NWS Forecaster Discussion
BOX
Area Forecast Discussion National Weather Service Boston/Norton MA.
000
FXUS61 KBOX 251129
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
729 AM EDT Mon Oct 25 2021
.SYNOPSIS...
Widespread steady rain will depart by mid to late morning, but
a few showers and areas of patchy fog and drizzle will persist
this afternoon. A developing strong coastal storm will bring the
potential for heavy rain, flooding, and damaging winds Tuesday
into Wednesday. Exact impacts will depend on the eventual storm
track. Drier weather may return Thu/Fri before more unsettled
weather returns next weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
730 AM Update...
The back edge of this morning`s more widespread, stratiform rain
has reached eastern CT/central MA early this morning and will
continue to edge east through the morning. Even so, not
expecting a dry day, with continued patchy light rain and
drizzle. No significant changes needed with this update.
Previous Discussion...
Monday...
* Steady rain departs by mid/late morning and is replaced by
patchy fog and drizzle
Initial surge of warm air advection impacts the region this morning
in the form of a steady to light to moderate rain at times. As low
to mid level jet moves offshore, steady rains will transition to
drizzle and patchy fog, as drier air aloft overspreads the region.
Hence wettest portion of the day will be this morning. Sharp temp
gradient sets up across the region today, with warm front draped
along the south coast, with highs in the 60s including Cape Cod and
the Islands. However, elsewhere cool NE flow will keep highs in the
50s with upper 40s across northwest MA. Big pattern change from our
recent weather.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
430 AM update...
Monday night...
Mid level trough over the eastern Great Lakes and OH valley,
amplifies and takes on a negative tilt as it advects toward southern
New England. At the surface, the response will be for developing low
pressure off the NC coast, to rapidly intensify as it lifts
northward toward southern New England. This will result in rain
redeveloping and overspreading the region from south to north. The
combination of PWATs rising rapidly and elevated instability,
isolated thunderstorms are possible, which will enhance the rainfall.
Also, strengthening offshore low combined with 1030 mb high over
southeast Canada, will result increasing pressure gradient and ENE
winds ramping up toward daybreak.
Tuesday...
*** Heavy rain, flooding and strong to damaging winds ***
Rapidly deepening closed low south of New England will bring
multiple facet storm to impact the our region Tue. Uncertainty is
centered around the exact track of the closed low and its wind and
moisture anomalies.
Heavy Rain/Flood Potential...
Anomalous wind and moisture anomalies with closed vertically stacked
low south of New England will bring very heavy rainfall to MA/RI/CT
Tue. HREF offering low probs of 2-3" rainfall in 6 hrs 18z Tue to
00z Wed. Heavy rain will begin to overspread the region in the
morning from SSW to NNE, with heavy rain likely impacting the entire
region for the late day commute. Given this strong heavy rain signal
we issued a flood watch for much of the region. Heaviest rainfall
likely will be across the hilly terrain of CT/RI and into the
Worcester Hills, as strong ENE inflow provides upslope rainfall
enhancement. Some uncertainty if heavy rainfall tracks into NW MA,
thus left this area out of the watch for now.
Strong to Damaging Wind Potential...
All model guidance has strong low level ENE wind anomaly pivoting
into SNE Tue, ranging from 55 kt to 75 kt depending on model of
choice. Model soundings support 50-60 mph winds possible across RI
and eastern MA, with 60-70 mph gusts possible Cape Cod and Islands.
Thus we continued the high wind watch. Wind damage may overachieve
given trees remain fully leaved. Hence, power outages are possible.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Highlights...
* Heavy rain, potential flooding, coastal erosion, and damaging
winds possible Tuesday night into Wednesday
* Drier Thu/Fri before unsettled weather returns next weekend
* Seasonable temperatures continue
Details...
Tuesday night and Wednesday...
A highly amplified intermountain west trough-midwest ridge-northeast
trough pattern persists into Tuesday night with a rex block over our
region. Wednesday the upper low finally kicks out as the surface low
center exits to the east. Before it`s gone the copious moisture and
strong forcing associated with that lingering system will bring an
additional 1-2 inches of rain to portions of southern New England
along with strong, damaging winds. Where the heaviest rain and
strongest winds materialize will be dependent on even small wobbles
in the track of the low. That will determine where the moisture and
wind anomalies are. What we have more confidence in is that heavy
rain is in store, as are strong winds. Ensemble guidance continues
to hammer southern New England with 3-5 inches of rain (mean value).
Though the GEFS is less robust than the EPS, the wetter EPS solution
does have support from other guidance. Given at least 50% confidence
that we`ll see rainfall amounts capable of producing some urban/poor
drainage/small stream flooding, a Flood Watch is in effect for most
off southern New England. Clogged storm drains from recently fallen
leaves have the potential to exacerbate flooding issues.
Winds look to be ramping up and peaking overnight Tuesday as that
impressive 60-70 kt 925 mb jet moves over the region. Best chance of
the strongest winds will be southeast Massachusetts and Rhode
Island, though if the track of the storm shifts that is subject to
change. BUFKIT soundings show anywhere from 45 to 65 kts at the top
of the mixed layer Tuesday night deepening on how pronounced a 850
mb warm nose is. For now will stick with a forecast of generally max
gusts to 60 mph, best chances over the Cape and Islands. This is
capable of producing damage, especially given the relative abundance
of leaves still left on our trees.
As for coastal flooding and erosion, low astronomical tides will aid
in minimizing impacts. However, the sheer duration of this event in
which the high N/NE winds could span 4 high tide cycles will
increase likelihood of some minor coastal flooding issues in the
typical spots; coastal erosion will likely be a bigger concern.
Thursday through the weekend...
Guidance has remained consistent in showing the mid level low
beginning its exit, replaced by a ridge of high pressure on Thursday
into Friday. This will bring mostly dry conditions, though the
pressure gradient is slow to relax, so high winds likely linger,
especially for the southeast coast and offshore waters Thursday.
Another upper level low moves out of the midwest into New England
around Friday/Saturday which will bring the return of rain chances
as early as Friday evening, with a wet and unsettled weekend ahead.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
12Z TAF Update...
Today...high confidence.
IFR with patchy LIFR possible, especially in the hilly terrain
of MA/RI/CT. Steady morning rain gives way to afternoon drizzle.
VFR conditions possible along the south coast, especially the
islands this afternoon. Marginal LLWS this morning across
CT/RI/southeast MA with WS020/24040KT. Sharp wind shift across
the region, with SW winds along the south coast of MA/RI, and NE
winds remainder of CT/RI/MA.
Tonight...high confidence. IFR/LIFR across much of the region
in drizzle and fog. MVFR/VFR possible along the south coast of
MA/RI. Low risk of isolated heavier showers with embedded
thunder during the evening across CT/RI and southeast MA. Warm
front likely settles farther south, with south winds confined to
the islands, and NE winds elsewhere.
Tuesday...high confidence.
Widespread IFR with LIFR across the hilly terrain. Rain
overspreads the region early, then heavy rain much of the late
morning into the afternoon. NE winds increasing rapidly with
speeds 25 to 35 kt, gusting up to 50 kt possible Cape Cod and
islands.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Tuesday Night through Friday/...
Tuesday Night: MVFR/IFR conditions possible. Strong winds with
gusts up to 50 kt. SHRA.
Wednesday: Mainly VFR, with local IFR possible. Strong winds
with gusts up to 45 kt. Chance SHRA.
Wednesday Night: Mainly VFR, with local MVFR possible. Windy
with gusts up to 35 kt. Chance SHRA.
Thursday: VFR. Windy with local gusts up to 30 kt. Slight
chance SHRA.
Thursday Night: Mainly VFR, with local MVFR possible. Breezy.
Friday: Mainly VFR, with areas MVFR possible. Breezy. Slight
chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
*** Storm Watch Remains in Effect ***
Today...
Warm front draped across the region, with SSW winds across the
southern MA/RI waters, and ENE winds over northern MA waters. Vsby
reduced in steady rain this morning, then patchy fog and drizzle
this afternoon.
Tonight...
Low pres develops off the NC coast, then intensifies and move north
toward SNE. ENE winds increase 20-30 kt toward daybreak Tue. Rain
becomes widespread as the night progresses. Vsby reduced at times in
rain and fog.
Tuesday...
Gale Center south of New England may intensity into a storm with NE
winds 25 to 35 kt gusting up to 60 kt possible. Heavy rain reduces
vsby. Dangerous seas develop, peaking 20-25 kt east of Nantucket and
Cape Cod!
Outlook /Tuesday Night through Friday/...
Tuesday Night: gale force winds with gusts up to 45 kt. Rough
seas up to 25 ft. Rain showers.
Wednesday: gale force winds with gusts up to 45 kt. Rough seas
up to 22 ft. Rain showers likely.
Wednesday Night: Strong winds with gusts up to 35 kt. Rough
seas up to 18 ft. Chance of rain showers.
Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 12 ft. Chance of rain
showers.
Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Slight chance of rain
showers.
Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 13 ft. Slight chance of rain
showers.
&&
.TIDES/COASTAL FLOODING...
*** Minor Coastal Flooding with moderate erasion possible ***
Strong coastal storm develops south of New England Tuesday and given
its slow movement, likely lingers into Wed. Thankfully astro tides
are low but strong onshore winds for two days over multiple tide
cycles will result in a storm surge of 2 to 3 ft. Low astro
tides likely limit coastal flooding to minor but multiple tide
cycles impacted may result in moderate erosion.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from late tonight through Wednesday evening for
CTZ002>004.
MA...Flood Watch from late tonight through Wednesday evening for
MAZ003>021-026.
High Wind Watch from Tuesday morning through Wednesday
afternoon for MAZ007-013>024.
RI...Flood Watch from late tonight through Wednesday evening for
RIZ001>008.
High Wind Watch from Tuesday morning through Wednesday
afternoon for RIZ001>008.
MARINE...Storm Watch from Tuesday morning through Wednesday afternoon
for ANZ230>237-250-251-254>256.
Small Craft Advisory until 8 AM EDT Tuesday for ANZ231>235-237-
251-255-256.
Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254.
&&
$$
SYNOPSIS...Nocera/BW
NEAR TERM...Nocera/BW
SHORT TERM...Nocera
LONG TERM...BW
AVIATION...Nocera/BW
MARINE...Nocera/BW
TIDES/COASTAL FLOODING...