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Weekend outlook: sun & thunder

No, the severe storms never quite materialized as expected Thursday.

Update: 11:00 am Friday. The “slight risk” of severe thunderstorms (SPC) covers roughly the southeastern third of Minnesota today, we’re not quite out of the woods just yet in terms of T-storms. The greatest risk: south/east of the Twin Cities, but a few rough/severe storms may bubble up over central Minnesota later today. Stay tuned for possible watches/warnings. A few isolated storms may contain large hail and strong, potentially violent straight-line winds. The next cool front sweeps through by evening, setting the stage for a sunny, breezy, refreshingly cool Saturday with much lower humidity – a taste of September. Saturday still appears to be the better outdoor-day of the weekend.

No, the severe storms never quite materialized as expected Thursday. The strongest storms slid off over far southwest and south central Minnesota, and by the time a severe storm watch was issued (late evening) for parts of south central Minnesota the main risk had shifted to large hail. Why? Much of the day the atmosphere was “capped”, a stable layer of warmer air aloft preventing rising thermals from mutating into severe storms. The cap finally broke late yesterday, allowing strong storms to surge northward into the Twin Cities area.

The fickle front responsible for strong/severe thunderstorms over southern Minnesota during the day Thursday, reaching up into the Twin Cities Thursday night will be pushing from west to east across the state today, turning winds around from the south to a more northwesterly direction by evening. Summer rain is always hit-or-miss, and yesterday was no exception. Far southwestern Minnesota picked up the most rain, nearly an inch on many farms, but the rain wasn’t early as steady or widespread as we need now, with the southern half of Minnesota too dry, and a nagging drought continuing over east central and southeastern Minnesota.

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Today will be partly sunny and still a bit unsettled ahead of the front, the best chance of a couple hours of showers and storms coming well south of a line from Willmar to the Twin Cities. I think St. Cloud may stay dry, along with Brainerd and the Mille Lacs area. But towns from Rochester and Owatonna to La Crescent may pick up .25″+ of rain in the form of scattered showers and storms. There’s even a slight risk of a few isolated severe storms, mainly south/east of Rochester, where large hail can’t be ruled out.

SPC Outlook for Today. There is a slight risk of isolated T-storms over far southeastern Minnesota, but the main threat shifts south/east, toward Madison and Chicago.

WRF/NMM Model Prediction for 7 pm today. This graphic displays expected rainfall from 1 pm to 7 pm today, showing a lingering shower risk (opportunity) from the Twin Cities south/east, generally east of I-35.

The good news:

Saturday Overview: high pressure moves in with plentiful sunshine, a fresh breeze – gusty in the afternoon, and a nice assortment of popcorn (cumulus) clouds by afternoon. Temperatures hold in the 70s statewide, maybe a bit on the cool side at the lake up north. Think of it as free air conditioning, a gift from our friends in Manitoba.

Conditions: Partly to most sunny.

Winds: Blowing from the west, 10-20 mph.

Visibility: Unlimited.

Dew point: Upper 50s to near 60, quite comfortable for mid July.

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Rainfall: Little or no risk, statewide.

* Saturday should definitely be the nicer day of the weekend for outdoor plans, in spite of afternoon temperatures running 4-7 degrees cooler than average.

WRF/NMM Model for 7 pm Saturday. The models consistently show Saturday as the sunnier, drier day statewide, a cool front shoving showers well south of the state. If you’re driving/flying to St. Louis or Chicago you will run into leftover showers and T-storms.

The so-so news:

Sunday Overview: Another disturbance dropping out of Canada sparks showers and storms, some locally heavy.

Conditions: More clouds, growing risk of showers and T-storms, 2-4 hours of rain.

Winds: Blowing from the East/Northeast at 10-15.

Visibility: 5-10 miles, more haze.

Dew point: Low/mid 60s, more humid.

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Rainfall amounts: .50 to 1.50″ possible.

WRF/NMM Model Output valid 7 pm Sunday evening. The best chance of showers/storms should come over the southern half of Minnesota. Little or no rain is printed out north of Brainerd, in general the farther north your cabin is, the better the odds of salvaging a half-decent Sunday.