Summery Friday, with a late-afternoon thunder chance; weekend 70s

This final day of meteorological spring will feel like mid-summer. We call the three warmest months of the year (June through August) meteorological summer. If you're a stickler for astronomical seasons, the summer solstice is June 21 this year.

Smoke-filtered sunshine

A veil of smoke from Canadian wildfires will linger over much of Minnesota and Wisconsin this Friday:

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Noon update:

The Minnesota Pollution Control Agency has issued an air quality alert for much of central and southern Minnesota, including the Twin Cities metro area, this Friday afternoon and evening:

Details of today's alert:

Air quality is expected to worsen Friday to unhealthy levels. Wildfires in northern Alberta, Canada have produced large amounts of pollutants including smoke, nitrogen oxides and volatile organic compounds, which have been carried by the winds into the region over the past several days. Sunny skies and hot temperatures will cause these pollutants to react in the air to produce high levels of ground-level ozone. Air Quality Index (AQI) values are expected to climb into the low 100s today in the alert area. This is considered unhealthy for sensitive groups. Ozone concentrations will be the lowest in the morning hours Friday, and will gradually rise midday through the afternoon. Air quality will improve Friday evening into the weekend, with thunderstorms expected on Friday evening and cooler air moving in on Saturday.

People whose health is affected by unhealthy air quality include:

People who have asthma or other breathing conditions like chronic obstructive pulmonary disease (COPD), chronic bronchitis, and emphysema

Children and teenagers

People of all ages doing extended or heavy physical activity such as playing sports or working outdoors

Some healthy people who are more sensitive to ozone even though they have none of the risk factors. There may be a genetic base for this increased sensitivity.

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Temperature trends

The southern two-thirds of Minnesota, plus much of western Wisconsin, will see Friday highs well into the 80s. A few spots could creep above 90, even in the Twin Cities metro area. Roughly the northern third of Minnesota will top out in the 70s, with some 60s in parts of the northeast.

Our average high temperature is 74 degrees this time of year in the Twin Cities metro area.

Saturday highs retreat to the 70s south, with 60s in the north:

Similar highs are on tap for Sunday:

Twin Cities metro area highs are projected to be in the mid 70s Monday, followed by upper 70s Tuesday through Thursday.

Rain and thunder chances

Scattered showers and thunderstorms are possible in central Minnesota late Friday afternoon and Friday evening. The shower and thunderstorm chance will expand into the Twin Cities metro area plus southern Minnesota and west-central Wisconsin Friday evening and continue into the overnight hours.

The National Oceanic and Atmospheric Administration's High-Resolution Rapid Refresh (HRRR) forecast model shows the potential rain pattern Friday afternoon through Saturday morning:

The rain chance tapers off early Saturday morning in the Twin Cities metro area, but lingers into late morning in parts of southeastern Minnesota and southwestern Wisconsin.

The color chart to the right of the loop refers to the strength of the signal that returns to the radar, not to the amount of rain. It will rain in some areas that look dry in the HRRR loop, but the loop illustrates the scattered nature of the rain pattern.

The severe weather risk is low, but the Storm Prediction Center of the National Weather Service shows a marginal risk of severe weather Friday and Friday night in portions of Minnesota (including the Twin Cities metro area) and western Wisconsin:

Marginal risk means that an isolated severe thunderstorm is possible.

As always, updated weather information can be heard on the Minnesota Public Radio Network, and you’ll also see updated weather info on the MPR News live weather blog.

Rivers are rising

Recent rainy weather has caused river levels to rise again across much of southern Minnesota, and rivers have reached flood stage at many locations.

You can click on any location on the NWS Advanced Hydrologic Prediction Service  (AHPS) site to get hydrographs of recent and forecast river levels. Some locations list levels in feet above sea level, others list levels in feet above a local reference point.

Here’s the Friday morning hydrograph for the Mississippi River at St. Paul:

You can see that the Mississippi River is at moderate flood stage Friday morning at the St. Paul location and it's expected to fluctuate very little this weekend. The river level at St. Paul is expected to slowly fall next Monday and Tuesday.

There are flood warnings along some rivers in Minnesota. You can get flood warning updates by clicking on any green-shaded location on the National Weather Service Twin Cities website.

Here’s how the National Weather Service map looked Friday morning:

Projected river levels are updated on a regular basis, so check back to the AHPS site and the National Weather Service point forecasts for the latest info on the rivers near you.

If you’d like to scroll through hydrographs along a certain river in central or southern Minnesota, check here.

Programming note

You can hear my live weather updates on Minnesota Public Radio at 7:49 a.m. Thursdays and Fridays, and at 7:35 a.m., 9:35 a.m. and 4:35 p.m. each Saturday and Sunday.