In the last few weeks, our weather pattern across the country has been exactly what the late winter into spring pattern suggested in conjunction with wetter analogues in my Summer Outlook. The headline above tells the story along with normal to below normal temperatures. Why? Put simply; the rather strong upper low and troughing periodically slipping into place over southeastern Canada has and continues to block summer-like air masses from fully taking over our region for more than just a few days. And thus, this conflict of the upper jet along with summer-type air masses and associated humidity that periodically set up a battle ground to our south this spring; has now crept north into the Lakes Region.
This upcoming projection of this Friday's upper jet stream shows an example of this well with the Canadian jet winning out at this time. Note; the warm jet stream surging from the southwest and southeast sections of the country while the quasi-stationary cool polar trough remains anchored over central to eastern Canada. This "conflict of interests" in air masses has created a battle zone (on map in green) this spring into early summer which is now showing signs of lifting north the past few weeks. This certainly would be expected by this time so that's not unusual. What is more the question "Will this continue for a longer duration and if not; which upper air feature will dominate the rest of the summer?" Typically, one would expect the upper ridge to become the more dominant with summer-time advancing but as our analogues suggested, this was not always the case and we either ended up with a cooler summer (with the Canadian trough holding) or a normal to warmer than normal summer as the upper ridge pushed more often into the region. In addition; now that Great Lakes Region has been brought into the conflict zone; the question of how wet will the summer become is also up for grabs.
From the original Outlook:
As the summer ridge builds into the center part of the country, I look
for it to oscillate over the Great Lakes and the East, routinely
bringing warm to hot weather to the region. However; it should be duly
noted that the distinct upper air pattern that has been a key player
since mid winter into spring, albeit naturally weakening with time and
becoming less frequent, shows no signs of leaving during the
summer. I'm speaking of the occasional blocking across the northern
latitudes in which I expect to play a distinctive role this summer. By
occasionally phasing with weaker mid continental impulses, troughing
will dive into the Great Lakes and points east and thus, intermittently
deliver enough cooler spells of weather to balance out somewhat, the
heat and humidity we do get for a more normal and comfortable summer
than the past several.
Rainfall and Severe Weather
Rainfall averaged decidedly below normal in the analogue set with about
75% below normal...a strong trend. However; the remaining years were
very wet and while a minority of years, it still is an important subset of wet years!
This suggests to me that the pattern portrayed in my hemispheric
discussion could lead to a stalling of the frontal conflict and
storminess and thus, runs the risk of repeating in the same general
region. While analogues state drier summers prevailed; we still run the
distinct risk of a stormier summer including training echoes if the pattern happens to stall in our neck of the woods.
We have just entered this conflict zone the past few weeks which has brought above normal rainfall since late May. Much of May itself was very dry with all regions painting 1.5"- 2.0" below normal until the last week when roughly up to two inches fell. Another one to two inches (or more) has fallen since June 1st so we are off to a good start
for the growing season now. And latest indications suggest this pattern will persist for the time being.
Just this week we had one impulse slide over and to our south Monday which generated heavy rains across the region, with a second due shortly later Wednesday into Wednesday night. This low pressure and attendant warm and cold fronts is expected to ride near the Tri-State border of Indiana/Ohio/Michigan by Wednesday evening. Perhaps close enough to bring not only heavy rains but possibly severe weather as the very warm, tropical like atmosphere steams up over the Ohio Valley and runs rudely into our cooler, more stable air over the central Great Lakes Region (sound familiar).
The Storm Prediction Center has Southeast Lower Michigan outlined for the potential of severe weather Wednesday and Wednesday night with a greater risk over the Ohio Valley.
Stay alert to the NWS-DTX for any watches or warnings Wednesday and Wednesday night. Pop over here for a slide presentation from DTX for the potential for severe weather Wednesday into early Wednesday night.
Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian