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207
FXUS61 KBOX 201948
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
348 PM EDT Mon May 20 2019

.SYNOPSIS...

Warm, summer-like day ahead of a sweeping cold front this afternoon
into evening with isolated to scattered showers and thunderstorms,
some of which may be strong to severe. Dry, cool air building in
overnight. Seasonable weather with windy conditions Tuesday. Dry
weather continues Wednesday into Thursday with less wind, then
a period of showers will likely impact the region sometime late
Thursday into early Friday. Summer like warmth may return by the
end of next weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

4 pm update ...

*/ Highlights ...

 - Isolated to scattered showers and thunderstorms
 - Strong to severe threat expected to be very isolated, if any
 - Biggest threat of strong to damaging winds with any strong to severe
 - Exiting this evening

*/ Discussion ...

Now (4 pm update) ...

Isolated to scattered showers have developed, struggling to mature
further into thunderstorms with decent reflectivity above -10C given
marginal lapse rates aloft and pronounced dry air above H7. With any
updrafts, more than likely they are being choked off, keeping activity
low-topped. Despite the instability and effective shear, confident
that we`ll not see widespread strong to severe, rather very isolated.
Perhaps lift along the sweeping cold front will push storms higher,
in an environment of SW-NE uni-directional shear yielding a potential
strong to severe wind threat along with heavy rain, frequent lightning.
But low confidence. HREF and especially NSSL WRF have the right trends
in mind with isolated to scattered activity, some of it multi-cellular
mini-clusters given the environment and anticipated pulsing storm-mode.

Will hold with SEVERE THUNDERSTORM WATCH 198 for the time-being, see
if something gets going. Likely a pulse will go up here and there,
then come down, and with the model forecast inverted-V soundings,
could see some localized wind damage.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...

Tuesday into Tuesday night ...

Cool, dry airmass in place. Scattered cloud decks developing as
the boundary layer becomes well mixed with highs getting up to
around 70 degrees. Momentum mix down along with drier air,
looking at dewpoints in the 30s and NW wind gusts up around 20
to 25 mph. Should winds subside during the evening and overnight
periods, then perhaps radiational cooling could proceed,
especially over N/W MA and CT sheltered valleys allowing
temperatures to drop into the upper 30s.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

Highlights...

* Dry and pleasant Wed into Thu with less wind
* A period of showers possible late Thu into early Fri
* Summer like warmth may return next Sunday-Monday

Details...

Wednesday...

Pleasant day Wednesday as surface high pressure moves in with a
building ridge at the mid levels. Winds come down from Tuesday and
should be light with a relaxed pressure gradient. Plenty of sun to
be had, and high temperatures expected to climb into the upper 60s.

Thursday and Friday...

Thursday will be mostly dry as the ridge axis crosses southern New
England, but our next shot of rain comes late in the day through the
overnight hours. A shortwave riding over the ridge moves through
Thursday night bringing increased moisture in the form of clouds
during the day Thursday, and increasing risk of showers Thursday
evening through at least early Friday. Ahead of the low, PWATs top
1.5" with plenty of low level forcing given a 35-40kt LLJ at 925mb.
System moves off to the southeast and rain comes to an end later
Friday. Placement of the low over SNE or just to the east will bring
easterly winds Friday and cooler than average temps in the low 60s
(50s along the coast).

Saturday through Monday...

Behind Friday`s departing system we see building high pressure and
the return of mid level ridging. This should lead to a dry and sunny
Saturday before a low over QC swings a cold front through Saturday
night into Sunday bringing another chance of rain. Uncertainty
increases for the far extended forecast, but trends are toward a
warmer and mostly dry forecast late Sunday into Monday under
building high pressure. Temps look to reach into the 70s each day.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...

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.

Today and Tonight...
Low-end VFR SCT-BKN CIGs. FEW-SCT SHRA, lower threat TSRA, so will
not make any mention and keep with VCSH. With any -RA/RA, localized
MVFR 010-030 possible. Otherwise, winds around 20015G20KT. Improving
1z-6z especially along the S/SE-coast. W/NW winds at around 28015G25KT,
strongest along the high terrain.

Tuesday into Tuesday night ...
VFR. SCT 040. NW sustained 15 to 20 kts, highest gusts around 30 kts,
strongest along the high terrain. Winds diminishing evening and
overnight.

KBOS Terminal...
FEW-SCT SHRA threat, lower risk TSRA through 1z.

KBDL Terminal...
FEW-SCT SHRA threat, lower risk TSRA through 0z.

Outlook /Wednesday through Saturday/...

Wednesday: VFR. Breezy.

Wednesday Night: VFR.

Thursday: VFR. Breezy. Chance SHRA.

Thursday Night: Mainly VFR, with local IFR possible. Breezy.
Chance SHRA, isolated TSRA.

Friday: Mainly VFR, with local IFR possible. Windy with local
gusts up to 30 kt. Slight chance SHRA.

Friday Night: VFR.

Saturday: VFR. Chance SHRA.

&&

.MARINE...

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.

4 pm update ...

Today...
SW winds sustained around 15 kts with gusts around 20 kts. Seas of
3 to 6 feet. Isolated to scattered showers and thunderstorms
approaching the waters towards evening. Keep with present SMALL
CRAFT headlines, dropping Boston Harbor and Massachusetts Bay
with the expectation of remaining just below criteria.

Tonight...
Isolated to scattered showers and thunderstorms along a sweeping
cold front. Some could be strong, especially for the E-waters off
of MA. Frequent lightning. SW winds continuing with sustained around
15 kts, gusts around 20 kts, backing out of the NW behind the cold
front pushing through this evening. Seas around 3 to 6 feet. Maybe
some renewed fog along the S/SE coast before the cold front sweeps
through.

Tuesday into Tuesday night ...
Breezy NW winds. Gusts up to 30 kts possible over the E waters.
Can`t rule out attendant wave heights 5-7 feet.

Outlook /Wednesday through Saturday/...

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

Wednesday Night: Winds less than 25 kt.

Thursday: Winds less than 25 kt. Chance of rain showers.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers, isolated thunderstorms.

Friday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of rough seas. Chance of rain showers.

Friday Night: Winds less than 25 kt. Local rough seas.

Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Tuesday for ANZ231>237-250.
     Small Craft Advisory until 8 AM EDT Wednesday for ANZ254>256.

&&

$$

SYNOPSIS...Sipprell/BW
NEAR TERM...Sipprell
SHORT TERM...Sipprell
LONG TERM...BW
AVIATION...Sipprell/BW
MARINE...Sipprell/BW