Minnesota tornadoes in November

On Saturday, a powerful cold front swept through the state.  Temperatures in the warm sector were near 70 degrees, with 40 degree temperatures behind the front.  This contrast, along with ample wind shear, set the stage for thunderstorms.  Due to the lack of instability, significant severe weather was not expected.  What ended up being garden variety thunderstorms in the western Twin Cities metro, turned out to be damaging winds, hail, and even two brief tornadoes across the southeastern metro.  No watches or warnings were in effect at the time, however the Storm Prediction Center had an outlook for 2% tornado probabilities across roughly the southern two-thirds of Minnesota for Saturday,

November tornadoes in Minnesota are rare, but not unprecedented.  Before this year, there were three known tornadoes in the state’s history:

• November 1, 2000 near Prinsburg (Kandiyohi County), rated F1.
• November 2, 1938 north of Nashwauk (Itasca County) to 14 miles northwest of Virginia (St. Louis County)
• November 16, 1931 near Maple Plain (Hennepin County)

The first tornado from Saturday occurred at 10:58 PM in Burnsville near the intersection of McAndrews Road and Dakota County Road 5.

Narrative from the National Weather Service:

AN EF-0 TORNADO SPUN UP JUST NORTHEAST OF THE INTERSECTION OF COUNTY ROAD 5 AND MCANDREWS RD AND TRACKED NORTHEAST TO JUST SOUTHWEST OF THE INTERSECTION OF BURNSVILLE PKWY AND HWY 11. NUMEROUS TREES AND POWER LINES WERE BLOWN DOWN ALONG THE PATH...SOME FELL ONTO HOUSES. A STOP SIGN WAS BENT ALL THE WAY TO THE GROUND AND A GRILL LID WAS FLOWN ABOUT 200 YDS NEAR NICOLLET JR HIGH SCHOOL. MAXIMUM WIND SPEEDS WERE AROUND 80 MPH.

The velocity radar scan from 11:00 PM shows a small couplet along the I-35E corridor, evidence of a possible tornado.  No warning was likely issued because of the time of the year, and severe weather threat was not highlighted by the National Weather Service.  Since the activity was at night and brief in nature, an approaching tornado would have been difficult to detect visually.  These tornadoes this day formed from low-topped convective activity similar to the August 19, 2009 series of tornadoes that caught many people off-guard, including the local National Weather Service office.

The second tornado occurred in Eagan seven minutes later to the northeast of the previous tornado.  It spun up near the intersection of Skyline Drive and Minnesota Highway 13.

Narrative from the National Weather Service:

A BRIEF EF-0 TORNADO SPUN UP NEAR SKYLINE DRIVE EAST OF HWY 13 AND TRACKED NNE TO THE LOST SPUR GOLF COURSE JUST SOUTH OF I-494. NUMEROUS TREES WERE BLOWN DOWN AND EXHIBITED A CONVERGENT DAMAGE PATTERN. SOME TREES FELL ONTO HOUSES AND POWER LINES. OTHERWISE...LITTLE STRUCTURAL DAMAGE. ESTIMATED WINDS 75 MPH.

A couplet was more visually evident with the second tornado.  Much like the Burnsville episode, no warning was issued even as reports of tree damage and power outages were coming into social networks.  By the time reports came into the National Weather Service, the tornadic activity had dissipated.  However, additional wind reports were still being received from the St. Paul area.

For a good ten minutes, the radar was hinting at the possibility of brief tornadoes:

Thankfully no one was serious hurt from the late year tornado that came at night, and without warning.  If indoors and the storm sounds bad outside, always use common sense and head to the lowest floor.  Each individual is ultimately responsible for his or her own safety.

RS

Minneapolis tornado: One year later

On Sunday, May 22, 2011, an EF-1 tornado tore through western and northern sections of Minneapolis.  There was one fatality in north Minneapolis.  The majority of the damage came from fallen trees on top of vehicles and roofs, but in some cases the wind was strong enough to lift entire roofs off of structures.  On the same day, an EF-5 tornado leveled Joplin, Missouri, resulting in 158 deaths and over 1,000 injured.  In retrospect, Minneapolis got off easy this day.  While the Minneapolis twister traveled 6.25 miles mainly over residential areas causing structural damage to homes, the Joplin tornado wiped the surface clean of any structures.

Recent Google satellite imagery shows the scar left behind from the Minneapolis tornado.  It began near the Theo Wirth Park area, where I surveyed the aftermath on this Sunday afternoon.

A closer look at the damage path reveals residences with blue tarp, indicating rooftops in disrepair.

Now take a look at the Joplin damage.  Entire subdivisions of the city gone!  Everything is unrecognizable.

With all the attention the anniversary of the Minneapolis tornado will receive from media outlets, I feel it is important to put the impacts of the tornado in perspective.  We were lucky compared to other areas of the United States on May 22, 2011, and during that year in general - Alabama was hit very hard by a tornado outbreak in April 2011.  The damage in those locations was catastrophic, and it will take many years for them to rebuild from scratch.

RS

Severe weather situation unfolding for Tuesday

The focal point for thunderstorms, some of which could be severe will be found in the warm sector of a lifting warm front during the day on Tuesday.

This warm front will allow temperatures to soar to near 80 degrees across southern Minnesota during the afternoon with dew points into the 60s behind the front.

This will create enough instability for severe thunderstorms during the latter half of the day.  The darker colors below are where conditions will come together for the best chance of severe weather.

Where the jet stream intersects with the warm front will be the most favorable area for a few tornado threat if convection can become rooted in the boundary layer.  This includes the Interstate 35 corridor north of the Twin Cities from near Hinckley to just south of Duluth.  Shear is not terribly impressive, so I don’t think we’ll see any kind of tornado outbreak today.

The low-level jet, which typically strengthens at night, increases to 40 knots by 7 PM and enhancing the thunderstorm risk for the Twin Cities metro and areas along Interstate 35.  It is around this time where I feel conditions are most favorable for severe thunderstorms.  I don’t think tornadoes are as favorable in the Twin Cities.  The primary threats for MSP will be large hail and damaging winds.

“The big if”  Cloud cover will play a big role in whether we see severe weather Tuesday as this will limit instability.  With marginal wind shear, instability will absolutely be necessary for storms to form and survive.  If clearing does not occur until the afternoon, then expect regular thunderstorms throughout the day.

Current satellite shows clouds from showers and thunderstorms across north central Minnesota.  Timing will be everything.

The NAM, GFS, and Euro model all depict some degree of cloudiness by midday:

If clearing happens before noon, then I expect storms to initiate across southwestern Minnesota during the early afternoon by 2 PM near the warm front with more storms firing to the northeast across the state along the boundary layer. As convection moves eastward, it should approach the eastern half of the state by 5 PM and into the Twin Cities by 6 PM. Between 6 and 9 PM is the time table for any rough weather to roll through the metro.

As always, more updates will be posted as they become warranted!

RS

Active week ahead with severe weather possible

Warm and humid air from the Gulf of Mexico will move northward to start the work week, bringing with it the possibility of thunderstorms between Tuesday and Thursday.  The best chance for any severe weather will come on Tuesday.

Looking at Tuesday’s weather setup, an area of low pressure, with associated warm and cold front, will move in from the Rockies towards the Fargo vicinity by Tuesday night.

Behind a warm front and out ahead of a cold front and dry line in the Plains, the central United States will see the greatest risk of severe storms.  The area highlighted below is of most concern.

Strong, southern wind flow will cause temperatures to climb into the low 80s across southern and southwestern section of the state by Tuesday afternoon:

Dew points are forecasted to be into the 60s across roughly the southern two-thirds of Minnesota:

The heat and humidity will create enough energy for thunderstorm development across southwestern Minnesota during the afternoon hours under a moderately unstable atmosphere.  The movement of these storms will be towards the east as the night progresses, pushing into western Wisconsin by the overnight.

The primary concerns will be large hail and damaging winds.  The jet stream is positioned on the NAM to be north of the greatest area of concern.  If the jet is forecasted to shift further south over the next 24 hours, then a threat for a tornado outbreak would increase.

Mid-level winds in excess of 40 knots would support severe thunderstorms:

Winds veer from the west towards the south at the surface to support rotating updrafts and perhaps a few tornadoes.  A strong low-level jet Tuesday night will help fuel thunderstorm development.

Stay tuned on additional details of this potentially active week!

RS

Minnesota’s cold-core tornadoes

A rather unexpected tornado event occurred Saturday from a cold-core weather system that moved through the state during the day.  Cold-core thunderstorms tend to form with steep lapse rates – a rapid change in temperature with height to create an unstable air mass.  Cold-core funnels are often seen behind cold fronts where there is enough instability and moisture, along with vorticity, to support rotating updrafts in towering, but low-precipitation cumulus clouds.  These funnels may briefly spin up a tornado, but tornadoes in this kind of environment tend to be less violent than your typical twisters found on the Plains.

The Saturday forecast from most, if not all, accounts called for rain, but no mention about the possibility of cold-air funnels or tornadoes.  Since cold-air funnels can occur in clouds not tall enough for thunder, they are difficult to predict and often appear without warning.  The Storm Prediction Center (SPC) forecast for Saturday issued at 11:53 PM (all times noted are CDT) Friday did not outline any portion of Minnesota in a thunderstorm area.

When the SPC updated their Saturday forecast at 7:21 AM that morning, they included southwest Minnesota in a general thunderstorm category, but no mention of funnels or tornadoes were made in the forecast discussion.

At 1 PM, a low pressure area was centered near Fargo, North Dakota with an associated cold front stretching along the Minnesota/Dakotas border and warm front extending across central Minnesota.  Most of eastern central Minnesota was under a shield of rain, while snow feel across the Arrowhead of Minnesota, ahead of the warm front.

Storms began to fire right around the noon hour in the vicinity of the the low pressure area.  Temperatures were in the mid-40s across western Minnesota with 60s just across the border into South Dakota where the sun was able to break through during the morning hours.

In the area of convective activity, 500 millibar (18,000 feet) temperatures were running on the order of about -25°C, or -13°F.  That’s some very cold air aloft!

This temperature difference with the cold pool of air created lapse rates at the low to mid-levels of 7 to 7.5°F for every 1,000 feet across western Minnesota, behind the precipitation band in the eastern part of the state.

CAPE instability values were running around 250 to 500 J/kg.  Marginal instability for convection.

With these conditions in place, the National Weather Service in Grand Forks issued a Special Weather Statement at 12:44 PM for the Fargo area, indicating conditions were favorable for cold-air funnels and possible brief touchdowns.  The first damage report came in earlier from near Glyndon in Clay County at 12:23 PM.

INCLUDING THE CITIES OF...CROOKSTON...EAST GRAND FORKS...HALSTAD...MOORHEAD...FOSSTON...MAHNOMEN...
DETROIT LAKES... BRECKENRIDGE...FERGUS FALLS

BRIEF COLD AIR FUNNELS ARE POSSIBLE. THE CURRENT ENVIRONMENT IS NOT CONDUCIVE FOR SEVERE THUNDERSTORM BASED TORNADOES. THE FUNNELS MAY BRIEFLY TOUCH DOWN...BUT RARELY CAUSE DAMAGE. CONTACT LOCAL LAW ENFORCEMENT OR THE NATIONAL WEATHER SERVICE IF YOU OBSERVE A FUNNEL.

Additional damage reports were coming in south and east of Fargo during the noon and 1 PM hours.  The Grand Forks office decided to forgo issuing tornado warnings during this event.  At 1:55 PM, the Storm Prediction Center highlighted western Minnesota as a favorable area for a “brief/small tornado” through 5 PM, but felt the need for a weather watch box was unlikely in it’s discussion.

Radar replay of the storms during the afternoon and evening.  As the storms marched east towards the evening hours, they lost their tornadic characteristics moving into a more stable environment.  The last tornado was reported at 3:45 PM in Redwood County.

Just after 3 PM, this rope tornado was seen east of Milan and north of Montevideo in Chippewa County.  Photo provided by KARE-11 meteorologist Jerrid Sebesta.

Here is how storm reports stacked up with the SPC’s Saturday morning forecast for the day to measure accuracy.  The weather system was responsible for 10 tornadoes - eight in Minnesota and two in Iowa.  One Iowa tornado was located near the City of Spencer, the largest populated area to be affected this day.

Tornado reports received across Minnesota on Saturday. Adding the eight tornado reports received with the four tornadoes prior to this day, gives us a preliminary count of a dozen for the year.

1. 5 SE Glyndon [Clay Co, MN] trained spotter reports TORNADO at 12:23 PM CDT -- spotter reported 4 foot by 6 foot pieces of tin scattered on both sides of hiway 9. numerous funnels reported in the area with touchdown.
2. 4 SE Kent [Wilkin Co, MN] law enforcement reports TORNADO at 01:24 PM CDT -- damage to pole barn...trampoline blown on top of garage...and roof damage to trailer. numerous funnels reported in area with touchdown.
3. 5 S Fergus Falls [Otter Tail Co, MN] law enforcement reports TORNADO at 02:40 PM CDT -- grain bin and shop damaged. numerous funnels reported in the area with brief touchdown. time approximate.
4. 4 E Milan [Chippewa Co, MN] law enforcement reports TORNADO at 03:11 PM CDT -- barn and grainerys damaged
5. 6 NNE Walnut Grove [Redwood Co, MN] law enforcement reports TORNADO at 03:23 PM CDT -- multiple reports of funnels with brief touchdowns over 10-15 minutes...time is estimated as is location.
6. 6 E BIG Bend City [Swift Co, MN] law enforcement reports TORNADO at 03:28 PM CDT
7. 2 NE Farwell [Douglas Co, MN] law enforcement reports TORNADO at 03:30 PM CDT -- 30-40 foot pole barn taken down...damage to a second barn as well. neighbor witnessed a funnel. time is estimated based on radar.
8. 7 S Lucan [Redwood Co, MN] law enforcement reports TORNADO at 03:45 PM CDT -- time estimated between 330 and 400 pm cdt. damage to a flower shop.

RS

Minnesota tornado facts

In conclusion of Severe Weather Awareness Week across Minnesota, here are some facts when it comes to tornadoes in the state:

• Minnesota’s first recorded tornado in history occurred on April 18, 1820 at a camp that eventually became Fort Snelling.
  
• There has not been an EF-5 tornado in Minnesota since the Enhanced Fujita scale started February 1, 2007.  The last F-5 tornado in the state was on June 16, 1992, affecting the City of Chandler.
  
• Minnesota led the nation in tornadoes with 113 in 2010. 48 of those occurred June 17 as part of largest known outbreak in state history.
  
• 31 tornadoes were reported in Minnesota during 2011. Three of those were rated EF-2, the strongest of the year.
  
• Since the Enhanced Fujita scale became operational, there have been 229 tornadoes in the state through 2011.   The percentages are as follows: 59% EF-0, 29% EF-1, 7% EF-2, 3% EF-3, 2% EF-4.

RS

Severe Weather Awareness Week

This week (April 16-20) is Severe Weather Awareness Week in Minnesota.  According to Minnesota Department of Public Safety’s Homeland Security and Emergency Management, “The Severe Weather Awareness Week campaign helps teach Minnesotans about weather hazards and provides resources to minimize the risks associated with severe weather.”  In the past 10 years, more than 40 people have died and dozens more injured as a result of weather-related events in Minnesota (not including motor vehicles).  This blog post will present an overview on what to expect this week as part of Severe Weather Awareness, explain terminology used in weather alerts, and provide alternative methods to traditional media sources for receiving these alerts to stay safe during severe weather.

On Thursday, April 19th, sirens will sound twice as part of a simulated tornado warning.  Once at 1:45 PM, and again at 6:55 PM (all Minnesota counties in the evening except: Aitkin, Becker, Carlton, Hubbard, Itasca, Kanabec, Kittson, Lincoln, Norman, Otter Tail, and Yellow Medicine).  This will provide an opportunity to review action plans at work, school, and home in the event of a natural disaster, such as a tornado.  Sirens will sound for about three minutes.  When the sirens are activated, NOAA Weather Radios will sound an alert tone for a tornado warning.

So what does a watch and warning mean?  A watch means weather conditions are favorable for dangerous weather to occur.  In other words, a "watch" means watch out for what the weather could do, and be ready to act accordingly.  You may wish to alter or have a “Plan B” for any outdoor activities or travel.  A warning means the weather event is imminent or occurring somewhere in the defined warning area and that people need to take shelter as soon as possible.  In 2010, Minnesota had the most tornadoes of any state in the United States with 113.  Tornadoes can occur any time of day or night, but often occur in the late afternoon or evening.  A tornado watch is issued by the National Weather Service when weather conditions are favorable for tornadoes and persons should remain alert for approaching storms.  A tornado warning is issued when a tornado has been sighted or indicated by weather radar.  Take shelter immediately!  Whether a tornado has been radar indicated or confirmed, people should NOT be outdoors looking for the tornado.  There’s a chance it’s already on your doorstep, and by then it’s too late to take cover - leading to injury or possibly death!

How can I stay alert of the latest weather conditions?  I always believe that everyone should have two sources for receiving weather alerts other than outdoor sirens.  An outdoor siren was NOT designed to be heard indoors, and it should NOT be your primary means of warning to take shelter.  Counties and cities own the sirens and therefore decide how and when to activate them, not the National Weather Service.  All sirens are not the same.  There are many different policies by counties and cities.  Some will activate them across the entire county for a tornado warning only.  Others will activate sirens countywide for tornado warnings and all severe thunderstorm warnings.  Some will activate sirens across the entire county for tornado warnings and severe thunderstorms that have winds of at least 70 or 75 MPH, while others will activate sirens only for portions of counties.  Also, local officials may sound the sirens anytime they believe severe weather is a threat, even if there is no warning from the National Weather Service.  In the Twin Cities, Dakota County activates the sirens for any severe thunderstorm warning as well.  A severe thunderstorm warning is issued when thunderstorm winds are indicated or measured to be 58 MPH or greater, and/or contain hail at least one-inch in diameter.  Scott County will typically activate outdoor warning sirens if a tornado warning is issued, according to Chris Weldon, Scott County Emergency Management Director.

Quite frankly, every home should have a NOAA Weather Radio.  They are as essential as smoke detectors in homes.  This is potentially a life-saving device.  The alert technology has been around well before the Internet boom and cell phones, but with enhancements along the way.  Depending on the features, these radios cost anywhere between $20 to $200.  Most brick and mortar retail stores carry these radios (RadioShack tends to have the largest selection), and can also be purchased from online retailers, such as Amazon, using keyword search “weather radio”.  These radios with battery backup are designed to be loud enough to wake you up during a severe weather emergency in the middle of the night, and programmable to broadcast the alert text from the weather service.  Radios with SAME (Specific Alert Message Encoding) technology allow the weather radio to broadcast alerts only for counties you specify using a six-digit code number.  SAME codes can be found here.  It is recommended to select a weather radio with the “Public Alert” certification.  These radio have met certain technical standards and come with many essential features.

There are dozens of radio transmitters covering Minnesota for receiving weather broadcasts.  NOAA weather Radio broadcasts on seven different frequencies, which are pre-configured in most radios as channels.  Nearly every location in the state should receive a good signal.  The one exception is north of Bemidji in Beltrami County near Red Lake.

With the increase in usage of smartphones, apps are becoming more sophisticated.  For iPhone users, iMap Weather Radio is a highly recommended app to alert of approaching hazardous weather for any location using GPS tracking.  When an alert is received, a loud “chirp” tone will sound, and type of alert will be announced.  More details can be found in a review I did here.  According to app maker Weather Decision Technologies, an Android version is currently in development.

Speaking of phones, CellWarn from Convective Development sends weather watches, warnings, and advisories to your email and/or cell phone for free (carrier text message rates may apply).  The free service includes delivery options such as severe thunderstorm watches and warnings, tornado watches and warnings, winter watches, warnings, and advisories, and severe thunderstorm outlooks.

Social media is also a great way to stay informed.  My weather-related Twitter account, @ShakopeeWeather, and Facebook page post warnings for Minnesota as they come in from the National Weather Service.  Other accounts such as @iembot_mpx, posts all Twin Cities National Weather Service products, and @severewarn, posts warnings issued anywhere in the United States.  From my experience, most meteorologists are active on these social media sites during severe weather events, and are prompt with posting weather information pertaining to a dangerous situation.

As we get deeper into the severe weather season across Minnesota, I encourage the general public to start preparing this week for the thunderstorm season by establishing access to alert services and understanding the different weather alerts issued by the National Weather Service.  It will help eliminate any confusion during an actual emergency.  If you would like to get involved as a storm spotter in Minnesota (there are never enough), class schedules are posted here for outstate residents, and here for Twin Cities residents.

Additional information for Severe Weather Awareness Week:

• National Weather Service – Twin Cities
• Minnesota Department of Public Safety - Homeland Security and Emergency Management

RS

A look back at the first week of April

This week we said goodbye to March and hello to April.  March 2012 was one of the warmest relative months I have ever experienced here in Minnesota.  I could not remember the last time there was a stretch of 70 degree temperatures in March.  We hit 80 on the 17th, which was the earliest date to record such a mark during the year.

It was a whopping 15.5 degrees above normal at MSP Airport, and warmest March on record.  Pretty much the same story across the state with temps at least 10 degrees above normal everywhere.

The trend over the last 115 years indicates that the our Marches have indeed become warmer in Minnesota.  Since 1895, the average temperature has increased nearly three degrees, or an increase of around a quarter-degree per decade.  Is this cyclical or climate change?  Honestly, I don’t know.

The warmth also brought strong storms to the area Monday as a low level jet interacted with a trough of low pressure.  Hail was the primary concern with these storms into the night as they tracked across the southern Twin Cities metro.

I decided to venture out as the western most storm cell headed into Scott County and the Shakopee area.

All I saw out of this was some pea size hail, lightning, and much needed rainfall.

Most of the hail reports where below severe levels of one-inch, but one report from Burnsville indicated one-inch hail.

A more potent storm system took aim across the southern United States on Tuesday with a chance of severe thunderstorms, including tornadoes.

Shortly after noon central time, a tornado watch was issued for the Dallas-Fort Worth (DFW) metroplex.

Between noon and 3 PM, DFW was under the gun for tornadic activity.

Radar summary of the supercells producing the tornadoes from that afternoon.

One of the most awe-inspiring images and video from this tornado outbreak was watching semi-truck trailers, upwards of 15,000 pounds (7.5 tons!), being tossed into the air like toys.

New data is still coming in, but the National Weather Service in Dallas/Fort Worth has determined that at least 15 tornadoes occurred in the metro area and areas to the east. While there were injuries, miraculously no deaths were reported.  Most of the tornadoes were of EF-0 strength, which affected populated areas such as Dallas and Arlington, Texas.  The strongest tornado was an EF-3 in Forney, Texas.

What is helping fuel these thunderstorms across the south is the warm Gulf of Mexico water temperatures, which are in the upper 70s and low 80s.  With the mild winter, the Gulf of Mexico really did not have a chance to cool down.  Under these conditions, moisture is very easily transported into the atmosphere.

Looking ahead to the remainder of April, much of the United States is expected to see above normal temperatures according to the Climate Prediction Center.

Temperatures in the Twin Cities are already running above average for the month.  Back on April 2nd, we saw a low temperature that we typically see for a high temperature on that day!

As far as precipitation, we should be dry generally until the middle of the month.  For the last several days, the GFS model has been hinting at significant rains around the 14th to 16th time frame.  After this system moves through, new model guidance suggest that we will be in blocking pattern into the fourth week of April, keeping us dry.

In the short term, this weekend will be very nice.  Some showers are possible around mid-day Saturday (as much as a tenth of an inch of rain), but Easter is looking mild and dry.  Couldn’t ask for better weather on this holiday.

Happy Easter!  Hope it’s a good one for you and your family.

RS