When looking at the 5-day mean 500mb height anomalies off the models, there is one aspect which really sticks out. The warm water of the eastern Pacific has differing influence on the atmosphere depending upon latitude. The El Nino and dramatic warming over the eastern equatorial Pacific is already significantly influencing the US atmospheric pattern but our old friend, the warm Gulf of Alaska also continues to influence.

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Check out the below GFS 5-day mean 500mb height anomalies and notice the persistency in Alaska/NW Canada RIDGE vs the Southwest Desert TROUGH. Both are caused by feedback off a warm Pacific Ocean.

GFS operational

The unusually persistent trough over California and the Southwest is due to the warming waters down towards the equator while the unusually persistent and strong ridge 1,500 miles to the north continues to rule Alaskan air space. Both a result of an abnormally warm east Pacific but that warm water is having differing effects on mid and upper level pressure, dependant upon latitude.

Warmer than normal water in the tropics tends to lower pressure above whereas warm water into the mid or high latitudes tends to support higher than normal pressure. So, because of this we’re seeing unusual precipitation and cool in places that should be naturally heating and drying out (California) and where it’s typically cool and damp (Alaska), it’s warmer and drier than normal. Of course that warm NE Pacific has lead to 2 and a half years of abnormal warmth up in Alaska and this extends down the western flank of the continent.

As a direct consequence to the strengthening El Nino, we’re seeing a cooler and even more impressive, WET pattern for California and the Southwest in the now ‘dry season’. Where rainfall has been prolific, it’s been the Southern and Central Plains.

Check out the past 7 day anomaly over the Central Plains.

A lot more to come in the next 10 days.

The Palmer Drought Index already suggests that the Southern Plains drought is over!

US drought monitor still shows drought but this is shrinking big time.

If the El Nino continues strengthening and I believe it will into fall then we may have another event similar to 97-98 on the way for California come winter 2015-16 which means major rainstorms and potential flash flooding and mudslides. What we’re seeing now in the Plains, we may see by the spring of 2016.

A very El Nino-like precipitation outlook for much of United States now through to the start of winter.

No video tonight due to technical issue. Apologies.

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Tags: el nino, ENSO, southern oscillation index