Drought grows across Minnesota; next rain chance Saturday

Friday brings another dry but beautiful day to Minnesota

U.S. Drought Monitor for Minnesota
U.S. Drought Monitor for Minnesota
U.S. Department of Agriculture, University of Nebraska-Lincoln

It’s official. Drought has returned to much of Minnesota.

This week’s U.S. Drought Monitor for Minnesota at the top of this post shows more of Minnesota is now in moderate drought.

Here are the numbers:

  • 12.4 percent of Minnesota is in the moderate drought category this week, up dramatically from .84 percent last week

  • 72.8 percent of Minnesota is now abnormally dry (pre-drought), a big jump from 30.2 percent two weeks ago.

Flash drought

I’ve been talking on the weather chats and writing on Updraft all week about Minnesota’s rapid descent into flash drought.

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Flash drought is the hydrologic term of art that describes our recent weather patterns. The combination of warmer-than-average temperatures, little rainfall, and high evaporation rates dries out soils and surface water quickly.

Here’s a description of flash drought from the National Oceanic and Atmospheric Administration:

Flash drought is simply the rapid onset or intensification of drought. It is set in motion by lower-than-normal rates of precipitation, accompanied by abnormally high temperatures, winds, and radiation. Together, these changes in weather can rapidly alter the local climate.

Higher temperature increases evapotranspiration—the process by which water is transferred from the land to the atmosphere by evaporation from the soil and by transpiration from plants—and further lowers soil moisture, which decreases rapidly as drought conditions continue.

If not predicted and discovered early enough, changes in soil moisture that accompany flash drought can cause extensive damage to agriculture, economies, and ecosystem goods and services.

Soils can lose one-quarter inch of moisture per day this time of year. We’re running a rainfall deficit of 3.5 inches in the Twin Cities and across much of central Minnesota since April 1.

You can see on the map below that while southwestern Minnesota has recorded above-average rainfall (green areas) in the past month, most of Minnesota recorded between 25 and 75 percent of average rainfall over the past 30 days.

30-day precipitation departure from average
30-day precipitation departure from average
Midwest Regional Climate Center

Saturday storms

Friday brings another dry but beautiful day to Minnesota. Highs will run in the 80s in most areas, with the typically cooler temperatures near the North Shore.

Our next significant rainfall chance arrives Saturday when a cold front will slide south across Minnesota. Scattered thunderstorms are likely along the frontal zone.

The best chances for rainfall in central Minnesota and the Twin Cities favor the later afternoon hours. Here’s NOAA’s FV3 model between 7 a.m. and 7 p.m. Saturday:

NOAA FV3 model
FV3 model between 7 a.m. and 7 p.m. Saturday
National Oceanic and Atmospheric Administration, via Tropical Tidbits

Overall rainfall coverage looks scattered once again. But some lucky spots could pick up one-half inch of rain or more under heavier downpours Saturday. The European Centre for Medium-Range Weather Forecasts model shows the likely spotty coverage of rainfall Saturday.

European model (ECMWF) precipitation output
Precipitation output forecast through 7 a.m. Sunday
European Centre for Medium-Range Weather Forecasts, via Pivotal Weather

Such is life in the drought zone.

Smoke update

Air quality will be in the good to moderate range Friday across Minnesota.

Air quality forecast for Minnesota
Air quality forecast for Minnesota Friday
Minnesota Pollution Control Agency

Saturday’s cold front may also drive a bit of smoke to ground level in northern Minnesota. Fires in northwest Canada have reinvigorated and are pumping out more smoke.

NOAA’s High-Resolution Rapid Refresh model shows some smoke near ground level across northern Minnesota Saturday behind the cool front.

NOAA HRRR near surface smoke
High-Resolution Rapid Refresh near-surface smoke product for 1 p.m. Saturday
NOAA, via Pivotal Weather

We’re not out of the woods yet on smoke episodes this summer for Minnesota.

Stay tuned.