The average temperature for the month was less than one degree above
normal. No temperature records were broken, but the low of 76 on the
23rd tied the record high low for that date set in 1994.
At the airport, the only triple digit high was the 102 on the 22nd.
The normal for July is 4 days of 100 or higher. The normal for
summer (June-August) is 7. Last summer had 14, with 9 in July and
the rest in August, including the 110 on August 10.
Only 0.01 inch of rain fell at the National Weather Service office in Boise,
which ranks in the driest 15 percent of Julys.
July and August are normally the driest months, averaging 0.33 inch
and 0.24 inch respectively.
As is common at this time of year, upper level troughs from the
north Pacific weakened as they encountered the strong summer high
pressure ridge over the western U.S. The ridge diverted these
systems too far north to bring measurable rain to the Boise area.
Upper-level winds were usually from the southwest, with enough
westerly component to shunt monsoon moisture east before it reached
the Treasure Valley. When it did manage to drift this far north and
west, it usually brought only cloud cover, which hindered the
heating that drives convection, so only a few sprinkles resulted.
Weak cold fronts accompanying the Pacific systems were followed by
slightly cooler and much drier air. For example, the afternoon
humidity dropped to 7 percent on the 19th and 8 percent on the 24th
after frontal passages. On the other days minimum humidities were in
the teens and 20s.