WEATHERAmerica Newsletter, Sunday, September 13, 2025; EXTENDED PERIOD FORECAST

[Larry Cosgrove]

EXTENDED PERIOD FORECAST

(Between Day 11 And Day 15)

 

Two Question Marks: Another Amplified Upper Air Pattern? And What's With The Tropics?

CIMSS (3)

TropicalTidbits.Com (Dr. Levi Cowan) (3)

NOAA/PMEL

NOAA/CPC

HPRCC/University Of Nebraska (2)

Environment Canada

TropicalTidbits.Com (Dr. Levi Cowan) (5)

WeatherBell.Com (4)

NOAA/CPC

The near term and medium range may seem almost boring, but that is a common theme when the tropical weather systems go quiet. Rest assured that the lack of depressions or named storms will not go on forever; history tells us that the second seasonal maximum occurs in the first two weeks of October, and that the number of junk storms in higher latitudes will increase the final total for subtropical and tropical features. The longer term can tell us something about how the winter will develop in North America, and I can already see systems organizing which give us valuable clues on pattern evolution for the DJF trimester.

Even though the ENSO signature is unquestionably La Nina, you may have noticed that the eastern equatorial Pacific Ocean theater is far more active than the Atlantic Basin and its branches. It looks like the Mexico/Central America named storm list will top out with 17 named cases of warm-core cyclogenesis. My earlier calls for an active year from the Cape Verde wave train have admittedly not verified, and we may have less organized systems than to the left of the West Coast. The constant pulsing of the Saharan Air Layer is probably at fault. A concern has arisen that with weaknesses a recurrent theme in the 500MB configuration, any storm could easily turn north and affect the lower 48 states to the east of the Rocky Mountains. Keep in mind that some of the most major weather events in autumn in the USA are due to a combination of waves, depressions, etc. with mid-latitude storms and frontal structures.

Occasionally, the upper air alignment across and about the continent has amplified, with ridging in the -EPO, +PNA, -AO, and -NAO positions. Deep polar intrusions have formed and dug southward, with the most recent covering the eastern two-thirds of North America. The cooler values last about four days, and it seems probable that another cPk regime could influence the nation in the upcoming 11-15 and/or 16-20 day time frame. If elongation of these trends occur as we head through the autumn and into winter, this could mean a colder outcome. The La Nina episode will likely peak in February, then start to go toward a positive-neutral environment in Sector 3.4 around and after April 1. Climatology on such developments does not assure a cold winter; do not make the mistake of using one synoptic or index parameter to make a prediction. But looking at this set-up, there is an increasing chance that the 10 year run of mostly mild national winters could end.

 

Prepared by Meteorologist LARRY COSGROVE on 
Sunday, September 14, 2025 at 2:15 A.M. CT

Disclaimer: 
The previous statements are my opinions only, and should not be construed as definitive fact. Links provided on this newsletter are not affiliated with WEATHERAmerica and the publisher is not responsible for content posted or associated with those sites.

Copyright 2025 by Larry Cosgrove

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