NWS Technical Forecast Discussion

000
FXUS61 KBOX 101354
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
954 AM EDT Mon May 10 2021

.SYNOPSIS...
Low pressure east of New England that brought a soaking rain
last night, continues to move out to sea with dry weather
overspreading the region today along with peeks of sunshine.
Other than a few isolated showers Tuesday, but much of this
week will be dry with moderating temperatures. Next potential
shot for rain showers is late this week into this weekend, but
by no means a washout.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...

10 am update...

Short wave ridging advecting across the region and resulting in
dry weather along with clouds breaking for a few peeks of
sunshine. Expecting this trend to continue thru this afternoon.
Temps aloft only +2C at 850 mb and +6C at 925 mb, supportive of
highs only rising into the upper 50s and lower 60s. Thus, cooler
than normal with avg high this time of year is 65-70. Light NNE
winds will become NNW this afternoon, helping to maintain dry
weather along with breaks in the overcast.


&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Not much change to the overall pattern tonight into Tuesday. Low
pressure continues to move away, but a mid level trough and cold
pool remain to our north. Mid level lapse rates are rather
steep for our region, over 6.5C/km. While this should be more
than enough lift to support showers, most of the guidance
indicates too much dry air to generate more than some clouds
across our region. This will need to be watched with later
forecasts. The greatest risk for showers should be across
northern New England.

Below normal temperatures continue, although there should be
more sunshine Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Highlights...

* One more day of slightly cooler than normal temperatures then
  warming up into the upper 60s near 70 Thu-Sun

* Dry through at least Thursday. Rain and thunderstorm chances
  return around Friday/Saturday but confidence is low

Details...

Tuesday night through Thursday...

A bit cooler Tuesday night thanks to a transient lobe of colder
air aloft. 850 mb temps in the -3 to -4 C range briefly move
overhead, and with clear to partly cloudy skies we should get
down near 40 in most locations; upper 30s for the slopes of the
Berkshires.

Wednesday temps will rebound quickly as the mid level trough
axis lifts out and heights begin to rise. At the surface the low
is removed even further into the maritimes and high pressure
from the Great Lakes builds. Together these will bring dry and
pleasant weather, if a bit gusty thanks to the lingering tighter
pressure gradient. Expect gusts up to 20 to 25 mph. We will deal
with one more day of near to below normal temperatures in the
low to mid 60s. By Thursday the warm up begins in earnest as the
airmass moderates under the building ridge. 850 mb temps surge
+5C, and with very efficient mixing surface temperatures should
reach the upper 60s, even low 70s in the Connecticut River and
Merrimack valleys.

Friday through the weekended...

We will start with the good news: the warmer weather is not
going anywhere. Confidence is high that this airmass and the
resultant upper 60s/low 70s at the surface sticks around through
at least Sunday. On the other hand, confidence in precipitation
timing is lower. It does not look like a washout and PWATs
do not even get over 0.75 inches during the forecast period,
but some showers are possible each day, especially in the
afternoon/evening each day as diurnal heating increases
instability beneath a broad upper trough. This instability also
means the chance of thunderstorms each afternoon. Stay tuned.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels.

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

14Z update...high confidence for any lingering MVFR cigs will
trend into the VFR category this afternoon. Dry weather prevails
along with light NNE winds trending to NNW. Earlier discussion
below.

===============================================================

Tonight and Tuesday...High confidence.

VFR with mid to high cloud cover diminishing. Winds out of the W
at 5-10 kts.

KBOS TAF...High confidence. Afternoon seabreeze likely.

KBDL TAF...High confidence in trends, moderate confidence in
timing.

Outlook /Tuesday Night through Friday/...

Tuesday Night through Wednesday: VFR. Breezy.

Wednesday Night through Thursday Night: VFR.

Friday: VFR. Slight chance SHRA.

&&

.MARINE...
Low pressure moves away from the coastal waters today. Rough
seas expected across the southern outer coastal waters. Some
gusts up to 30 kt possible this morning. Reduced visibility in
rain and fog this morning. Improving visibility late this
morning into this afternoon. Local seabreezes this afternoon.
Westerly flow becomes more dominant tonight into Tuesday, but
should remain less than 20 kt through Tuesday morning. A few
gusts up to 25 kt possible Tuesday afternoon. Small Craft
Advisories extended into Tuesday mainly for seas. Highest seas
south and east of Nantucket.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft.

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

Thursday through Friday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Belk/BW
NEAR TERM...Belk/BL/BW
SHORT TERM...Belk
LONG TERM...BW
AVIATION...Belk/Nocera/BW
MARINE...Belk/BW

NWS BOX Office Area Forecast Discussion

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