Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 261350
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
950 AM EDT Tue Oct 26 2021

.SYNOPSIS...
A developing strong coastal storm will bring the potential for 
heavy rain, flooding, and damaging winds into Wednesday.
Much quieter and mainly dry weather returns Thursday into at least 
part of Friday. Another system will likely bring more rain to
our region late Friday into Saturday, but it does not look near
as strong or impactful. Dry weather returns sometime Sunday, 
and probably continues into next Monday with temperatures 
averaging a bit above normal.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

950 AM Update...

Forecast is mainly on track, with rain moving northwest across
CT and RI...eventually to reach Western MA this afternoon.
Additional rain extends south of the Islands. As this moves
northwest, expect rain developing later this afternoon in
Eastern MA. Low level east flow supported growth of showers that
moved into Northeast MA. These are moving north of the border
but with additional showers offshore than may move ashore later
today. Temperatures range from the upper 40s Central Hills to
the mid 60s South Coast. Similar temperatures expected this
afternoon. No changes to headlines.

Previous Discussion...

Today will be all about an approaching low pressure moving north
along the coast. This low pressure is expected to arrive later
this afternoon. This will be a dynamic system, meaning it will
intensify as it approaches. Plenty of ingredients in place to
make this happen. This low pressure will be moving underneath a
strongly negatively tilted trough, which will help it absorb the
energy from a dissipating low pressure over the Mid Atlantic.

Wind remains the greatest concern with this event. Strong low
level winds remain. Typically with these dynamic systems, they
tend to overperform most of the statistical guidance. When
compared to prior forecasts, the onset of the strongest winds
may be 2-3 hours slower. This was not enough to change the
overall messaging of headlines, so those remain unchanged.

First round of rainfall this morning is expected to briefly end
for some late this morning, before the main low pressure arrives 
late today. 

Flood Watches continue unchanged. Still looking at abundant lift
and moisture resulting in downpours. Poor-drainage flooding is
most likely, but cannot rule out some more significant flooding
in spots. Will need to see the impact of the rainfall during
this event on area waterways.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Strongest winds expected tonight, then diminishing Wednesday.
Synoptic pattern favors a circular departure for this surface low
pressure, which will keep it closer to our region longer.
Maintained some rainfall chances into Wednesday, especially
across the eastern half of southern New England. When all is 
done, thinking total rainfall with range from about 1.5 inches
towards the Berkshires, up to 4 inches in places towards the
east coast of MA.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Highlights...

* Strong wind gusts continue across southeast MA Wed night with
  lingering coastal flooding concerns

* Quieter weather returns Thu into early Fri with generally dry
  weather other than a few lingering showers Thu across
  southeast MA

* Another system likely brings more rain later Fri and Sat, but 
  should not be nearly as impactful as the Tue/Wed event

* Dry weather likely returns sometime Sun and continues into Mon

Details...

Wednesday night...

As the storm system of concern in the short term period exits, 
lingering wind gusts up to 35-40 mph at times continue overnight
Wednesday. The other concern is with the risk of coastal 
flooding during the high tide cycle due to the cumulative effect
of northeast winds over the past few days. 

Thursday and Friday...

The major storm system will have finally lifted well to our 
northeast by Thursday with brief ridging building in. This 
coupled with a ridge of high pressure building down from eastern
Canada will result in mainly dry weather Thu into early 
Fri...despite lingering clouds and a few left over showers 
possible on Thu across southeast MA. This a result of lingering 
NNE low level flow keeping the 925- 700mb level moist. High 
temps should mainly be in the 50s Thursday and Friday, except 
for the CT River valley that may see highs approach 60 degrees 
since they are more removed from the onshore flow. Average highs
for late October across Southern New England are in the mid 50s
to low 60s, so we are looking at just below normal to near 
normal temperatures. So while it is not the nicest of fall 
weather, it is no washout either and we don't have to deal with 
strong winds. We do, however, have to see if we get some lighter
rain moving in sometime on Fri in advance of the next system 
over the weekend. While the GFS/CMC keep us dry, but the ECWMF 
and even some GEFS ensembles indicate onshore moist flow to 
allow some light rain to break out during the day Friday ahead 
of the next system.

Minor coastal flooding remains a concern for the north and 
east- facing beaches due to the cumulative effects of 
northeasterly flow during Thursday's high tide cycle but the 
effects should subside by Friday. 

Friday night and Saturday...

Another wave of low pressure will approach from the southwest 
Friday night into Saturday. This will likely bring another round
of rain Fri night into Saturday. This system does not look 
nearly as strong as the Nor'easter mentioned in the short-term 
discussion. And given its progressive nature, not expecting 
significant weather impacts at this time other than localized 
urban and poor drainage flooding as ensemble guidance indicates 
a broad swath of 1-2 inches of rainfall on top of grounds 
saturated from the heavy rainfall earlier in the week. 

Sunday and Monday...

There remains some uncertainty whether the rain lingers into 
Sunday, especially at this time range. We do expect improving 
weather especially the latter half of Sunday and especially into
Monday as ridging builds in and the flow turns westerly, which 
allows the low- levels to dry out. So expect the return of 
sunshine along with dry weather and slightly above normal 
temperatures in the upper 50s to mid 60s as we turn the calendar
into November. Highs derived from the blended guidance look a 
tad low but reasonable at this time frame.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent.

This afternoon and tonight...High confidence.

Widespread IFR/LIFR. Periods of rain, heavy at times especially
this afternoon through tonight. Increasing NE winds this
afternoon, with winds peaking tonight with gusts 50-60 kt east 
coastal MA and Cape/Islands, 40-50 kt back to I-95 corridor and 
25-35 kt CT valley. LLWS across SE MA and Cape Cod Tue night. 

Wednesday...High confidence.

Conditions improving to VFR from west to east during the 
afternoon. IFR/MVFR likely to longer towards the east coast.

KBOS Terminal...High confidence in TAF trends.

KBDL Terminal...High confidence in TAF trends.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Mainly VFR, with areas MVFR possible. Strong
winds with areas of gusts up to 40 kt. Chance SHRA.

Thursday: Mainly VFR, with local MVFR possible. Windy with
local gusts up to 30 kt. 

Thursday Night: Mainly VFR, with local MVFR possible. Breezy. 

Friday: Mainly MVFR, with local VFR possible. Breezy. Chance
SHRA.

Friday Night through Saturday: Mainly MVFR, with local IFR
possible. Breezy. SHRA likely.

&&

.MARINE...
Forecaster Confidence Levels.

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Storm Warnings continue for all waters from this afternoon into
Wed morning. Winds ramp up, with worst of the wind and seas 
tonight. Max wind gusts to 60-65 kt possible over waters east of
Cape Cod. Dangerous seas develop, peaking 20-25 ft east of Cape
Cod to outer NE MA waters. A dangerous storm for mariners. 
Vsbys will be reduced in rain and fog. 

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Strong winds with gusts up to 40 kt. Rough
seas up to 19 ft. Chance of rain showers. 

Thursday: Strong winds with gusts up to 30 kt. Rough seas up to
16 ft. Slight chance of rain showers. 

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 20 kt. Rough seas up to 12 ft. Slight chance of
rain showers. 

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of rain showers. 

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 9 ft. Rain showers likely. 

Saturday: Winds less than 25 kt. Rough seas up to 10 ft. Rain
showers likely.

&&

.TIDES/COASTAL FLOODING...
* Minor Coastal Flooding, with significant erosion possible
 
The high tides of main concern are the early Wed morning and Wed
afternoon tide cycles. Thankfully, astronomical tides are quite
low which will limit the magnitude of flooding. A 3 to 3.5 ft 
surge is possible with seas 20-25 ft offshore which will be 
enough to produce areas of minor coastal flooding around the 
times of high tide. 

We are not as concerned with this afternoon's high tide as the 
combination of winds, waves and surge will not likely be built 
enough to cause flooding. However, persistent easterly wind 
wave over multiple tide cycles may result in areas of 
significant beach erosion.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch through Wednesday evening for CTZ002>004.
     Wind Advisory from 6 PM this evening to 2 PM EDT Wednesday for 
     CTZ004.
MA...High Wind Warning from 2 PM this afternoon to 2 PM EDT 
     Wednesday for MAZ007-013>024.
     Flood Watch through Wednesday evening for MAZ003>021-026.
     Coastal Flood Advisory from 3 AM to 7 AM EDT Wednesday for 
     MAZ007-015-016-019-022>024.
     Coastal Flood Advisory from 3 PM to 7 PM EDT Wednesday for 
     MAZ007-015-016-019-022>024.
     Wind Advisory from 6 PM this evening to 2 PM EDT Wednesday for 
     MAZ005-006-012.
RI...High Wind Warning from 2 PM this afternoon to 2 PM EDT 
     Wednesday for RIZ005>008.
     Flood Watch through Wednesday evening for RIZ001>008.
     Wind Advisory from 6 PM this evening to 2 PM EDT Wednesday for 
     RIZ001>004.
MARINE...Storm Warning from 5 PM this afternoon to 5 PM EDT Wednesday 
     for ANZ232>235.
     Storm Warning from 8 PM this evening to 8 AM EDT Wednesday for 
     ANZ230-236.
     Storm Warning from 5 PM this afternoon to 8 PM EDT Wednesday 
     for ANZ231-250.
     Storm Warning from 5 PM this afternoon to 2 PM EDT Wednesday 
     for ANZ237-251.
     Storm Warning from 2 PM this afternoon to 8 PM EDT Wednesday 
     for ANZ254-255.
     Storm Warning from 2 PM this afternoon to 5 PM EDT Wednesday 
     for ANZ256.

&&

$$
SYNOPSIS...Belk/Chai
NEAR TERM...WTB/Belk/Chai
SHORT TERM...Belk
LONG TERM...Chai
AVIATION...WTB/Belk/Chai
MARINE...WTB/Belk/Chai
TIDES/COASTAL FLOODING...