Alaska Weather Summary - September 2011

October 10, 2011


Temperatures were above normal in September for most of Alaska. High positive deviations (greater than 3 degrees Fahrenheit) were observed in declining order for Barrow (4.6 degrees), Fairbanks (4 degrees) and Big Delta (3.9 degrees). Like the previous two months, Barrow reported the largest positive deviation of the eight-city summary. The only negative deviation was observed in Juneau at minus 1.2 degrees Fahrenheit. Precipitation was above normal for only two stations: Ketchikan, where twice the expected rainfall was observed, and Barrow, with 28 percent above the normal value of precipitation. Juneau received the expected amount, while the remaining five other stations recorded a precipitation deficit. The greatest deviations in precipitation were observed in Anchorage and Big Delta. Both stations recorded only a quarter of the normal values. 


Anchorage recorded an average temperature of 48.8 degrees Fahrenheit, just slightly (0.2 degrees) above normal. The maximum temperature of the month occurred September 13, with 65 degrees. A minimum temperature of 32 degrees was observed on three consecutive days – September 26, 27 and 28. No new records were set and the observed daily temperature ranges followed fairly close to the expected values. Precipitation was reported at 0.78 inches, which represents only 26 percent of the normal value. Nevertheless, mean monthly cloudiness was high (78 percent) and not a single clear day was observed during the entire month. The average monthly wind speed was 5.2 mph. A gust of 47 mph was recorded September 13.


In September, Barrow reported an average temperature of 36.7 degrees Fahrenheit, 4.6 degrees above normal. The maximum temperature occurred September 11. It was 51 degrees. The lowest temperature observed was 20 degrees on September 30. In general, the temperatures during most of the first half of the month were far above normal, while the second half were closer to normal. No new temperature records were observed during September. Precipitation in Barrow totaled 0.92 inches, 28 percent above the normal value of 0.72 inches. Additionally, 4.9 inches of snow fell. The greatest amount of snow, 1.3 inches, occurred September 27. Trace or more amounts of snow were recorded on 18 days of the month. The mean monthly wind speed was 11.8 mph. Gusts of 37 mph occurred on September 17 and 18.


Big Delta reported a mean temperature of 47.8 degrees Fahrenheit, which is 3.9 degrees above the long-term mean temperature for September. The high temperature of the month, 71 degrees, was observed September 13, surpassing the maximum temperature recorded for August 2011 by one degree. Furthermore, the temperature on September 13, 2011 set new maximum daily record for the date, surpassing the old value of 67 degrees, which occurred in 1965 and 1956. The low temperatures for the month occurred September 26 and 29. On both days, the temperature was 30 degrees Fahrenheit. The first day of frost occurred September 26, which is quite late in the season. Precipitation totaled 0.27 inches, 74 percent below the expected amount. No new precipitation records were set during the month.


The average temperature in Fairbanks was 48.9 degrees Fahrenheit in September. This was a substantial four degrees above the long-term mean for the month. The month’s high temperature was 72 degrees on September 5 and 13. The lowest temperature of September was 28 degrees, observed on the 30th. September 26 was the first day the temperature dropped below the freezing point, ending the growing season. Even though this did not set a record, it continues a trend of later frosts in fall. The mean annual temperature of Fairbanks has increased 2.5 degrees over the last century, a substantial value and about twice the global mean increase. Perhaps even more impressive is the change in the duration of the frost-free season that increased by 45 percent over the same time frame. Precipitation in September was 0.65 inches, 41 percent below the expected value. The combination of warm temperatures and below normal precipitation made for a pleasurable month. Wind speed averaged 3.6 mph and the highest gust was 26 mph on September 19. No new temperature or precipitation records were observed. 


In Juneau, the average temperature in September was 48.8 degrees Fahrenheit, 1.2 degrees below normal for the month. The maximum temperature for the month, 65 degrees, occurred September 12. The month’s minimum temperature, 33 degrees, occurred September 25. No frost was observed. Precipitation totaled 8.58 inches, which was very close to the normal of 8.33 inches. Sky cover was high in Juneau, with no clear days, eight partly cloudy days and 22 cloudy days. Average wind speed at the Juneau International Airport was 8.8 mph, with the highest wind gust, 71 mph, occurring September 21. 


Ketchikan's average temperature of 53.8 degrees Fahrenheit in September was 1.3 degrees above the long-term mean. The highest temperature of the month, 70 degrees, was measured on September 12. The month’s low temperature, 40 degrees, occurred September 25. Even though the mean monthly temperature was somewhat above the expected value, the daily temperature ranges followed fairly closely to the long-term means. No new temperature extremes were recorded. Monthly precipitation was heavy and totaled 28.33 inches, slightly more than twice the expected amount of 13.79 inches. Precipitation occurred on 28 days of the month. Of note was September 20, with a daily total of 5 inches of precipitation. Despite the heavy rainfall, no new precipitation records were set during the month.


In September, King Salmon reported an average temperature of 47.8 degrees Fahrenheit. This temperature was very close to the long-term mean of 47.6 degrees. The month’s high was 63 degrees recorded September 6 and 9. The month’s low temperature occurred September 28. It was 25 degrees Fahrenheit. The first frost occurred September 26, which ended the growing season. The precipitation total was measured at 2.25 inches, 29 percent below normal. Some rain, if even just a trace, was recorded every day of September. The average wind speed was 7.1 mph and the highest gust was recorded at 49 mph on September 12. 


For Kodiak, the average monthly temperature, 49.2 degrees Fahrenheit, was close to the long-term mean of 49.6 degrees. The highest temperature occurred September 3. It was 60 degrees. The lowest temperature of the month was 32 degrees on September 29, which led to the first and only frost of the month. No temperature records were set in September. In general, the daily temperature ranges were very narrow for the first half of the month and larger than expected for the second half. The mean wind speed was 8.3 mph. The highest gust, 53 mph, was recorded September 5. Monthly precipitation was heavy and totaled 15.49 inches, more than twice the expected amount of 7.07 inches. Precipitation, if even a trace amount, occurred on 28 days of the month. Three new daily precipitation records were set in September. The first one was set on September 2, with 2.21 inches, breaking the old record of 1.47 inches that had been in place since 1943. On September 5, 1.59 inches of rain narrowly broke the 1982 record of 1.54 inches. Finally, September 12 saw a heavy 3.46 inches of rain, shattering the old total of 1.7 inches from 1979. This last record resulted in mudslide on the Chiniak Highway near Kodiak.


Nome reported a mean monthly temperature of 45.1 degrees Fahrenheit in September, which was a positive deviation of 2.3 degrees from the long-term mean. The month’s warmest temperature was 62 degrees observed September 16. The coldest temperature occurred on the two last days of the month. It was 27 degrees Fahrenheit. No new temperature extremes were observed during September. Precipitation was light, totaling 0.9 inches, representing only 37 percent of the expected amount. Eighty-eight percent of that precipitation total occurred on just three days – September 9, 10 and 24. The average wind speed for the month was 9.1 mph. The highest gust was observed September 6. It was 48 mph.


This information consists of preliminary climatological data compiled by the Alaska Climate Research Center, Geophysical Institute, University of Alaska Fairbanks. This summary is based on the 20 first order stations in Alaska operated by the National Weather Service. Extreme events of other stations are also mentioned. It should be noted that the new climate normals for the time period of 1981-2010 are applied for the calculations of the deviations, and they can be slightly different from the old normals (1971-2000), which were in use up until end of July 2011. 


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