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Tuesday but primarily Wednesday potential pockets excessive rain-wet microbursts Wednesday 2PM-10PM


wdrag
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It's a bit early, but while Tuesday may be a subdued day compared to this afternoon in NJ, it appears Wednesday afternoon-evening should be our big convective event of the Mon/6th-Thu/9th time frame, similar or a bit less compared to what occurred today near PHL.  KI/CAPE/PWAT slow movers in a fairly steamy uncapped environment developed on the remnant warm front/sea breeze boundaries and subsequent outflows, should promote thunderstorms-"potential"prolific rain producers in part of NNJ/se NYS, spilling east-southeast over Long Island (heaviest for LI probably NYC vicinity, but unknown).  Since we saw probable 5-7" rainfall in isolated locations of Morris County NJ and down near PHI on Monday the 6th,  it won't surprise if similar isolated 5"+ rainfall occurs in the NYC forum Wednesday. My main concern: do we get enough heating (temp upper 80s)?

Potential for short fuse warnings flash flooding and maybe severe wind.  Will reassess Tuesday morning, possibly updating this topic.  I'm not thinking about the Friday (low chance FAY? per NHC 2PM/6 5D TWO 40%)-weekend cold front events, understanding in part that the Friday event may need to drop into the tropical portion of the forum? (if it becomes named).

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644 AM Tuesday update to this topic:

Unleashing rainfall yield for Wednesday: have some doubts per max T forecast and basic 00z/7 QPF modeling.

Today:  Subdued convectively due to cloud cover but I would think scattered heavy showers and thunderstorms this afternoon, not as widespread-intense as yesterday and not easily-reliably modeled. Might be more near the PA/NJ/NYS tri state border on down to vicinity TTN?  IF these occur, potential for 1.5" spot-rainfall in a concentrated tiny area. That per WPC D1, SPC HREF. Moderate confidence. 

Late tonight: subtle WAA, might yield a cluster of heavy showers and thunderstorms toward eastern LI ~ dawn Wednesday. Low confidence. 

Wednesday: Featuring NNJ/se NYS with some possible east southeastward storm drift into NYC, sw CT after ~6PM.  PWAT 1.8-2",  More unstable than Tuesday but if temps cant make the upper 80s... then potential yield for big storms and isolated 5+ in doubt. It still appears Wednesday afternoon-evening should be our big convective event of the Mon/6th-Thu/9th time frame, similar or a bit less compared to what occurred near PHL Monday.  KI/CAPE/PWAT slow movers in a fairly steamy uncapped environment developed on the remnant warm front/sea breeze boundaries and subsequent outflows, should promote thunderstorms-"potential"prolific rain producers in part of NNJ/se NYS, spilling east-southeast over far western Long Island. Since we saw probable 5-6" rainfall in isolated locations of Morris County NJ and down near PHI on Monday the 6th,  it won't surprise if similar isolated 5"+ rainfall occurs in the NYC forum Wednesday. My main concern: do we get enough heating (temp upper 80s)?

Potential for short fuse warnings flash flooding and maybe severe wet microburst wind.   I'm not thinking about the Friday (low chance FAY? per NHC 2AM/7 5D TWO 40%)-weekend cold front events, understanding in part that the Friday event may need to drop into the tropical portion of the forum? (if it becomes named).

Just need to take one day at a time (Tue-Wed) and look for subtle instability/moisture pooling along any boundaries to produce big summer thunderstorms.

 

 

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237PM quick update: next update, probably not til ~7am Wednesday.   Cutting back max rain amount from wet microburst-outflow thunderstorms back to about 4" (isolated). Just not quite as robust as Monday... less intense heat, not quite as unstable but ~2" PWAT still modeled to be bullseyed somewhere vicinity NYC or just west-northwest.  Capable of isolated SVR/FF mainly se NYS/northern NJ, southern boundary of convection probably near I78.  Spillage of storms (east-southeast) into NYC sw CT.  Did notice SPC extended the D2 Marginal risk southward to the northern border of the NYC forum area.  So, in advance, had to cut back my expectations - probably too much cloud and not enough heating. CAPE only to about 2000J and this is modeled more into nw NJ. SPC HREF for D2 has some 1.5" MAX amounts west northwest of NYC and these max amounts in the ~8 member ensemble can be a little underdone, provided robust convection occurs. 

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10 minutes ago, wdrag said:

237PM quick update: next update, probably not til ~7am Wednesday.   Cutting back max rain amount from wet microburst-outflow thunderstorms back to about 4" (isolated). Just not quite as robust as Monday... less intense heat, not quite as unstable but ~2" PWAT still modeled to be bullseyed somewhere vicinity NYC or just west-northwest.  Capable of isolated SVR/FF mainly se NYS/northern NJ, southern boundary of convection probably near I78.  Spillage of storms (east-southeast) into NYC sw CT.  Did notice SPC extended the D2 Marginal risk southward to the northern border of the NYC forum area.  So, in advance, had to cut back my expectations - probably too much cloud and not enough heating. CAPE only to about 2000J and this is modeled more into nw NJ. SPC HREF for D2 has some 1.5" MAX amounts west northwest of NYC and these max amounts in the ~8 member ensemble can be a little underdone, provided robust convection occurs. 

50% of Monday would be a massive hit for someone. 

Some of us need really need it. 

Great stuff as always BTW. 

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28 minutes ago, Allsnow said:

Great information in this forum the last few weeks! We are really getting good information out about are thunderstorm chances. 
 

The general discussion thread has been great also 

No rain/snow lines or sun angles to fight about

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No changes to thinking: certainly have no thought to increase the impact.  Continued concern about sunshine-heating.  Dont like to forecast real heavy convection for stratus regions, unless its WAA (CT/LI look like stratus at least in the morning).  Noticed some showers late today eastern LI, now departing. Maybe more toward dawn?  Anyone see the radar estimated 1" w of TTN this eve in those small showers. That tells me that if convection does light up as still modeled for NNJ, interior se NYS Wed afternoon, that it will produce torrents in the path of the storms. PWAT still modeled nr 2" 18z Wed, higher than the TTN showers modeled 1.7"ish pwat of this Tue eve. CAPE still modeled near 2000J ~18z Wed. I like the look for big storms NNJ/inteior se NYS. We'll see if it happens and will check back ~7A Wed. 

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Good Wednesday morning: PWAT-CAPE look good...convection is likely. Believe worst of this is interior se NYS/NNJ with east southeast dying spillage into NYC (not e LI) and maybe sw CT. Cant increase confidence any further, since am concerned about 90F heat making it into the NYC forum. It will be close-just south in central NJ. HRRR convection seems in part related to its modeled hot 90+F temps, so am a little concerned this is overdone. Still, PWAT-CAPE might make up for not much deep layer shear to allow 1 or 2 wet microbursts SVR/brief small FF episodes in our forum area, again mainly se NYS and NNJ, west and northwest of NYC.  Please monitor your own favorite resources, including NWS products and forum friends.  Not posting anything for Thursday, with lesser chance of anything big, and mainly extreme nw NJ into se NYS early Thursday afternoon. Friday is unknown on whether a named storm so not touching that.  628A/8

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Good signs for heavy convection here: convection in progress advancing eastward into ne PA. TD 70-74 as far as I can tell in nw NJ at 1140z...when TD exceeds 1000-500MB  last 2 digit thickness value, considerably raises the chance for rain (my own observation over the years-no science). In this case around a 574 thickness and TD here at the house ~73F. Big thunderstorm afternoon appears likely for NNJ/se NYS. 1153z/8

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Not sure what to make of 12z modeling?  It doesn't recognize the heavy rainers very well to start and doesn't do too much with these storms moving toward our NYC forum area. Have seen 2" rainfall rate in ne PA...per digital radar interp.  I'd think that is likely...but NWS radar #s are less. Jury out but barring the 12z modeling, I'd be concerned for big storms nNJ, interior s NYS this afternoon.  I have to give some credence to modeling.  I did note the 00z GGEM did a similar shutoff after 12z today. Unsure. Meanwhile SPC expanded marginal to near our nw NJ border. 77.4/73.6 in Wantage at this time. 

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1 hour ago, wdrag said:

Not sure what to make of 12z modeling?  It doesn't recognize the heavy rainers very well to start and doesn't do too much with these storms moving toward our NYC forum area. Have seen 2" rainfall rate in ne PA...per digital radar interp.  I'd think that is likely...but NWS radar #s are less. Jury out but barring the 12z modeling, I'd be concerned for big storms nNJ, interior s NYS this afternoon.  I have to give some credence to modeling.  I did note the 00z GGEM did a similar shutoff after 12z today. Unsure. Meanwhile SPC expanded marginal to near our nw NJ border. 77.4/73.6 in Wantage at this time. 

none of them match reality. toss

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Mesoscale Precipitation Discussion: #0451
(Issued at 1133 AM EDT Wed Jul 08 2020 )
 
MPD Selection
 


Graphic for MPD #0451
Mesoscale Precipitation Discussion 0451
NWS Weather Prediction Center College Park MD
1133 AM EDT Wed Jul 08 2020

Areas affected...Eastern PA...Northern NJ...Southern NY

Concerning...Heavy rainfall...Flash flooding possible

Valid 081533Z - 082133Z

Summary...Convection developing late this morning will be capable
of producing rain rates 1-2"/hr across eastern PA, northern NJ,
and southern NY. Localized flash flooding will be possible.

Discussion...Along a higher moisture axis characterized by PWs in
the 1.7 to 1.9" range and an instability pool (upwards of 3000
J/kg SBCAPE as of 15Z), scattered convection has developed across
portions of eastern PA and southern NY per latest GOES-E IR
imagery and radar returns. This activity is developing within weak
but persistent warm advection and likely initiating off old
outflow boundaries from earlier convection. Through 21Z, the
uncapped environment and weak mean flow should allow for continued
development of storms with pulse to loosely organized modes driven
by cell mergers and boundary interactions that will drift east.
After 17Z, the RAP suggests an increase in low level inflow to 25
kts along with increasing CAPE values to above 2000 J/kg MUCAPE.
This will support higher rain rates that could approach
1.5-2.0"/hr - the 12Z HREF probabilities for exceeding 1" are in
the 60-80 percent range and around 20-30 percent for 2"/hr.
Through 21Z, total amounts of 2-3" are possible with some isolated
amounts 3-4" possible (supported by the 6-hr probs for 3"+ around
40 percent). Antecedent conditions vary across the outlook area
with some portions having seen recent heavy rainfall and 7-day
preip departures up to 300 percent of normal. The hi-res guidance
does favor the drier areas which could limit the flash flood
potential, but the intense near-term rain rates would overcome
poor drainage, the highly urban corridor, and other low-lying ares
and may lead to flash flooding into the afternoon hours.

Taylor

ATTN...WFO...ALY...BGM...CTP...OKX...PHI...

ATTN...RFC...MARFC...NERFC...NWC...
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14 minutes ago, weathermedic said:
Mesoscale Precipitation Discussion: #0451
(Issued at 1133 AM EDT Wed Jul 08 2020 )
 
MPD Selection
       
 


Graphic for MPD #0451
Mesoscale Precipitation Discussion 0451
NWS Weather Prediction Center College Park MD
1133 AM EDT Wed Jul 08 2020

Areas affected...Eastern PA...Northern NJ...Southern NY

Concerning...Heavy rainfall...Flash flooding possible

Valid 081533Z - 082133Z

Summary...Convection developing late this morning will be capable
of producing rain rates 1-2"/hr across eastern PA, northern NJ,
and southern NY. Localized flash flooding will be possible.

Discussion...Along a higher moisture axis characterized by PWs in
the 1.7 to 1.9" range and an instability pool (upwards of 3000
J/kg SBCAPE as of 15Z), scattered convection has developed across
portions of eastern PA and southern NY per latest GOES-E IR
imagery and radar returns. This activity is developing within weak
but persistent warm advection and likely initiating off old
outflow boundaries from earlier convection. Through 21Z, the
uncapped environment and weak mean flow should allow for continued
development of storms with pulse to loosely organized modes driven
by cell mergers and boundary interactions that will drift east.
After 17Z, the RAP suggests an increase in low level inflow to 25
kts along with increasing CAPE values to above 2000 J/kg MUCAPE.
This will support higher rain rates that could approach
1.5-2.0"/hr - the 12Z HREF probabilities for exceeding 1" are in
the 60-80 percent range and around 20-30 percent for 2"/hr.
Through 21Z, total amounts of 2-3" are possible with some isolated
amounts 3-4" possible (supported by the 6-hr probs for 3"+ around
40 percent). Antecedent conditions vary across the outlook area
with some portions having seen recent heavy rainfall and 7-day
preip departures up to 300 percent of normal. The hi-res guidance
does favor the drier areas which could limit the flash flood
potential, but the intense near-term rain rates would overcome
poor drainage, the highly urban corridor, and other low-lying ares
and may lead to flash flooding into the afternoon hours.

Taylor

ATTN...WFO...ALY...BGM...CTP...OKX...PHI...

ATTN...RFC...MARFC...NERFC...NWC...

Excellent discussion and thanks for the post.  Cutting white pine limbs outside so am in and out.  Let's see what happens. 

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1 minute ago, wdrag said:

Excellent discussion and thanks for the post.  Cutting white pine limbs outside so am in and out.  Let's see what happens. 

Unless things change quickly, you and I about to get 7 10 split screw job. Shocker.

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