NWS Forecaster Discussion
BOX
Area Forecast Discussion National Weather Service Boston/Norton MA.
000
FXUS61 KBOX 021147
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
647 AM EST Wed Dec 2 2020
.SYNOPSIS...
Seasonable temperatures return today and cannot rule out a scattered
rain or snow shower across the interior. Dry and milder Thursday
then a few showers are possible Friday as a weak disturbance moves
through. There is the potential for a storm impacting the region
Saturday into Saturday night with mostly rain for southern New
England but may end as some snow over higher elevations. The storm
exits Sunday, then mainly dry and colder weather Monday and
Tuesday.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
645 AM update...
Deep mid level trough across New York state with scattered snow
showers in the vicinity of the trough axis. As the trough and
accompanying shortwave energy slides east across New Eng today,
expect a few snow/rain showers to move into interior SNE,
especially northern and western MA. Meanwhile ocean effect
clouds are moving across the Cape/Islands. Delta T from SST to
top of the boundary layer is near 20C south of New Eng so expect
a few rain showers to develop south of the coast. With SW
trajectory, a few showers may impact portions of the
Cape/Islands this afternoon. Otherwise, a mix of sun and clouds
expected today.
850 mb temps around -8C today. This will support highs ranging
from upper 30s higher terrain to mid 40s along the south coast.
Gusty SW winds along the immediate south coast and especially
Cape/Islands where occasional gusts to 25-30 mph.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Tonight...
Diminishing winds and clearing skies should allow for a rather
decent radiational cooling night. Expect most interior locations to
fall into the 20s, except for areas along the immediate South Coast
and the Cape and Islands where the mixed layer does not decouple.
Have trended overnight lows towards the 25th percentile but it`s not
out of the question we could trend overnight lows even colder
towards the low 20s if winds completely decouple in the usual
radiational cooling hot spots in the interior.
Thursday...
As the upper low moves off to the north, the flow over New England
becomes briefly more zonal with weak surface high pressure building
in from the Mid Atlantic region. Expect dry weather with sun and
mixing, and mixing to 925 mb would support max temps in the mid 40s
to low 50s. By the afternoon hours, expect increasing high cirrus
coverage thanks to a shortwave being ejected by a closed low over
the Oklahoma/Texas Panhandle region.
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Highlights...
* A few showers possible Fri
* A storm brings mostly rain Sat/Sat night, possibly ending as snow
higher terrain
* Improving conditions Sunday, then mainly dry and turning colder
early next week
Thursday night into Friday...
Northern stream trough digs across the Gt Lakes with multiple
shortwaves tracking to the north of SNE through Friday. Meanwhile,
120 kt upper level jet lifts north across SNE during Fri. Thu night
will be dry, then a deepening moisture axis will develop ahead of
the trough on Fri and moving into SNE which may bring a few showers
under the upper jet. Axis of moisture and potential showers is not
certain but consensus of guidance favor interior locations for a few
showers Fri afternoon. Mild temps in the upper 40s to mid 50s with
gusty SW winds at times.
Friday night into Sunday...
Forecast confidence decreases in this period due to uncertainty with
timing, track and intensity of a potential storm. Rather complex
pattern with split flow and multiple northern and southern stream
shortwaves interacting with each other. Lots of moving parts and
significant spread exists among deterministic and ensemble guidance.
It will likely take another few days before model guidance can get a
better handle on how this plays out. A storm is likely but timing
and details are uncertain. Lack of initial cold air and guidance
favoring an inside runner suggests a mostly rain event for SNE with
possible changeover to snow over the higher terrain on the backside
of the storm. Storm may be exiting by Sunday with improving
conditions but changes to timing and precip type/amounts are
possible as we move closer to the event. Latest ensemble guidance
suggesting only a moderate wind event but this will depend on the
intensity and track of the storm which remains uncertain.
Monday and Tuesday...
Low confidence forecast. Consensus of the guidance favors mostly dry
and colder weather with below normal temps, but still a lot of
spread in the upper air pattern which features an amplified mean
trough across the eastern US, but several shortwaves rotating
through the flow in the northern and southern streams. It remains a
chaotic pattern which is impossible to resolve at this time range so
changes in the forecast are likely.
&&
.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Today...High confidence.
Mainly VFR with localized MVFR higher terrain and Cape/Islands
where a few rain or high terrain snow showers possible. SW wind
gusts to 25 kt over the Cape/Islands and up to 20 kt elsewhere.
Tonight...High confidence.
VFR conditions with skies becoming clear. WSW winds at 5-15 kts. The
higher elevations, Cape Cod and the Islands may see gusts of 15-25
kts.
Thursday...High confidence.
VFR conditions with WSW winds 5 to 10 kts except 15 to 20 kts near
the coast.
KBOS TAF...High confidence in the TAF.
KBDL TAF...High confidence in the TAF.
Outlook /Thursday Night through Sunday/...
Thursday Night: VFR. Breezy.
Friday: VFR. Breezy. Slight chance SHRA.
Friday Night: Mainly MVFR, with areas VFR possible. Breezy.
Chance RA.
Saturday: Mainly MVFR, with local IFR possible. Breezy. RA
likely.
Saturday Night: Mainly IFR, with areas MVFR possible. Windy
with areas of gusts up to 30 kt. Chance RA, chance SN.
Sunday: Mainly MVFR, with local IFR possible. Windy with local
gusts up to 30 kt. Chance SHRA, chance SHSN.
&&
.MARINE...
Small Craft Advisories continue for all waters today except for
Boston Harbor and Narragansett Bay. This is due to SW winds at 15-25
kts with gusts 25-30 kts as well as 5-10 ft seas for the open
waters. There may also be scattered showers for waters off the south
coast and the Cape and Islands during the day today. Winds shift to
the W Wednesday night with 10-20 kt winds and gusts of 20-30
kts.
Outlook /Thursday Night through Sunday/...
Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 20 kt. Seas up to 5 ft.
Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft.
Friday Night through Saturday: Winds less than 25 kt. Seas up
to 5 ft. Rain likely.
Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain.
Sunday: Moderate risk for Small Craft Advisory winds with areas
of gusts up to 30 kt. Rough seas up to 12 ft. Chance of rain
showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EST Thursday for ANZ231>235-
237-251.
Small Craft Advisory until 7 PM EST Thursday for ANZ250-
254>256.
&&
$$
SYNOPSIS...KJC/Chai
NEAR TERM...KJC/Chai
SHORT TERM...Chai
LONG TERM...KJC
AVIATION...KJC/Chai
MARINE...KJC/Chai