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Sunday's Screaming Southeaster

CT Rain

By CT Rain,
in New England

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powderfreak

powderfreak

Posted
Posted
31 minutes ago, Baroclinic Zone said:

Here is the 12z WRF-ARW.  Rips Philippe up 'Gannsett Bay.  Would be a brutal solution.

wrf-arw_mslp_wind_neus_20.thumb.png.d405bf2a8a907ba7aed0ed5b8d4d12bb.png

ARW!  My favorite winter model...always bringing those coastal lows west for us in the winter.

ARW hitting the downslope winds real hard NW of the high terrain ridges.

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Baroclinic Zone

Baroclinic Zone

Posted
Posted
8 minutes ago, CoastalWx said:

18z NAM bring that tropical low right into SE MA. May cut down the period of stronger winds a bit to its west, but this is flying. In fact, 3 hr model progs misleading because strongest winds only last 1-2 hrs.

That's been trending westward all day.  Would not be surprised if it comes up into our area.

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bobbutts

bobbutts

Posted
Posted
30 minutes ago, moneypitmike said:

LOL at whatever that 103 is doing on the Pit2 roof.

 

 

Would be quite an event for Sagadahoc county if it gets anywhere close to that.  I'm still holding a few undeveloped acres there, hopefully there isn't too much tree damage.

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Baroclinic Zone

Baroclinic Zone

Posted
Posted 
000
FXUS61 KBOX 292021
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
421 PM EDT Sun Oct 29 2017

.SYNOPSIS...
Intensifying early season coastal storm off the Mid-Atlantic
coast brings strong to damaging winds, a few strong to severe
thunderstorms and the potential for flash flooding late today
and tonight. Drier and cooler weather moves in behind the
weather system through midweek. A cold front may bring a few
showers late week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
2 pm update...

The situation is evolving fast. Roughly 2 mb/hr pressure falls
emerging off the NC coast where presently a 995 mb is deepening
S/E. Starting to see stronger wind gusts emerge per isallobaric
and gradient wind response.

Previous discussion below applies and has been slightly edited.
Upon the latest suite of 12z guidance and also evaluating near-
term hourly guidance, with a blend of the 3 km NAM with the HRRR
forecasting secondary tropical circulations to rotate round and
into the mid-level disturbance, sweeping into S New England,
across the E waters and up into Maine.

Couple of things we need to monitor:

1.) Whether we`ve underdone the winds and/or whether we need to
extend the 70 mph wind field. Presently 50 to 60 mph gusts
forecast across the interior with 60 to 70 mph gusts along the
shore. Higher gusts possible along the immediate coast. Could
see places, like the Buzzards Bay tower for example, gust up to
80 mph. This may require further extension of STORM WARNINGS to
HURRICANE FORCE WIND WARNINGS. One thing of note, for HFWW you
need at least 2 hours of hurricane force winds. Such gusts may
occur only briefly as the storm quickly wraps N across the region
later this evening. Will evaluate.

2.) Heavy rain threat. Forecasting a 2-4 inch event over much of
the region keying on higher amounts along the E slopes of high
terrain where the main atmospheric river of sub-tropical moisture
is going to slam into S New England later today. Coordinating
with the NE River Forecast Center, can`t rule out locally higher
amounts. And to add to that the severe weather threat ...

3.) Severe weather threat. Talking to SPC, an upgrade to marginal
over SE New England. A concern that on the back end of the dry
slot that mid-level lapse rates steepen in a region of strong 0-1
and 0-3 km helicity. Reflectivity modeling out of the HRRR, some
concern on two issues: series of fine line signatures / banding
and subsequent enhanced damaging wind threat, and also whether
such signatures, likely with some rotation, can pose a tornadic /
waterspout threat.

Instability may seem weak, on the order of 250 J/kg at most it
would seem, but it`s the dry slot and enhanced mid-level lapse
rates that could really kick off the severe weather potential.
This storm is powerful and should not be underestimated.

Previous discussion...

*/ Highlights...

 - Strong to damaging winds across SNE this evening into tonight
 - Potential for hurricane-force wind gusts
 - Heavy rainfall with localized flash flood threat into tonight
 - A few strong to possibly severe storms into tonight

*/ Discussion...

A dynamic, multi-faced storm system developing off the mid-Atlantic
coast, taking aim on the Northeast. Again, a lot of moving parts and
a lot of uncertainty in the near-term that are likely going to lead
to rapid-fire forecast changes. From the mid-level disturbance out
of the interior, to secondary tropical circulations developing off
the FL coastline (referred to as Phillipe), between interactions and
rapid cyclogenesis, there is the potential for change as we go into
tonight through Monday.

The baroclinic zone is set per clash of airmass over the interior.
The mid to upper level disturbance slowed by downstream blocking
will undergo a negative tilt and obtain greater cyclonic curvature
as its parent main vortlobe digs through the base of the trof. An
evolving H3 dual-jet structure aloft beneath which conveyor belt
motions enhance, the isentropic draw of warm-moist air into the core
of the low promotes rapid cyclogenesis across the baroclinic zone
straight N into Upstate NY, retrograding beneath the closing off,
stacking mid to upper level low in the process, from maturation
towards occlusion.

While earlier questioned, expecting the mid-level disturbance and
the synoptic process to interact with the aforementioned secondary
tropical circulations off the FL coast presently lifting N off the
Carolinas. Do expect that we`ll see an evolution towards a warm-
core, hybrid low with such secondary circulations becoming backed
beneath the mid-level disturbance towards lower heights. Taking
on the crux of the higher sub-tropical thetaE and instability along
with the main low to mid level convergent forcing along the nose
of an attendant 90-100 mph jet at H925, potentially as low as H95,
coupling with the strong QG-forcing back over the interior of the
NE CONUS (think jet coupling with the surface cold front), we will
still see the rapid deepening across the Hudson River Valley with
the mid-level disturbance, but now capturing tropical energy and
the warm-core hybrid low becoming a powerful disturbance with a
central pressure down around 970 mb forecast over the Hudson River
Valley. Again, the 1.5 PVU surfaces are just simply impressive, the
tropopause fold just showing how dynamic the system. Can not under-
estimate the power of this storm. Simply put, expect the unexpected.

*/ Threat and Impact Specifics...

DAMAGING WINDS...

Advertising 40-50 mph SE gusts across the interior, higher more so
over the high terrain, 50-60 mph for the coastal plain, and along
the coast, 60-70 mph. Conditionally unstable lapse rates, potentially
steeper as noted by the prior forecaster as the dry slot wraps into
the system, expected that would allow for mixing. Stronger wind
gusts with any heavy rain given mechanical mixing / precip-drag,
especially with any strong to potentially severe thunderstorms
(more on that below). Can not rule out hurricane- force wind
gusts along the coast simply associated with the bombing low at
roughly around 4 mb / hr, as subsequent isallobaric response.
Would require an update to HIGH WIND WARNING headlines, but would
like to see the 12z 3km NAM before making that decision. Will keep
with HIGH WIND WARNINGS. Anticipating widespread tree damage lending
to scattered to widespread power outages, likely some structural
damage occurring. Keeping in mind fully leafed trees.

A note on Monday, strong to damaging W winds expected behind the low
given +3-4 mb/hr pressure rises. The isallobaric response, W gusts
up to 60 mph are possible in an environment of steepening lapse
rates of 8-9 C/km, especially over the warmer waters along the
immediate coast. Boundary layer mixing dominating allowing the easy
mix-down of faster momentum for especially the early-half of Monday.

INTERIOR FLOODING...

Forecasting a 2-4 inch event with locally higher amounts. The FLASH
FLOOD WATCH continues with the expected threats of urban / poor
drainage flooding and the potential swell of small streams and
tributaries. Threat is across all of S New England. While there is
greater concern along the E-slopes of high terrain, and within urban
centers, flash flooding is possible everywhere.

Much of the focus on the strong punch, cyclonic, trowaling branch of
the warm-moist conveyor belt of sub-tropical air tonight with
precipitable waters up to 2 inches. High thetaE water content that
is completely abnormal for late October. Ushered in by a SE jet at
H925, as said earlier, of 90-100 mph, convergently focused into S
New England. High freezing level heights (+12 kft agl) beneath
strong deep-layer forcing, a saturated column throughout, resulting
in efficient, warm-rain processes. Looking at a slug of heavy rain
where 1-2"/hr rainfall rates are not out of the question, especially
with any strong to potentially severe thunderstorms.

Greater concern if the aforementioned hybrid warm-core low sweeps
across the interior. If so, would see greater and stronger onshore
flow of sub-tropical moisture along with a more enhanced threat of
strong to potentially severe thunderstorms in addition to the heavy
rain coincident with convergent forcing along the nose of the
aforementioned 90-100 mph low-level jet. Ensemble / CIPS Analogs
still hold the heaviest rain threat over W New England and into the
Hudson River Valley, but feel the signal as advertised by the HRRR
can not be ignored. This could result in more widespread 3-5 inch
rainfalls with locally heavier amounts. Could see the heaviest
rain over S/SE coastal New England.

Recalling, some areas received 4 to 5 inches of rain earlier in the
week. Some small creeks and streams remain a bit high than as of
earlier in the month. Also to consider leaf clogged drains.

STRONG TO SEVERE THUNDERSTORMS:

Still a risk for strong to possible severe storms this afternoon and
during the overnight hours, especially more so if the hybrid warm-
core low sweeps into the interior or hugs closer to the coast.
Dynamic system resulting in broad lift for the region. High amount
of 0-6 km shear with LI values below 0 and some SB cape moving through.
Southern New England will be in the warm sector at this time and
could see some iso strong to severe storms. Even the NCAR ensembles
is hinting at this potential, as well as CIPS Analogs. While confidence
is on the lower side, something to watch today.

COASTAL FLOODING...

In brevity, anticipating splashover, especially along Atlantic-facing
beaches, with impacts to vulnerable shoreline roads. With low astro-
nomical tides, and noting wave heights of 10 to 15 feet for a short
duration along the Atlantic facing beaches, while a surge of 1 to
3 feet can`t be ruled out, there isn`t a lot of time for swell to
develop. To address the potential threat, we have issued a COASTAL
FLOOD STATEMENT.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
*/ Highlights...

 - Another round of strong to damaging wind gusts during the day

*/ Discussion...

Negatively tilted trough across the region will begin to phase the
two upper level lows during this time. Thus pushing another strong
vort max through the region. Strong CAA behind the departing low in
combination with dry slot moving through will result in strong,
gusty westerly winds for SNE.

925mb LLJ nearing 40 kts will be overhead as the system departs.
Notice very strong pressure rises and steep lapse rates that will
tap into the jet and mix it fully down. Wind headlines will be
needed but will wait until we get through the first storm.

Even under CAA, temps still remain near seasonable thanks to some
downslope component and slight lag in the cooler air aloft. Highs
mainly in the upper 50s and low 60s.

Lastly, heavy precip will come to an end by Monday morning. However,
we could see lingering showers as the vort max rotates through the
region.
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