Friday, August 7, 2009

One too many extremes

Weather Headlines

1). Fickle Rains. The best chance of heavy/strong/severe showers & T-storms will come over southern Minnesota, including the Twin Cities metro area, where the latest (NAM) model prints out nearly 1.5" of rain. The northern half of Minnesota, north of St. Cloud and Lake Mille Lacs, will see precious little rain over the weekend, while some counties near the Iowa border could easily pick up 1-3" of rain, even hail and high winds from isolated severe thunderstorms.

2). Timing? Best chance of showers/storms in this warm frontal pattern tend to come during the early morning/breakfast hour and again late afternoon and evening. I don't envision any all-day rains for the southern third of Minnesota, just a couple of hours of rain possible today, again Saturday night.

3). Wettest Day? Probably today. Have a Plan B. But right now it appears the heaviest, most widespread showers/T-storms will stay south of St. Cloud. The Twin Cities metro area stands a much better chance of 1-2" rains today and tonight. The best window for heavy rain/storms: morning/midday hours today.

4). Highest Probability of Hail & High Water (severe storms)? Today. SPC has most of central/southern MN in a "slight risk". Looking more carefully at the probabilities [see below] it appears that the greatest risk of large hail and isolated tornadoes will come over far southeastern MN, including the immediate Twin Cities metro area.

SPC Day 1 (Today) Probability of Severe Weather. According to severe storm specialists monitoring conditions 24/7 from their weather lab in Norman, OK there is roughly a 30% chance of severe weather within 25 miles of any location in southeastern Minnesota.

5). Sweatshirt.....or inappropriate Speedo? While campers in northern Minnesota spoon (to conserve body heat) with lows dipping into the 40s tonight, residents of far southern Minnesota will be sweating out - highs well in the 90s Saturday and possibly Sunday as well. With dew points reaching the mid 70s I still wouldn't be surprised to see a Heat Index of 105-110 near the Iowa border late Saturday. We'll see, but the worst of the swamplike, blast-furnace heat should slide off just to our south.

6). Now it's "Extreme Drought" We've gone from "severe" to "extreme" drought conditions north/east of St. Paul. Northern Washington, eastern Anoka and southern Chisago counties are hardest hit right now.

7). Crazy Temperature extremes on tap this weekend: highs in the 60s over northern Minnesota to mid/upper 90s near the Iowa border, where a 75 degree dew point could make it FEEL like 105-110 F. O.K. What's a 40-45 degree temperature spread among friends? And that's just across one state!

Paul's Outlook for the Twin Cities

Today: Mostly cloudy, cool and damp with showers and T-storms likely. Locally heavy rain possible, even a few severe T-storms. Winds: SE 10-20+ High: 72

Tonight: Another shower or storm. Low: 68

Saturday: Partly sunny, hot and very humid. Chance of a few nighttime T-storms. High: 94 (heat index near 100).

Sunday: Mix of clouds and sun, best chance of a T-shower early morning and again late afternoon. High: 88

Monday: Sunnier, slightly cooler, less humid. High: 86

Tuesday: Mostly sunny and pleasantly warm. High: 89

Wednesday: Sunny, bordering on hot. High: near 90

Thursday: Less sun, chance of a T-shower. High: 88

Percentage of Minnesota suffering from dry weather. Nearly 46% of the state is too dry, moderate drought impacting 17% of Minnesota, severe drought 3.4% and (new this week) extreme drought just under 1% of the state.

Timeline of a Deepening Drought. This chart shows the evolution of the drought over time, conditions worsening significantly since April and May (the latest conditions are on the far right side of the graph).

Heat Advisories may have to be issued for far southern Minnesota, from Mankato to Albert Lea and Austin, where it may FEEL like 105 in the shade by Saturday afternoon. Gulp.

GFS Temperature Prediction for 7 pm Saturday. 90s are likely over far southern Minnesota, including the Twin Cities. Latest guidance is hinting at 100 degrees near Austin, Albert Lea, even Rochester. meanwhile temperatures hold in the 80s for St. Cloud, 70s over the northern quarter of Minnesota.

Predicted Heat Index for Sunday. Check out the huge expanse of America in the brown/purple shading, where the heat index is forecast to be 100-110. Yes, we're getting a break over the northern tier states of the USA, but the brunt of America is not quite so lucky.

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