Flash flood watch: 2 to 4 inches-plus south of metro?
We've seen this movie before. Another June in Minnesota, another dose of torrential rainfall and potential flooding.
Radars across southern Minnesota will glow bright yellow and red Thursday. A tropically enhanced low pressure center tracks through Iowa Thursday. The system will crank out torrential rainfall in southern Minnesota, northern Iowa and central Wisconsin.
Flash flood watches are flying for a swath of the Upper Midwest centered on the Interstate 90 corridor.
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INCLUDING THE CITIES OF...NEW ULM...ST. PETER...LE SUEUR...FARIBAULT...ST. JAMES...MANKATO...WASECA...OWATONNA...FAIRMONT...BLUE EARTH...ALBERT LEA
141 PM CDT WED JUN 10 2015
...FLASH FLOOD WATCH IN EFFECT FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT...
THE NATIONAL WEATHER SERVICE IN TWIN CITIES/CHANHASSEN HAS ISSUED A
* FLASH FLOOD WATCH FOR A PORTION OF SOUTH CENTRAL MINNESOTA...INCLUDING THE FOLLOWING AREAS...BLUE EARTH...BROWN...FARIBAULT...FREEBORN...LE SUEUR...MARTIN...NICOLLET...RICE...STEELE...WASECA AND WATONWAN.
* FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT
* HEAVY RAINFALL...WITH LOCALIZED AMOUNTS NEAR 6 INCHES POSSIBLE.
* RUNOFF FROM EXCESSIVE RAINFALL WILL LEAD TO RAPID RISES ON AREA CREEKS AND STREAMS ALONG WITH PONDING OF WATER IN LOW LYING AREAS.
The system
Take a look at our latest weather culprit. The deepening low pressure system gets a turbo boost as it sucks in residual tropical moisture from once Pacific Hurricane Blanca.
This will be an efficient rainmaker, wringing our bands of heavy rainfall over the Upper Midwest Thursday.
The National Oceanic and Atmospheric Administration keeps track of what it takes to cause flash flooding. Here's the flash flood guidance for Minnesota:
Bottom line? Rainfall totals approaching 2 inches in a few hours will trigger flash flooding.
The latest rainfall projections with the system favor the heaviest rain bands just south of the metro centered on the I-90 corridor, but it could be a close call if the system jogs slightly north. Rainfall totals of 2 to 4 inches look likely, and I can't rule our some 6 inches-plus totals if deep convection sets up and produces "training echoes" passing over the same ground.
Here's another look at NOAA's projected rainfall totals. The latest model runs have shifted the heaviest totals just south of the Twin Cities.
Twin Cities rides the edge of heavy rain zone
Where have I seen this movie before? This looks like one of dozens of winter storms where the metro rides the northern edge of the heavy precipitation zone.
Depending on storm track, we may see as little as 1 inch in the metro (southern track) to as much as 2 to 4 inches (northern track) by Friday.
Some projected model rainfall totals for Minneapolis-St. Paul International Airport.
1.04 inches (12Z NOAA Global Forecast System)
1.76 inches (12Z European Centre for Medium-Range Weather Forecasts)
4.57 inches (18Z NOAA North American Mesoscale Forecast System)
Here's a graphical look at the ever changing model rainfall output meteogram for MSP Airport courtesy of Iowa State University.
Bottom Line: Expect potentially heavy rain Thursday from the Twin Cities south. Several inches of rain is likely, with the heaviest rainfall bands (and highest flood potential) favoring southern Minnesota.
Keep the weather radio, and the umbrella handy. Expect longer commutes, and the potential for flooding to impact roads in southern Minnesota Thursday into Friday.