Tornado watch for the Twin Cities

(Update: 9:10 pm. More rough storms tracking across central Minnesota, Doppler radar estimates of 1.25″ diameter hail in these storms. Time to batten down the hatches, move the kids indoor, move the car into the garage – if you have that option). Winds up to 50 mph may accompany these storms, even an isolated tornado. The best chance of metro-area storms will be from 10:30 to 1:00 am. A tornado watch remains in effect until 11 pm).

BULLETIN – EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
851 PM CDT THU JUN 18 2009

THE NATIONAL WEATHER SERVICE IN THE TWIN CITIES HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR…
STEARNS COUNTY IN CENTRAL MINNESOTA…

* UNTIL 945 PM CDT

* AT 851 PM CDT…RADAR INDICATED A LINE OF SEVERE THUNDERSTORMS…
CAPABLE OF PRODUCING QUARTER SIZE HAIL AND DAMAGING WINDS IN EXCESS
OF 65 MPH. THESE STORMS WERE LOCATED ALONG A LINE EXTENDING FROM 5
MILES NORTHWEST OF MELROSE TO 4 MILES WEST OF MEIRE GROVE TO 5
MILES NORTHWEST OF BELGRADE…AND MOVING EAST AT 30 MPH.

* LOCATIONS IN THE WARNING INCLUDE…
ELROSA…
BELGRADE…
MEIRE GROVE…
MELROSE…
GEORGEVILLE…
NEW MUNICH…
ST ROSA…
FREEPORT…
LAKE HENRY…
ALBANY…
ROSCOE…
HOLDINGFORD…

Tornado Watch ’til 11 pm, possible MCS later?

Update: 7:45 pm. The longer I look at the pattern the more I’m starting to believe we’re looking at an MCS scenario. An MCS is a “mesocyclonic system”, a swarm of severe thunderstorms that tends to intensify at night, producing straight-line winds, torrential rains and (sometimes) almost continuous lightning. These MCS systems are fairly common in June and July here in the Midwest, forming on the northern edge of an expansive dome of hot, humidified air. I’m not minimizing the tornado risk, but I have a strong gut feel that we may be looking at a different feature later tonight, with the best chance of severe weather/torrential rain from 10 pm to 1 am or so, possibly arriving after 9 pm in the St. Cloud area. The tornado watch remains posted until 11 pm, but my hunch is that this watch will transform into a series of severe storm watches later tonight as an MCS system gets going and intensifies as it approaches the Twin Cities, Rochester and Mankato. Stay tuned…

Latest visible satellite image showing the tops of thunderheads being swept to the north and east. There is an extensive area of heavy weather moving in from the Dakotas/Red River Valley, and a significant potential that these storms will mutate into a boomerang-shaped MCS as the night goes on, with a possibility of damaging straight-line (and tornadic) winds, and torrential rains capable of street and stream flooding.

2.5″ diameter hail west of St. Cloud

BULLETIN – EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
447 PM CDT THU JUN 18 2009

THE NATIONAL WEATHER SERVICE IN THE TWIN CITIES HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR…
SOUTHWESTERN MORRISON COUNTY IN CENTRAL MINNESOTA…
NORTHEAST STEARNS COUNTY IN CENTRAL MINNESOTA…

* UNTIL 530 PM CDT

* AT 443 PM CDT…RADAR INDICATED A SEVERE THUNDERSTORM…CAPABLE OF
PRODUCING QUARTER SIZE HAIL AND DAMAGING WINDS IN EXCESS OF 60 MPH.
THIS STORM WAS LOCATED 4 MILES SOUTHWEST OF UPSALA…OR ABOUT 19
MILES SOUTHWEST OF LITTLE FALLS…AND MOVING EAST AT 25 MPH.

* LOCATIONS IN THE WARNING INCLUDE…
ELMDALE…
HOLDINGFORD…
BOWLES…


Update: 4:12 pm. Latest “Supercell Composite” image from SPC, showing the greatest threat of tornadic T-storms (for now) over Iowa, and the Brainerd-Wadena area of Minnesota. The longer the sun stays out, the more unstable the atmosphere over central and southern MN will become. Factor in strong wind shear and ample moisture near the ground and you have all the necessary ingredients for a significant tornado outbreak. In the coming hours we hope to zero in on the counties in Minnesota most at risk.


This is a technical post, but I want to err on the side of providing more, rather than less information about today’s tornado risk.

Update: 3:23 pm. Tornado watch posted until 11 pm for much of central and southern MN, including St. Cloud, Mankato and the Twin Cities. Conditions overhead are ripe for tornadic, “supercell” thunderstorms capable of large hail and isolated tornadoes. Stay tuned and stay alert for possible warnings, issued on a county-by-county basis later today.

Update: 3:30pm

BULLETIN – EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
227 PM CDT THU JUN 18 2009

THE NATIONAL WEATHER SERVICE IN THE TWIN CITIES HAS ISSUED A

* TORNADO WARNING FOR…
SOUTHEASTERN DOUGLAS COUNTY IN WEST CENTRAL MINNESOTA…

* UNTIL 315 PM CDT

* AT 225 PM CDT…RADAR WAS TRACKING A SEVERE STORM WITH STRONG
ROTATION. THE MOST DANGEROUS PART OF THE STORM WAS NEAR
ALEXANDRIA…OR ABOUT 6 MILES NORTH OF FORADA…AND MOVING EAST AT
15 MPH.

* LOCATIONS IN THE WARNING INCLUDE…
CARLOS…
NELSON…
BELLE RIVER…
OSAKIS…

Greatest threat now is west of St. Cloud – but strong/severe storms are likely closer to the Twin Cities by late afternoon or evening. The potential for hail/isolated tornadoes is high today – I do expect a tornado watch to be issued close to home, with warnings issued for specific counties later in the day, closer to the dinner hour. Check back in for more updates…

Update: 1:05 pm. Severe storm warning posted for western Douglas county until 1:45 pm for quarter-size (1″ diameter) hail. The cell is moving northeast toward Evansville. People living in the Alexandria/Carlos area should be prepared to move to shelter. Although no tornado watches are currently in effect we can’t rule out an isolated tornado with this cell – although the greatest danger will probably come later this afternoon, after 3 or 4 pm, when the atmosphere overhead is most unstable. Keep checking in for more updates.

(remember to click on the image below to see it full screen, so you can see all the details and read the text of the NWS warning!)

Updated 12:04 p.m. The latest from SPC, the Storm Prediction Center, showing a MODERATE risk of severe storms extending into almost all of central and southern Minnesota. With high dew points, an unstable atmosphere, strong “wind shear” aloft and boundaries left over from last night’s storms, conditions are ripe for more potentially violent weather later today and tonight. I do expect watches and warnings to be issued by mid afternoon, the threat of large hail and isolated tornadoes increasing as you head south toward the Iowa border. Statistically, there is a 5-10% probability of a tornado within 25 miles of any town south of St. Cloud through the late evening hours. Stay alert, check back to this site often for updates (including Doppler radar and warning information on a county by county basis). I’m pretty confident there will be more tornado touchdowns around the dinner hour – hard to pin down which part of the state has the highest risk of violent weather – hopefully that will crystallize over the next few hours.



In a tornado the safest place to ride out the storm:

* Basement, under the stairs. Statistically this is the safest place to be, under a desk or heavy piece of furniture if possible.

* Small, windowless room on the ground floor, like a closet or bathroom. People have survived F-5 tornadoes by hiding in their bathtubs, a mattress or blanket (or pillows) on top of them.

* Avoid outer walls/windows. Most tornado injuries are the result of flying debris and head trauma. That’s why it’s preferable to get below grade, underground if at all possible.

* In a school or office seek shelter near the interior of the floor, a concrete-reinforced stairwell or bathroom usually provides the best protection.

* Avoid mobile homes (which can become airborne at wind speeds as low as 80 mph). Avoid large rooms, gymnasiums, auditoriums – these are the first to collapse when a tornado hits.

* In a vehicle you can usually drive away from the storm. If that’s impossible get out of your vehicle and seek shelter in a nearby building – OR – a ditch. Do NOT ride out the storm inside a car or truck or underneath a vehicle. Do NOT seek shelter under a bridge overpass (a wind-tunnel effect can increase the threat of flying debris hitting you there).

*****

Only in Minnesota can one be ankle-deep in mud with dust blowing in your face. The weather changes fast up here, if you blink, sneeze, turn away from just a second or two, the sky draped overhead is likely to change on you, often taking a sudden turn for the worse. Just last week the talk was drought, expanding across much of central and southern Minnesota. We were shivering (in June!) with a few days in a row of 50s, setting records left and right. There was even frost reported up north, with a rare June coating of snow over far northern counties! Many of us were experiencing a rare “where-am-I-living” moment!

Summer has arrived all right, in a hurry. Like turning on a light swtich. Seemingly overnight we went from drought-speak to tornado-talk, jackets gave way to shorts (and neighbors predictably complaining about the humidity). All those tired, tantalizing warm fronts that lurked to our south much of May and the first half of June finally surged north, sparking outbreaks of storms, and yesterday: the first official tornadoes of the year. During an average year Minnesota experiences about 25 tornadoes. Wednesday evening we saw nearly a third of that tally (at least 8 separate tornado reports).

Today will be muggy, murky and potentially violent, with a MODERATE risk of severe storms over roughly the southern third of Minnesota later today. As is always the case any severe weather will ultimately affect a tiny percentage of the state, but I’m pretty impressed with the dynamics, the ingredients lining up for later today. Strong instability, ample moisture near the ground, wind shear aloft (changing wind speed/direction with altitude). The result: a few isolated, spinning “supercell” thunderstorms capable of softball size hail and a tornado or two once again later today.



There’s no way to predict exactly where a tornado will touch down. It’s the meteorological equivalent of a SNEEZE. All we can do is tell when conditions are ripe for tornadic storms, in which case a tornado watch is issued for a big portion of the state, as many as 30-60 counties can be under a watch. If and when a rotating, tornadic storm is spotted on Doppler (or by professionally trained SKYWARN storm spotters) a warning is issued for counties, or specific parts of counties, so people aren’t needlessly warned. A warning means that severe weather is imminent, time to seek shelter.

Doppler radar from 7:16 pm yesterday. Click on the image to bring it full screen, and you can see the “hook echo” bearing down on Austin. A tornado warning was in effect when the storm hit the Austin area, the same thunderstorm had a history of producing funnels and tornadoes near Waseca and Blooming Prairie. The storm was also a “right-turner”, veering off to the right of the other storms in the area. These rogue, right-veering storms are often tip-offs of tornado-producing conditions, and the Austin storm was no exception.

Since the mid 70s the average lead-time for tornadoes, the time from when the tornado is detected/warned for, and when the violent winds actually strike, has expanded from 7 minutes to nearly 15 minutes, allowing more time for Americans to seek shelter and avoid injury.

In a tornado the safest place to ride out the storm:

* Basement, under the stairs. Statistically this is the safest place to be, under a desk or heavy piece of furniture if possible.

* Small, windowless room on the ground floor, like a closet or bathroom. People have survived F-5 tornadoes by hiding in their bathtubs, a mattress or blanket (or pillows) on top of them.

* Avoid outer walls/windows. Most tornado injuries are the result of flying debris and head trauma. That’s why it’s preferable to get below grade, underground if at all possible.

* In a school or office seek shelter near the interior of the floor, a concrete-reinforced stairwell or bathroom usually provides the best protection.

* Avoid mobile homes (which can become airborne at wind speeds as low as 80 mph). Avoid large rooms, gymnasiums, auditoriums – these are the first to collapse when a tornado hits.

* In a vehicle you can usually drive away from the storm. If that’s impossible get out of your vehicle and seek shelter in a nearby building – OR – a ditch. Do NOT ride out the storm inside a car or truck or underneath a vehicle. Do NOT seek shelter under a bridge overpass (a wind-tunnel effect can increase the threat of flying debris hitting you there).

The good news? Watering the lawn/garden/field should be optional. Many yards will pick up a cool 1-2″ of rain between now and Friday afternoon as a slow-moving storm tracks across the state. Skies should start to dry out (and sunny-up) Saturday – most of the day looks dry with only an isolated midday shower or two. Most of Sunday looks sunny, hazy and lake-worthy, with highs topping 80 (even up north at the cabin!) A few late-day T-storms may rumble in from the west late Sunday afternoon/evening, so keep that in the back of your mind.

No more cool fronts are brewing – in fact 90 degrees is not out of the question by Tuesday of next week. Computer models are hinting strongly at the rest of June being wetter than average, and warmer than normal, with highs mostly in the 80s by day.

Welcome to instant-summer, complete with all the unpleasant side-effects, including hail and high water. Thunder-wear gets a work-out through tomorrow, but our reward should be a warm, mostly-pleasant, mostly-dry weekend with temperatures warm enough to make just about everyone get a running start, and go jump in a lake!

Weather Headlines

* At least 8 separate tornado touchdowns reported in Minnesota Wednesday, the first of the year. Hardest hit: the Austin, MN area, where a large, violent tornado was reported around the dinner hour, possibly a “multi-vortex” tornado comprised of multiple, smaller tornadoes all swirling around a common center.

* Slight to moderate risk of severe storms again today: potential for damaging hail and isolated tornadoes.

* Rainfall amounts of 1-2″ quite possible by Friday as a slow-moving warm frontal boundary lifts northward across Minnesota.

* Very high dew points today: near 70 (tropical levels of moisture streaming northward).

* Drying out in time to salvage a sunnier, drier Saturday with lower humidity levels.

* More T-storms may rumble into Minnesota (from west to east) later in the day Sunday.

* Stormy patterns lingers into most of next week. Computers hinting at warmer-than-average temperatures and wetter-than-normal conditions through the end of June.

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