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Area forecast discussion
National Weather Service Taunton Massachusetts
350 PM EDT Fri Jun 23 2017

Synopsis...
mild, humid air continues into tonight out ahead of the
remnants of Cindy which will bring the threat of heavy rain and
possible flooding Saturday morning. A cold front will sweep the
remnants of Cindy out to sea through late Saturday, improving
overnight. Seasonably warm and less humid conditions Sunday
will be followed by cooler weather and few diurnally driven
showers/isolated thunderstorms Monday and Tuesday. A return to
summerlike warmth and humidity is expected by the end of the
work week.

&&

Near term /until midnight tonight/...

400 PM update...

Clearing skies early this afternoon has resulted in cape values
increasing to over 2000 j/kg. This combined with shear values of 30-
35 kts and low level lapse rates near 8 c/km has resulted in a few
scattered showers. Current dynamics and Storm Prediction Center meso-analysis indicates
that the main risk could be heavy rain and gusty winds. Skinny cape
and inverted v soundings would also indicate the potential for wet
microburst. While most of the region will remain dry this afternoon,
the risk for isolated showers will continue through the evening.
While risk is low, cannot rule out a quick spin-up as dewpoints are
in the 70s. However appears the better helicity and 0-1 km shear
will be southwest of the area. Something to watch over the next few
hours.

While it is difficult to pin where exactly and strong storm will
develop, believe the CT valley will be the area to watch over the
next few hours, esp with the help of the terrain.

This evening...

Warm, moist southwest flow will continue across the region this
evening into the overnight hours. Precipitable water values are increasing to 2
inches as tropical airmass continues to pool into southern New
England. Biggest question is shower potential for this evening.
Increasing low level jet at 925 mb as well as lingering instability should be
enough will to trigger scattered showers and thunderstorms across
the region. This is support in the hi-res guidance and the latest
hrrr.

Otherwise a muggy evening is on tap for the region as dewpoints
remaining in the 70s. Will have to watch for fog develop along the
South Coast.

&&

Short term /midnight through 6 PM Saturday/...

After midnight into Saturday...

*** increasing localized flood potential for southern New England ***

Active weather pattern for tonight and for the first half of tomorrow
as southern New England remains in the warm sector for this period.
Overnight lows will remain mild, dropping into the upper 60s to low
70s. This may result in another round of fog and stratus with the
highest confidence across the South Coast once again. May need to
watch for a possible dense fog advisory as surface dewpoints will
be in the 70s. Muggy to start the day tomorrow but depending on how
quickly the front will push through, the later half of the day will
begin to improve. Highs will remain in the mid 80s.

Biggest focus is on precipitation potential for this time period.
Increasing moisture will begin to pool into the area with precipitable water values
increasing to above 2.5 inches by tonight. This tropical moisture
from Cindy will push precipitable water near 3 to 4 Standard above normal. In fact,
moisture flux values at 850 mb during this timeframe is nearing
4 Standard above normal. Thus within any heavy shower, the potential
for flooding rains is possible.

Models are struggling with the placement of the axis of heavy
precipitation as there are several features to note. Aside from the
approaching front out west, a low level jet will be across the southeast
portion of the area. However, the higher instability values will be
across the western half of the area. If both of these features
could align, then we could see widespread heavy rainfall. But
because there is some separation, believe that the threat is more
localized. Again the heavy rainfall axis amongst the guidance are
in different locations, but there is agreement that the potential
for over 1.5 to 2 inches. If this falls in just a few hours, then
flash flooding is possible. Best timing for this to occur will be
after midnight and into Saturday morning.

Cold front will begin to sweep through the region on Saturday.
The latest hi-res guidance is a lot slower than synoptic models so
have blended the forecast down the middle. More widespread showers
and embedded thunderstorms are anticipated along the frontal
passage. Convection along the front continues to be a possibility
especially across eastern Massachusetts during the late morning hours. Cape
values will be near 1000 j/kg with 40 kts of 0-6 km shear. The
caveat is poor lapse rates and the bulk of the moisture will be
pushing offshore. One thing to watch for is the potential for a
quick spin-up thanks to the tropical airmass with 70f dewpoints and
lower LCLs. Hodographs do show some helicity and good 0-1 km shear.
The frontal system should push through by Saturday afternoon
resulting in clearing skies and drier air as westerly flow takes
hold.

&&

Long term /Saturday night through Friday/...

Highlights...

* seasonably warm/less humid sun with a spot shower/T-storm possible
* a few showers/iso T-storms possible Mon/Tue but not a washout
* below normal temps Mon/Tue return to summerlike readings Thu/Fri

Details...

Saturday night...

Dry and a much less humid airmass will work into the region behind
saturday's cold front. This should allow low temps to fall into the
50s across many outlying locations, to between 60 and 65 in some of
the urban centers.

Sunday...

A pleasant end to the weekend across southern New England. 850
temps between +11c and +12c should allow highs to reach into the
lower to middle 80s in most locations, but dewpoints in the 50s will
make it feel much more comfortable outside. Mainly dry weather
anticipated, but approaching shortwave may be enough to trigger an
isolated shower/T-storm or two by mid-late afternoon across the
interior.

Monday and Tuesday...

Anomalous upper trough/cold pool aloft overhead will result in
slightly below normal temps with comfortable humidity levels. Highs
mainly in the 70s are expected both days. The cold pool
aloft/shortwave energy will result in the potential for a few
diurnally driven showers/isolated thunderstorms both days. Not
expecting a washout by any means, but the main risk for any activity
will be during the afternoon/early evening hours.

Wednesday...

Axis of upper trough will probably have shifted to the east of the
region. This should allow temps to warm a few more degrees than
Mon/Tue and result in mainly dry weather. However, if trough ends up
slower than currently expected there would be the risk for a few
more showers/isolated thunderstorms.

Thursday and Friday...

Upper trough lifts northeast of the region with rising height
fields. This should result in a warming trend for the end of the
work week, with a return to summerlike warmth and humidity.

&&

Aviation /20z Friday through Wednesday/...
forecaster confidence levels...

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

Short term /through Saturday/...moderate confidence.

Today...
VFR for most of the region with iso MVFR within any shower/tsra.
Stratus and fog will overspread the South Coast closer to
sunset.

Tonight into Saturday...
MVFR-LIFR cigs with MVFR-IFR vsbys with br/fg. Scattered rain showers/thunderstorms and rain
tonight approaching from the west, with more widespread
potential Saturday morning. Improving conditions from west to
east around midday ahead of a wind shift from the west. Prior to
the wind shift will continue to see SW winds with potential
gusts 25 to 30 kts low level wind shear possible for southeast coastal terminals as is
some embedded thunderstorms and rain. Improving towards evening to low-end VFR /
sky clear.

Kbos terminal...high confidence. VFR today with gusty SW winds
up to 25 kts, lower cigs into this evening with increasing
rain/thunder chances.

Kbdl terminal...VFR cigs today with blustery SW winds that will
lower into evening prior to onset of ra/+ra.

Outlook /Saturday night through Wednesday/...

Saturday night through Wednesday...high confidence. Mainly VFR
conditions other than a few mainly diurnally driven showers and
perhaps isolated T-storms.&&

Marine...
forecaster confidence levels...

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

Short term /through Saturday/...

SW winds continue to gust up to 25 to 30 kts through early
tomorrow prior to a cool frontal passage. Waves building around
5 to 7 feet on the waters as the remnants of Cindy are advected
NE across the waters around the morning hours. Prior to and
during this time, likely to be either a combination of low
clouds and fog with visibility down to a quarter mile or less
possible. Improving late Saturday as winds become westerly while
beginning to diminish along with wave action.

Outlook /Saturday night through Wednesday/...

Saturday night through Wednesday...moderate to high confidence.
Quiet boating weather overall during this time period. A few hours
of near shore lower 20 knot wind gusts and choppy seas are possible
on both sun and Mon afternoons.

&&

Tides/coastal flooding...
astronomical tides are rather high through this weekend during the
night time cycles. Boston has a 12.3 ft tide just before midnight
tonight, a 12.4 ft high tide around midnight Sat night and 12.2 ft
just after midnight Sun night. While, offshore winds are forecast
current conditions suggest a 0.4 surge which will result in
minor splashover. Thus will go ahead an issue a coastal flood
statement for tonight's high tide.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 3 PM EDT Saturday for anz231>234.
Small Craft Advisory until 9 PM EDT this evening for anz230-
236.
Small Craft Advisory until 8 PM EDT Saturday for anz235-237-
250-254>256.

&&

$$
Synopsis...Frank/dunten
near term...dunten
short term...dunten

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