Sunday, July 25, 2010

Severe Tuesday? (online climate controversy at St. Thomas)

I hope you had a chance to sneak outside Sunday. What a day - a meteorological mirage, an atmospheric daydream come to life, a glorious reminder of how incredible a summer can be at this latitude. It sounds cliche (something I'm not above, come to think of it), but it just doesn't get any better than yesterday. The sky draped over Minnesota was definitely on its best behavior.

The reason? Canada leaked some comfortable airmass south of the border - a slight northwesterly component to the jet stream pulled drier air out of Manitoba, a bubble of high pressure centered directly overhead (did you see that big "H" drift overhead around lunchtime?) Winds drop off under the center of high pressure bubbles, the air overhead stable under this mass of dry, sinking, warming air.

Saturday: Ragged Sky. A stiff wind whipping up behind a cool front triggered a partly sunny sky statewide on Saturday, but a lingering swirl of unusually cold air aloft sparked a few instability showers during the afternoon hours.

Sunday: Postcard Perfect. Under the center of a Canadian high pressure bubble winds subsided, warmer air aloft preventing PM showers from popping up. Photo: Pelican Lake, near Breezy Point.

Atmospheric Perfection. For the first time I can recall, every major reporting station in Minnesota experienced a). highs in the 80s AND b). a lack of rain. It was one of the most memorable days of summer, at least meteorologically. Folks in Hibbing went from sweatshirts to bathing suits in less than 6 hours, waking up to a chilly 47, only to finish with a respectable high of 83!

Hot Flash. We don't have much to complain about in the temperature department: only 1 day above 90 in June in the Twin Cities. Compare that to 18 days above 90 in Washington D.C. - July is turning out just as hot. New York City is running 5.5 F. warmer than average. More on the intense heat gripping much of America here.

We've been lucky. The battle zone between pleasant, 50-degree dew points and sauna-like 90 and 100 degree temperatures has set up JUST to our south over Iowa and Illinois. A shoving match between radically different airmasses, one relatively cool and comfortable over Minnesota, the other sweaty and horrific pasted over Kansas City, where lately the combination of heat and humidity has made it feel like 105-110 F! Heat warnings have been issued from the central Plains to the east coast. Bottom line: much of America is sweating through the hottest summer in at least a decade, but enough cool, dry, comfortable air has seeped southward out of Canada to keep the worst of the heat (and thunder) just to our south. To be sure we've been brushed by occasional tornadoes and hail storms as that frontal boundary has lurched north, but the worst of the summer weather has set up 150-300 miles south of town, and for that we can all be very thankful.

Severe Tuesday? Get ready for a hot Tuesday, there's a good chance we'll see highs in the 90-92 degree range, creating a very unstable atmosphere by late afternoon. Throw in a gusty south wind (with considerable shear) and dew points approaching 70 - and the result may be a severe weather outbreak, mostly hail, but a few isolated supercells could form out ahead of the main band of thunderstorms. It's the stray (rotating) storms that form out ahead of the main squall line that you have to watch - these are the cells most likely to become tornadic.

We hang onto bright sun most of today, as Sunday's protective high pressure bubble migrates toward the Great Lakes a clockwise wind flow will turn our breeze around to the south, allowing 60-degree dew point air to flow northward - yes, it will feel sticky out there again by late afternoon, but still tolerable. An approaching (cooler) front may spark an outbreak of strong to potentially severe T-storms late Tuesday - too early to try to pinpoint precisely where and when, but watches and warnings may have to be issued close to home after 3 pm tomorrow. Behind that latest burp of drier, slightly cooler Canadian air: a fine Wednesday, and much of Thursday looks pleasant. A return flow sets us up for more haze and humidity by the end of the week, although any T-storms should be isolated Friday & Saturday, probably affecting less than 5% of the state. Sunday may be just as nice as the strongest T-storms rumble off to our south across Iowa, sparking yet another round of potential flash flooding. It's still too far off to get specific but I'm cautiously optimistic next weekend will be warm, mostly-dry and lake-friendly. I don't see a string of 90s returning anytime soon - no evidence the heatwave gripping much of the USA will expand north into Minnesota, at least not through early next week.

Make it a good Monday, check back in later for an update on the severe weather potential for Tuesday afternoon/evening. May have to plug the Doppler back in and point to more red, pulsating blobs within 24 hours. Can't wait.

Lake Delhi, Iowa Dam Break. Historic rains have swamped parts of Iowa and Illinois (7"+ rains in Chicago in recent days). Some counties just south of Minnesota have seen well over a FOOT of rain in just the last week. People living downriver of the Lake Delhi dam had to be evacuated when water was observed breaching the top (and the bottom) of the dam. More on the record rains and their impact here.

Supercell. This is one of the more spectacular examples of a "supercell", a rapidly rotating thunderstorm capable of large hail and tornadoes - captured on July 23 outside Kimball, South Dakota.

Tornadoes in Unlikely Places. Here is home video of a tornado observed passing over Chautauqua Lake, in upstate New York - forming along the leading edge of a slightly cooler, Canadian airmass pushing into New England, breaking some of the 90-100 degree heat of recent days.

June Stats. Yes, we all lived through an historic June - the hottest month ever recorded around the planet. More details here.

Diminishing Arctic Sea Ice. As of July 15 arctic sea ice covered 3.23 million square miles. That's 625,000 square miles less than the 1979-2000 average, but still 137,000 square miles more than July 15, 2007, the all-time record for the least arctic ice ever observed. The latest data is here.

Odd Behavior on the Sun, but the Explanation Remains Elusive. Click here for an interesting article in Scientific American. The sun goes through fairly predictable 11-year cycles of maximum and minimum activity (solar flares, sunspots, etc). The most recent solar minimum was probably the the most significant on record - but scientists are at a loss to explain why.

University of St. Thomas At The Center of a Heated (Climate) Controversy. More on an increasingly nasty back and forth between a professor at St. Thomas and Lord Christopher Monckton in the U.K. More on the growing imbroglio here.

Paul's Conservation MN Outlook for the Twin Cities and all of Minnesota

Today: Plenty of sunshine, warmer, a bit more humidity in the air. Late-day T-storms flare up over far northern MN. Winds: S 10-15. High: 87

Monday night: Mostly clear and mild. Low: 69

Tuesday: Sunny start, bordering on HOT. A few strong/severe storms are possible by late afternoon/evening. High: 91

Wednesday: Wet start, then increasingly sunny and nice, cooler and less humid. High: 84

Thursday: High pressure holds - lot's of sun, seasonably warm. High: 86

Friday: Partly sunny, slight chance of T-storms PM hours. High: 87

Saturday: Mix of clouds and sun, looking pretty good right now. High: 86

Sunday: Partly cloudy, another fine, lake-worthy day. High: 85

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