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E PA/NJ/DE Fall 2021 OBS Thread


Rtd208
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Mount Holly on tomorrow:

Guidance consensus suggests a stripe of MLCAPE values around 1000+
J/kg ahead of the front driven by low-level WAA and cooling in the
mid-levels as it pushes into eastern PA and New Jersey. This
combined with very favorable forcing for convection is expected to
result in the development of widespread thunderstorms in the 21-00Z
timeframe. The mesoscale and hi-res guidance has been consistent in
developing a potent LLJ ~30-40 kts in the 00-03Z timeframe across
Delmarva, SE PA, and New Jersey immediately ahead of the approaching
synoptic cold front and leading mid-level shortwave. Forecast
effective SRH values are fairly high (200-250 m2/s2) and effective
inflow layer shear on the order of 25-30 kts. The 06Z and 12Z NAM
hint at a secondary low pressure maxima developing along the front,
which would further back the surface winds in the warm sector and
increase the SRH. Deep layer shear appears to be on the order of 35-
40 kts immediately ahead of the cold front. These shear and
kinematic values will be supportive of organized convection and
rotating updrafts. The mean flow being largely parallel to the
cold front suggests a mainly linear convective mode, but cannot
totally rule out a few more discrete cells, especially ahead of
the main front.
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New MD just released for some of us:

https://www.spc.noaa.gov/products/md/md1715.html

   Mesoscale Discussion 1715
   NWS Storm Prediction Center Norman OK
   0315 PM CDT Wed Sep 08 2021

   Areas affected...Eastern Pennsylvania...northwest New
   Jersey...southeastern New York

   Concerning...Severe potential...Watch possible 

   Valid 082015Z - 082215Z

   Probability of Watch Issuance...40 percent

   SUMMARY...The threat for severe weather will gradually increase into
   early evening across parts of the Mid-Atlantic. Damaging wind gusts
   and isolated large hail are the main concerns. A conditional tornado
   threat exists in eastern Pennsylvania and southeastern New York.
   Timing and coverage of severe storms is uncertain. Trends will be
   monitored for a possible watch.

   DISCUSSION...The 18Z observed Albany sounding showed relatively weak
   capping, but signs of subsidence aloft. This general profile seems
   to capture what is being observed on visible satellite across the
   Mid-Atlantic. Areas of cumulus, particularly within eastern
   Pennsylvania where temperatures are in the mid 80s F, have shown a
   gradual increase in depth. The subsidence aloft is likely limiting
   vertical development. With time, and additional mid-level cooling,
   storms should be able to initiate in the warm sector. Farther west,
   warm conveyor belt precipitation has generally been weak with only
   small embedded convective elements. A gradual increase in convective
   character may occur as this activity encounters more buoyant air.

   The greatest severe potential likely exists with any warm sector
   storms that can develop. Damaging winds, isolated large hail, and
   perhaps a tornado could occur. Eastern Pennsylvania into
   southeastern New York would be the favored zone for low-level
   rotation given slightly backed surface winds. Storms within the warm
   conveyor belt should exhibit a more linear storm mode and pose
   primarily a damaging wind gust risk.

   There is some uncertainty as to when storms will intensify this
   afternoon. Much of the guidance suggest it may not be until around 
   or after 8 PM EDT. With potentially unfavorable timing diurnally,
   trends will have to continue to be monitored for a possible watch
   later this afternoon.

   ..Wendt/Hart.. 09/08/2021

   ...Please see www.spc.noaa.gov for graphic product...
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Timing on this one seems pretty poor but with the dynamics in place it may not matter much. The CAMs are pretty hit and miss in the overnight hours. N and W definitely has the best chance, it remains to be seen if the convection holds together for the 95 area overnight. The models that hold it together don't have it pushing through until after midnight. Lehigh valley looks to get slammed though in the 9 pm - 11 pm range. Line is still well off to the west right now.

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There's about a 10-20° temperature gradient across the front, with the larger differences to the south, though I think the loss of daytime heating as this thing moves east is going to reduce the threat for the I-95 corridor at least. The line looks much more robust more north of us.

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This event seem way overhyped to anyone else? I mean, I'm all for a good storm but the news mets have all been squawking about this for a couple of days, getting everybody all riled up. Please correct me if I'm wrong, but this all seems pretty run-of-the-mill. I think they all need to dial it back a notch. People are storm-warning-fatigued enough as it is. On one hand, yes, everyone please pay attention, it might get stormy tonight. But on the other hand, it's not like every event has to be billed as OMG tHe WeAtHeR aPoCaLyPsE is upon us once again! Yeesh, maybe I'm the one who's fatigued...

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28 minutes ago, CoolHandMike said:

This event seem way overhyped to anyone else? I mean, I'm all for a good storm but the news mets have all been squawking about this for a couple of days, getting everybody all riled up. Please correct me if I'm wrong, but this all seems pretty run-of-the-mill. I think they all need to dial it back a notch. People are storm-warning-fatigued enough as it is. On one hand, yes, everyone please pay attention, it might get stormy tonight. But on the other hand, it's not like every event has to be billed as OMG tHe WeAtHeR aPoCaLyPsE is upon us once again! Yeesh, maybe I'm the one who's fatigued...

I think it is more due to the potential for creek and river flooding, particularly to the north.  For example, the Passaic near Pine Brook and Morristown in Jersey has been under a flood warning since Ida -

pinn4_hg.png

And if that line moves as slowly as it has been, any training would just exasperate the flashier creeks.  Plus you have people who were impacted by tornadoes last week with obliterated and/or damaged homes and I expect that if any cells pop up with some gusty winds, those can take down any trees that made it through Ida.  I have heard (at least on KYW and from the NWS AFD) that it wasn't going to be anything like last week but because the ground is so saturated, it might not take much to overwhelm an area.  I even heard that here in Philly, PennDOT literally pumped out 30 million gallons of water out of what I dub the "Vine Street Expressway Canal", in a couple days, so thankfully they got that out of the way. :o

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SPC woke up and threw up Severe Thunderstorm Watches for the CWA -

Quote

Severe Thunderstorm Watch

SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 491
NWS STORM PREDICTION CENTER NORMAN OK
755 PM EDT WED SEP 8 2021

SEVERE THUNDERSTORM WATCH 491 IS IN EFFECT UNTIL 1200 AM EDT
FOR THE FOLLOWING LOCATIONS

PAC011-017-029-077-089-091-095-103-090400-
/O.NEW.KWNS.SV.A.0491.210908T2355Z-210909T0400Z/

PA
.    PENNSYLVANIA COUNTIES INCLUDED ARE

BERKS                BUCKS               CHESTER
LEHIGH               MONROE              MONTGOMERY
NORTHAMPTON          PIKE
$$
Quote

Severe Thunderstorm Watch

SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 491
NWS STORM PREDICTION CENTER NORMAN OK
755 PM EDT WED SEP 8 2021

SEVERE THUNDERSTORM WATCH 491 IS IN EFFECT UNTIL 1200 AM EDT
FOR THE FOLLOWING LOCATIONS

NJC003-019-021-027-031-035-037-041-090400-
/O.NEW.KWNS.SV.A.0491.210908T2355Z-210909T0400Z/

NJ
.    NEW JERSEY COUNTIES INCLUDED ARE

BERGEN               HUNTERDON           MERCER
MORRIS               PASSAIC             SOMERSET
SUSSEX               WARREN
$$

 

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1 hour ago, Hurricane Agnes said:

I think it is more due to the potential for creek and river flooding, particularly to the north.  For example, the Passaic near Pine Brook and Morristown in Jersey has been under a flood warning since Ida -

pinn4_hg.png

And if that line moves as slowly as it has been, any training would just exasperate the flashier creeks.  Plus you have people who were impacted by tornadoes last week with obliterated and/or damaged homes and I expect that if any cells pop up with some gusty winds, those can take down any trees that made it through Ida.  I have heard (at least on KYW and from the NWS AFD) that it wasn't going to be anything like last week but because the ground is so saturated, it might not take much to overwhelm an area.  I even heard that here in Philly, PennDOT literally pumped out 30 million gallons of water out of what I dub the "Vine Street Expressway Canal", in a couple days, so thankfully they got that out of the way. :o

Ok those are valid points. Hope I'm right all the same.

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Bit noisy out there, actually. Usually we see discrete cells producing bursts of lightning, but this whole line is producing. I feel now that I was a bit premature in my previous statements regarding the perceived reduced intensity of this system. Batten down the hatches.

image.thumb.png.117e385532e581562f8b675cc7e8cab0.png

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11 minutes ago, Birds~69 said:

Canceled tornado warning...heavy rain though. 

There were two spin-ups near me according to velocity scan, one headed right towards my subdivision. Front came through and the rain was loud enough to hear in the basement, thought that was all we heard, thankfully. Wish I was closer to a better radar. Threat has passed, now just heavy rain. .88" in the bucket. image.png.60f56e8f173a3b77578a4b995bed875b.png

 

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