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Breathing easier — weekend preview

Yesterday we got the heat and humidity, without any thundery relief to cool things down. We dodged a bullet – severe storms rumbled across far southern Minnesota spitting hail and 60 mph.
By Paul Douglas

Update: 10:47 am. The Twin Cities are on the northern fringe of a broad area of showers and embedded thunderstorms, occasional rain (and a few lightning strikes) are likely through midday, but it still looks like the brunt of the rain will pass off south of town over the next few hours. With the clouds and more of a west/northwest breeze temperatures today should be considerably cooler than yesterday, when we “enjoyed” 95 degrees. With the clouds and rain readings may hold in the 70s today, and in spite of a threatening sky your late afternoon/evening activities are not in grave danger – I do expect a gradual drying trend this afternoon with some late afternoon clearing – you may get a peek at the setting sun at 9:03 pm.

Latest visible satellite image showing a thick shield of clouds (anvil tops of T-storms passing south of the Twin Cities). But the northwestern half of Minnesota is bathed in sunshine, and most of the day should be dry north of a line from Willmar to Albertville and Taylor’s Falls.

Yesterday we got the heat and humidity, without any thundery relief to cool things down. We dodged a bullet – severe storms rumbled across far southern Minnesota spitting hail and 60 mph. gusts. Another swarm of storms dumped .42″ of rain on Brainerd with golf ball size hail north of Lake Mille Lacs, where warnings were issued.

No rain fell in St. Cloud, with only a “trace” of rainfall in the Twin Cities, grazed by a midday squall line of intense storms. I grabbed a frame of MPX Doppler, showing an “outflow boundary” out ahead of the squall line, which you can clearly see in the image (a thin blue ribbon of radar return a few miles out ahead of the main storms). This was literally a miniature cold front, rain and hail-cooled air reaching the ground, spreading out and outracing the actual storm itself. These boundaries can often become a focal point for subsequent storms that redevelop, providing enough lift or “spark” to fire off more storms, sort of a thundery chain-reaction. That didn’t happen yesterday, the “cap” of hot, dry air a few miles overhead strong enough to put a lid on additional convection/storm development.

Heat advisories were posted for much of Minnesota yesterday, a rare Excessive Heat Warning issued for the immediate Twin Cities for a combination of heat and humidity that could make it feel as hot as 105. The midday storms, clouds kept daytime highs a few degrees cooler than they would have been, MSP saw a high of 95, just 4 degrees shy of an all-time record. St. Cloud sampled 91 degrees, just about 13 degrees above normal for June 23. In the winter we torment you with the wind chill, now we have the “Heat Index” to throw around, sometimes called “Humature”. The concept behind this is really quite simple: on days when the dew point and relative humidity are high, with more water in the air, your body can’t cool itself naturally via perspiration. When you step out of the shower and feel chilled, it’s because water is evaporating off your skin. Evaporation leads to cooling. But when the air is thick with moisture sweat can’t evaporate nearly as efficiently, and its much easier to overheat.

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Today will be a big step in the right direction with a noticeable drop in temperature and humidity, temperatures 5-10 degrees cooler than yesterday with a little less water in the air. Yesterday’s frontal boundary has stalled just to our south, draped from east to west across Iowa, close enough to spark more heavy/severe showers/storms across far southern Minnesota, most of the rain staying south of the Minnesota River. We can’t rule out a stray, passing shower or thundershower today, but computer models print out less than .05″ of rain – odds favor dry weather most of the day.

Thursday looks pretty spectacular with warm sun, lake-worthy highs in the 80s. The more I stare at the models (weather models, by the way) the more I think we’ll top 90 again Friday before the next front arrives with heavy/severe showers and thunderstorms late Friday and Friday night. The GFS model keeps showers and storms across much of Minnesota Saturday, at least through mid afternoon. Some clearing is possible by mid or late afternoon, from west to east, so the day won’t be a total loss, but Sunday still appears to be the nicer, drier, sunnier day, better to hang out up at the lake.

You may want to take a sweatshirt up to the cabin though. A cooler northwesterly wind puffing behind Saturday’s frontal passage will keep highs in the 70s up north, Sunday night lows will easily dip into the 50s, maybe even some 40s far north. Sunday may look and feel more like mid or late September, with clouds and a few showers lingering over the Minnesota Arrowhead.

Not a perfect weekend, no, but we’ve seen worse. I don’t see any steady, sustained rain (a few hours of showers and storms, when it does rain it could come down pretty hard). Sunday we’ll enjoy a little free air conditioning, with clouds building in the afternoon. The best time to get out this weekend may be late in the day Saturday, and the morning and midday hours Sunday. Just a semi-educated hunch. We’ll keep fine-tuning the all-important weekend forecast and hope the outlook brightens as new data arrives. It’s a distinct possibility!

Weather Headlines

* No rain from Tuesday storms in St. Cloud, Twin Cities sees a trace of rain, with .42″ at Brainerd.

* 91 in St. Cloud, 95 Tuesday in the Twin Cities, 4 degrees shy of a record. Average high now is around 79.

* Best chance of showers/storms today over far southern Minnesota, temperatures run a good 10+ degrees cooler than yesterday.

* Thursday: driest day in sight. Weak bubble of high pressure treats us to blue sky and 80s.

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* Friday heat: low 90s possible, another round of strong/severe T-storms possible late.

* Saturday: probably the wetter day of the weekend with a few hours of showers/storms as a cool front passes overhead.

* Sunday: drier but cooler, highs hold in the 70s with a fresh, northwest breeze. Clouds build in the afternoon, showers linger much of the day north/east of Grand Rapids and Duluth.

* Cooler trend next week with a series of weak cool fronts, keeping highs mostly in the 70s and low 80s – probably no extreme heat next week.

SPC Outlook for Wednesday, showing a slight threat of isolated severe storms over far southern Minnesota, along the Iowa border. The biggest risk: large hail and potentially damaging, straight-line winds.

GFS Computer model valid 7 am Saturday morning, showing heavy showers and storms pushing into western and central Minnesota ahead of a fairly vigorous cool front. Skies should clear from west to east during the afternoon – you should be able to salvage the late afternoon and evening hours as winds shift around to the northwest, pushing drier, cooler air back into Minnesota.Grab my hand as we tip-toe out on a big, shaky limb. Here is the 10-Day Outlook (GFS), hinting at a wet, thundery start to the big holiday weekend. To be brutally honest the 4th is still too far away to even try to get specific, but if I had to place a bet I’d go relatively cool (highs mostly in the 70s) with the best chance of showers/storms coming Friday the 3rd, with a few late-day, instability shower or thundershowers possible on the 4th. The biggest weekend of summer – what on earth can possibly go wrong?