Updraft: July 30, 2009 Archive

Rainfall: Metro skunked again

Posted at 8:30 AM on July 30, 2009 by Paul Huttner (2 Comments)

NWS doppler storm total rainfall shows lack of rain near the metro with higher amounts south.

This is getting old.

Another is a series of rain systems moved through southern Minnesota last night. Again the drought areas most in need of rain got mostly skunked. We're starting to see a pattern here, and it may not just be luck of the draw.

It would be tempting to say this one just "slid south" of the metro again, but there may be something more going on here. As I watched the radars last night when rain was approaching the metro, you could just see the rain evaporating as it approached the severe drought areas. The rain sustained itself much better in those areas south of the Minnesota River.

Surface reports and the rainfall image above indicate rainfall amounts overnight between .25" and .50" in southern Minnesota.

-Twin Cities .02"
-Red Wing .25"
-Zumbrota .31"
-Rochester .46"
-Blue Earth .47"

There is even a narrow swath of rainfall in excess of 1 inch from near Wabasha to Mondovi, Wisconsin evident on the storm total rainfall image above.

Why is this happening?

One reason may be a faulty moisture "feedback loop" near the surface. There is usually some moisture transfer into the lowest levels of the atmosphere from evaporation. In July we would normally expect to evaporate about .25" per day from the soil into the lower atmosphere. This moisture is usually available for incoming rain systems to tap into to help rain that forms aloft survive the trip to ground level.

Topsoil in and near the metro this year is powder dry. With rainfall deficits of 7 to 8 inches this year in the metro, there just isn't any available moisture in the topsoil to evaporate back into the low levels of the atmosphere to prevent rainfall from evaporating before it reaches ground level. This was evident as I watched the doppler radar loop as the solid rain area move from South Dakota into western Minnesota toward the Twin Cities. It was like watching the radar in Arizona as virga evaporates before hitting the desert floor.

As you moved south into southern Minnesota last night the rain was able to sustain the trip to ground level much easier where the soil moisture feedback loop is still intact.

It appears that old saying "the rich get richer" applies to drought conditions too.

PH

(2 Comments)

Summer 2009: Extreme weather

Posted at 11:54 AM on July 30, 2009 by Paul Huttner (1 Comments)

This is going down as the summer of weather extremes in many locations in the U.S. and around the globe. Check out some of these weather events.

-Hottest day ever recorded in Seattle Wednesday.
-All-time heat record broken in Vancouver, Oregon Washington, near Portland. Second hottest July ever in Portland.
-Hottest month ever in Austin and San Antonio Texas?
-Coolest July ever in International Falls.
-Coolest July in Chicago in 67 years.
-Rain cancels farm show in Wales for the first time in 254 years.
-Extreme weather batters India.
-Fires rage in Spain and Greece.

Kind of makes you long for "average."

PH

(1 Comments)

Drought: Twin Cities lake near all-time low record

Posted at 3:27 PM on July 30, 2009 by Paul Huttner

Kayaker enjoying high water on Minnehaha Creek in 2007.

At least one Twin Cities lake is nearing an all-time record low water level this summer, and others are dropping fast.

White Bear Lake is currently within two inches of the lowest level ever recorded. The water level in White Bear is down well over 2 feet from last year. The current water level in White Bear is 920.1 feet above sea level (ASL). The lowest level recorded is 919.89 ASL feet in 1991.

In the west metro, Lake Minnetonka is also down nearly 2 feet from last year. The current level stands at 927.86 feet ASL. It was at 929.71 feet ASL as recently as last June.

To help maintain the lake level the Minnehaha Creek Watershed District has closed Gray's Bay Dam since early this summer. That means no water is flowing into Minnehaha Creek from the lake. In Deephaven, the headwaters that flow into Purgatory Creek which runs into the Minnesota River are dry.

Many metro area residents are observing marshes that usually hold water are very low or bone dry in some cases. These are the visible signs of hydrologic drought in the region. The Twin Cities is about 8 inches below average rainfall this year, and over 10 inches below average since last summer.

Your lawn is no doubt feeling the effects of drought too. Want some good news? It seems mosquito counts are way down to near zero this summer at the Huttner Weather Lab. At least we can sit out and enjoy the weather, even if it's hard to launch your boat in the nearest lake.

PH