Scientific Forecaster Discussion
fxus61 kbox 251948
Area forecast discussion
National Weather Service Taunton Massachusetts
348 PM EDT Thu may 25 2017
* near- and short-term updates only...
Low pressure and its attendant warm front will bring a steady
rain and drizzle to the region through tonight along with cool
northeast winds. The rain will be heavy at times tonight into
Friday morning as the low tracks across southern New England.
Big improvement to start of the Holiday weekend as weak high
pressure delivers dry weather with mild days and cool nights
both Saturday and Sunday. However by Sunday night and into
Monday another coastal low may bring the risk of showers,
although a washout is not expected.
Near term /until 6 am Friday morning/...
345 PM update...
- widespread light rain / drizzle
- moderate-heavy rain towards midnight into early morn Friday
- increasing onshore easterly winds, cooler air off waters
- this all prior to a warm front and low pressure sweeping over
S New England Friday morning
*/ latest discussion...
Into this evening...
Cool and damp. Continued broadscale, isentropic ascent, I.E., Over-
running, over the warm-moist conveyor belt beneath diffluence aloft
is lending to widespread light to moderate rain. The dry slot slowly
advancing as discerned via water vapor imagery, should see rain
change over to mainly drizzle. This as the low deepens across the
mid-Atlantic as it begins its transition from the mature to dying
phase as it begins to undergo occlusion. The increasing pressure
gradient resultant, already seeing an increasing onshore East-Draw of
cooler air north of the stalled surface warm front off the coast of New Jersey
and S of Long Island. That combined with the saturated atmosphere,
we are seeing temperatures cool to their respective wet-bulb giving
way to the development of areas of mist / fog. Temperatures mainly
steady through the remainder of today, in and around the low 50s.
Not very representative for late may.
Moderate to heavy rain expected with the possibility of a rumble of
thunder. Low occlusion sweeping NE across S New England overnight.
Crux of deep-layer synoptic forcing out ahead of the low through a
fairly moist profile well up to 300 mb beneath the left front quadrant
of the upper level cyclonic jet streak. Strong Omega forcing not out
of the question that will easily and efficiently wring out moisture,
rather the nature and magnitude of said moisture wrapping into the
occlusion, its associated precipitable waters / Theta-E. Confident
as to moisture pooling along the low to mid level warm front lifting
gradually north across the region. Conditionally unstable moist profile
aloft, and given strong Omega, can not rule out thunder. The system
itself is quick-moving, short duration, the bulk of the rain falling
around midnight into the 6a timeframe. But there's still spread,
even between the gefs and sref members, with the sref exhibiting
members with higher amounts up around 2.0 to 2.5 inches.
Quite an anomalous system with winter-like characteristics, taking
nothing for granted, and as such am leaning more towards the high-
res guidance as consensus of ensemble probabilities along with cips
analogs signal a low-prob of greater than 3-inches storm total rain-
fall over east/southeast Massachusetts and Rhode Island. Can not rule out an inch of rainfall in
the roughly 6-hour period noted earlier. Potential urban and poor
drainage issues, mainly inland as low tide proceeds after midnight
into morning along the shores. Not thinking any impact to the rivers
rather nuisance issues along area roadways, low-lying spots and
culverts notorious for having issues. Focusing on the I-95 corridor
and immediate roadways surrounding.
Short term /6 am Friday morning through Friday night/...
Scattered shower activity lingering within the wrapping comma-head
occlusion. Influx of cooler air rearward as the pressure gradient
tightens with the low lifting east with a weak ridge of high pressure
building from the W, will see a steepening boundary-layer profile
allowing for both moisture and momentum to mix out. So thinking bulk
of wet-weather activity will be early on, with the later-half mostly
dry as winds increase out of the northwest. Clouds breaking, more sunshine,
given the time of year and the fact that the low lacks a more pole-
Ward connection of colder air, with the cooler air an artifact of
being dragged down from aloft, should turn out near-seasonable with
highs around the mid to upper 60s, warmer SW CT while cooler NE Massachusetts.
Drying out. Occlusion continues to lift east out to sea. Still a north flow
on the backside with cooler air, the boundary layer remains well-
mixed beneath rising heights from the west and an inversion around 800 mb.
Some scattered to isolated shower activity initially, diminishing
through the overnight hours. Low clouds linger given boundary-layer
mixing and moisture pooling beneath the inversion. With the warm
warm blanket in place, keeping it mild with lows down into the upper
40s to low 50s.
Long term /Saturday through Thursday/...
* mainly dry weather W/mild days and cool nights Saturday and Sunday
* risk of rain returns Sun night into Monday
* seasonably warm Tue & Wed but low risk of scattered showers
Improving weather as closed mid level low over the Gulf of Maine
exits seaward and allows rising heights along with mid level
anticyclonic flow to move across New England. This will promote a
drying trend overnight. Temps will be seasonably cool with lows in
the upper 40s and low 50s.
West-northwest flow aloft with mid level mean ridge axis across the eastern
Great Lakes will provide dry weather and seasonable temps across
southern New England. Models do differ on cloud cover Sat with GFS
showing much more low level moisture. Given the west-northwest flow aloft
thinking at least partial sunshine will verify. This combined with
light winds will provide very pleasant conditions with highs 70-75
CT River Valley and 60s elsewhere. Weak pressure gradient will
support cooling afternoon seabreezes for the coastline.
Deep layer ridging lingers across the area promoting dry weather
much of the day. However model time sections and moisture profiles
indicate lots of clouds likely on Sunday. 00z deterministic and
ensemble guidance in good agreement that rain/showers associated
with upstream system should arrive into southern New England either
late in the day or after sunset. So as of now the bulk of the
daylight hours of Sunday appear dry, especially across Rhode Island and
eastern Massachusetts. Given the expected cloud cover highs should be a few
degs cooler than Saturday. Fortunately south-southeast winds should be fairly
light but will keep the immediate coastline cooler.
Weak coastal low may pass south of New England along with its precip
shield impacting the area. Doesn't look like a washout but enough
support to keep showers in the forecast. Somewhat cool with highs in
the 60s given cloud cover and light onshore winds.
Not as cool as parent low pressure over the Great Lakes provides
warmer southwest flow into New England. With the milder temperatures
comes the risk of scattered showers as mid level flow becomes
Aviation /20z Thursday through Tuesday/...
Forecaster confidence levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short term /through Friday night/...moderate confidence.
18z update...no major changes to the forecast. Minor tweaks to
account for trends. Otherwise, on track.
into midday -ra/rain transitioning to dz with increasingly lower
visibility with fog. Lowering cigs S to north with time towards IFR.
North/NE winds becoming more east/NE, gusty at times potentially as
high as 30-35 kts though thinking isolated. Mainly 20-25 kts.
IFR-LIFR cigs and vsbys. Rain/+ra potential mainly from 6-12z with
embedded thunderstorms and rain possible. East winds continue with mainly 20-25 kt
IFR/MVFR cigs with scattered-broken -shra, on and off through the day.
Conditions may improve to VFR across western terminals in the
late afternoon. Northwest winds for all terminals, becoming
gusty into the later half of the day.
rain showers dissipating while improving VFR. Northwest winds blustery
initially, relaxing. Cigs becoming broken to scattered.
IFR-LIFR through overnight. Winds a challenge. Strong easterly
sustained at first, becoming light overnight while turning
counter-clockwise NE to northwest with low passage. Closely watching
the 6-12z Friday timeframe for +ra potential and possible tsra,
whether there will be impacts to the am push. Adverse weather
may impact prior.
hold north winds funneling through the CT River Valley, turning northwest
with low pressure passage overnight. Fog/dz into evening, more rain
and possible +ra/thunderstorms and rain overnight 6-12z. IFR-LIFR, especially with
cigs through Friday morning.
Outlook /Saturday through Tuesday/...moderate confidence.
Saturday and Sunday daytime...
VFR. Light winds Sat with seabreezes at the coast. Winds Sunday
more from S-southeast direction at fairly light speeds.
cigs/vsbys trending to MVFR/IFR in showers. Winds from the
southeast, trending from the south Monday.
Forecaster confidence levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short term /through Friday night/...high confidence.
rain and fog, possible thunder. This as low pressure lifts North/East
across S New England ahead of which along a warm frontal boundary
east/NE winds will be sustained around 15 kts initially, becoming
somewhat light with low passage and beginning to turn N/NW. Seas
6 to 8 feet on the outer waters.
Friday into Friday night...
low pressure exiting behind which showers will linger as winds
will be initially blustery out of the northwest with sustained flow
around 15 kts, gradually diminishing with time as a weak ridge
of high pressure builds in from the west.
Outlook /Saturday through Tuesday/...
Saturday and Sunday...
Fairly light winds and tranquil seas as high pres crest over the
area. Dry weather and good vsby too.
Sunday night and Monday...
A series of weak lows may develop and pass south of New England,
near the 40n/70w benchmark.
Combination of a very high astronomical tide and onshore flow
will result in widespread minor coastal flooding tonight, mainly
for the east Massachusetts coast.
Persistent easterly flow around 15 mph will result in a surge of
0.8 to 1.0 feet along the east Massachusetts coast. In addition to very high
astronomical tides will result in minor flooding. Greatest concern
continues to be from Salisbury to Cape Ann. This is because this
is where the strongest easterly flow is forecast along with a
combination of east swell and wind wave direction. Greatest risk of
both minor coastal flooding and beach erosion.
A coastal flood advisory continues for the Massachusetts East Coast including
Cape Cod and Nantucket for tonight's high tide. Waves will not
be a major factor but looks like enough low level wind gradient
to produce 6 to 8 foot waves in the near shore waters in Ipswich
Bay, about Cape Ann, and Massachusetts Bay could be an issue.
Some erosion is likely along the Salisbury and Plum Island
shorelines where wave action will be somewhat more significant.
Elsewhere along the Massachusetts and Rhode Island coasts, the combination of the high
astronomical tide and a tidal departure near a half foot may be
enough to cause pockets of minor coastal flooding as has become more
common during such King tide cycles. But our confidence continues
to be low and will not be issuing a statement for the remaining
*/ Friday night into very early Saturday morning...
A surge of 0.2 to 0.4 feet is forecast and combined with the peak
of astronomical tides (boston at 12.41 feet), should see at a
minimum coastal flooding of low-lying locations notorious for
becoming inundated during such tides (i.E., Morrissey Boulevard
in boston). Additional coastal flood statements may be necessary.
Will continue to monitor and make updates after this evenings tide
Massachusetts...coastal flood advisory from 10 PM this evening to 3 am EDT
Friday for maz007-015-016-019-022-024.
Marine...Small Craft Advisory until 4 PM EDT this afternoon for
Small Craft Advisory until 6 am EDT Saturday for anz235-237-
Small Craft Advisory until 6 PM EDT Friday for anz251.