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4/14 - 4/15 Heavy Rain and Squall Line Thread

Santa Claus

By Santa Claus,
in New York City Metro

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Santa Claus

Santa Claus

Posted
Posted

I hope you kids are enjoying a balmy mid-April day while you rush to complete your taxes.

Quote 

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
***Enhanced severe weather threat for tonight***

Sent an update for a flash flood watch across far northwestern
NJ, southern Poconos, Lehigh Valley, and Berks County. More
information in the hydrology section.

Main story will be severe weather threat for tonight. In the
meantime, as of mid afternoon, strong low pressure was located
over Ohio with a warm front extending east and northeast from it
across NE PA toward Long Island placing most of the CWA in the
warm sector. Temperatures generally in the 60s and 70s with dew
points climbing into the 60s as moisture continues to advect
northward in the southerly flow. This moisture has kept low
clouds and mist locked in for much of the area which has kept
conditions a bit more stable than farther S/W where
destabilization is occuring. Some showers currently across
central PA extending southward however the stronger storms we
expect for later tonight have yet to form.

As we head through the late afternoon into this evening, higher ML
CAPE values should continue to develop northward towards MD and
eastern PA. As this occurs, weak impulses in the upper level
flow combined with terrain effects look to develop scattered
showers and storms into eastern PA by this evening but these
don`t look to be well organized and should generally weaken with
time. Still, gusty winds and heavy downpours will be possible
in any of these given the very strong flow aloft.

The main concern for severe weather looks to be for the very late
evening and especially overnight as forecast models continue to
indicate a strong squall line forming to our west ahead of a
cold front and moving west to east across the CWA roughly in the
6-10z time frame. Overall, severe weather parameters are some
of the most favorable seen for the mid Atlantic this time of
year. 0-1/0-3/0-6 km shear values look to be 30/45/65 knots
respectively. This, coupled with ML CAPE values looking to be
500+ j/kg as convection enters our eastern PA zones. Not
terribly impressive on its own but plenty given the very strong
shear and dynamics along with L57 lapse rates that look to be in
the 6.0 to 6.5+ C/km range. Of additional concerns is 0-1 km
SRH values progged to be 300+ m2s2. What this all means is that
damaging winds look to be a big concern as this squall line
moves through with the SPC having placed an enhanced risk for
severe weather for a large portion of the CWA except the coast
and far northern NJ. In technical terms, a QLCS type event.
Damaging straight line winds are typically the biggest threat
with these types of events but given the parameter is place,
isolated tornadoes are possible. In addition, the very heavy
rain accompanying the showers/storms will bring a good potential
for at least urban, small stream, and poor drainage type
flooding with isolated flash flooding also possible. The only
real good news is that the line will be progressive and should
be rapidly exiting by sunrise Monday. For further details on
what we expect tonight, a briefing is at
weather.gov/media/phi/current_briefing.pdf.

I'm going to guess the tornado watches progress to the east as the night goes on.

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SRRTA22

SRRTA22

Posted
Posted
4 minutes ago, Dan76 said:

meh..

Not meh....it's April 14 and we have a reasonable severe threat.  Not the greatest of all threats but it's something. Of course during this time of year you really cannot expect much on the immediate coast but it it is an early am threat...which never failed to impress in the past decade. I think EPA to atleast New Brunswick are good for strong to severe storms. 

As for NYC metro, strong garden variety is a good bet. Severe not ruled out but def gonna be more isolated

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Stormlover74

Stormlover74

Posted
Posted

Updated Upton discussion 

Strengthening low pressure moves from the Ohio Valley this evening
to Upstate New York by late. LLJ helps push a warm front farther
north, with the entire forecast area in the warm sector. A trailing
cold front then reaches west of the Hudson towards daybreak. There`s
enough moisture and lift for chances of showers at any given point
tonight, but high res models continue to key on the main focus for
showers and thunderstorms after midnight. The main line of showers
and thunderstorms will enter western zones 06z to 09z, and then
quickly move across the NYC/NJ metro 09z to 12z, and then across
eastern zones shortly thereafter. The line will be forced by
convergence of a +3 to +4 standard deviation PWAT subtropical
moisture plume ahead of the front as well as deep layered lift
enhanced by upper jet dynamics.

Forecast rainfall amounts are generally 1/2 to 1 inch across the
region with locally higher amounts possible. Much of this rain may
come within the line of showers and thunderstorms. Minor urban and
poor drainage flooding is the main threat. The relatively fast
movement of the showers and thunderstorms should limit any flash
flooding threat, but WPC does have marginal to slight risk for
excessive rainfall from around NYC and points west.

SPC has placed portions of NE NJ, NYC, and the Lower Hudson Valley
in a slight risk for severe thunderstorms. This is where there is
some surface based CAPE progged by some models. The main threat
appears to be damaging wind gusts. The environment is highly sheared
with low CAPE, so there is potential for rotation, but the potential
is very low. A stronger low-level inversion should limit the severe
threat east of the Hudson River where instability is elevated.
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