NWS Technical Forecast Discussion

FXUS61 KBOX 300217

Area Forecast Discussion
National Weather Service Taunton MA
1017 PM EDT Mon May 29 2017

Weak high pres will build across the region Wednesday bringing
dry weather but temperatures remaining below normal. An
approaching cold front may bring a few strong thunderstorms to
the northwest of a Boston to Providence corridor late Wednesday
afternoon and evening. Dry and seasonable weather follows
Thursday, but unsettled weather with showers at times may return
Friday into early next week but plenty hours of dry weather
will be mixed in too.



Only minor tweaks to the forecast this evening. Continuing to
monitor development of fog. Low levels remain quite humid, so
would not be surprised for areas of fog to develop just prior to

Temperatures not expected to change much, but made some tweaks
to bring the forecast back in line with observed trends.

Previous Discussion...

The last of the showers were exiting the coast early this
evening along with the shortwave/deeper moisture. However, low
level moisture will remain trapped beneath the inversion. This
will allow low clouds to persist and some patchy fog overnight.
There may even be some spotty drizzle across eastern New
England. Not much change in temps tonight with mins mostly in
the upper 40s to the lower 50s.



Mid level trof moves into the Gt Lakes with SW flow aloft
across New Eng. High pres will slowly drift offshore but SNE
will remain under marine influence with onshore winds which will
keep temps cooler than normal. In addition, expect clouds to
linger across the region, especially in the west where low level
moisture is more prevalent. Some sunshine may develop in in the
afternoon across eastern New Eng where low levels dry out a
bit. Highs mid/upper 60s but cooler along the coast.

Models show decent instability axis developing across NY state
in the afternoon which will lead to some convection developing
to the west. No surface instability is forecast across New Eng
due to marine influence, but instability parameters indicate
some elevated instability moving into the west in the afternoon.
Low risk of a few showers across western MA late afternoon,
otherwise dry conditions.

Tuesday night...

As mid level trof moves east across the Gt Lakes, low level
theta-e ridge moves into SNE. Still no surface instability, but
expect a period of showers and isolated t-storms, especially
interior as weakening convection from the west moves into the
region, supported by deepening column moisture and elevated
instability axis with subzero SWI and TT around 50. Mild night
with lows in the low/mid 50s.



* A few severe thunderstorms possible late Wed afternoon and
  evening mainly northwest of the Boston to Providence corridor

* Dry and nice weather on tap for Thu

* Periods of showers possible at times Fri into early next week but
  timing uncertain and plenty hours of dry weather expected too

* Seasonable temps likely Wed into Sat but perhaps a return to
  unseasonably cool weather next Sun/Mon



The main concern will revolve around convective/severe weather
potential Wednesday afternoon and evening.  As is typically the case
in southern New England, plenty of uncertainty at this point but
there are certainly some ingredients there that need to be watched.
Will break things down a bit more below.

A shortwave and bulk of its scattered precipitation will likely have
lifted east of the region by mid morning Wed.  The result will be a
period of subsidence with mainly dry weather into mid afternoon Wed.
By late Wed afternoon and evening a potent shortwave/cold pool aloft
will be approaching from the west. 500T drop to around -19C
resulting in relatively steep mid level lapse rates between 6.5C and
7C/KM. 0 to 6 km shear looks impressive between 40 and 50 knots.

With all that said, the biggest uncertainty is the amount of surface
heating that we receive, as model cross sections do indicate the
potential for lingering low clouds.  If some partial sunshine
develops and high temps can reach the lower to middle 70s with
dewpoints in the 50s to near 60, surface instability should easily
exceed 1000 j/kg.

So in a nutshell, the biggest uncertainty remains do we receive
enough heating to realize the potential instability/wind fields.  If
so, the risk for a few severe thunderstorms would exist. While
locally strong damaging wind gusts would be possible, the potential
for severe hail would also exist given the anomalous cold pool
aloft. The main risk is to the northwest of the Boston to Providence
corridor, particularly across western and northern MA closer to the
better dynamics and timing for that matter.


A nice day looks to be in the cards behind Wednesday`s cold front.
Plenty of early June sunshine and a dry airmass in place should
allow for highs to reach into the lower to middle 70s in
many locations with comfortable humidity levels.

Friday through Monday...

The overall weather pattern will feature an upper trough over
eastern Canada and into New England with below normal height fields.
This will suppress summertime heat and humidity well to our south.
Seasonable temps likely Fri/Sat, but some indications that a high
over eastern Canada may result in another round of unseasonably cool
temps next Sun/Mon but too far out to say for sure.  The upper
trough nearby will make our region prone to periods of showers at
times, but also extended intervals of dry weather will also occur.
Timing is highly uncertain and it is really impossible to give much
more information in this time range.


Forecaster Confidence Levels...

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

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

Through tonight...MVFR/IFR conditions will continue with the
lower conditions across eastern New England. Patchy LIFR fog
developing tonight, especially near the coast where there also
may be some drizzle.

Tuesday...MVFR/IFR cigs will lift to VFR/MVFR in the afternoon.
A few showers or an isold t-storm possible across western MA by
late afternoon.

Tuesday night...More MVFR/IFR conditions with sct showers and
isold t-storms moving across the region.

KBOS TAF...Moderate confidence in TAF.

KBDL TAF...Moderate confidence in TAF.

Outlook /Wednesday through Saturday/...Moderate confidence.

Wednesday...Low to moderate confidence.  MVFR-IFR conditions early
may improve to MVFR-VFR by afternoon.  A few strong thunderstorms
possible late Wed afternoon/evening mainly northwest of a Boston to
Providence corridor.

Thursday...Moderate to high confidence in mainly VFR conditions.

Friday and Saturday...Low to moderate confidence.  A period of MVFR-
IFR conditions possible in some low clouds and some showers, but
timing uncertain.  Greatest risk for lower cigs/vsbys late Fri into
early Sat.


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.

Through tonight...Extended the Small Craft Advisory across the
outer RI coastal waters for a couple more hours as latest buoy
reports still have seas lingering around 5 ft. Will continue to
evaluate the need to extend it further in time. Seas still
expected to subside later tonight.

Tuesday...SE flow with speeds increasing to 15 kt in the
afternoon. Vsbys may be reduced in the morning due to fog, but
improving by afternoon.

Tuesday night...Southerly flow with speeds mostly 15 kt or less
but a few gusts to 20 kt possible across NE MA waters. Sct
showers developing with low risk for an isold t-storm. Patchy
fog may reduce vsbys.

Outlook /Wednesday through Saturday/...Moderate confidence.

Wednesday through Saturday...

Wednesday and Thursday...Moderate to high confidence.  Pressure
gradient should be weak enough to keep winds and seas below small
craft advisory thresholds.  Main concern for mariners will be for
some fog, especially across our southern waters during the late
night/early morning hours.  Also, a few strong thunderstorms are
possible across our adjacent northeast MA waters late Wed/Wed

Friday and Saturday...Moderate confidence.  Persistent long
southwest wind ahead of a cold front may result in seas building to
between 4 and 7 feet across our southern waters later Fri into Sat.
Some showers and fog patches also may impact mariners at times.


Expecting about a 0.5 ft surge for the high tide tonight but
astronomical tides are lower than previous nights and minimal
wave action so do not expect any issues.


MARINE...Small Craft Advisory for hazardous seas until midnight EDT
     tonight for ANZ256.


NEAR TERM...Belk/KJC/Frank

NWS BOX Office Area Forecast Discussion

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