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Heat advisory this weekend; a few severe storms possible

Weekend highs in the 90s; heat index values could reach 100

Heat advisory
Heat advisory
Twin Cities National Weather Service office

Lazy. Hazy. Crazy.

Lazy because temperature and humidity levels this weekend will make it easy (even advisable) to take it easy. Heat index levels could reach 100 degrees in parts of southern and western Minnesota this weekend.

NOAA GFS heat index
Global Forecast System heat index values for 4 p.m. Sunday
National Oceanic and Atmospheric Administration, via Pivotal Weather

Hazy because high dew points and some lingering Canadian wildfire smoke may bring a hazy tint to our skies.

Crazy because the atmosphere is loaded with high dew point rocket fuel for a few severe thunderstorm clusters this weekend.

Heat advisory

A heat advisory covers the Twin Cities and most of western Minnesota this weekend. Heat index values will reach 95 to 100 degrees across southern and western Minnesota. Here’s the National Weather Service:

Hennepin-Anoka-Ramsey-Washington-Carver-Scott-Dakota- Including the cities of Blaine, Stillwater, Minneapolis, St Paul, Shakopee, Hastings, Victoria, Chanhassen, and Chaska

201 PM CDT Fri Jul 12 2024

..HEAT ADVISORY IN EFFECT FROM 2 PM SATURDAY TO 8 PM CDT SUNDAY...

* WHAT...Heat index values up to 98 expected.

* WHERE...Anoka, Carver, Dakota, Hennepin, Ramsey, Scott, and Washington Counties.

* WHEN...From 2 PM Saturday to 8 PM CDT Sunday.

* IMPACTS...Hot temperatures and high humidity may cause heat illnesses.

* ADDITIONAL DETAILS...Long term heat advisory was issued across the Twin Cities Metro due to the expected afternoon heat index values above 95 degrees and little in the way of relief overnight, as Sunday morning lows are forecast to remain in the low to mid 70s.

Highs Saturday will reach 90 degrees in Minnesota’s south and west:

Forecast high temperatures Saturday
Forecast high temperatures Saturday
NOAA

Sunday brings another day of intense summer heat:

Forecast high temperatures Sunday
Forecast high temperatures Sunday
NOAA

Tropical dew points

A rich pool of Gulf of Mexico moisture will advect (blow horizontally) into Minnesota through this weekend. The combination of moisture advection from the Gulf and corn sweat pulling moisture from soggy soils means dew points in the 70s could peak near 80 degrees Sunday afternoon and evening.

Here’s the National Oceanic and Atmospheric Administration’s Global Forecast System model:

NOAA GFS dew point output
Global Forecast System dew point output between 7 p.m. Friday and 7 p.m. Sunday
NOAA, via Tropical Tidbits

Spotty storm risk

Storm coverage this weekend looks spotty, but those clusters that get going may reach severe limits. To my eye, the highest severe risk is north of Interstate 94, but a couple of strong storms could sneak into the Twin Cities this weekend.

Forecast models are all over the place on storm coverage and timing this weekend. A few models favor storms Saturday morning crossing northern Minnesota and possibly clipping the Twin Cities Saturday morning into midday.

Another possible window for storms appears to be overnight Saturday night into early Sunday morning.

I wouldn't take any forecast model as gospel in this iffy, weak synoptic weather pattern. But NOAA’s High-Resolution Rapid Refresh solution seems as good as any right now. It favors a few storm clusters fading Saturday morning, then another batch overnight Saturday night into Sunday morning.

The forecast model loop below runs between 7 a.m. Saturday and 1 p.m. Sunday.

NOAA HRRR model
High-Resolution Rapid Refresh model between 7 a.m. Saturday and 1 p.m. Sunday
NOAA, via Tropical Tidbits

NOAA’s Storm Prediction Center has laid out risk areas this weekend. A slight severe risk covers much of Minnesota Saturday.

A marginal risk is up for Sunday.

Enjoy your weekend plans but keep one eye and ear out for possible severe weather watches and warnings.