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October 2018 Discussions & Observations Thread


Rtd208

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For those looking towards the horizon for more highly anomalous weather, the GFS has been periodically advertising the storm that @earthlight mentioned in his twitter post. While the different runs have varied the outcome, the general idea is to take a piece of energy that comes into Southern California in about 8 days and phase it with a trough that drops through the plains a few days later. The end result is a powerful low pressure system which deepens rapidly thanks to a tremendous amount of baroclinic forcing. 

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Through October 15, the temperature has averaged 66.2° in New York City’s Central Park. That makes 2018 the 11th warmest October 1-15 period on record. Records go back to 1869.

The second half of October looks to be notably cooler than the first half. In fact, it could be among the coolest periods to close October from among the cases where the first 15 days had averaged 65° or above, with a mean temperature of 54° or below for the 10/16-31 period.

Select data for 15 prior cases with an October 1-15 mean temperature of 65° or above:

October 16-31:
Mean temperature: 55.7°
Lowest: 49.8°, 1922
Highest: 60.7°, 2007

October Monthly Average Temperature:
Mean temperature: 61.1°
Lowest: 58.1°: 1922
Highest: 64.1°, 2017

Sensitivity analysis applied to the guidance:

Probability of a warmer than normal October: 66%
Estimated range for the October 16-31 period: 49.0°-54.0°
Estimated range for the October 2018 mean temperature: 56.8° - 59.7°

The relatively cool conclusion to October after a very warm start has often coincided with a snowy winter. From among the 15 cases cited above, 6 had a mean temperature below 55° during the October 16-31 period. Four of those cases saw 30” or more snow during the following winter.

Even as the GFS has persistently signaled the potential for a significant storm to close October, the forecast state of the teleconnections suggests that such a storm could take a course in which the heaviest precipitation misses the Philadelphia to New York City corridor. Areas on Long Island into New England could have a better chance of seeing 1” or more precipitation. Much can still change, as the period in question is approximately 9-12 days away.

Finally, the latest EPS weekly guidance is colder than the CFSv2 for the first week in November. The former maintains a fairly deep trough in the means in the East.

 

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More banter, but also relevant given the patterns we have seen twice in the last 13 months:

 

Anyone else worried about the extreme flip pattern from Sept 2017 and January 2018 returning after this cool snap?

If that pattern holds, mid November, thru much of December would be AN, correct?

I believe that we are expecting an El Nino December as well...

 

 

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37 minutes ago, jfklganyc said:

More banter, but also relevant given the patterns we have seen twice in the last 13 months:

 

Anyone else worried about the extreme flip pattern from Sept 2017 and January 2018 returning after this cool snap?

If that pattern holds, mid November, thru much of December would be AN, correct?

I believe that we are expecting an El Nino December as well...

 

 

El Niño winters are traditionally back loaded, ie colder and stormier late winter than early. Hopefully blocking can show up but not too stout like often in 09-10. 

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