Summary

September 2014 precipitation was well above normal for a large portion of southwest Idaho and southeast Oregon, thanks to the first major low pressure system of the season near the end of the month. During September 26 through 29, a closed low moved slowly east across the northern Great Basin and produced widespread rainfall of 0.75 to 1.50 inches from extreme southeast Oregon across most of southwest Idaho.  Portions of the Upper Payette Basin and Upper Boise Basin received over 2.00 inches of rain during the period. Aside from the end of the month system, September was rather dry and warm.

September 2014 Precipitation

The temperature anomaly for the month was generally +2°F to +4°F across southwest Idaho and southeast Oregon.

September 2014 Temperature Anomalies

Long-term drought continues to plague much of the area with the worst conditions across southeast Oregon.

October 21, 2014 Drought Monitor

August was an uneventful month in Boise, but another story south and east in the central Idaho Mountains and the Magic Valley.  While Twin Falls recorded 5.57″ in August, we don’t have a sufficient climate record to compare with other August years, with climate data back to only 1998.  Instead, let’s take a look at the climate data from Jerome, Idaho, which extends back to 1915.

While we often present historical data in chronological order by year, it can be helpful to view the data in ascending order.  Putting the data in ascending order helps us see how unusual the precipitation was for this area and particular month. Here we look at the precipitation data for Jerome, Idaho from 1915 through 2014.

August Precipitation (1915-2014) at Jerome, ID

The average precipitation in August for Jerome is 0.29″ and the median precipitation is 0.125″.  The median represents the 50% value at which years are drier or wetter.  An interesting fact from looking at this data is how skewed the data is: 72.4% of the time August precipitation is below normal, and  27.6% of the time August precipitation is above normal.  Thus, if you want to look smart in front of your friends, make a bet with them each year that August will be below average, you will have a 72.4% chance of being right. Notice how the average is skewed by a handful of wet August months in the past, most notably 1968 and of course this year. August 1968 is the only August in history which comes close to the 2014 precipitation record.  August 1968 was also the highest August precipitation recorded in Boise, with 2.37″.