Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 220147
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
947 PM EDT Sat May 21 2022

.SYNOPSIS...
Near record high temps with Heat Indices between 95 and 100
degrees are expected Sunday away from the south coast. A few 
strong to severe thunderstorms are possible from mid-afternoon
into the early hours on Sunday across interior southern New
England. A return to cooler/seasonable temps follows Monday 
into mid-week with dry weather. Warmer temps and humidity return
by the end of the week along with the risk for a round of 
showers and thunderstorms with a cold front on Friday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
930 PM Update...

Fairly quiet evening across the region with temperatures falling
back into the 60s and 70s for the most part. Coolest spot
remains ACK where the temp is 57F and conversely the warmest is
BDL at 80F. Overall the forecast does remain on track tonight
and we only had to modify near term temperatures to bring back
in line with the observations. Satellite shows clear skies and a
bank of low stratus north of Cape Ann. We do still expect low
stratus and fog to redevelop along the coast tonight, but not as
extensive at last night. Overall forecast remains in good shape.
Please see previous discussions for more information. 


630 PM Update...

Sea-breeze circulation beginning to weaken as winds begin to
prevail out of the south/southwest for this evening.
Temperature still in the low 60s at BOS, may see a warm up in
the city this evening as winds shift to the south/southwest and
push that cool maritime air offshore. Elsewhere temperatures
remain hot in the upper 80s to low 90s across the interior. We
are past peak heating and thus should begin to see temperatures
start falling soon. Temperatures will remain mild tonight across
the interior with lows struggling to fall below 70 degrees.
Closer to the coast expect temps to fall to the low to mid 60s.
May see some patchy fog develop near the coastal areas of The
Cape Islands tomorrow morning as well. See previous discussion
for more details.

Previous Discussion


Tonight...

* Unseasonably mild & a bit muggy tonight

Upper level ridging centered to our south will remain in control
of our weather tonight. Despite an EML in place along with
impressive instability; upper level ridging and a capping
inversion will keep us dry tonight. Low risk of a spot
shower/t-storm across far northwest MA this evening; but it
would be short-lived if it even happened so opted not to 
include in the forecast.

The main story tonight will be unseasonably mild and somewhat
muggy conditions. Low temperatures should only drop into the
middle to upper 60s except near the south coast, Cape and
Islands where onshore flow will result in overnight lows in the
upper 50s and lower 60s. 

Surface winds tonight will be light; but from a south to
southwest direction. This will confine any risk of low clouds
and fog to mainly the Cape/Islands. Across the rest of the
region; mainly clear skies should prevail with perhaps just
brief patchy ground fog/haze in the typically prone spots.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Highlights...

* Near Record Highs generally in the 93 to 98 degree range Sun 
  to the northwest of a Providence to Taunton line

* A few strong-severe t-storms possible across the interior
  between 2 & 10 pm Sun with locally damaging wind gusts 

Details...

Sunday...

1) Heat & Humidity

A hot day is on tap for Sunday with near record high 
temperatures generally northwest of a Providence to Taunton 
line. While 850T are around +19C on Sunday; which is a few 
degrees cooler than today we expect surface temps to be higher. 
The reasons for this are that we are not expecting the low 
clouds that we saw this morning; so temperatures will be off to 
the races much earlier. In addition, mixing will be much better 
than today and we expect southwest wind gusts of 20-25 mph with 
perhaps a few gusts near 30 mph. So we are thinking that high 
temperatures will generally be in the 93 to 98 degree range 
northwest of a Providence to Taunton area. This includes Boston;
which unlike today will have a westerly component to the wind 
and their temperature will respond. Dewpoints will be a few 
degrees lower than today; given better mixing. However, Heat 
Indices on the order of 95 to 100 degree are expected. While 
these readings are just a few degrees higher than the forecast 
high temperatures; The Heat Advisory remains valid and will 
continue away from the south coast. 

Temps will be cooler near the south coast, Cape and Islands 
generally in the 70s to the lower 80s given the modified marine 
airmass with the gusty southwest winds. 

2) Strong to Severe Thunderstorm Risk across the Interior

The other main concern will be for the development of a few
strong to severe thunderstorms during the mid-late afternoon and
evening hours across interior southern New England. A strong
cold front and pre-frontal trough will be approaching from the
west. 0 to 6 KM shear is rather marginal; generally on the order
of 20 to 30 knots. In addition...the core of the EML currently
in place will be shifting to our east. However, given the
anomalous hot airmass in place SPC SREF is indicating high probs
of MLCapes exceeding 2000 J/KG along with some low level
convergence with the pre-frontal trough. Many high resolution
CAMS seem to initiate a few showers and t-storms across the 
interior after 1 or 2 pm. Perhaps more in the way of activity by
late afternoon/early evening as better convergence arrives with
the approaching surface cold front. Given the anomalous heat; 
large temp/dewpoint spreads around 30 degrees are anticipated. 
This will increase the potential for locally strong to damaging 
wind gusts roughly between 2 and 10 pm across interior southern 
New England. We can not rule out a bit of small hail, but 
thinking locally strong-damaging wind is the main threat. This 
is supported by the NCAR ensembles as well as the CIPS analogs. 
Brief heavy rain/typical poor drainage street flooding is also a
concern given Pwats on the order of 1.5 to 2 inches. 

The activity will move east; but should weaken on approach to
the I-95 corridor Sunday evening given the later arrival time
and increasing marine influence. So we feel the main severe
weather threat will be across interior MA & CT.

Sunday night...

Scattered showers & t-storms weaken Sunday evening as the
approach the I-95 corridor. Perhaps a few showers with a rumble
of thunder survive, but not expecting much more than that.
Otherwise...the rest of Sunday night will feature dry but
significantly cooler weather returning. Low temps by daybreak
Monday should be back down into the middle 50s to the lower 60s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
* Highlights *

- Seasonable temperatures early in the week
- Increasing temperatures and humidity mid-late week
- Thunderstorms possible late week with a passing cold front


Monday through Wednesday

Anticyclonic flow around a large area of high pressure 
positioned north and west of New England will result in a 
northerly flow for the first half of the week. Predominantly 
northwesterly flow on Monday will support a seasonable day with 
high temps in the low 70s. By Tuesday the high pressure center 
is forecast to be due north of southern New England which will 
result in a more northeasterly flow into the region. This will 
allow cooler maritime air to advect into the region supporting 
below normal temperatures for Tuesday and Wednesday, especially 
along the coast where temperatures will be confined to the low 
60s. 

Wednesday night through Saturday

High pressure shifts east of the region late Wednesday/early 
Thursday bringing us back to a southerly flow pattern. Southerly 
flow will help lift a warm front through the region Wednesday night 
into Thursday with some showers and possibly a thunderstorm. 
Southerly flow persists into Thursday and Friday allowing for an 
increase in both temperatures and humidity. Temperatures may get 
back into the 80s Friday afternoon. Models in agreement that a cold-
front will push through the region at the end of the week. With a 
warm/humid air mass in place, the potential will exist for this 
front to produce thunderstorms in southern New England. A lot of 
uncertainty at this time range, but will be monitoring the end of 
next week closely.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent. 

00Z TAF Update...

Through 06Z

VFR. Possible IFR/LIFR visibilities at Cape/Islands terminals
where fog may redevelop prior to 06Z. Sea-breeze at Boston
should fade and transition to a south/southwesterly flow in the
next 2 to 3 hours. Some uncertainty in that department, but
expect a southerly flow by 03Z.

Tonight...High Confidence. VFR conditions should generally
prevail outside a bit of patchy ground fog possible overnight in
the typically prone spots. The exception might be the Cape & 
Islands where some IFR-LIFR conditions in low clouds/fog may 
impact those areas for a portion of the night. Light S winds.

Sunday...High Confidence. Mainly VFR conditions expected.
However, scattered showers and t-storms are expected to develop
across interior southern New England during the mid to late
afternoon hours. A few storms may be contain brief heavy rain
and locally strong wind gusts. The activity will weaken as it
approaches the Boston to Providence corridor, but some may
survive in a weakened form by early evening. SW wind gusts of 20
to 25 knots are expected to develop by afternoon but may be
briefly stronger in any thunderstorm.

Sunday night...High Confidence. Scattered showers and t-storms
weaken as they approach the I-95 corridor during the evening. 
Otherwise, VFR except for perhaps some low clouds/fog in the 
evening across the Cape/Islands before the cold front crosses 
the region. SW winds early in the evening will shift to the 
northwest at 5 to 15 knots by late evening/overnight.

KBOS TAF...High Confidence in TAF. Medium confidence in end time
of sea-breeze this evening.

KBDL TAF...High Confidence in TAF.

Outlook /Monday through Thursday/... 

Monday through Tuesday: VFR. Breezy. 

Tuesday Night: VFR. 

Wednesday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.

Wednesday Night: Mainly MVFR, with local VFR possible. Chance
SHRA.

Thursday: Breezy. Chance SHRA.

&&

.MARINE...
Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent. 

Tonight...High Confidence. Upper level ridging in place will
keeps winds/seas below small craft thresholds tonight. However,
main concern for mariners will be for fog re-developing mainly
across our southern waters.

Sunday and Sunday night...High Confidence. Southwest wind gusts
of 20 to 25 knots will develop by Sunday afternoon ahead of an
approaching cold front. Strongest of those winds will likely be
near shore given better mixing over the land. It is marginal,
but we may need some near shore small craft headlines in the
afternoon for gusty winds/choppy seas. Winds shift to the
northwest late Sunday night behind the cold front; with perhaps
some more marginal small craft wind gusts of 20 to 25 knots.
This time the strongest wind gusts will be over the open waters;
so perhaps some marginal small craft headlines may be needed for
a few or our eastern waters.

Outlook /Monday through Thursday/...

Monday through Monday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. 

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. 

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. 

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers. 

Thursday: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.

&&

.CLIMATE...
Daily record high temperatures...

Sat May 21st...
BOS 93F (1921) 
PVD 93F (1996) 
BDL 93F (1996) 
ORH 88F (1975)

Sun May 22nd...
BOS 93F (1959)
PVD 94F (1941, 1992)
BDL 95F (1992)
ORH 90F (1911, 1992)

Monthly record high temperatures...
BOS 97F (05/26/1880)
PVD 96F (05/26/2010)
BDL 99F (05/26/2010, 05/20/1996)
ORH 94F (05/26/2010)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Air Quality Alert until 11 PM EDT this evening for CTZ002.
     Heat Advisory until 8 PM EDT Sunday for CTZ002>004.
MA...Heat Advisory until 8 PM EDT Sunday for MAZ003>006-010>018-026.
RI...Air Quality Alert until 11 PM EDT this evening for RIZ001>008.
     Heat Advisory until 8 PM EDT Sunday for RIZ001>004.
MARINE...None.

&&

$$
SYNOPSIS...Frank/RM
NEAR TERM...Frank/Gaucher/RM
SHORT TERM...Frank
LONG TERM...RM
AVIATION...Frank/RM
MARINE...Frank/RM
CLIMATE...