Posted at 9:50 AM on August 20, 2009
by Paul Huttner
NWS storm reports show severe weather events clustered around the Twin Cities.
They don't teach you this stuff in meteorology school.
Wednesday's severe weather and tornado event was highly unusual. This was far from your classic textbook severe weather day. Here's why.
-A potent upper level low was producing rain in the area. A smaller mini low or "vortex" rotated around the larger parent low right over the Twin Cities around 2pm. This mini vortex triggered the tornadoes that hit the metro.
-This was a "non-supercell" type event. There were not classic individual supercell thunderstorms marching toward the metro as is usually the case with tornado outbreaks.
-There was no clearing to cause surface heating.
-There was very little lightning with these storms.
The unusual synoptic situation did not signal a classic severe weather day. As a result there was:
-No Storm Prediction Center (SPC) risk area for the metro. That means the best severe weather minds in Norman, Oklahoma did not see this one coming.
-No severe thunderstorm or tornado watch was posted for the area.
-No warnings issued before the first (likely to be confirmed today) tornado touchdown in south Minneapolis.
-No sirens sounded in Minneapolis before the first twister.
The Twin Cities NWS did do an excellent job of reacting once the first tornado was sighted. I believe all subsequent tornado touchdowns were covered by tornado warnings after the first event.
The event then evloved into a non-tornadic high wind event for Duluth. It was remarkable in that the system resembled a mini hurricane at times. NWS Duluth even noted an "eye-like structure" and "spiral rain bands" in the description of the high wind warning.
In 25 years of watching weather professionally I have never seen a day exactly like Wednesday. It's amazing how things can come together in unusual ways to trigger severe weather events. Wednesday was likely a once in a lifetime severe weather event.
Posted at 9:02 AM on August 20, 2009
by Paul Huttner
NWS rainfall forecast shows more rain for the Upper Midwest Thursday.
The slow moving low pressure system that triggered severe weather Wednesday is hanging around the Midwest today. We may not see widespread severe weather today, but you can expect more rain and the possibility of a few strong thunderstorms.
We are on the back side of the upper low today. That means cooler weather with areas of rain and maybe a few thunderstorms this afternoon. Because of the spin around the low center, we may see cold air funnels this afternoon. Some of the storms may also contain hail and gusty winds today, so be prepared.
Funnel cloud west of the metro this summer is similar in appearance to cold air funnels.
Cold air funnels are common on days like today. Cold air aloft and spin in the atmosphere can work down to cloud bases and trigger the funnels. While cold air funnels are usually not as strong as most tornadoes, they can occasionally touch down and do minor damage. It is not out of the question that tornado warnings could be issued this afternoon for cold air funnel sightings.
Bring your umbrella, and keep a weather eye on the sky today.
Posted at 3:51 PM on August 20, 2009
by Paul Huttner
The NWS survey team from the Twin Cities office has confirmed what looks like 4 tornadoes Wednesday.
The report says the first tornado touched down near East 53rd and Park Avenues in Minneapolis, did the most damage around Portland and 44th street, then damaged the area near the Minneapolis Convention Center. No word from NWS on intensity yet, but I would estimate winds between 80 and 100 mph with EF0 to EF1 damage.
Other tornado damage is confirmed in Cottage Grove, Hudson and in Brown and Blue Earth Counties where minor crop damage was observed. There is still no word on what caused the damage in North Branch.
Forecast: Summer returns this weekend.
The pesky and drizmal low pressure system will pull out of the area tomorrow. Look for plenty of sunshine and a return to summer like temperatures over the weekend.
Enjoy! We've earned it.