Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 221802 
afdbox

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
202 PM EDT Fri Mar 22 2019

Synopsis...
scattered to numerous showers will continue into the afternoon
with some wet snow in the highest terrain. Scattered showers
will change to a period of snow tonight with some accumulations
expected in the high terrain. Windy and colder conditions are
expected Saturday with another warm-up on Sunday. Conditions
turn colder again Monday into the middle of next week.

&&

Near term /until 6 PM this evening/...

2 PM update...

Numerous showers continue to rotate around the upper level low.
While most of the precipitation was in the form of rain outside
of the higher elevations, there was one exception. A band of
heavier precipitation across eastern Massachusetts was resulting in enough
dynamic cooling for pockets of wet snow. No accumulations
though with temperatures above freezing. Ptype should change
back to rain in all locations over the next few hours except the
highest terrain, as precipitation intensity diminishes. This a
result of the upper level low lifting northeast of the region.
Westerly winds will begin to increase to between 20 and 30 mph.

&&

Short term /6 PM this evening through 6 am Saturday/...
4 am update ...

* accumulating snow likely high terrain but some snow all areas
* strong northwest winds up to 45 mph & colder

Potent Arctic short wave pivots along the southern New England coast
with comma-head precip overspreading the entire region, intensity
peaking around 06z. As cold air advection increases and column cools
any rain showers early this evening flips over the snow later this
evening and overnight, all areas including Cape Cod and the islands.
In fact the entire region could pickup a coating to an inch or two
possible as cross sections reveal most of the lift occurring in the
snow growth region, maximizing snowfall potential. Tho with min
temps hovering around freezing across eastern Massachusetts snow accumulations
may be confined to colder/non paved surfaces here. However
significant accumulations (4-8") are possible in the upslope
regions of the Berkshires (above 1000 ft) and perhaps 1-3" in the
Worcester Hills into Tolland County of CT per the hi res guidance.
Not enough confidence to expand Winter Weather Advisory into the
Worcester Hills and northeast CT, but if 12z model guid continues
this increased qpf trend an advisory may be needed.

As 980 mb low tracks along the ME coast, strong northwest winds on the
backside of the low overspreads southern New England. As cold air advection
increases low level lapse rates steepen and support northwest winds gusting
up to 40 mph at times. Strongest winds will be across western Massachusetts/CT
where gusts up to 45 are possible. If 12z models trend upward with
winds may need a Wind Advisory for western Massachusetts/CT tonight.

Temps falling into the upper 20s across CT and western-central Massachusetts
with low 30s in Rhode Island and eastern Massachusetts.

&&

Long term /Saturday through Thursday/...

Highlights...

* windy Saturday, then milder Sunday.
* Cold front brings rain showers Monday, possibly starting as snow
showers inland.
* Colder weather follows through midweek.

Overview and model preferences...
occlusion, stacked with upper lvl cutoff shifting into the
Maritimes, will lead its lingering impacts in the form of cold
and blustery conditions Sat. However, between this, and a second
Arctic lobe moving S from baffin island, height rises suggest a
very mild, Spring conditions sun into Mon. The more robust
wave, settles across the NE as a longwave trof with links to
Arctic air. Anticipate a period of colder than normal weather
into mid week. The sfc baroclinic zone, and where it ends up
will ultimately determine timing/track of a frontal wave late
Mon into Tue. Something to watch, but the positive ao/nao
support a progressive west-east movement, keeping it mainly to the S.
Otherwise, amplified ridge which has been a persistent feature
across the Continental Divide and Pacific regions of the Continental U.S.
Will begin to shift east late week, yielding height rises and a
return to more Spring-like conditions.

Details...

Sat...
lingering shsn end early as dry slot wraps into the occluding
low pres early. However, slight continuation of deepening of the
sfc low as it moves toward the Bay of Fundy. Meanwhile, high
pres upstream is building toward +1030mb. This suggests both a
tight pres gradient and strong pres rises through the daytime
Sat. Low level jet values to 45-50kt which should be tapped thanks to
enhanced mixing under cold air advection. Wind advisories may well be needed
from early Sat morning into the early evening hours, at which
point diurnal decoupling will begin to limit gusts. Otherwise,
chilly, with 850 mb temps dipping to about -8c, which will allow
ambient temps to reach the low-mid 40s. The winds will keep wind
chills in the 20s to low 30s.

Sun...
although book-ended by Arctic influences, rapid height rises
thanks to meso-ridging will allow 850 mb temps to reach +2c to +4c
by peak heating. West component to the low lvl flow also suggests
downsloping. Given this, anticipate highs in the 50s, with a
possibility of approaching 60 in some spots where the
downsloping can be maximized.

Mon into Tue...
secondary Arctic front will be settling gradually across the
region late Mon, slowing as it does so. Noting that guidance
continues to support two baroclinic wave development with the
passage, the first which may lead to precip across S New England
deepening on timing. The second remains suppressed late Tue
given the synoptic pattern. Will need to watch this period,
because if a coastal passage is close enough (some ensemble
members support this), accumulating snow could be possible.
Otherwise, precip will remain mostly rain given the first wave
passes near peak heating Mon.

Mid week...
regardless of the frontal waves, expect a trend toward colder
than normal conditions as 850 mb temps approach record low values
per Storm Prediction Center sounding climatology. Even if full mixing is realized,
highs may struggle to break out of the 30s Tue/Wed. Mins will be
dependent on pres gradient, but if weak enough as the high
approaches, cant rule out low teens or even isolated single
digits in the typical cold spots across the interior. Mainly dry
once a near 1035mb high pres crosses the region.

Late week...
ridging influence, even though weakening will allow for height
rises and warm advection late week, allowing temps to return to
near or above seasonal normals.

&&

Aviation /18z Friday through Wednesday/...
forecaster confidence levels...

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

Short term /through Saturday/...

This afternoon...moderate to high confidence. Lingering IFR
conditions should continue improve to mainly MVFR thresholds
through late afternoon. This a result of showers of rain and wet
snow diminishing in areal coverage/intensity. Ptype should
mainly change back to rain showers as precipitation diminishes
in intensity. Westerly wind gusts increase to between 20 and 30
knots.

Tonight...moderate to high confidence. Rain and snow showers
will increase in areal coverage this evening with ptype
transitioning to snow, even in the lower elevations. A few
inches of snow are likely in the higher terrain. In the lower
elevations, expect a coating to 1 inch with perhaps localized
amounts up to 2 inches. Most runways in the lower elevations
will remain wet, but a brief slushy coating of snow would be
possible in any heavier snow showers. MVFR conditions will
dominate tonight, but IFR thresholds will be met in bands of
snow showers with brief LIFR conditions not out of the question.
Westerly wind gusts of 30 to 40 knots expected.

Saturday...high confidence. Some lingering MVFR ceilings in the
morning will improve to VFR by afternoon. Northwest wind gusts
of 30 to 40 knots expected.

Kbos terminal...moderate to high confidence in taf.

Kbdl terminal...moderate to high confidence in taf.

Outlook /Saturday through Tuesday/...

Saturday: mainly VFR. Strong winds with areas of gusts up to 40
kt.

Saturday night: VFR. Windy with areas of gusts up to 30 kt.

Sunday int Sunday night: VFR.

Monday into Monday night: mainly VFR, with areas MVFR possible.
Chance rain.

Tuesday: mainly VFR, with local IFR possible. Breezy. Slight
chance snow.

&&

Marine...
forecaster confidence levels...

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

Short term /through tonight/...

*** northwest gales tonight and Saturday ***

Today ...

NE wind gusts of 30 to 40 knots across our eastern waters
temporarily diminish and shift to the northwest. Renewed gusts
of 20 to 30 knots develop this afternoon behind strengthening
low pressure. Rain and fog will lower vsby to 1-3 nm at times.

Tonight ...

Gale center in Maine waters moves northeast with northwest gales force
winds across southern New England waters. Rain showers change to
snow showers lowering vsby 1-3 nm.

Outlook /Saturday through Tuesday/...

Saturday into Saturday nigh: moderate risk for gale force winds
with gusts up to 40 kt. Rough seas up to 14 ft.

Sunday: low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas.

Sunday night into tuesday: winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain.

&&

Tides/coastal flooding...

The early afternoon high tide has past and no additional coastal
flooding is anticipated from this storm. We did receive a few
minor coastal flooding reports from the typically prone
locations with the earlier high tide.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...coastal flood advisory until 3 PM EDT this afternoon for
maz007-015-016-019-022.
Winter Weather Advisory until 8 am EDT Saturday for maz002-008.
Rhode Island...none.
Marine...Gale Warning until 4 PM EDT Saturday for anz232>235-237-
254>256.
Gale Warning from midnight tonight to 4 PM EDT Saturday for
anz230-236.
Gale Warning from 8 PM this evening to 4 PM EDT Saturday for
anz231-250-251.

&&

$$
Synopsis...nocera/doody
near term...Frank

National Weather Service Glossary of Abbreviations