Update 6/12 - Severe Weather Potential Now Decreasing Today

Update 6/12...

The combination of a suppressed surface wave, residual precipitation from an old outflow boundary and cool easterly winds off the Great Lakes are all making it difficult for the projected surface wave and subsequent instability to advance northeast into southern lower Michigan.

As of early afternoon Friday, the low pressure and associated instability and conflict of air masses is remaining south of the Michigan border. At this time, it looks as though just the southeast corner of  the region has the best chance of any severe weather. I'm mainly referring to Lenawee and Monroe counties (as has been the case all week) and possibly pushing as far north as the Ann Arbor and Metro Detroit areas. Therefore the risk of severe thunderstorms should pretty much hold over the Southeast corner...generally around I-94 and south.

The next risk of severe weather at this time looks to possibly be Sunday.

Original 6/10 -
I have yet to write about any severe weather potential this season as there really hasn't been too much to get excited about except for some scattered or isolated events; with the most widespread being the flooding rains of May 30-31st.

I'm seeing an increasing potential for severe weather across the region, especially the southern two thirds of Southeast Lower Michigan possibly beginning overnight Thursday but more likely Friday. Actually the evolution of the event has roots in my Summer Outlook and the two main jets I discussed that would affect the summer's weather. One of course, is the Polar Jet diving through Canada into the northern tier of the country and the other; the potent sub-tropical jet enhanced by warmer than normal water temperatures out over the Pacific.

I depicted the Summer 2015 Weather and it's main influences in the following maps;

Focusing on the interactions of these two jets in the Summer Outlook and then again; in the severe potential for Friday gives a clearer picture and parallels. Note the cropped version of the above expected Summer upper wind pattern and then, the following discussion for the severe weather potential.

Late Thursday Into Friday

The past couple of days; our forecast models have been intimating a frontal postion would become hung-up across the northern Ohio Valley or Southern Great Lakes area. Where, exactly that happened would dictate the best risk of severe weather. This has been happening to our southwest and south this late spring into early summer and thus; it's been busy and wet down there. Moisture from the Pacific and at times Gulf; ran into the predominantly cooler winds coming in from Canada that dove south and east through the southern Plains and Ohio Valley.


However as the summer advances, we are getting into the time of year that is normally our busiest thunderstorm and severe weather season, June into July or more specifically mid June to mid July. And, as though cue'd by the summer upper wind pattern discussed, this change into more typical summer weather for the Great Lakes seems to be upon us now.


Particulars& Maps

Fri morn


                             Phasing Upper winds and subsequent Bulk Shear available

By late afternoon Friday; 

Many things come together for a severe weather event; good instability and shear as the low and colliding frontal positions move across Southeast Lower Michigan. CAPE approaching 2500-3000, Li's -7 to -9 and even helicity in the 150 range. Precipitable water bursts through two inches to our west, so torrential rains are also included as these storms march northeast around 40-45 mph - but there's one caveat; it's all model driven. And, it's the NAM model which tends to be a bit "hot" sometimes. Therefore, we'll watch later model runs to see if the severe weather looks as promising as it does Wednesday eve.


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





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