4/19 - 4/20 Long-Duration Heavy Rain and Wind Event

[Santa Claus]

We look to be in for a dynamic grab bag of interesting weather.  A strong southerly flow will fuel a flash flooding threat, with less favorable conditions existing for possible severe wind events.

Quote

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
The weather will turn active on Friday. Synoptically, an impressive
evolution as a pair of shortwaves phase over the Southeast, leading
to a single deep trough extending well into the Gulf of Mexico. This
creates a very high amplitude meridional flow with jet level winds
to our west turning due south if not east of south over a large
distance. This flow pattern will mean the storm system to our west
will continue to be slow to approach. Southerly surface flow will
keep temperatures on the warm side, with rising dew points as well.
Dew points well into the 60s will create a downright humid feel for
much of Friday. Breezy conditions also as the pressure gradient
tightens up in the southerly flow and the LLJ begins to increase.
The shower and storm risk will increase later in the day, though
there is uncertainty as to when the window for more widespread
activity will open, which is discussed more below. A few pop-up
showers are also possible in the morning, though any of those should
be more widely scattered and progressive given lack of instability
and forcing.

Two main concerns continue heading into Friday afternoon and beyond,
those being the potential for heavy rainfall and severe weather. The
heavy rain threat is most apparent, as PWATs surge to around 1.6-1.8
inches, near record territory for this time of year. Highly
anomalous tap of moisture extending all the way into the Caribbean.
Any heavier showers and thunderstorms will produce high rain rates
capable of causing flash flooding. The extent of flooding potential
will depend mainly on the duration of convective activity and the
extent of any training of cells. Some guidance shows a more
progressive and broken line of heavy showers and storms which would
limit overall concern. The NAM for instance is on the dry side with
generally near to below an inch of rain. However, other guidance
shows more in the way of training cells with the potential for
localized corridors of two or more inches of rain. Given the
amplitude of the flow and anomalous air mass, am inclined to feel
there will be at least some flash flooding issues, especially over
eastern PA where the most rain has been seen recently. In
particular, if an initial round of showers or storms develops during
the daytime tomorrow, this will better prime areas for flash
flooding once the main lines goes through. See the hydrology section
further below for more on the rainfall threat.

In terms of severe potential, there are a couple things to watch
for. Two potential periods of interest exist. The first concerns
would come Friday afternoon with cells developing ahead of the main
line. This would be most likely over eastern PA and western NJ. We
should see a couple hundred to a few hundred joules of surface based
CAPE develop in the afternoon with decent shear as well. Main
question with that first round would be whether we have the forcing
needed to take advantage, and on that matter there is a good deal of
disagreement. Hi-res CAMs are all over the map. A lot of cloudiness
is expected Friday; any breaks would help build the instability and
improve storm chances, but a thicker overcast would reduce the
chances for afternoon convection. Anything that develops will need
to be watched for the potential to become strong, but feel this
activity is more likely to be garden variety with perhaps a couple
of stronger cells and mostly just a heavy rain threat. Second period
of concern would be with the passage of the main frontal line
overnight. Less instability to work with when the line passes, but
very impressive wind fields, so damaging winds would be a concern
with any thunderstorms. Most of the activity (once again) should
occur in the predawn hours.  The main line should be approaching the
coast by 12z Saturday, but may still be hanging around if the timing
is a little slower. SPC maintains a marginal risk for most of the
area with a slight risk over our far southern zones. Generally agree
with this idea; not expecting a repeat of a few days ago as the
setup is overall not as favorable, but especially given the wind
fields we will still have to keep a close eye on things.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Heavy rain and embedded thunderstorms with the surface cold front
will move east and north of our area Saturday. A closed low aloft
over the upper Ohio Valley combined with diurnal heating will
generate some instability showers during Saturday afternoon and
at night.

 

[Rtd208]

Breaks of sun thru the clouds here.

Current temp 67/DP 61/RH 74%

[Rtd208]

I think the SPC will bring the marginal/slight risk of severe storms further north in subsequent day 1 outlooks.

[MJO812]

62 with showers now 

[SI Mailman]

Small little popup shower by the Outerbridge.

[hooralph]

When do we think this realistically exits? We're flying out of JFK at 11 AM tomorrow.

[gravitylover]

8 minutes ago, hooralph said:

When do we think this realistically exits? We're flying out of JFK at 11 AM tomorrow.

I have friends going out of LGA at 10.

[Drz1111]

We’re getting near our convective temp - the SPC outlook is too conservative up here.  

[NycStormChaser]

Spc brought the slight risk up into PA / NJ on their latest update. With that also comes the 2% tornado risk further north as well and 10% wind damage.

 

 

 

 

[SnoSki14]

We're getting a lot of sunny breaks with temperatures now forecast to hit almost 80F. 

So definitely think threat will be larger than expected. I would've expanded the slight risk even further north. 

[LongBeachSurfFreak]

Absolute steam bath in the city right now. Building up low level instability. 

[Rtd208]

Current temp 78/DP 64/RH 56%

Skies: Partly Sunny

[NycStormChaser]

 

[Rtd208]

Just now, NycStormChaser said:

 

I swear KDIX breaks down everytime we are expecting significant weather. Very unreliable.

[Rtd208]

Temp up to 79 here.

[IrishRob17]

I’m leaning towards the under on the rainfall tonight up here, we shall see. 

[psv88]

Bust. Today was largely a beautiful day 

[gravitylover]

3 hours ago, IrishRob17 said:

I’m leaning towards the under on the rainfall tonight up here, we shall see. 

Yeah it sure looks like a bunch of the rain slid by to our west already doesn't it. 

2 hours ago, psv88 said:

Bust. Today was largely a beautiful day 

It sure was. Low to mid 70's with a nice breeze always makes for a nice day.

[IrishRob17]

10 minutes ago, gravitylover said:

Yeah it sure looks like a bunch of the rain slid by to our west already doesn't it. 

It sure was. Low to mid 70's with a nice breeze always makes for a nice day.

Upton calling for .75-1” IMBY but it’s looking like I’ll split the uprights with heavier to my NE and SE.  The HRRR and NAM 3K have me under .50” tonight, the 18z Euro spits out .60” here.  Time will tell. 

[NycStormChaser]

Hrrr continues to look Impressive for parts of Pennsylvania and New Jersey tonight. I think we see quite a few severe warned thunderstorms over the next few hours. I don't think a spin up is out of the question. 

[NycStormChaser]

As expected 

 

 

[SRRTA22]

It's gotten pretty chilly here in Jersey City over the last hour or so. 

[TriPol]

I need a sweater to go outside. Turned the heat up inside.

[Rtd208]

Wind has picked up quite a bit here, had a heavy rain shower move thru about 20 mins ago.

Current temp 70

[Santa Claus]

21 minutes ago, TriPol said:

I need a sweater to go outside. Turned the heat up inside.

 

36 minutes ago, SRRTA22 said:

It's gotten pretty chilly here in Jersey City over the last hour or so. 

The tropical fetch is held aloft while the lower level winds are pulling air off the ocean from the SSE.  Very legal, very cool.

Tell you what I'll take some of that temperature and humidity relief.  Today was a sauna in Middlesex County.

[TriPol]

I get cold very easily. I get hot very easily. I have no idea what climate to live in.

[Cfa]

Temp is creeping back through the 60’s now after having dropped into the 50’s.

Currently 62/62.

[Rtd208]

LOL!

 

[Rtd208]

Current temp 70/DP 65/RH 83%

[NorthShoreWx]

The wind has been howling here for what seems like days.  It is literally roaring through the trees now.  Not much rain to speak of.  Got to 72 briefly this afternoon, but unless exercising still needed a sweatshirt otherwise too chilly with the wind.