June 2015 Warmest June ever in Boise

June 2015 was the warmest June ever in Boise. 2.8°F warmer than previous warmest June in 1934. 110°F on 28th was the warmest June day on record.  Mean high and low temperatures were also the warmest on record.  June had 16 days over 90°F (average is 5), and 5 days over 100°F, which was the most recorded in June.

June 2015 Climate Stats at Boise

Burns, Oregon; McCall and Jerome, Idaho also had their warmest June on record.

Annual Timing of Severe Weather in the NWS Boise forecast area.

As we move into spring, we also enter severe weather season in the NWS Boise forecast area. Research conducted locally on severe weather reports in our area from 1955 to 2005 yields important information about the onset of each of the major severe weather threats in our area: tornadoes; hail; wind; and flooding. NOTE: Hail is defined as 1″ or greater, wind is defined as 58+mph.

This first image shows time as a circle, with Jan 1 at the top and June 30 at the bottom, and time progressing clockwise. The four different colored lines indicate the relative frequency with which separate types of severe weather occur. The numbers on the concentric circles indicate the total number of occurrences of a given type of severe weather in a moving 19-day window (to smooth the raw data a bit and make it more presentable). As you can see below, wind (red) and hail (purple) reports ramp up rapidly in April, with flooding (green) increasing in May. Tornadoes (blue), while minimal in number, show a narrow peak in late April and a longer peak in from late May into early July. The hail (purple) maximum is in late June. Wind has two significant peaks in activity, with one in late June and another from late July to early August. The late June peak is probably associated with stronger late- Spring weather systems, while the second peak is associated with hot (relatively) dry days when evaporation of rain produces downbursts.


The second image contains the same data presently differently. The height of the peak for each day is the total number of reports (within the moving 19-day window) of all four phenomena. This is a good way to view the period with the highest overall threat of severe weather. Here we can see that the period of maximum severe weather shows the same basic two peaks as the wind (red) reports. This makes sense because wind is our most common form of severe weather. Clearly, June is our “busiest” month, with late July into August a close second.


One type of “severe” weather not touched on in this study is fire weather. Experience indicates that the storms that lead to the second wind maximum often start fires via lightning and then may lead to rapid spread due to the high winds.

Finally, here’s a map showing the location of severe weather reports from roughly 1955 to 2010. The brownish dots are wind, the green are hail, and the purple are tornadoes (Note: this map was originally created for a different study and therefore the colors do not match the graphs above).



2014 Boise Weather Stats


2014 was the 5th warmest year on record, and the 11th highest yearly precipitation total at ‪Boise since records began in 1877.  There were 28 days in July that were above 90°F, including seven days above 100°F.  The 30-year average for days above 90 °F is 16.  August precipitation was below normal, while locations south and east of Boise saw record August precipitation, especially at Twin Falls and Jerome. October was the second-warmest on record, thanks to 18 days of 70°F or higher (30-year average is 10 days).  Even though November was 4.2°F below normal, there was still a daily record high of 65°F set on Thanksgiving, 3 daily record low temperatures set, the daily precipitation record for November (1.15″, 11/1) and the greatest 2-day snowfall (7.6″, 11/13-14).  The coldest temperatures of 2014 came on November 15th, when the mercury plunged to 1°F, while temperatures nine days earlier reached 69°F (November 6th).

September 2014 Climate Overview

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

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

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

October 21, 2014 Drought Monitor

August Precipitation in Context

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

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″.