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

Why It's a Big Deal That Half of the Great Lakes Are Still Covered in Ice & Recent April Snow

I decided to relay a very interesting article on the the effects on the cold and snowy winter of 2013-14 had (and should have) on the Great Lakes...much of it positive. What is probably the most notable is the possibility of dramatic jumps in water levels - which already are expected to rise around a foot. Note the following from the article;

"Though *Kompoltowicz says the usual March and April rise in water levels is occurring later than usual this year, already the lakes are seeing water levels that they haven't had for several years. This past March marked the first time since April of 1998 that Lake Superior had reached its long-term average. And over the next few months, melting snow will feed the lakes and colder water could lower the rates of summer and fall evaporation. The amount of rain could either add to or subtract from this total. The Army Corps of Engineers and the National Oceanic and Atmospheric Administration generally forecast water levels six months out, and predicted levels for this September, Kompoltowicz says, range from 10 to 13 inches higher than lake levels were a year ago".

*Keith Kompoltowicz, the chief of watershed hydrology for the Army Corps of Engineers' Detroit District. The entire article can be found here.


And finally, on the subject of our recent April snow;

I think the following picture of the snow on 4/15 and the fatigued crocuses smothered in it - reflects most of the feelings of the inhabitants of Southeast Lower Michigan. Get Lost Winter & Bring On Spring!! LOL

Hopefully (and most likely) it was our last measurable snow on 4/15...Next Up; The Incredible Winter of 2013-14  

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

40TH Anniversary of the Tornado Super-Outbreak - April 3-4, 1974

I remember the night well, it was a Wednesday evening - April 3, 1974. Just 19 years old and going to college, I had worked the previous summer at the National Weather Service Detroit /DTW/ and was on the doorstep of my career. I had arrived home, anxious to put on my NOAA NWR (of course at time, there was no internet, no TWC - just local news which paled in comparison to today's local news stations). Our "new" NOAA Weather Radio /NWR/ was blasting the risk of severe weather along with radar summaries that were updated just once an hour. As the northern end of the severe storm complex approached; severe weather warnings were read over the NWR - KEC-63 Detroit - for the southeast corner of Lower Michigan. While extreme south-central and southeast lower Michigan was clipped by severe weather and tornadoes, by far the main show was to our south (see map) as all hell broke lose.

 

An excellent account of the Super-Outbreak can be found on Nashville's NWS site. Also, check out the re-analysis of the monstrous synoptic storm and severe weather event; Revisiting the 3–4 April 1974 Super Outbreak of Tornadoes - STEPHEN CORFIDI AND STEVEN WEISS at the NOAA/NWS/NCEP/Storm Prediction Center, Norman, Oklahoma. I had the pleasure of working with Steve Weiss at the WSFO-DTW in 1974 during our early days in the NWS.

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