Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 251956
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
356 PM EDT Wed Apr 25 2018

.SYNOPSIS...

Low pressure will push northeast from the mid Atlantic coast,
crossing the region tonight. This will bring locally heavy
downpours may result in some brief poor drainage street flooding
and possibly an isolated thunderstorm or two. Seasonably mild
temperatures will follow for the remainder of the week with
mainly dry weather other than a period of showers Friday. A cool
down will occur Saturday night and Sunday, but this will be
short lived as unseasonably warm temperatures are in store for
the region by the middle of next week.

&&

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

*** Locally heavy rainfall and isolated thunderstorms possible
during the evening commute ***

400 PM Update...

Surface low still remains across the DELMARVA late this afternoon as
upper level shortwave pushes towards the region from the north and
west. This current batch of precip is colocated with the nose of the
LLJ and high theta-e plume. This region also has strong omega in the
mid-levels and is associated with 3-4 STD above normal moisture
transport. Feel that along the I-95 corridor including the BOS to
PVD metro and points eastward will see the highest amount of QPF.
Especially as latest radar trends continue to redevelop precip in
this region over the past few hours. Overall a slow evening commute
looks to be in place for this evening.

Biggest impact will be widespread heavy rainfall with some gusty
winds and heavy rainfall. Nuisance and poor drainage urban flooding
looks to be the main issue with the ongoing precip. Cannot rule out
a flood adv across a portion of the region, and slight rises in some
of the area streams. Wind gusts across the area have already
increased across the south coast with WST gusting to 31 kts and FMH
around 23 kts. Expect the wind gusts to continue over the next few
hours across the south coast into the coastal plain which is where
the strong LLJ is located.

Lightning is still sparse across the region, but cannot rule it out
for late this afternoon into the evening.  Latest RAP guidance
continues to show MU Cape values increasing and showalters dropping
below 0. Best area is across RI and southeast MA, which could
increase QPF amounts to above 2 inches.

Bulk of the precip will be moving through with a dry slot starting
to push into from the south. This is noticed via the drop in the K
values across NJ. Despite the clearing that will come towards the
late afternoon, low level moisture is still quite saturated so
cannot rule out fog and drizzle potential.

Tonight...

Surface low still in the vicinity with digging upper level trough
approaching from the west. The evening will start off with a dry
weather trend as mid-level dry slot pushes through. Still quite
saturated as the low levels so fog and drizzle may be an issue. As
the upper level low rotates through, the mid and upper levels begin
to saturated and there could be a redevelopment in strong showers
moving through SNE. Best timing is between 3-9z as strong mid-level
omega pushes through. The east coast of MA has the best shot of
seeing the strong downpours. Still cannot rule out the thunder
potential as RAP data has several hundred julep of MUCape and
showalters dropping below 0C. Heavy rainfall will be the main threat
as well as gusty winds, especially along the passing cold front.

Ahead of the passage of the front, patchy dense fog is possible
across the region. This is due to the saturated low level moisture
as well as weak pressure gradient ahead of the FROPA. Both the HRRR-
TL and the NARRE indicated high probs that visibilities will drop
at or below a mile, with some potential for less than 1/4 mi.
Locations along Long Island are starting to drop below 1/2 mile, but
still see coastal above 1-2 miles. So confidence isn`t quite high to
issue a dense fog adv at this time.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...

Thursday...

Upper level low will begin to pivot out of the region during the day
on Thursday. Still some lingering moisture in the mid-levels with
steep lapse rates which will yield to sct showers in the morning.
Deep layer moisture will push northward towards Maine resulting in
low precip chances by the afternoon hours. Still expect sct to
broken clouds but overall trend will be dry by sunset.

Gusty WNW flow expected along as the mid level shortwave passes
through. Steep lapse rates and downsloping flow will result in good
mixing to near 850mb. Expect wind gusts to near 25-30 MPH by the
afternoon as highs reach into the mid to upper 60s. Overall a
pleasant Spring day.


&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...

Highlights...

* A period of showers Fri afternoon/evening
* Scattered showers Sat, mainly interior
* Dry and cooler Sun then seasonably mild Mon
* Dry with a significant warming trend Tue/Wed

Friday...

Southern stream shortwave will be lifting northward into SNE during
the afternoon/evening. Shortwave is deamplifying but modest low
level jet and PWAT plume will bring a period of showers to much of
SNE, especially afternoon into early evening. There may be a focus
for brief heavy showers and an isold t-storm across RI and SE MA
where some elevated instability is present along the nose of the low
level jet. Highs will range from the upper 50s to lower 60s.

Saturday...

Next mid level shortwave and cold front approaches from the west.
This will lead to an increasing risk of sct showers, mainly across
central/western MA and northern CT during the afternoon. Otherwise,
expect pt-mosunny skies in the coastal plain with increasing
afternoon clouds in western New Eng. There is a low risk a few
showers could move into eastern New Eng Sat night as the front moves
through. With pre-frontal SW flow, milder temps expected Sat,
reaching mid 60s to near 70, except cooler along the south coast.

Sunday...

Cooler post-frontal airmass as deep trough settles over the
northeast and 850 mb temps cool to around -4C. Temps will remain
mostly in the 50s, with a few locations topping out near 60 in RI
and eastern MA. Chilly night Sun night with lows in the 30s but
close to 30 across the typical colder locations.  Frost headlines
may be needed where growing season has started, with greatest risk
across northern CT.

Monday through Wednesday...

A pattern change will occur next week as deep trough lifts out Mon
and is replaced by building heights and mid level ridging through
the middle of the week. Monday will be the transition day with
seasonably mild temps after a cold start to the day. Then warming
mid level temps will result in temps reaching into the 70s Tue with
potential for some lower 80s Wed. But SW flow will result in cooler
temps along the south coast.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...Moderate to High confidence.

Before 00z...IFR this afternoon with LIFR conditions possible.
Bands of +RA developing across central and eastern areas this
afternoon. Isolated thunder late. Low risk for 35 kt gusts
across the south coastal terminals. Otherwise strong LLWS
through much of the day.

Tonight...IFR-LIFR conditions. -SHRA across the region
overnight. Still cannot rule out isolated TSRA through around
midnight, then moving offshore. Low CIGS and areas of fog will
linger across the terminals much of the night.

Thursday...Improving conditions to VFR with mix of MVFR north of
the Pike during the day. Gusty westerly winds between 20-30 kts
by the afternoon.

KBOS Terminal...Moderate confidence in TAF. IFR conditions in
rain and lower ceilings through the evening push. Low risk for
TSRA from 21Z-04Z.

KBDL Terminal...Moderate confidence in TAF. IFR conditions in
rain and lower ceilings through the evening push. Dense fog is
possible during the overnight.


Outlook /Thursday Night through Monday/...Moderate to High

Thursday Night: VFR. Breezy.

Friday: MVFR/IFR conditions possible. Breezy. SHRA likely.

Friday Night: MVFR/IFR conditions possible. Breezy. Chance
SHRA.

Saturday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.

Saturday Night: Mainly VFR, with local MVFR possible.

Sunday through Sunday Night: VFR. Breezy.

Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...

Tonight...Moderate confidence. Small Craft Advisories for all
waters except Boston Harbor. Expect E-SE winds gusting up to 30
kt. Low risk for a few 35 knot gusts early in the evening across
the southeast waters. Rough seas up to 10 to 12 ft. Rain
showers, heavy at times along with areas of fog and isolated
thunderstorms. Visibility locally below 1 nm at times across
the southern waters tonight.

Thursday...Moderate to high confidence.
Small craft conditions continue as winds shift to W, though
winds diminish during the day. May see gusts up to 25-30 kt
through midday. Seas remain at 5 feet or greater through the
day across the open waters as well as the south bays and sounds.

Outlook /Thursday Night through Monday/...Moderate to High

Thursday Night: Winds less than 25 kt. Rough seas up to 9 ft.

Friday: Winds less than 25 kt. Seas up to 5 ft. Rain showers
likely.

Friday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain showers.

Saturday through Sunday Night: Winds less than 25 kt. Seas up
to 5 ft.

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

&&

.EQUIPMENT...
The NOAA Weather Radio transmitter serving Providence is out of
service due to phone line problems. The phone company has
prioritized the issues and is working to get the weather
broadcast back on the air as soon as possible. The transmitter
serving Hyannis is back in service.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT Thursday for ANZ232>234-
     251.
     Small Craft Advisory until 3 AM EDT Thursday for ANZ231.
     Small Craft Advisory until 11 AM EDT Thursday for ANZ236.
     Small Craft Advisory until 8 AM EDT Friday for ANZ235-237-250-
     254>256.

&&

$$
SYNOPSIS...KJC/Dunten
NEAR TERM...Dunten
SHORT TERM...Dunten
LONG TERM...KJC
AVIATION...KJC/Dunten
MARINE...KJC/Dunten
EQUIPMENT...Staff



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