September Climate Data

Looking back at September climate anomalies in Alaska, I think the most unusual aspect statewide was the excess cloud cover that was produced by low pressure aloft extending east from Russia.  The abundant cloudiness prevented temperatures from dropping off at night and therefore held frost at bay until the very end of the month in some places.

Here's the estimated percentile of September solar radiation compared to the prior 30 years: below normal nearly everywhere, and among the lowest (cloudiest) in the SE interior, the western North Slope, and the central Aleutians.

Here's the mid-atmosphere pressure anomaly pattern:

Overall temperatures (day and night combined) were not a whole lot different from normal in much of the state, but the North Slope was an exception, with very unusual warmth.  It was the second warmest September on record in Utqiaġvik (formerly Barrow).  In contrast, a lot of unusual coolness persists in the Bering Sea, associated with a very strongly negative PDO phase.

Precipitation was below-normal in parts of northwestern Alaska, a welcome change after an extremely wet summer; but the SE interior was wetter than normal, which also reflects a change from summer.

As for wind, September was much calmer - relative to normal - than summer, and was much less windy than normal in the north and east of Alaska.  This change is closely linked to a major reversal in the Arctic pressure pattern: the Arctic Oscillation was strongly positive in August (Arctic low pressure), but it flipped to significantly negative in September (Arctic high pressure).  This phase reversal appears to be somewhat typical of La Niña.