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CP 3 consecutive months of 10"+ and can we exceed the 3 month 2011 total of 34.43"?


wdrag
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Good Friday morning everyone,  CP is closing in and within range of a first time ever 3 consecutive months of 10+". As of 510AM the storm total of 2.02" has brought the monthly total to 9.75 with a little more to go this morning before it's all over by 8 or 9A.

Then we watch the sharp negative tilt trough out of the Great Lakes this Saturday the 24th, to see if NYC is on the western fringe of what could be a sizable rainfall for eastern LI, especially Montauk.  

Thereafter, there are possibilities NYC will be on the northern or northwest fringe of a complex mid Atlantic coast-western Atlantic low pressure system that may yet ingest a bit of SAM RH, or at the least have it's overall Western Atlantic flow altered in such a way that LI-NYC is in the mid level deformation zone yielding qpf here of .05 to .75" next Wednesday-the 29th through Saturday October 2. Timing and northwest extent of the showery rains all uncertain but not a zero chance.  Modeling of this is going may be very sensitive to overall western Atlantic response to SAM.  I just don't know but worthy of monitoring. 

AND, as a final observation of modeling: 00z/24 guidance has virtually all members showing SAM not posing a direct threat to the northeast USA, except for 2 tor 3 members.  Will monitor future modeling trends. 

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This I extracted from Don's very recent Sept post. Thought it good add here as we await further developments. Thank you for this Don!!!

Central Park picked up 2.03” of rain bringing its monthly total to 9.76”. 2021 is the first year on record with 3 consecutive months of 9.50” or more rainfall. Annual rainfall in New York City has reached 51.69”. That surpassed the 51.38” that fell in 1871 to make 2021 New York City’s 34th wettest year on record.

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New York City's Central Park still needs 0.24" of rain before the end of September to register its 3rd consecutive month with 10" or more of precipitation.

The EPS ensembles have grown a little wetter around 9/29-30. The 9/24 0z run saw 10% of members with enough rainfall to reach 10" for the month. The 12z run saw 29% of members with sufficient rainfall to reach 10" for the month.

Below is a list showing the percentage of outcomes to month's end from tomorrow and then from each day when no additional rain has fallen. The historic probability for cases when no rain was recorded through 9/28 (as is the case with the EPS) is just a little higher than the current share of EPS members showing sufficient rainfall to reach 10" for September.

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Through September 27, New York City is just 0.24" of rain away from an unprecedented third consecutive month with 10" or more of precipitation. It all comes down to this afternoon and evening as to whether the City will receive enough rainfall to make history or fall agonizingly short. No additional precipitation is likely for the remainder of September.

The 9/28 0z run of the EPS ensembles shows 29/51 (59%) members with just enough rain to push the monthly total to 10".  The ensemble mean and the 0z ECMWF operational forecast both show enough precipitation.

The individual models are about as divided as the U.S. Congress has become. Here's where things currently stand with perhaps a fragile consensus leaning against sufficient rainfall:

Yes:
0z ECMWF
6z HRRR
6z RGEM
0z UKMET (0.70"!)

No:
6z GFS
0z GGEM
0z HREF
6z NAM/3 km NAM
11z NBM (0.19")

And historic experience (1869-2020) is no more decisive. Of the 50 cases that saw measurable precipitation on September 28, 46% reached 0.24" or above.

And the SPC discussion:

Scattered showers and thunderstorms should be spreading across the central Appalachians vicinity at the start of the period, ahead of a weak/fast-moving mid-level short-wave trough.  This convection -- and associated cloud cover -- casts some uncertainty over northern portions of the risk area with respect to subsequent heating/destabilization.  In general however, areas from northern Virginia eastward across the Delmarva Peninsula to southern New Jersey should experience ample pre-frontal heating such that -- given rather steep mid-level lapse rates being advected eastward and ample low-level moisture -- a zone of 1000 to 2000 J/kg CAPE is expected by late afternoon.

All said, the outcome is going to be a nail-biter. But if a thunderstorm crosses Central Park, we'll probably get the needed rainfall.

 

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3 minutes ago, wdrag said:

Yea!  Bluewave/Don et al must have some stats for us on what this might portend. 

Somehow, I always thing of going back to the means...ie, drying out below normal sometime ahead. 

hopefully its not during the winter like 2012...

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35 minutes ago, wdrag said:

I'm leaving this to our more informed mets-statisticians about the oscillation interactions.

lucky for us the enso is slightly weaker than 2011-12 and the QBO was twice as strong but fading...This year's QBO was getting stronger as of last month...

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8 hours ago, wdrag said:

Yea!  Bluewave/Don et al must have some stats for us on what this might portend. 

Somehow, I always thing of going back to the means...ie, drying out below normal sometime ahead. 

I will have a look tonight or tomorrow. I share your concern about drying out, especially if summer and fall are very wet.

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9 hours ago, donsutherland1 said:

With 0.25" rain through 12:08 pm, New York City's Central Park has now reached 10.01" rain for September.

That's just squeaking by imho, but I guess it passes muster....

On the East side, near 72nd St, I don't think it came close to 0.25".

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4 minutes ago, donsutherland1 said:

That could mean less snowfall in the winter all other variables notwithstanding.

I'm thinking that this is our new average rainfall....I think we've had 50 or more inches of rain more often than not, compared to the 80s when it only happened in 1983.  I'm not sure it happened at all in the 90s.

 

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7 minutes ago, LibertyBell said:

I'm thinking that this is our new average rainfall....I think we've had 50 or more inches of rain more often than not, compared to the 80s when it only happened in 1983.  I'm not sure it happened at all in the 90s.

 

Rainfall totals increased fairly abruptly after 1970.

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