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Revisiting the AQI

Revisiting the AQI: With persistent Air Quality Alerts this week, I wanted to revisit this topic which we talked about last August when we had persistent air quality alerts due to smoke from Western USA and Canada wildfires. In fact we had 11 Air Quality Alerts last summer, a larger than normal number.

This week the Air Quality Alerts have been provoked due to high particulate matter trapped in the lower atmosphere by persistent inversions (warmer temperatures with height). The Air Quality Index (AQI) is calculated by the EPA as a mandate from the Clean Air Act (first passed by Congress in 1963 and amended several times since). The EPA meteorologists partner with the NOAA National Weather Service in issuing Air Quality Alerts. The EPA regularly monitors for five pollutants: ground-level ozone (O3); particulate matter (microscopic); carbon monoxide (CO); sulfur dioxide (SO2); and nitrogen dioxide (NO2). For each of these pollutants there are air quality standards (thresholds) us…
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Significant Snowfall on December 1-2

Significant Snowfall on December 1-2: Many climate observers in southern Minnesota have reported at least a trace of snowfall on each of the first six days of the month (MSP, Rochester, and St Cloud included). The most significant snowfalls came over December 1-2, especially in the southern half of the state where many observers reported 6 to 11 inches. Several climate stations reported new daily snowfall records for December 2nd including:
Lakefield 11.0”
Windom 8.3”
Winnebago, Tracy, and Owatonna 8.0”
Caledonia 7.0”
Spring Valley 6.5”
Minneota, Austin, and Grand Meadow 6.0”
Hokah 5.0”

Much of the snow remains on the ground as temperature have generally stayed below the freezing mark around the state all week. Over 25 climate stations reported subzero overnight temperatures this week, led by -15°F at Warren (Marshall County). Also noteworthy is the fact that the weekly snow depth map from the Minnesota State Climatology Office shows an unusual pattern for Minnesota with both t…
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November Climate Summary

November Climate Summary:
Cold and dry are the words for November. It was the coldest November since 2014 with average monthly temperatures around the state ranging from 5 to 7 degrees F below normal. Approximately two-thirds of the days brought cooler than normal temperatures. Extremes for the month ranged from 61°F at Marshall on the 1st to -20°F at Cotton (St Louis County) on the 20th. Within the state climate network over 75 low minimum temperature records were set or tied during the month, while over 90 low daytime maximum temperature records were set or tied.

Precipitation was less than normal for the month in most places, ranging mostly from 0.50 to 1.50 inches. Some places received over 2 inches, topped by 2.70 inches at La Crescent and 3.11 inches at Grand Portage. Snowfall was variable, with many areas around the state reporting 3 to 6 inches, and higher amounts in the north. In the northeast many climate stations reported 10 to 19 inches for the month. Grand Porta…
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Cold November Continues

Cold November Continues: Through the first three weeks of November observers around the state reported an average monthly temperature that ranges from 7 to 9 degrees F cooler than normal. Over 80 climate stations in Minnesota have reported at least one subzero temperature so far this month, topped by -20°F at Cotton (St Louis County) on November 20th. Though much of the state has been spared from a lot of snowfall, the northeastern area has received from 12 to 18 inches, topped by 18.5 inches at Grand Portage.

The Minnesota State Climatology Office posted a Thanksgiving Weather Retrospective o their web site. It provides a look back at all the weather in the Twin Cities history associated with the Thanksgiving Holiday.
Weekly Weather Potpourri: Authorities issued a public health alert for Sydney, Australia on Thursday as the 500km-wide (310 miles) dust band began to reach the city. One of the largest dust storms in recent history blanketed many parts of SE Australia and caused a…
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Widespread subzerio temperatures this week

Widespread subzero temperatures this week:
Last week on MPR's Morning Edition we talked about the widespread snow cover around the state and up until that time only about a dozen climate stations had reported a subzero minimum temperature so far this autumn. Since then we have seen severe cold weather dominate the landscape, and subzero temperatures have become far more common. In fact over November 13-14 this week over 40 climate stations reported morning low temperatures that were subzero with readings of -10°F to -15° in portions of St Louis and Lake of the Woods Counties. In fact on November 13th (Tue) many Minnesota climate stations saw the daytime high temperature remain in the teens F.

The week of November 7-13 brought temperatures that ranged from 11 to 15 degrees F colder than normal. In fact for the Twin Cities it was the coldest such week in history (1872-present). Here is a ranking of the five coldest weeks of November 7-13 for the Twin Cities climate:

2018 mean …
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