We saw Polar Vortex In The Winter...Now we Have Mega-Vortex To Bring an Unseasonably Cool Beginning To May

Whether Polar or Mega; one word comes to peoples mind; "cool to cold weather" for the time specified and that's no different this time as an extra-ordinary large, cool upper low pressure system organizes over the Midwest and Great Lakes this week.

This is the same system that has produced the violent severe weather over the deep south over the weekend. The unseasonably deep and cool upper low pressure is in stark contrast to the warmer surface air in the south as the higher, later spring sun angle bubbles up the heat at the surface. This heat, rudely surges upward into the cool to colder upper level atmosphere, creating extreme instability along with tornadic producing wind shear. The deep upper low pressure, "mega-vortex" due to it's size, also contains a powerful jet stream aloft..more typical of late winter or early spring. A wind jet with a core of wind close to 120 miles an hour at 30, 000 ft projected by Tuesday morning, 4/29/14.

It is the combination of instability, strong jet and cold air aloft we run the risk of some strong to possibly severe weather on Tuesday. While the main action will be south of Southeast Lower Michigan, it would be wise to keep abreast to the potential for a brief  period of severe weather, mainly Tuesday afternoon and early evening.

From Severe Prediction Center...

...MIDWEST/OH VALLEY...
   THE AIR MASS SHOULD DESTABILIZE IN THE WAKE OF EARLY DAY
   CONVECTION/CLOUD COVER...PRIMARILY WITHIN A RELATIVELY NARROW ZONE
   NEAR/AHEAD OF THE EASTWARD-MOVING COLD FRONT AND THE SURFACE LOW
   OVER THE UPPER MS VALLEY. WHILE THE BOUNDARY LAYER WILL NOT BE
   PARTICULARLY MOIST /50S F SURFACE DEWPOINTS MOST AREAS/...COOL
   TEMPERATURES ALOFT/STEEP MID-LEVEL LAPSE RATES WILL CONTRIBUTE TO AS
   MUCH AS 750-1000 J/KG SBCAPE ACROSS PARTS OF THE REGION TUESDAY
   AFTERNOON. AS SUCH...SOME OF THE STRONGEST LOW-TOPPED TSTMS THAT
   DEVELOP WILL BE CAPABLE OF SEVERE HAIL AND PERHAPS A TORNADO OR TWO
   /STRONG LOW-LEVEL SHEAR AND AMBIENT VERTICAL VORTICITY/ TUESDAY
   AFTERNOON THROUGH EARLY EVENING.

By Wednesday, the huge low pressure system stacked throughout the atmosphere will
have spun up into the Great Lakes and Ohio Valley. Bringing cooler, wet conditions
across the region through the rest of the week. I'm keeping my eye on that colder shot of air that is projected to round the North Pole and head due south. How far south it gets will determined the frost/freeze risk into early next week. In any event, the first week of May will average cool over the region with most days, with the exception of Tuesday, temperatures climbing only into the 50s. On average the first week of May sees temperatures climb into the mid 60s with record highs flirting with 90. A bit closer to our expected weather; record lows drops into the mid 20s to around 30, while record low max's are in the upper 30s to mid 40s...lets hope we don't visit them.

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian