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September 2018 Discussions & Observations Thread


Rtd208
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Warm minimums really driving the temperature departures this month. Pretty lopsided results so far with all the clouds and high humidity.

LGA

AVG....+3.1

MIN....+4.8

MAX....+1.4

ISP

AVG....+3.8

MIN....+5.8

MAX....+1.9

EWR

AVG....+2.9

MIN....+4.8

MAX....+0.9

ALB

AVG....+4.6

MIN....+6.9

MAX....+2.3

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The first 6 days of September saw the temperature average 80.2° in Central Park, the 8th warmest start on record. Back then, it was noted that 57% of the prior cases saw September finish with a monthly average temperature of 70.0° or above. The statistical probability of such an outcome based on a sensitivity analysis for 6 days of data, MEX MOS for the following 10 days, and EPS for the subsequent five days was also 57%.

Since then, the monthly average has declined on account of cooler readings. Through September 12, the monthly average had decreased to 73.2°. That ranks 36th warmest for the 1869-present period.

During the 1869-2017 period, there were 42 cases in which the first 12 days of September had a mean temperature of 73.0° or above. 60% of those cases wound up having a monthly mean temperature of 70.0° or above. The statistical probability was 56% for those cases. The lowest monthly mean temperature among those cases was 66.5° in 1966. The highest was 74.5° in 2015. Both the mean and median figures for those 42 cases were 70.3°.

Re-running the sensitivity analysis for the 12 days of data and same approach to the guidance (MEX MOS and EPS), the implied statistical probability of September’s finishing with a mean temperature of 70.0° or above has increased to 59%. The likely range for the monthly mean temperature was 69.2° - 72.6°. So, at least at this point in time, September 2018 appears to have remained on course for yet another exceptionally warm monthly average temperature.

Finally, with this morning’s 0.13” rain, New York City’s annual precipitation has risen to 43.70”, which ranks 81st. It is very likely that New York City will receive 50” or more precipitation in 2018 and somewhat likely that it could approach or reach 60”.

Using the historical 1869-2017 period, the associated probabilities are:

50” or more: 94%
60” or more: 22%

Using the 1971-2017 period, which is a wetter regime, the associated probabilities are:

50” or more: 96%
60” or more: 39%

In terms of significant rainfall in the medium-term, the  9/13/2018 0z ECMWF took the remnants of Florence on a course that would bring New York City more than an inch of rain (the ECMWF forecasts >2” for a large part of the area). But that’s still 4-6 days away, so such an outcome remains subject to considerable uncertainty.

 

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1 hour ago, SACRUS said:

More like Denmark in the spring.  If you looked at the 500 MB map the last 8 days youd think we would have been +8 - 10.  ONce we clear in 2023 we should warmup nicely.

 

In all seriousness - ECM is back to predominant higher heights in the Sep 20 - 24 period perhaps the next window for a little late season heat. 

This pattern is probably on lock until the wave lengths change. It's crazy how it just stays locked in for months.

A lot more cloudy days in store though with plenty of onshore flow. 

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Percentage of cloud cover for the first half of September ahead of February. Hopefully, the second half brings more sun and we fall behind the full month of February percentage.

https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=45&network=NY_ASOS&zstation=LGA&hour=12&year=2018&month=9&dpi=100&_fmt=png

network-NY_ASOS--zstation-LGA--hour-12--year-2018--month-9--dpi-100.png.0c31402658dfa3f1503d0cccfdb466a4.png

 

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11 hours ago, gravitylover said:

Every time I try to explain this to people they tell me I'm wrong :whistle:

Those people are probably lonly ooking at October through March when the city averages about 75% of its average yearly total. We sought of get imprinted with those monster fall and winter Pacific lows that crash into the nortwest coast. Summer there seems very dry.

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4 hours ago, rclab said:

Those people are probably lonly ooking at October through March when the city averages about 75% of its average yearly total. We sought of get imprinted with those monster fall and winter Pacific lows that crash into the nortwest coast. Summer there seems very dry.

IME it is very dry there for a good part of the year, I've only been there in June and July but I've never seen more than a few clouds in the sky and temps over 80*. As with most of the Pacific coast the days start out grey but it's low level fog that burns off by ~10am, that's why it's so lush from about Santa Barbara north into Canada and the Redwoods are able to grow to such staggering heights even though it's so dry for so many months.

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