Flash flood emergency: 100 to 200+ year rainfall hammers metro

-Updated 10 pm-

Wednesday’s long forecast flash flood event delivered. Rainfall totals of 3″ to 10″ hammered parts of the metro Wednesday evening.

The torrential rainfall overwhelmed some storm sewers in the metro.

In Maple Grove, 3.5-inches came down in an hour. That’s the equivalent of a 1 in 100-year flood according to NOAA’s ATLAS 14 rainfall recurrence tables. Totals near 10″ are being reported in Maple Grove. That could translate into a 1 in 500 to 1,000-year rainfall event when the final tallies come in.

Flash flood watches continue into Thursday morning. Overnight rain may trigger additional warnings.

-Updated at 7:00 pm-

A flash flood warning includes northern parts of the Twin Cities metro until 10:45 pm tonight. The warnings may be expanded as storms producing torrential rains sag south this evening.

Flooding is already visible on some MNDOT cams in the north metro.

Stay tuned to updates on MPR News 91.1 FM in the Twin Cities. This could turn into a significant flash flood event.

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Wet enough for ya?

That question depends on precisely where you live in relation to where the heaviest rain bands set up into Thursday morning. Our atmosphere remains juiced with plenty of moisture to fuel tropical downpours into Thursday morning. A strong warm frontal boundary is still parked over southern Minnesota. That’s the focus for thunderstorm development, a slight severe risk and heavy rainfall potential as we move through the overnight hours.

Slow moving front

It seems like I’ve been talking about this stalled front for days now. Oh wait, I have. The front lingers across southern Minnesota into Thursday, then drifts mercifully south to Iowa, taking the heaviest rain cells with it. Scattered (lighter) rain showers may remain in the storm’s wake. Saturday looks summery and probably lake-worthy, the next front brings more rain Saturday night.

NOAA

How much more rain?

Coverage for heavy convective rainfall is always scattered in nature. One town gets half an inch, the next gets 3 inches. NOAA’s NAM 4 km model captures the scattershot nature of the rains into Thursday. We’ll still likely be dealing with some scattered pockets of multi-inch rainfall by Thursday morning.

NOAA via College of Dupage

Here are the nuts and bolts of the rain threat into Thursday from the Twin Cities NWS.

Bottom line: Expect occasional rain which will be heavy at times into Thursday morning. Flash flooding of streams, low lying areas and urban flooding is likely in areas that get the heaviest rainfall. The Thursday morning commute will likely be impacted in the Twin Cities metro area. Stay ‘situationally aware’ through the overnight hours into at least Thursday morning.

Ryder Cup: ‘British Open’ conditions? 

Next week’s Ryder Cup is one of the biggest sporting events on earth. A quarter of a million people from all over the planet will walk through the gates at Hazeltine next week. It’s ironic that our extended summer may end just as the Ryder Cup gets started.

ryder-cup-logo

Next week’s forecast is still in flux, but the trends are leaning much cooler with some scattered rain. Foer the practice rounds Tuesday into Thursday, morning temps favor the upper 40s yielding to daytime temps in the 50s and 60s. Throw in a few scattered showers and it may feel more like Royal Troon at times early next week. An upper level low pressure system spinning over Minnesota will bring much cooler weather early next week.

NOAA

NOAA’s GFS suggests sunnier and miler weather by the start of competition play on Friday. The usually trusty Euro model hangs on to rain showers and cooler with slightly warmer temps. Winds look relatively light so far.

Norwegian Met Institute. Temps in Celsius.

I’ll be on location at Hazeltine at times next week covering weather angles for the Ryder Cup.

Stay tuned for forecast updates.