September ties record for heat

By Rod Hill on 2014-10-01


September continued Portland's hot summer. Climate numbers from the National Weather Service show September tied the all-time PDX record for mean temperature of 67.6 degrees. The average low last month was 56.5 degrees, which was the 2nd warmest on record. (Records at PDX date back to 1941.) Both the mean and low temperature average were more than 3 degrees above normal. The average high temperature of 78.7 degrees did not crack the list of top 5 warmest months. The trend of warm nights leading to records while hot afternoons fell short of record territory began back in July. Take a look:

July low temperature average: 4th place all-time at PDX.

August low temperature average: Warmest all-time at PDX.

September low temperature average: 2nd place all-time at PDX.

In each of the three months above, warm low temperatures set the pace for near and record mean temperature averages. The summer of 2014 did in fact finish with no daily record high temperatures. In contrast, September tied or set 4 daily low temperature records and the summer months of July, August and September combined to tie or break 11 daily low temperature records.

The weather pattern likely responsible for record nights and hot afternoons falling short of record territory was a south to southwest wind flow and few summer days with strong east winds. Warm air masses overall helped to keep 24 hour temperatures often above normal. Most of Portland's extreme record highs of 100 degrees or better have come with intense high pressure and east winds, a combination the valley seldom saw this past summer. It may be true, that often smoky skies also played a role in holding temperatures up at night and slightly cooler during the day, although many of the record low temperatures occurred prior to wildfire smoke covering the skies in August and September.

(Mean temperature is the average temperature of a 24 hour day.)

Meteorologist Rod Hill