Excessive Heat Watch issued for much of the southern half of Minnesota

Friday certainly has been a delight with just partly cloudy skies all around.

Afternoon visible satellite photo from NOAA

But a returning surge of heat and moisture has begun.  Dewpoints have been climbing this afternoon, especially across southern Minnesota where they have reached the gooey 70-degree mark in some cities, including Owatonna, St. James, Windom, New Ulm, Faribault, Pipestone and Montevideo.

The moisture could kick off a few showers in southwestern Minnesota as early as this evening.  Then look for a scattering of showers and thunderstorms to advance across Minnesota from west to east tonight and into Saturday.  Although my backyard rain gauge has been dry for the past 16 days and rain would be welcome, it is more likely that the showers will miss most of us.

(Weather image from the Duluth NWS Office)

Sunday will bring a chance of scattered showers mainly to northern Minnesota. That’s also when the heat is expected to hit full blast. The National Weather Service has issued an Excessive Heat Watch for much of the southern half of Minnesota from Sunday afternoon through Wednesday evening.

Dry ground warms more rapidly than does wet ground, so areas of central Minnesota that have been rain free should become the toastiest.  I am looking for highs Sunday and Monday to range from the upper 80s in far northern Minnesota to the low 90s in the south (where it rained recently) to the mid and upper 90s across central Minnesota including the metro area.

The heat wave might weaken slightly around mid week, but overall look for hot and muggy weather all of next week until next weekend.

Nights will remain exceptionally warm, especially in the metro area where lows could remain in the upper 70s near the downtown areas.

The combination of hot days, warm nights and muggy weather explains the heat watch. While temperatures in the 90s, even the mid 90s, are not uncommon in late August, stretches of mid 90s are rare.  The NWS did some checking and found that back in 1948 the high temperature in the Twin Cities reached 94 or hotter on four days during the State Fair.  That is a record that might be approached this year.

Days of 94 degrees or hotter during the State Fair.

Meanwhile, wildfires continue in the western United States.  A large fire west of Yosemite National Park remains out of control.  As of this morning it had grown to 165 square miles and had spread eastward into part of Yosemite, but was not impacting Yosemite Valley.  And that is just one of the many fires being fought by ground crews and aircraft.  Expect our skies to be a bit smoky.

(Smoke from western wildfires. Credit:NOAA)

Otherwise, if you are out where the night sky is dark this weekend, take a look for northern lights.  The sun sent out two coronal mass ejections in our direction recently.  They might trigger auroras in our part of the world.  Last night northern lights were spotted in locations including Scandinavia, western Canada and Ironwood, Mich.