to around 60/lower 60s in most locations.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
Wednesday...
Mid-upper level trough axis will be moving across SNE in the morning
then exiting by midday with gradual drying in the column behind the
trough. It will start to dry out in the early morning in western New
Eng, with lingering morning showers and embedded thunder across RI
and eastern MA before drying by midday. Locally heavy rainfall Wed
morning will be confined to the Cape/Islands and HREF is indicating
high probs of 1+ inch in 3 hours at Nantucket with even a 10 percent
prob of 3 inches in 3 hours so will have to watch this closely.
Otherwise, drying from N to S develops during the day with partial
sunshine developing in the afternoon, especially north of the MA
Pike. Clouds will likely linger closer to the coast and the risk of
showers will linger in the afternoon over the Islands. NE flow and
pocket of cool temps aloft will result in temps well below normal,
with highs upper 60s to near 70 RI and SE MA to low-mid 70s interior
northern MA and CT valley. A period of gusty NE winds to 20-30 mph
are expected in the morning across Cape/Islands assocd with a modest
low level jet north of the surface wave.
Wednesday night...
Surface ridging from high pres to the north will extend south into
SNE with area of drier air leading to dry weather and partly cloudy
skies. Winds diminish which will allow low temps to fall into the
50s in most locations, except low 60s Cape/Islands and immediate SE
MA coast.
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Key Points...
* Main Concern Heavy Rain/Flood Risk Thu night into Sat
* Axis of Heaviest Rain uncertain...Highest risk west of us?
* Low risk for Severe Weather Sat
* Pleasant weather returns Sun through Tue...temps a bit below normal
Details...
The main concern with this forecast will revolve around the track
and what will be the remnants of Debby late this week. We do think
much of the daylight hours Thu will remain dry...although the ECMWF
is faster than the other guidance and indicates some rain may arrive
during the afternoon. The focus for heavy rain along with the risk
for Flash Flooding and River Flooding will be Thu night into Sat.
The heaviest of the rain will probably be Fri night into Sat...as
the main energy from the remnants of Debby gets closest to our
region. Given this is a tropical system with Pwats near 2.5 inches
associated with a southerly low level jet of 2-3+ standard
deviations above normal...the risk for both Flash Flooding and River
Flooding will exist...but the area remains in question. While the
modest LLJ will result in gusty southerly winds later Fri into
Sat...nothing too significant is expected wind wise at this time. We
will break it down more below.
This forecast is still 3-4+ days out and model track error is in the
range of 100 to 200 nm. This means that a shift west or east will
have a huge implication on the axis of heaviest rain and greatest
flood threat. The trend over the last 24 hours has been to shift the
heaviest rain axis further west. So if this trend holds...the higher
risk for flooding will be west of our region but we are not out of
the woods by any means. We will have to see if this trend continues
or shifts back further east...but that is the way things look right
now. It does look like the track will be speeding up as the remnants
push northeast which would also indicate the higher risk west of our
region.
The other thing will have to watch is a low risk for severe weather
on Saturday. Given we will be on the east side of this system in a
tropical environment with modest low level wind fields/high
dewpoints and low level helicity...an isolated risk for severe
weather will exist with a low tornado potential too. Whether this
comes to fruition remains to be seen...but thinking this would be
mainly an isolated risk but something to watch.
Pleasant weather arrives Sun into early next week with upper trough
setting up across the northeast. We can not rule out a few diurnal
spot showers at times...but much of this time will feature dry
weather. Highs mainly well into the 70s to the lower 80s...a bit
below normal of this time of year.
&&
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Through 12z...Moderate Confidence.
MVFR/IFR. periods of light to moderate rain. ENE to NE winds 5 to 10
knots.
Today...Moderate Confidence.
IFR to start, becoming MVFR/VFR late morning to early afternoon,
from north to south, with the exception being Cape Cod and Island
terminals. There IFR conditions are expected much of today. NE wind
10 to 15 knots with possible gusts to 25 knots in the morning over
the Cape and Islands.
Tonight...Moderate Confidence.
Mainly VFR interior, with areas of MVFR ceilings along the south
coast. Patchy late night fog developing. Light N to NE winds.
Thursday...High Confidence.
Dry and VFR. Increase clouds late day from southwest to northeast. E
winds around 10 knots.
KBOS TAF... Moderate confidence in TAF.
Varying VFR/MVFR will become MVFR/IFR shortly after 08z or 09z with
periods of light to moderate rain through 13z, though hit and miss
showers may continue through 16z. Ceilings improve to MVFR late
morning to early afternoon, with VFR ceilings by mid afternoon 20z.
Winds are ENE with periodic gusts 17 to 20 knots between 16z-20z.
KBDL TAF... Moderate confidence in TAF.
Varying MVFR/IFR ceilings this morning along with periods of light
and moderate rain through 12z/14z. Drying trend with MVFR ceiling
through early afternoon with VFR ceiling after 18z/20z. WInds are
light and generally out of the NNE.
Outlook /Thursday Night through Sunday/...
Thursday: VFR. Chance SHRA.
Thursday Night: Mainly VFR, with local IFR possible. SHRA
likely.
Friday: Mainly MVFR, with areas IFR possible. SHRA, slight
chance TSRA.
Friday Night: Mainly MVFR, with local IFR possible. Windy with
local gusts up to 30 kt. SHRA, chance TSRA.
Saturday: Mainly MVFR, with areas IFR possible. Windy with
gusts up to 35 kt. SHRA likely, slight chance TSRA.
Saturday Night: VFR. Breezy. Slight chance SHRA.
Sunday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight though Wednesday night...Moderate Confidence.
Increasing NE winds late tonight tonight into Wed morning as surface
wave tracks to the south. A period of 25 kt gusts possible over the
nearshore south coastal waters. We issued a SCA for waters adjacent
to Cape Cod where our confidence is highest but the SCA may need to
be extended further west in later forecasts. SCA also in effect for
southern outer waters for increasing seas. Winds will begin to
diminish later Wed afternoon and night but 20 kt gusts will likely
continue over southern waters through Wed night. Scattered showers
and tstorms over the southern outer waters through this evening with
showers becoming more widespread across rest of waters tonight into
Wed morning.
Outlook /Thursday Night through Sunday/...
Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.
Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers.
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Rain showers likely, slight chance of thunderstorms.
Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Chance of rain showers,
isolated thunderstorms.
Saturday: Low risk for gale force winds with gusts up to 35 kt.
Rough seas up to 11 ft. Rain showers likely, isolated
thunderstorms.
Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 11 ft. Slight chance of
rain showers.
Sunday: Winds less than 25 kt. Areas of rough seas.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 6 AM this morning to 2 PM EDT this
afternoon for ANZ231-232.
Small Craft Advisory from 6 AM this morning to 10 PM EDT this
evening for ANZ254.
Small Craft Advisory from 8 AM this morning to 10 PM EDT this
evening for ANZ255-256.
&&
$$
SYNOPSIS...KJC/Frank
NEAR TERM...KJC/Frank/Dooley
SHORT TERM...KJC
LONG TERM...Frank
AVIATION...KJC/Frank/Dooley
MARINE...KJC/Frank
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 7, 1:58 AM EDT----------------
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