The changeable weather of March 2018 was typical of late winter and early spring. The progression of low pressure troughs and high pressure ridges brought alternating periods of warm and cold temperatures, yielding a close-to-normal average. There were no record highs or lows.
Episodes of active weather and moderate precipitation occurred as each trough and its accompanying cold front entered our area.
The 0.54 inch rainfall on the 14th tied the record for the date set in 1927. The 1.89 inches for the month was 0.50 inch above normal and ranks in the wettest 20 percent of Marchs at the airport, and the wettest 25 percent at all Boise locations.
Snowfall for the month was 2.6 inches, mostly falling on the morning of the 25th. The monthly normal is 1.3 inches.
The first four days of March were dominated by an upper level trough which brought cold temperatures but little precipitation. The 23°F on the 4th was the low for the month.
Temperatures rose above normal on the 8th as an upper level ridge began to build over the region.
The ridge reached its maximum amplitude on the 12th, allowing temperatures to rise into the low 60s. As the ridge began to exit, southerly flow ahead of the next upstream trough pushed the temperature to 69°F on the 13th, the high for the month.
The trough sent a strong cold front inland, and convective showers ahead of the front were preceded by northwest winds gusting over 30 mph. When the showers reached the Boise airport just after 4 am, moderate rain began and persisted for about an hour before tapering off and ending. The trough drifted slowly inland on the 16th and 17th, preventing temperatures from rising above the upper 40s on those days.
The last weather maker of the month was another strong upper level trough which stalled off the coast of British Columbia on the 22nd. This trough extended far enough south to tap subtropical moisture.
Like its predecessor, moderate rain preceded the cold front on the afternoon of the 22nd. The front passed the airport at about 7:30 pm, accompanied by the first thunderstorm of the spring season. The strongest convection and heaviest rain stayed west and north of Boise.
As the trough moved inland and weakened on the 25th, it produced the last measurable precipitation of the month, falling as 2.1 inches of snow. The cold north pacific air was responsible for a high of only 45°F that day, the chilliest maximum since the start of spring.
Following this system, west-northwest flow aloft returned temperatures to near normal from the 28th through the 31st.