Event Discussion-OBS uncertain tracking thread for possible moderate impact event 8A Thu-8A Fri 10/30-31. Mainly 1-3" rains, G 45-55 MPH-mainly coast, and high prob of at least minor coastal flooding - Thursday afternoon high tide cycle.

[wdrag]

Please follow any NWS Watches, warnings, statements that may arise from this coming minor or moderate event.

This is a D4-5 advance heads-up thread for those who have a need to be advised. Modeling has plenty of spread in solutions so that the ensembles are somewhat muted.  There is no doubt in my mind that some sort of minor or possibly moderate impact event is coming. Modeling has been wavering for the past 4 days and hopefully uncertainties resolve by mid week.  If I had plans as a motorist or via air travel Thursday-early Friday, I'd think about delays and how to minimize adverse impact, then possibly implement changes Tuesday or Wednesday  Timing of the 6-10 hour worst case is uncertain. 

Beneficial rainfall should result in October totals at all NWS OKX-Upton climate sites roughly 3.3-4.3", within about 1/2" of normal. Not everyone will get 1"+ but the attached Sunday afternoon 10/26 WPC guidance is a best estimate for D4-5. Rainfall still could end up less than indicated.  A graphic of average return interval (ARI) for various event amounts, at NYC,  is attached-not alarming. 

This could still end up a routine event although I think wind can add impact. Rainfall intensity during one of the rush hours combined with potential for a period of east-southeast wind gusts 45-55 mph on the remaining wet fully leaved trees may result in a scattering of broken limb caused power outages, similar to the 10/12-13 event.

Lunar cycle argues for maximum worst case coastal flooding in the minor category. Modeling from P-Surge is attached.  It might be too robust (follow NWS), suggesting a worst cause 3 ft surge along parts of the coasts during the Thursday afternoon-evening high tide cycle (using Sandy Hook as example).  Lowered pressure this time compared to 10/12-13 contributes to the surge. Please be aware ensembles are not showing much more than 50-55knot se inflow here, limiting potential for excessive rainfall and surge.  

There is a slightest chance for isolated severe however CAPE seems to be very limited, despite the favorable strong shear and diffluent upper level flow.

A 100-150M 12 hour 500 MB Height Fall Center circles northeastward from the southeast central USA into PA/NJ early Friday.  That helps drive the relatively short duration heavy rain event. Presuming the upper Low continues to evolve northward through PA into NYS the eastern Great Lakes there should be a progressive rapid improvement sometime Friday morning.

Westerly winds may gust 25-35 MPH at times during Halloween evening but hopefully without any showers in the area. 

Ensemble rainfall from several modeling centers has been attached as something to look back upon Saturday 11/1 when all the totals are in.  The 500MB ensembles attached also show the 12 hr HFC.  Fairly modest in comparison to some of the operational cycles we've been seeing the past several days.  

If the 5h ensemble pattern prevails or is further west, then we've tracked a routine event. 

The thread current headline will eventually update if moderate impact potential decreases.  For now this hopefully adequately summarizes what is on the table for rain/wind/coastal concerns.

Let's see if its worth tracking. 620P/26

[psv88]

Thanks Walt, great write up 

[wdrag]

Update through 658A/27... no changes. Ensemble modeling continues similar with two groups..eastward wetter GEFS suites and slightly westward EC suites. Results are similar. 

I am not planning to work outside Thursday in northwest NJ, cleaning my gutters of leaves the day before-Wed AM... might need standby DVD in case of internet-power outage Thu afternoon as all modeled products this morning are similar to what we saw yesterday, including the high likelihood of coastal flooding with the Thu aftn-evening high tide cycle.

06z GFS went a little ballistic on qpf and that is related to the nearly stand still Thu aft-evening inflow pattern with PW over 1.5", caused by a suddenly intensifying 5H HFC across NJ---I cant figure the reasons for that... almost like a breathing 5H low HFC... 200M HFC TN Valley a day or two before, then weakens across VA and suddenly strengthens PA/NJ Thurs.   IF it happens, I'd have to add an inland flooding tag to the thread and update ARI since this sole GFS cycle has spot 6" amounts in se NYS.  I'm not buying that solution right now.

One thread change that I may have to make is beef up the chance of iso svr ... but will wait til Tuesday evening before any adjusting.

 

[wdrag]

High Shear Low Cape (HSLC) environment for e PA/NJ/LI Thu afternoon? Don't know. We'll monitor SPC etc on this. Right now flash density from the 12z/27 EC op has a possibility of thunder here Thu afternoon NJ/ NYC. 

Back tomorrow. 

[wdrag]

Last several GFS op cycles offering 4+ in a narrow band roughly MMU-POU... something to model monitor tomorrow. Likely my last on this til Tue am.

Unsure whether PHI or OKX are looking at HSLC etc.

 

[SnoSki14]

14 minutes ago, wdrag said:

Last several GFS op cycles offering 4+ in a narrow band roughly MMU-POU... something to model monitor tomorrow. Likely my last on this til Tue am.

Unsure whether PHI or OKX are looking at HSLC etc.

 

I wonder if Melissa shifting a bit more NW is helping to amp those totals too via tropical enhancement or some kind of PRE

[wdrag]

10 hours ago, SnoSki14 said:

I wonder if Melissa shifting a bit more NW is helping to amp those totals too via tropical enhancement or some kind of PRE

There might be some impact from Melissa--adjusting the flow patterns, but for now... I'm not attributing Melissa indirectly -- I'd have to prove it w some science and that for me is not easily done. Speculation herein warranted but not for media as yes (gospel pronouncement).

Basically what I see is a routine event Thursday... the 09z/28 WPC 3 day beneficial totals are within the 1 year repeat interval so its just a matter of impacts on travel.

I don't see anything worse than thread headlined. Wind advisory coasts Thursday ahead of the low, and then maybe again behind it Friday afternoon-eve; scattered tree limbs down here and there for power outages, but not extensive unless we get a good squall-line (HSLC) event Thursday afternoon-evening. Coastal flooding limited to minor, imo-psurge values into minor have decreased on the GFS/GEFS/NAEFS. Therefore, its the previously exposed (Oct 12-13 event) coastal locations that seem most vulnerable to coastal flooding (NJ),. 

Still time to adjust but for now my anticipation has waned a bit due to the upper 5h low arcing northeastward through western-central PA. 

 

[jm1220]

Hoping we get decent rain east of the city since it’s still needed. Looking like the best rain may be setting up west of us again.

[wdrag]

15 minutes ago, jm1220 said:

Hoping we get decent rain east of the city since it’s still needed. Looking like the best rain may be setting up west of us again.

Kind of agree...

still not to give up hope since neg tilt, instability aloft. In bands... probably best eastern PA into central NYS northwest of the 850 low, but all modeling continues with beneficial amounts for the forum. Impossible for me to know for sure...  ensembles (esp EC and ECAI ae larger than I anticipated when looking at their 00z/28 ops).

[Stormlover74]

Nam is still delaying the onset of the rain until mid afternoon Thursday 

[Stormlover74]

[jm1220]

5 minutes ago, Stormlover74 said:

Yep, looking like a shafting east of I-95. 

[Stormlover74]

6 minutes ago, jm1220 said:

Yep, looking like a shafting east of I-95. 

Its the most extreme model solution right now

[qg_omega]

21 minutes ago, Stormlover74 said:

Its the most extreme model solution right now

its just a cold front passage, run of the mill

[FPizz]

29 minutes ago, Stormlover74 said:

Its the most extreme model solution right now

CMC a bit wetter for NJ

[Sundog]

47 minutes ago, jm1220 said:

Yep, looking like a shafting east of I-95. 

It would really be something if a giant low came through the area and only dropped a couple of tenths in central NJ

[ForestHillWx]

That dry slot will suck. 

[WestBabylonWeather]

2 hours ago, FPizz said:

CMC a bit wetter for NJ

LOL if this verifies. Dry as a bone here 

[jm1220]

3 hours ago, Sundog said:

It would really be something if a giant low came through the area and only dropped a couple of tenths in central NJ

ESE flow ahead of a low tracking inland means lots of upslope for E PA/upstate NY and showery weather for the city/coast. Some places east of the low would get lucky with banding but by far the best would be well inland. Looking like a couple/few day nasty period without much drought help here. Thankfully we had the storm mid month to help a little. 

[MANDA]

Working in the yard the last few days and the top soil is dust.  Bone dry.

October rainfall to date at my location is 1.56".  That is FAR better than last October when the entire month had just a Trace.

Still need rain badly.  Think reasonable expectation for my area is 1" from the coming event based on current guidance.

Anything more will be a gift and anything less will be a disappointment.

 

 

[wdrag]

Probably my last til 8A tomorrow an then I'll be off line all day tomorrow roughly 830A-8P.

NO changes to the thread headline... I like it very much as is.  Mesoscale modeling will show bands of 3" and some spots 1/2-1". 18z HRRR and NAM have no dry slot til after 03z/31. 

18z WPC continues with their 1-1.75" isohyets for virtually the entire subforum.   They must have gone with the heavier 12z EPS/EPSAI ...maybe Deepmind? though I dont have access to Deep Mind.  12z CMCE and GEFS were less than WPC so there is always that possibility. The 12z ensembles were heavier than many of op runs. Lets see how it plays. I have not read any discussions today from NWS.. so there may be some reasoning I missed. 

PHI has started their advisory for coastal flooding NJ coast south of Monmouth. It's only a matter of time I think that the advisory expands northward, but FOLLOW NWS.

I suspect a wind advisory issues for coastal sections tomorrow morning (6 hr window in the aft or eve depending on location) and reserving the back side. That prepares folks for some delays etc. Friday wind advisory possibility NJ/LI reserves for a later issuance.  

HSLC thunder and squally gust possible late Thu. 

There is going to be significant impact for a few hours Thursday, especially afternoon-eve. 

One final addition at 450P. NAM 5H 12 hr HFC cyclicly at least last 3 cycles near 200M in e PA around 06z/31.  Should become a little unstable for a few hours ahead of it.