El Nino Arrives - Expected to Persist Through Winter 2009-10

Eastern Pacific sea-surface temperatures were at least 1 degree celsius above average at the end of June and NOAA scientists expect this trend to continue into the winter.  The warming equatorial waters of the Pacific Ocean are signaling a return of El Nino, a phenomena that can have varied and wide-ranging weather impacts around the globe.  Click here to read more about El Nino's return.

For Wyoming, the return of El Nino has signaled a drier than average October through March period in the past.  This has been more true across the northern-third of the Cowboy State.  However, in late spring - April through June - above average precipitation has previously been observed in areas of central Wyoming east of the Continental Divide.  As for temperatures, near normal to slightly above normal readings have been common statewide in past El Nino episodes.  It is important to note the effects of El Nino are more ambiguous across southern Wyoming.

General expectations for other portions of the western U.S. would be for a warmer and drier winter across the Pacific Northwest, Idaho, and Montana, while a cool and wet winter could be in store from southern California east across Arizona and New Mexico.  These general trends are the result of a persistent Pacific jet stream which is shunted farther south across the southern-tier of states, leaving the northwest drier and warmer.

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