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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
952 am EDT Sat Aug 17 2019

Synopsis...
mainly dry, seasonable conditions continue today, with a chance
for showers and an isolated thunderstorm north and west. Humid,
hot conditions return Sunday, with an increasing risk for some
showers and thunderstorms. These conditions continue through
midweek, when a cold front will sweep through. Drier and not as
warm late next week.

&&

Near term /until 6 PM this evening/...
950 am update...

Low clouds and patchy coastal fog persists across southern New England this
morning. High pres east of new eng with moist low level southeast flow
in place will result in slow improvement through the afternoon.
Expect partial sunshine developing in the interior, but clouds
may hang tough near the coast for much of the day. Temps should
reach 80-85 in the CT valley, and 75-80 across much of the rest
of sne, except a bit cooler along the immediate coast.

A few showers have developed across coastal CT and Li sound
where MUCAPES up to 500 j/kg. May see a brief shower/T-storm
through midday across SW Rhode Island. Otherwise, partial sunshine will
help to generate marginal instability this afternoon with CAPES
1000-1500 j/kg, mainly across the interior. Mid level shortwave
approaches Lake Ontario toward evening so best synoptic forcing
remains to the west and mid level lapse rates are poor so only
expect isolated to widely scattered showers/T-storms this
afternoon, mainly central/western Massachusetts into north CT.

&&

Short term /6 PM this evening through 6 PM Sunday/...
as of 300 am...

Models indicate a weak shortwave will zip across northern New
England overnight. Despite the loss of daytime heating, the
southern tail of that piece of energy will be close enough to
keep the threat of showers or a thunderstorm going through the
first half of the overnight -- especially for areas along and
north of the Mass Pike. In addition, the shortwave will help to
produce a decent amount of shear, with 0-6km shear progged to be
30-35kts in that area. That suggests the potential for some
organization so perhaps we'll see a strong storm during the
evening.

Otherwise across the eastern half of the region, all guidance
suggests a return of the low clouds and even better chances of
widespread fog, much of it could be rather dense.

Temperatures will only drop off to the mid 60s to low 70s in
urban areas, with dewpoints still running high -- so it will be
again muggy.

Sunday we'll see southwest flow get deeper, with even more
moisture pushing into the area. Precipitable water values will
be approaching 2" by afternoon. Models are also indicating
additional shortwave energy coming through at some point in the
day. GFS has a single stronger wave, while the NAM is a bit
disorganized with several weaker disturbances. Net result is the
same however, that we should see scattered showers and a few
T-storms develop. Primary area would be central and western Massachusetts
and northern CT. Lesser chances across southeast Massachusetts and the
cape/islands as low level southwest flow off the water will keep
things stable. Don't see indications of strong/organized
convection, but perhaps more Florida-like pulse type storms.
With the high moisture values, brief downpours would be the
primary threat.

Temperatures should be a few degrees warmer as 925mb
temperatures are in the 21-24c range. Given full sun, we would
be talking about surface temperatures pushing 90f. However there
should be a good deal of clouds, so I stuck a little bit toward
some of the "cooler" guidance. Lots of mid 80s for highs (cooler
along the coast)

&&

Long term /Sunday night through Friday/...
17/00z guidance remains in rather good agreement with the
overall synoptic pattern through the end of next week. With a
dominant ridge across the southern USA, the northern tier
remains under the influence of a decent mid level flow. This
mid level flow will steer a series of shortwaves in our
direction through mid week. While we have high confidence these
waves will pass nearby, the timing remains more uncertain. Will
continue to favor a consensus approach, with a bias toward
typical convective climatology for our region.

A cold front will start to approach our region Tuesday, but is
unlikely to get enough push to completely cross southern New
England until sometime Thursday. This will be the general
period of greatest risk for any showers and thunderstorms.

High pressure with drier weather expected for next Friday.

Until this front crosses our region, it should remain very warm,
if not hot, and very humid. Dewpoints should approach 70
degrees, raising the possibility of local downpours where it
does rain. With temperatures around 90 degrees early next week,
we may need heat advisories for a time.

&&

Aviation /14z Saturday through Wednesday/...
forecaster confidence levels...

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

Short term /through Sunday/...moderate confidence.

Low ceilings will be slow to lift/dissipate, so VFR conditions
aren't expected until 17z or so in most areas. MVFR ceilings
with local IFR will likely remain all day along/off the South
Coast of Massachusetts.

All available guidance indicates Saturday night has a higher
probability of seeing widespread IFR, not only ceilings but
visibility as stratus and fog is expected cover much of eastern
Massachusetts and RI, especially after 02z or so.

There is a small chance for a few showers or a thunderstorm
across northern CT and western Massachusetts late this afternoon, with the
chances increasing slightly Saturday night, and have included
vcsh for baf and bdl tafs.

Kbos terminal...honestly, the easiest aspect of the forecast are
winds, which will remain 10kts or less from 110-130 degrees.
Ceilings expected to drop under 1000ft through 12z or so, but
might stay a bit higher. Visibility forecast is low confidence
through 12z. More confident for IFR visibilities Saturday night.

Kbdl terminal...overall moderate confidence in taf.

Outlook /Sunday night through Wednesday/...moderate confidence.

Sunday night: mainly VFR, with local MVFR possible. Chance
rain showers with isolated thunderstorms and rain. Patchy br.

Monday through Monday night: VFR. Slight chance rain showers with
isolated thunderstorms and rain.

Tuesday through wednesday: VFR. Chance rain showers with isolated thunderstorms and rain.

&&

Marine...
forecaster confidence levels...

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

Short term /through Sunday/...high confidence.

Primary marine concern will be areas of fog. Fog today will be
primarily concentrated off the South Coast and south of Cape Cod
and around the islands. Most should diminish during the mid-day,
but some areas will persist. The fog will redevelop Saturday
night, and is expected to stretch even up the East Coast of
Massachusetts. Once again on Sunday, some fog will persist much of the day
offshore. Visibilities will be reduced to less than 1 mile in
the fog. Winds and seas aren't expected to be much of an issue.
Potential for a bump up in wave heights late this weekend and
into next week as we may see a short period southerly swell
develop due to several weak low pressure systems develop off the
North Carolina coast and move out to sea.

Outlook /Sunday night through Wednesday/...moderate confidence.

Sunday night through monday: winds less than 25 kt. Seas
locally approaching 5 ft. Slight chance of rain showers. Patchy
fog.

Monday night: winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

Tuesday through Tuesday night: winds less than 25 kt. Seas
locally approaching 5 ft. Chance of rain showers with isolated
thunderstorms.

Wednesday: winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers with isolated thunderstorms.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...Belk/Nash

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