FXUS61 KBOX 181851

Area Forecast Discussion
National Weather Service Boston/Norton MA
251 PM EDT Mon Mar 18 2019

High pressure will bring quiet weather through Wednesday, with
milder air filtering in on Wednesday. A coastal storm passes on
Thursday and lingers into Friday. A shot of cold air going into
Saturday as more seasonable conditions return for Sunday.


Broad trough over the Northeast USA with a couple of embedded
shortwaves but also lots of dry air. The first shortwave crosses
New England tonight. Model cross-sections do indicate a period
of increased relative humidity between 850 and 700 mb overnight,
but drier air below 850 mb. This should bring a few hours of
increased clouds, but then trend to clearing skies toward
morning. Can't rule out a few flurries, but too much dry air to
count on this.

Thus, fair weather with temps falling into the 20s.


Expect a period of mostly sunny skies Tuesday between
shortwaves. Cold pool aloft lingers the first part of the day,
so daytime heating should mix deeply in the atmosphere, likely
at or above 800 mb. This should again support max sfc temps in
the upper 30s to mid 40s.

Second shortwave sweeps through on Tuesday night. A second
period of clouds is possible at this time, but moisture values
look drier than tonight so probably fewer clouds. Dew points in
the teens with light winds, but clouds may interfer with
radiational cooling. We will go with min temps in the 20s.



*/ Highlights ...

- Mild Wednesday
- Potential coastal storm Thursday, watching tides
- Breezy Friday, turning colder into Saturday

*/ Overview ...

See-saw pattern. Seemingly +EPO with NE Pacific low pressure that
aids in maintaining a +PNA over western N America, Pacific / Arctic
energy downsheared W of a Baffin Bay tropospheric polar vortex into
preferred H5 troughing S into the E CONUS. An occassional cyclonic
wave break over the W CONUS adding to forecast challanges, looking
at a late-week potent coastal storm system tapping into sub-tropical
energy and moisture which forecast model consensus has continually
strengthened the last several runs. Brief and juxtaposed by central
CONUS storminess / latent heat release E as the N Atlantic is wide
open. Airmass swings communicated in meteograms, yet temperatures
hold near-seasonable with highs around the mid to upper 40s. Touch
on details below.

*/ Details ...

Wednesday ...

Mild. Return S air, breezy, dry. Expect highs up around 50 as the
boundary-layer mixes out as an inverted-V profile. Low dewpoints.
Increasing clouds late out of the SW.

Thursday ...

Potential coastal storm. Forecast guidance consensus continues to
step up the potency of N-stream energy diving S through preferred H5
troughing into the sub-tropics pulling back N beneath lower heights.
More favorable baroclincity beneath stronger dynamics / ascent, cold
air seemingly eroded the previous day, looking at mostly rain with
potential pockets of moderate to heavy, perhaps a rumble of thunder
as well. But nudging W high pressure ridge and a wide-open Atlantic,
not going with likely PoPs just yet, keep it at chance. Uncertainty
as to whether we can over-achieve on temperatures / dewpoints. Also
watching winds as tides will be astronomically high (Boston only a
foot shy of minor flooding). As to the 18.12z EC, near record with
respect to lowest surface pressures for mid-March, it is somewhat
suspicious but not ignoring it. If future model consistency, then
concern with respect to tides and / or potentially manifestation of
colder air yielding wet snow on the backside of the storm. Wait and

Friday ...

Blustery and turning colder, if the coastal storm manifests and also
strengthens E. Scattered shower activity lingering. H85 temperatures
dropping to around -10 to -12C Sunday morning. Mild Friday, but lows
Friday night could be back down into the teens. Mixing up around H8
possible, mix-down faster winds, drier air, 25 to 35 mph gusts with
gales over the waters, possibly stronger if the pressure / thermal
gradient strengthens on the backside of the departing system.

Weekend ...

Showery weather may linger early on. Overall, expecting mostly dry
conditions with near-seasonable temperatures as NW winds prevail. A
mix of sun and clouds beneath increasing high pressure.

Early next week ...

Squeeze play. N-stream energy continues to dip along the flat-base
of the preferred H5 trof as cut-off energy from the Central Plains
begins to exit E. Juxtaposition of airmasses, a low confidence


Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence.

VFR through the period. A period of greater than 50 percent sky
cover tonight with bases at 5000 to 7000 feet. A few flurries
possible. Mostly clear Tuesday and Tuesday night.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...

Wednesday: VFR. Breezy.

Wednesday Night: VFR. Breezy. Chance SN.

Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance

Thursday Night: VFR. Slight chance RA.

Friday: VFR. Breezy.

Friday Night: VFR. Windy with gusts up to 30 kt.

Saturday: VFR. Windy with gusts up to 35 kt.


Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence.

Quiet boating weather through Tuesday night with winds and seas
below Small Craft levels.

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt.

Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft. Chance of rain.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain.

Thursday Night through Friday: Winds less than 25 kt. Areas of
seas approaching 5 ft. Slight chance of rain.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

Saturday: Strong winds with gusts up to 35 kt. Areas of rough



In just three weeks, 70 degrees will change from near record to
no surprise...and in another 1 1/2 months just a part of the

Record High Temps March 18

BDL 72 / 2012
PVD 73 / 2011
BOS 74 / 2012
ORH 74 / 2012

Average First Occurence of 70 degree high (Pd of Record)

BDL April 1
PVD April 8
BOS April 8
ORH April 11

First Average 70 degree high temp (Pd of Record)

BDL May 10
PVD May 20
BOS May 27
ORH May 29




LONG TERM...Sipprell
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