Highs in the 90s linger into midweek; a look back at the mega-rain of July 25, 2020

I’ll start with a mention of the red flag warning for northeastern Minnesota and a portion of north-central Minnesota from 1 p.m. to 6 p.m. this Sunday:

Here are details of the red flag warning:

URGENT - FIRE WEATHER MESSAGE National Weather Service Duluth MN 916 AM CDT Sun Jul 25 2021 ...CRITICAL FIRE WEATHER CONDITIONS EXPECTED THIS AFTERNOON... .Low relative humidity, strong wind gusts, and dry fuels will be favorable for rapid fire growth this afternoon across northeast Minnesota. MNZ010>012-018>020-026-035-037-252230- /O.NEW.KDLH.FW.W.0009.210725T1800Z-210725T2300Z/ Koochiching-North St. Louis-Northern Cook and Lake-North Itasca- Central St. Louis-Southern Lake-South Itasca-Northern Aitkin- Carlton and South St. Louis- 916 AM CDT Sun Jul 25 2021 ...RED FLAG WARNING IN EFFECT FROM 1 PM THIS AFTERNOON TO 6 PM CDT THIS EVENING FOR WIND AND LOW RELATIVE HUMIDITY FOR NORTHEAST MINNESOTA... The National Weather Service in Duluth has issued a Red Flag Warning for wind and low relative humidity, which is in effect from 1 PM this afternoon to 6 PM CDT this evening. * AFFECTED AREA...In Minnesota, Koochiching, North St. Louis, Northern Cook and Lake, North Itasca, Central St. Louis, Southern Lake, South Itasca, Northern Aitkin and Carlton and South St. Louis. * WINDS...Northwest 15 to 20 mph with gusts up to 30 mph. * RELATIVE HUMIDITY...As low as 20 percent. * IMPACTS...These conditions are supportive of rapid fire growth. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Red Flag Warning means that critical fire weather conditions are either occurring now or will shortly. A combination of strong winds, low relative humidity, dry fuels, and warm temperatures can contribute to extreme fire behavior.

You can hear updated weather information for Minnesota and western Wisconsin on the Minnesota Public Radio network, and you can see updated weather info on the MPR News live weather blog.

Mega-rain last July 25

We’re dealing with drought across most of Minnesota right now, but we were talking about flooding rains in southern Minnesota one year ago.

The Minnesota State Climatology Office has a detailed post about the mega-rain that hit portions of southern Minnesota from the evening of July 25, 2020 to the early morning hours of July 26. 2020.

According to the Climatology Office:

The main event began as a large thunderstorm developed over Sibley County just after 5 PM. The storm intensified rapidly, and produced a confirmed tornado near Gaylord around 630 PM. With nothing to steer it or drive it away, the thundestorm moved little while expanding eastward slowly and "back-building" to the west. The thunderstorms reached into the southern Twin Cities metropolitan area by mid-evening, but they remained anchored over the same areas of Renville, Sibley, and Le Sueur Counties even as darkness fell. The growing but almost stationary storm complex produced vivid lightning, nearly constant thunder, and spectacular late-evening optics, even in areas that received little or no rainfall.

By 9 PM, heavy rains had been falling continuously for 2-4 hours from near Fairfax in Renville County to Gibbon and Winthrop in Sibley County, and over into much of Le Sueur County. The thunderstorms eventually pushed southeastward into Nicollet, Blue Earth, Waseca, and Rice Counties, but as they did were replaced quickly by new storms that resumed lashing the areas that had already been drenched by earlier rains. The National Weather Service in Chanhassen had issued Flash Flood Warnings for a multi-county swath of southern Minnesota.

Even at 3 AM, new strong thunderstorms were forming in southwestern and western Minnesota, as the surge of deep moisture into the region continued, and as the cold front inched its way eastward across the state. The heaviest rains began winding down after sunrise, but moderate rains persisted in some areas through 8 AM.

The expansive, regenerating, and long-lasting intense thunderstorms activity resulted in a wide swath of very high precipitation totals. Automated rain gauges and human observers in six different counties reported rainfall totals of six inches or greater.

The highest known total for the storm came from near Winthrop in Sibley County, where a volunteer observer for the county reported 11.50 inches. Other high totals in that area included 10.70 inches near Lafayette, and 9.15 inches in Gibbon. These amounts are near or exceed the 500-year threshold for 24-hour rainfall in that part of Minnesota.

Here’s the NWS plot of the July 25-26, 2020 rainfall totals:

According to the Minnesota State Climatology Office:

This storm produced six inches of rain or more over an area of roughly 1000 square miles, making this event the first "mega-rain" since 2016.

Temperature trends

Our average Twin Cities high temp is 83 degrees this time of year. Metro area highs are expected to reach the lower 90s this Sunday. Highs in the 90s are expected in roughly the southern half of Minnesota and in a few spots along the Red River Valley of northwestern Minnesota, with mainly 80s elsewhere in Minnesota and western Wisconsin. Dew points will be in the comfortable 50s and upper 40s.

Monday highs reach the 90s in much of Minnesota, with 80s in the far north:

Dew points creep into the sticky 60s:

Tuesday highs are mainly in the 90s, with 80s in the northeast:

Tuesday afternoon dew points reach the upper 60s in many areas:

Southern and central Minnesota could see dew points in the lower 70s on Wednesday, along with highs in the 90s. Heat index values could approach 105 degrees in some areas Wednesday afternoon.

Twin Cities metro area highs reach the upper 90s Wednesday, then retreat to the upper 80s for Thursday and Friday.

Rain chances

There’s a chance of scattered showers and thunderstorms Sunday evening in portions of west-central and southwestern Minnesota. That rain chance spreads across the rest of southern Minnesota overnight Sunday night. Rain could clip parts of the Twin Cities metro area late Sunday night or early Monday morning. Scattered showers and thunderstorms are possible Monday afternoon and evening in parts of northern Minnesota. Some of that activity could spread into central Minnesota and northwestern Wisconsin later Monday evening.

The National Oceanic and Atmospheric Administration’s High-Resolution Rapid-Refresh (HRRR) forecast model shows the potential rain pattern from Sunday evening through Monday evening:

We’ll have additional shower and thunderstorm chances Wednesday evening and overnight Wednesday night.

Programming note

You can hear my live weather updates on MPR News at 7:35 a.m., 9:35 a.m. and 4:39 p.m. each Saturday and Sunday.