Sunday, April 25, 2010

An expanding drought

Weather Headlines

* Massive "wedge" tornado grinds across almost the entire state of Mississippi Saturday, nearly 1 mile wide, possible EF-4 strength. Check out the video clip below.

* .50 to .75" across much of the metro area Saturday morning, badly needed rain. I've included a new web site that breaks out the rainfall amounts across the area.

* Moderate drought conditions across the northeastern half of Minnesota, including the northern suburbs of the Twin Cities - map below.

* A tale of "2 springs", unusually warm weather to linger for the next few weeks. Details below.

* Dry weather to linger through Thursday morning, slight risk of a few strong/severe storms Thursday PM.

* It's early, but right now the long-range models are optimistic for a nicer spell of weather returning next weekend, enough blue sky poking through for 60s.

"Wedge". The tornado that steamrolled across Mississippi was nearly a mile wide, so big it didn't even resemble a classic tornado funnel. It appeared as if the entire rotating thunderhead descended to the ground, the only visible evidence it was tornadic was the powerful rotation clearly visible in this video clip. Mercifully less than 2% of all tornadoes ever approach this strength, but the EF-4 and EF-5 tornadoes are responsible for 80% of all tornado deaths and injuries during an average year.

A Most Unpleasant Flight. Check out this amazing clip of video. Jets are engineered to survive direct lightning strikes, although it hasn't always been this way. A 707 with 74 passenger onboard exploded in midair over Elkton, Maryland in December, 1963. Since then major changes have dramatically reduced the risk. Fuel tanks are now isolated and insulated against possible combustion from a direct strike from on high - most passenger jets are hit an average of 1-3 times/year. Not a pleasant experience, but definitely not life-threatening.

Storm Reports. 54 tornadoes roared across the lower Mississippi River Valley Saturday, some of them monsters, EF-4 strength (across Mississippi). Notice the nearly straight line across the state of Mississippi. The same "supercell", rotating thunderstorm may have spawned as many as 10 separate tornadoes as it churned across the state, what meteorologists call "families" of tornadoes, all forming under the same spinning thunderstorm. Doppler radar works best on these big, obvious cells - it's much harder catching the small, brief EF0 and EF1 tornadoes, similar to the one that touched down on South Minneapolis last August. To see details of the destruction across the south check out SPC's site here.

Finally! I know, I know, weekend puddles are "verboten!" The rain has the audacity to it fall on a beloved weekend - but at least we can be partially consoled by the fact that we really, truly needed the rain. Looks like the northern suburbs saw the most, over .50" near Coon Rapids and Hugo, very little rain in the Mankato area. Yes, spring storms are very, very fickle. To see a high-resolution print-out of some rainfall amounts from the local CoCoRaHS network, click here. Check out the Drought Monitor map below and you'll understand why a lot of people were happy to see the raindrops splattering their windshields, in spite of the lousy timing.

Weather enthusiasts were up in arms Friday evening - a major tornado outbreak was taking place over the southern Plains, and the authoritative source of all-things-weather, the Weather Channel, was running a movie. It's a recurring theme (and I'm not necessarily knocking them in public). They're trying to be all things to all people: present the weather, yet be a "network", complete with specials, hour-long shows about storm stories and tornado chasing, even weather-themed movies, but when the meteorological crap is hitting the fan, as it was much of the weekend, this tends to alienate the hard-core weather enthusiasts who want to see....the weather. Not sure you can please all the people all of the time, but I've noticed that TWC rarely preempts their regular weekday schedule, even for severe weather. It's even more of an issue when a hurricane is approaching the coast. "We'll be back with more coverage of Hurricane Bertha, but first, the 213th showing of Twister!" There are, what, 6-8 different news channels out there: CNN, Fox, MSNBC, CNN Headline News, Bloomberg, CNBC, BBC America (what am I forgetting). It's a wonder that there is only 1 weather channel. Hmm. Interesting.

Supercell. From the high-res 250 meter NASA "Terra" satellite the severe, rotating thunderstorm that spawned a series of deadly tornadoes across Mississippi took on a "V-like" appearance, a hint that the storm is especially severe. You can see these same (amazing) high-resolution images from NASA by clicking here.

Aftermath. The storms that ripped into Yazoo City, Mississippi (where the governor of MS has a home) took some buildings right down the foundation - evidence of extreme winds, in the EF-4 range, possibly topping 180-200 mph. Even well-constructed brick/stone homes can be leveled if an EF-4 comes through - that's why it's imperative to seek shelter below grade, in a basement if at all possible.

Minnesota meteorologists will be at a rare and welcome loss for words the next few days, our weekend storm fizzling and pushing into New England, drier air chasing away the clouds today, leaving us with partly sunny skies (same as "mostly cloudy", btw). The two are synonymous, we just use the "partly sunny" expression when we want to emphasize that there will be some sunshine. No, partly sunny does not mean the same thing as partly cloudy. Let me try and explain the terminology (this is part of the weather challenge: making sure the words we choose in the forecast are accurately conveyed to you, the reader/viewer). There is plenty of opportunity for confusion.

Clear/sunny: 95-100% sunshine
Partly cloudy: 75-95% sunshine
Plenty of sun: 50-75% sunshine
Increasing cloudiness: 40-60% sunshine (reduced sun as the day goes on - obviously)
Variable cloudiness: 30-50% sunshine
Mostly cloudy (partly sunny): 20-30% sunshine
Overcast: 0-5% sunshine

Confused? Me too. We use the "partly cloudy" terminology at night, for obvious reasons. Let's just say the sun will be out part of the time today, most of the time Tuesday and Wednesday as winds pick up from the south, nudging the mercury above 70 by midweek. The next storm approaches Minnesota Thursday, enough moisture streaming out of the Gulf of Mexico for dew points in the 50s by then - marginal for a severe storm outbreak, but the "dynamics" aloft, the wind and instability profile over Minnesota - may be ripe for a few strong T-storms by Thursday afternoon/evening. We're due: it's been remarkably quiet in recent weeks, the storm track consistently setting up well south of Minnesota, carrying most of the rain (and embedded severe storms) from Denver to Dallas, Memphis and D.C. The pattern seems to be shifting, we SEEM to be sliding into a somewhat stormier pattern as the jet stream mutates and shifts northward, ever so slowly. Rain lingers on Friday, wrap-around moisture on the backside of the cold front - Friday may be fairly foul, windy and wet with a few hours of rain, probably not severe (too stable overhead). Although we may wake up to puddles first thing Saturday, a drying north/northwest wind should coax enough sun for mid 60s by late afternoon, and most of Sunday looks dry with highs nearly as mild. A fairly nice weekend is shaping up - I'll keep watching the models and see if our luck holds out. So far so good.

Growing Drought. The percentage of Minnesota under a "moderate drought" has increased from 1.7% on April 13 to 25.2% as of April 20 (!) Saturday's rain helped, but it wasn't the sustained soaking that we really needed. Hopefully the trend is toward a wetter pattern for Minnesota in the coming weeks (without the beachball size hail and wailing siren part).

Wall of Rain. Check out the storms as the approached St. Louis, courtesy of Just type a keyword into the search box and you get a series of photos, some pretty amazing. Every now and then a (nasty) photo pops up - best not to troll this site with your 5 year old daughter watching over your shoulder.

Tale of "Two Springs". Here is a bold prediction from a weather company called Planalytics, forecasting a continuation of Minnesota's abnormally warm conditions through early May, unusually cool weather predicted for much of the west.

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

Today: More clouds than sun, skies brighten up. Winds: N/NE 10-15. High: 64

Monday night: Partly cloudy. Low: 43

Tuesday: Lot's of sun, a bit milder. High: 67

Wednesday: Hard to be cooped up inside, lukewarm sun, a stiff south wind. High: 72

Thursday: AM sun fades, showers and T-storms possible by afternoon/evening, some may be strong, even severe. High: 67

Friday: Windy and damp with lingering showers, even a period of steadier rain possible. High: 65

Saturday: Getting better, becoming partly sunny. High: 67

Sunday: Sunny start, but clouds increase PM hours. High: 65

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