Overall, June was slightly warmer than normal, but daily averages fluctuated from 15 degrees above normal on the 7th to 12 degrees below normal just a few days later on the 11th. No records were equaled or broken.
Precipitation was slightly more than twice normal, although it was a mostly dry month. The anomaly occurred on the 11th and 12th, when 1.15 inches of rainfall was measured at the airport. The total for the other 28 days was only a quarter inch.
The first week was warm and dry, dominated by an upper level high pressure ridge extending from the Colorado Plateau to the northern Plains. The high for the month of 97°F on the 7th was repeated on the 25th.
On the 9th, a cold upper level low pressure area from the Gulf of Alaska began to invade the Pacific Northwest states. By the 12th, it was centered over the Idaho-Nevada border. The well developed counterclockwise circulation pulled in copious moisture which originated in the Gulf of Mexico and crossed the Rockies from eastern Montana. This resulted in the heavy rain which fell mainly overnight between the 11th and 12th.
Despite the subtropical origin of this moisture, cold north Pacific air kept Boise’s temperature well below normal.
Following this system, the temperature rebounded to normal on the 15th. And on the 19th and 20th the upper level ridge, having expanded north from the Desert Southwest, pushed the temperature up to 96°F both days.
Sojourns of westerly or northwesterly flow aloft kept temperatures close to normal from the 22nd through the 24th, and from the 28th through the 30th. A brief incursion of the upper level ridge brought more hot weather on the 25th, with a high of 97°F for the second time during the month, and a high of 96°F on the 26th.