Jump to content

  • Member Statistics

    17,584
    Total Members
    7,904
    Most Online
    LopezElliana
    Newest Member
    LopezElliana
    Joined

All-purpose Thunderstorm Discussion Thread II

CT Rain

By CT Rain,
in New England

Recommended Posts

  • Replies 243
  • Created
  • Last Reply
Damage In Tolland

Damage In Tolland

Posted
Posted

SGW part deux: 

130 pm update...

*/ Highlights...

 * Strong to severe storms today
 * Heavy rain and damaging winds the main threat
 * A tornado or two possible
 * Impacts: downed tree, tree limbs, power lines, urban and poor
   drainage flooding

*/ Discussion...

Now...

Heavy downpours developing across Central and W portions of S New
England. Some of these storms have exhibited a low-level rotation
even prior to producing lightning.

What We Know...

Instability building across the region, SW to NE, both surface-
based and mean layer on the order of 500-1000 j/kg, and 70 degree
dewpoints surge N attendant with the lifting warm front. This as
cloud breaks are allowing for a fair amount of sunshine resulting
in temperatures warming into the 80s. Boundary layer destabilization
with low-level lapse rates becoming steep, though mid-level lapse
rates are poor. Low LCL`s currently progged by SPC mesoanalysis of
around 2-3 kft agl. Precipitable waters beyond 2 inches as sub-
tropical moisture lifts with the stout H925-7 S/SW flow.

Initial height falls within the low to mid levels as the H925-7
ridge pushes to the E, both its grip and anti-cyclonic flow
weakening in influence. Region still largely absent of mid to
upper level support in the way of mid-level lift and favorable
venting.

Effective bulk shear increasing of 30 to 40 kts parent with the
lifting warm front and where heavy downpours are developing. Bulk
0-6 km shear still 30-40 kts while a veering wind profile still
exists across the region as per 12z soundings with "reaper" 0-1 km
profiles.

What We Don`t Know...

Still some question as to how far N the warm-front progresses.
Thinking with cloud breaks and subsequent low-level mixing will
allow the warm front to gradually lift N as S/SW flow are mixed
down. Expect the front to lift past the N MA border into the
afternoon into evening, but this depends on cloud cover allowing
boundary layer destabilization. Deck looks fairly thick over N/W
MA.

Anticyclonic flow and the lack of upper-level support may surely
lend to less robust storm development. Could lend to isolated
storm activity rather than scattered to widespread. Then again
with enough buoyancy in the atmosphere this may be overcome as
we`ve seen in prior convective episodes over the past 5 days. So
in other words the strength of the storms is in question. It is
just so challenging and there really is not any piece of forecast
guidance capturing the mesoscale well. Sort of have to go with gut
and intuition from the classroom.

Have to also watch whether storms can become hinged to the lifting
warm front, that is to say whether one place sees a prolonged
period of heavy rain and a flood threat. Tough to nail that down.

Still forecasting the greatest threats across the W-half of S New
England, but a bit surprised as to activity emerging well to the E
with the lifting warm front. This appears to be, perhaps, the
initial wave of activity for the afternoon period which is to be
followed by another round of weather late this evening towards
midnight with anticipated height falls and the cold front sweeping
through.

To that end, it is unclear as to what sort of activity will make
it through S New England along the cold front. Atlantic ridge is
likely to have some influence, plus the fact that diurnal heating
will have concluded. Mid-level energy will be stretched more N/E
and that`s where we`re thinking that activity overnight will be
more prominent.

Re-iterating some points...

Rainfall...Expect precipitation efficiency given 12z soundings
highlighting freezing levels around H6 (14 kft agl). Ensemble
probabilistics suggest potential rainfall rates of 1-2 inches per
hour with outcomes over N/W MA and CT with WPC highlighting a
slight risk of excessive rainfall. Thus there is a low risk of
flash flooding, but greater confidence of urban, poor-drainage
issues. Low confidence to warrant a flood watch of any type.
Already heavy downpours exhibiting instantaneous rainfall rates
upwards of 4-inches. High KDP from dual-pol indicating efficient
rain producers.

Severe...A SLIGHT risk has been posted by SPC accordingly with 5%
risk of tornadoes. A mesoscale discussion has noted an increasing
threat of shallow rotating storms should updrafts intensify. There
is the possibility of a tornado watch given increasing CAPE with
the strong belt of SW low to mid level flow above backed S/SE
flow netting a veering wind profile with decent helicity, this
along with 30-40 kts effective bulk shear, an environment supportive
for supercells. But in personal communication with SPC, will hold
off for now, awaiting as to whether the environment becomes more
severe and we anticipate activity to strengthen further.

Closing out...

Continue the greatest risk of strong to severe storms across the
CT River Valley of MA and CT and points W of there. May need to
extend this E with the warm front. Prevailing with gusty winds,
frequent lightning, and heavy rain. Again, there is the risk of
tornadoes.

For later tonight, afternoon activity lifting N/E during the
evening hours, and then attention turns towards midnight with the
cold front sweeping through with height falls through all levels,
though the crux of the mid-level energy is stretched N/E as the
Atlantic ridge remains stout, thus could get a final show into the
early morning hours mainly over N/E MA.

&&

 

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...