Lexington, Massachusetts, USA

1/23/2019 6:30am 
  • Lexington Conditions: Clear
  • Temperature: 19.2°F / -7.1°CWarmer 1.2°F than last hour.
  • Dew Point: 11.1°FIncreased 1.6°Fsince last hour.
  • Relative Humidity: 70%Increased 1.0% since last hour.
  • Wind: SSW 2 mph, 10-min avg: 2 mph, gust: 6 mph
  • Barometer: 30.35 inFalling 0.03  inHg/hr Falling Slowly
  • Visibility: 10 miles
  • Snow Today: 0.0 in
 Middlesex County - Special Weather Statement Special Weather Statement

Area Forecast Discussion
for Lexington MA

FXUS61 KBOX 230844

Area Forecast Discussion
National Weather Service Boston/Norton MA
344 AM EST Wed Jan 23 2019

Low pressure lifting across the Great Lakes into Quebec will 
result in considerably milder temperatures today. The risk for 
showers will increase tonight and reach maximum strength on
Thursday. Heavy rainfall and possible flooding, strong coastal 
winds and unseasonably mild temperatures are expected on 
Thursday. Mainly dry and more seasonable temperatures follow on
Friday, then turning colder Saturday. Snow showers are possible
Sunday then another frontal system may impact the region 


Upper trough over the Plains with 170 kt jet feeding up over the
Great Lakes. This will bring a plume of moisture up through the
Ohio Valley into the Eastern Great Lakes by this evening.
Satellite shows clouds spreading east toward New England. Expect
clouds increasing and thickening through the day. Southwest
winds will bring in milder air, and low level temps support
surface max temps in the low to mid 40s. Low level jet will be
increasing during the afternoon/evening and may bring gusts 20
to 30 mph. 

Overall, a dry day but note radar shows some very light pcpn and
temperatures are favorable initially for some light snow or
sleet, mainly in northwest MA, during the afternoon. We will
continue with a Special Weather Statement for this possibility.



Primary low pressure moves into Canada. Precip Water plume 
increases overnight as it is drawn north, with values reaching 
over 1 inch by Thursday morning. Upper jet shifts farther east,
and our area increasingly moves upper the right entrance region
of the jet, especially after midnight. Expect increasing
coverage of rain during the night. 

Southerly flow will bring milder air into the region with higher
dew point values as well. Temperatures will slowly rise
overnight...guidance suggests temperatures rising into the 50s.

Low level jet increases during the night, with speeds of 65 to
75 kt at 850 mb and 60 to 70 kt at 925 mb. Expect gust potential
overnight at 30 to 40 mph. Best chance for this wind will be
over RI and SE Mass, and may extend into NE CT.


Srn New England remains under the right entrance region, so
expect continued ascent combined with the well-above-normal
Precip Water values. Rain which increases overnight should fall
at its maximum rate during this time. Total amounts of 1-2
inches is favored, with small areas of 2-3" possible. K Index
reaches 30+ over RI and SE Mass during the afternoon, indicating
some instability that could generate isolated tstms during the
afternoon. This hold potential for urban and small stream
flooding, with focus over CT-RI and SE Mass. We will issue a
Flash Flood Watch for this area.

Another concern is the wind. The low level jet continues to
increase Thursday, with speeds of 95 kt at 850 mb and 70-80 kt
at 925 mb. Cold water temps may attempt to stabilize the 
surface layer but warm advection pushing land temps into the 50s
may be enough to draw strong winds to the surface, especially RI
and SE Mass. We will issue a High Wind Watch for this area, and
anticipate Wind Advisories will eventually be issued over a 
broader area.

Tides/Coastal Flooding: 
Astronomical tides were elevated yesterday, which is cause for 
concern along the south coast, but strongest winds and surge 
expected to occur after the Thu morning high tides which will 
minimize risk.



* Mainly dry and turning colder Fri into Sat
* Snow showers possible Sunday
* Another round of snow/rain showers possible mid week

Overview and model preferences...
As noted yesterday, long range ensemble guidance continues to 
favor predominantly negative NAO/AO and EPO setup. This pattern 
favors a broad, longwave trof settling across the E third of the
CONUS through much of the long term, and both operational and 
ensemble guidance support this. With this trof in place, lobes 
of the arctic vortex will be shifting S and E, impacting New 
England with modified arctic air, and robust upper lvl energy. 
While there remains some uncertainty in the sfc reflections of 
these features, given they are not currently well sampled, a 
general blend of guidance will be used as a baseline, giving a 
rough outline of the potential impacts.


Thu night...
Lingering precip as low pres moves toward Labrador. Timing 
dependent, as both cold and dry air will be filtering through 
the column. Low risk for some SN, especially across W MA/CT 
during the evening before the drier air cuts erodes the 
remaining moisture. Gradual clearing overnight, with mins 
falling into the 20s by early AM Fri. With mins below freezing, 
damp SFCs may have ice by AM.

Secondary arctic front introduces the coldest of the modified 
arctic air mass late Fri. Highs slightly colder than normal as 
the strongest cold advection does not arrive until late Fri. The
cold fropa is mainly dry per latest soundings, but a few SHSN 
cannot be ruled out thanks to some lower lvl instability and 
moisture pooling along the BL.

Fir night into Sat...
As previous forecaster noted, modified arctic airmass in place.
H85 temp anomalies run about -10C. Lows Sat morning and highs 
Sat below normal as a result.

Sat night into Sun night...
First lobe of the arctic vortex rotates through the Great Lakes
and Ontario with a sfc low pres in tow. Warm advection results 
across the NE CONUS along with a modest PWAT plume. A period of 
SHSN possible, and will need to monitor the potential 
development of an inverted trof linked to this low pres inland 
which could provide a focus for locally heavier SN. Most keep 
this to the N, but something to watch.

Modest ridging ahead of a second lobe of the vortex suggests a 
brief dry period.

Mid next week...
Secondary vortex rotates to the S, however the longwave trof 
has will have also shifted somewhat E. Suggesting that the final
track of any sfc low pres is further E than the inside runner 
from the weekend. Again, given the time period, low confidence 
in any one solution, but something to watch.


Forecaster Confidence Levels...

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

Short Term /through Thursday/...

Today...High Confidence.

VFR most of the day. MVFR cigs possible toward evening as rain
moves in from the southwest. Some rain/snow/sleet mix possible
in northwest MA. SW wind gusts of 20 to 30 mph develop during 
the afternoon.

Tonight...Moderate to high confidence.

Conditions lower to IFR most areas during the night. Rain
develops as milder air moves into Southern New England. High dew
points will also contribute to fog formation during the night.

Strong winds at 2000 feet will generate southwest wind gusts of
40 to 45 kt. The winds at 2000 feet will also generate low level
wind shear

Thursday...IFR cigs/vsbys with areas of MVFR in rain and fog. 
Strong wind gusts of 45 to 50 kt possible, as well as Low Level 
Wind Shear. A cold front swings through later in the day,
and may generate isolated thunder to go along with the rain.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF

Outlook /Thursday Night through Sunday/... 

Thursday Night through Friday: VFR. Windy with local gusts to
30 kt. 

Friday Night: VFR. Breezy. 

Saturday: VFR. 

Saturday Night and Sunday: Mainly VFR, with areas IFR possible.
Breezy. Slight chance SHSN.


Forecaster Confidence Levels...

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

Short Term /through Thursday/... 

Today...High confidence.

High pressure moves offshore, bringing a southwest flow of air
up across the waters. Winds should increase during the day,
although the stronger winds are just approaching our southern
waters late in the day.

Tonight... Moderate confidence.

Strong low level southwest winds above the surface will continue
to increase during the night. Winds in the jet will reach 60-70
kt and should support gale force gusts during the night. These
winds and the long fetch will build seas to 5-10 feet.
Developing rain will reduce vsbys to 1-3 miles at times. The 
increasing low level moisture will also help generate areas of
fog, which will also reduce vsbys.

Thursday...Moderate confidence.

Strong low level jet...about 2000 feet up...will continue much 
of the day with winds reaching 95 kt at about 5000 feet and 
70-80 kt at 2000 feet. This will support southwest gales and may
support low-end storm force gusts. We have bumped the Gale 
Watch up to a Storm Watch on most waters. Boston Harbor and 
Narragansett Bay will remain at a Gale Watch.

The strong winds will build seas especially across the southern
waters where heights may reach 15-17 feet. Rain and isolated
tstms will reduce local visibility to 1 to 3 nm.

Outlook /Thursday Night through Sunday/...

Thursday Night into Friday Night: Moderate risk for Small Craft
Advisory winds with gusts up to 30 kt. Rough seas up to 15 ft.

Saturday and Saturday Night: Winds less than 25 kt. Local rough

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain showers, chance of
snow showers. Areas of visibility 1 to 3 nm.


CT...Flash Flood Watch from Thursday morning through Thursday 
     afternoon for CTZ002>004.
MA...High Wind Watch from Thursday morning through Thursday 
     afternoon for MAZ007-019>024.
     Flash Flood Watch from Thursday morning through Thursday 
     afternoon for MAZ013-015>022.
RI...High Wind Watch from Thursday morning through Thursday 
     afternoon for RIZ007-008.
     Flash Flood Watch from Thursday morning through Thursday 
     afternoon for RIZ001>007.
MARINE...Storm Watch from Thursday morning through Thursday afternoon 
     for ANZ231>235-237-250-251-254>256.
     Gale Watch from Thursday morning through Thursday afternoon 
     for ANZ230.
     Gale Watch from late tonight through Thursday afternoon for