LexMAWeather

Area Forecast Discussion
for Lexington, MA

        
955 
FXUS61 KBOX 232353
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
753 PM EDT Sat Sep 23 2017

.SYNOPSIS...
High pressure, both at the surface and aloft, will extend from the 
eastern Great Lakes to New England tonight into early next week.  
It will bring unseasonably warm weather to the region into the 
middle of next week. Maria is expected to pass southeast of New 
England late in the week with strongest winds well offshore.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

GOES 16 fog product really showing the marine stratus and fog
across portions of eastern MA very well. Not seeing many signs
it will make a quick exit before midnight. Contemplated a Dense
Fog Advisory, but seeing the visibility bounce up at times,
still. Will need to monitor further this evening. A Dense Fog
Advisory is still a possibility later tonight. Weak flow should
mean this fog does not push much farther inland.

Made significant edits to account for the low clouds and fog
across eastern MA. Otherwise, just brought the forecast back in
line with observed trends.

Previous Discussion...

SREF probabilities of low ceilings are quite high along the 
southeast MA coast. NCEP time lagged rapid refresh ensemble 
system shows visibilities lowering from east to west in that 
same area. All indications are that Cape Cod and the islands, as
well as portions of interior southeast MA will have fog and low
cloudiness through the night. In fact, a Dense Fog Advisory may
be needed. 

Elsewhere, a pleasant night is in store, with just some cirrus 
clouds aloft and lows in the upper 50s to lower 60s. Some patchy fog 
may develop late over portions of the interior.

&&

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

Winds diminish tonight, which with clear skies will allow 
temperatures to cool to dew point. We trended toward the mos values 
for min temp, which was a couple of degrees lower than the standard 
guidance. Radiation fog possible in the interior, and marine 
fog/stratus is possible along the Cape/Islands/South Coast.

Sunday...
**RECORD HIGH TEMPERATURES EXPECTED**

High pressure over the region, both at the surface and aloft,
will mean sunshine and hot temperatures away from the coast.
Heights at 500 mb are forecast at or above 590 Dm, and 850 
temps are forecast at 18-20C. 925 mb temps are forecast to 
reach +24C. Expecting highs reaching the lower 90s in the CT
River Valley, which would be a record...see Climate section at
the end of this forecast discussion. Expecting upper 80s
elsewhere in interior southern New England. Light winds under 
the high pressure will allow daytime sea breezes, which will 
keep temps much cooler along the shoreline....only 70s to near
80. 

The one big exception to the above will be Cape Cod and the
islands, which are likely to begin the day with cloud cover and
areas of fog, which may linger through a big chunk of the 
morning, before becoming partly sunny. Expecting highs on the 
Cape and islands to range from the upper 60s on Nantucket to 
the mid 70s on the upper Cape.

With dewpoint temperatures only in the lower to mid 60s, the
heat indices are forecast to reach 90 to 94, just shy of heat
advisory criteria - although that criteria requires it to last
for two days. Will need to keep an eye on this.

Sunday night...

Expecting mostly clear skies. Could see marine stratus again
late at night over the Cape and islands. Patchy fog possible
late in some interior areas. Lows in the 60s.

Swells from Hurricane Maria will be reaching south coastal
areas, so a High Surf Advisory remains posted for those areas.

&&

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

* Summer warmth expected to the middle of next week
* Maria expected to sharply recurve out to sea southeast of New 
  England late next week

No major surprises in the 23/12Z guidance. Still expecting an 
anomalous mid level ridge to hover over our region through the 
middle of next week, although it should weaken with time after 
Tuesday. The strength of this ridge will be crucial in delaying the 
northward progress of Maria towards our region.

High pressure with dry weather expected Monday and Tuesday. 
Temperatures should be 10-15 degrees above normal Monday, but not 
quite as much Tuesday or Wednesday. A few interior spots may reach 
90 degrees Monday. Seabreezes should develop along both coasts, 
lowering daytime max temperatures there. 

A potential weak low level front just south of our region, may be 
enough to trigger a few showers Tuesday night into Wednesday. A 
greater risk for showers should be ahead of a cold front sweeping 
through our region Wednesday night into Thursday morning. This 
cold front and a potent mid level trough are expected to be the 
final kickers which steers Maria out to sea well to our south. 

Drier weather should prevail next Friday into Saturday, although 
cannot dismiss the possibility of some stray showers given the 
proximity of a mid level trough. The bigger change will be the 
temperatures, which should snap back to near normal levels during 
this time. 

The primary impact on our region from Maria will likely be another  
prolonged period of high surf and dangerous rip currents, mainly  
along ocean-exposed south coast beaches. For several days, Maria 
tracks near a great circle route in our direction and hence we will 
likely see significant long period swells from the S or SE propagate 
into our coastal waters most of next week. The slow northward speed 
of Maria for the next several days may enhance the swell activity 
during this period.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

Short Term /through Sunday Night/...

Tonight...Moderate confidence, mainly due to timing. 

IFR/LIFR conditions in fog towards the east coast of MA. Models
show that this will persist through the night, with the fog 
becoming locally dense. The low clouds and fog may spread 
westward into interior southeast MA, but is not expected to
reach RI.

Elsewhere, VFR conditions. Patchy fog with isolated IFR/LIFR
conditions possible over portions of the interior late.

Sunday...High confidence.

Any interior fog burns off early in the morning. IFR/LIFR in low
clouds and fog will be slower to lift over Cape Cod and the
islands and may persist through the morning. Otherwise VFR most
locations with light wind. Sea breezes expected along the
coastlines, including KBOS.

Sunday night...Moderate to high confidence.

VFR most areas, however, could see marine IFR developing again 
on Cape Cod and the islands. Patchy areas of fog may develop 
late over portions of the interior. 

KBOS TAF...Moderate confidence. Marine stratus and fog will
likely persist into the first half of the morning push. VFR
develops Sunday, with light seabreezes from late morning 
through the afternoon. 

KBDL TAF...High confidence in TAF. Patchy fog may develop 07Z- 
11Z tonight, although the chance of this is stronger over 
valley locations north of Springfield. 

Outlook /Monday through Thursday/...Confidence...High.

Monday through Tuesday...VFR expected. 

Tuesday night...Mostly VFR except MVFR in patchy stratus/fog 
some interior valleys and near the south coast. 

Wednesday...Generally VFR except MVFR ceilings/visibilities 
possible in scattered late day showers and patchy late night/early
morning stratus/fog.

Thursday...Generally VFR, with MVFR in scattered showers during
the morning.

&&

.MARINE...
Forecaster Confidence Levels...

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

Tonight...Moderate confidence.

Leftover swell was diminishing along the east coast of MA. 
Low clouds and fog will continue along the southern and 
southeast coasts tonight with poor visibilities, especially on 
the waters south and east of Cape Cod. Winds will diminish to 
less than 15 knots, but seas will linger at 5-6 feet on the 
southern outer waters.

Sunday...Moderate confidence.

High pressure building over the region will bring light wind, 
with sea breezes developing at the shoreline. Poor vsbys in fog 
early, slowly improving by late morning or early afternoon over
the southeastern waters. Seas of 5-6 feet will linger on the 
southern outer waters. A south swell sent north from Maria will
start showing itself in our southern waters late Sunday, with 
3-4 feet swell heights in the afternoon. 

Sunday night...High confidence. 

Seas build to 5 to 7 feet over the southern outer waters, mainly
due to swells from distant Hurricane Maria. High surf conditions
will exist on area beaches along the south coast. Patchy areas
of fog.

Outlook /Monday through Thursday/...Confidence...High

Relatively light winds are expected through this period. However, 
swells from Maria will propagate into the southern coastal waters, 
beginning late Sunday night or Monday. Small Craft Advisories will 
likely need to be extended due to rough seas for the waters south of 
the MA and RI coast for all of this period.

The swells from Maria will likely produce another round of high surf 
and dangerous rip currents.

&&

.TIDES/COASTAL FLOODING...
High Surf Advisories will expire along the east coast of MA this
evening, but remain in effect through Monday along the south
coast. Swells from Maria will likely increase the surf and 
associated rip current risk across our ocean-exposed south coast
starting late Sunday and continuing through the week. This will
be true even though Maria may eventually recurve out to sea 
well southeast of New England.

&&

.CLIMATE...
The Record High Max Temperatures for Sunday and Monday are

BOS  90/1959  89/1926 
ORH  85/2010  85/1970
BDL  89/1959  90/2007
PVD  87/1959  89/1920

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory until 6 PM EDT Monday for MAZ020-022>024.
RI...High Surf Advisory until 6 PM EDT Monday for RIZ006>008.
MARINE...Small Craft Advisory from 2 AM to 6 PM EDT Monday for ANZ235-
     237.
     Small Craft Advisory until 11 PM EDT this evening for ANZ250.
     Small Craft Advisory until 6 PM EDT Monday for ANZ254>256.

&&

$$
SYNOPSIS...Belk/GAF
NEAR TERM...Belk/GAF
SHORT TERM...GAF
LONG TERM...Belk
AVIATION...Belk/GAF
MARINE...Belk/GAF
TIDES/COASTAL FLOODING...
CLIMATE...