PDS Tornado Watch Spells Dangerous Storms & Tornadoes


In the last few minutes, the Storm Prediction Center issued a PDS Tornado Watch through 11 pm CT/12 midnight ET for SE Minnesota, NE Iowa, most of Wisconsin & the western third of the Upper Peninsula of Michigan. A PDS Tornado Watch is a particularly dangerous situation.

Below is the wording on the tornado watch. Read this carefully. You will see why this a situation that needs high amounts of monitoring.

The NWS Storm Prediction Center has issued a Tornado Watch for portions of northeast Iowa, parts of western Upper Michigan, a small part of southeast Minnesota, much of Wisconsin and adjacent coastal waters of Lake Superior effective this Sunday afternoon and evening from 320 PM until 1100 PM CDT.

… This is a particularly dangerous situation…

Destructive tornadoes, large hail to 4 inches in diameter, thunderstorm wind gusts to 70 mph and dangerous lightning are possible in these areas.

The Tornado Watch area is approximately along and 105 statute miles east and west of a line from 5 miles north northwest of Ironwood Michigan to 45 miles south of Camp Douglas Wisconsin.

Remember, a Tornado Watch means conditions are favorable for tornadoes and severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings.

Discussion: Rapid development of severe supercell thunderstorms imminent along the cold front from WI/MN border into nern IA. Air mass has destabilized ahead of front with MLCAPES to 2000 j/kg… coupled with a very intense wind field will lead to potential of both very large hail and tornados with any supercell. There is the threat of long lived supercells along with strong/damaging tornadoes.

Aviation… tornadoes and a few severe thunderstorms with hail surface and aloft to 4 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 24050.

Pretty stern wording there. If you know someone in the aforementioned areas, call them, alert them immediately. Things can and will get nasty in a very fast hurry.

Below is more of what this bulletin has said, plus other areas that could have impacts with severe weather.

Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0254 PM CDT sun Apr 10 2011
Valid 102000z – 111200z

There is a moderate risk of severe thunderstorms across far southeastern Minnesota, far northeastern Iowa, much of Wisconsin and portions of the Upper Peninsula of Michigan. There is a slight risk of severe thunderstorms from the upper Great Lakes region southwestward into northestern Texas.

Upper Great Lakes region southwestward into northestern Texas: Forecast remains on track for a regional outbreak of severe storms — including the potential for isolated strong tornadoes — across the upper MS valley/western upper Great Lakes region.

Storms have been slow to initiate this afternoon, as capping continues to hinder development. However, a strong vorticity maxima/jet streak evident in WV imagery is moving rapidly northeastward across Kansas into southeastern Nebraska…and should provide favorable ascent — focused along the surface cold front across southeastern Minnesota/central Iowa — for cap erosion and subsequent convective initiation.

Once storms initiate, moderately-unstable airmass combined with very strong/favorable deep-layer wind field will support rapid supercell evolution and subsequent threats for very large hail, damaging winds and tornadoes. Storms should eventually shift across WI into Upper Michigan and across Lake Michigan into the lower peninsula with continued threats for damaging winds…hail…and an isolated tornado.

Storms should also develop — in a generally more linear fashion — southwestward along the front…and then shift steadily eastward with time across MO/eastern OK/Arkansas and northestern Texas. Overnight…threat for damaging winds should also spread across the Midwest…waning slowly as the atmosphere diurnally stabilizes.

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