Wednesday, August 5, 2009

Tracking a Saturday Hot Front

So here's what should happen in the coming days (God-willing). Keep in mind I'm just a messenger, a reluctant one at that.

Thursday looks sunny and fine, temperatures close to where they were yesterday as high pressure floats overhead. A return south/southeast flow on the "dirty side" of today's fair weather maker will increase clouds on Friday, the best chance of T-storms Friday night, when rainfall may be locally heavy.

Depending on where those storms set up Friday night, the stage is set for what may be the first 90-degree day since late June. Saturday will bring back memories of the Dog Days, highs toppig 90 (south) with a heat index probably topping 100 degrees by 3 or 4 pm. If the storms linger longer south of the Minnesota River, then shave a few degrees off Saturday's highs. Heading north? Highs on Saturday in the Brainerd Lakes area may hold in the low/mid 80s, even some 70s far north. So expect a HUGE north-south temperature contrast Saturday.

Sunday looks unsettled as a slow-moving cool front approaches. A few hours of showers and storms are possible, highs ranging from 70s Red River Valley to 80s central counties (and most lakes up north) to near 90 over southeastern MN, including the Twin Cities. It probably won't be quite as hot as Saturday, but this weekend will be a subtle (yet blunt) reminder that summer is not going away anytime soon.

We cool off slightly early next week (low 80s, my kind of cool front). But long-range (GFS) guidance is indicating at another hot surge toward the end of next week, maybe a run of 90s - a few in a row? Too early to get specific, but as I've been telling you for some time, where Mother Nature giveth, she often taketh away. Unusual cool spells are often followed by unusual warm spells as the atmosphere tries to "even things out" and achieve equilibrium.

I know there's football in the air (NFL game Sunday evening - hooray!), back to school sales are everywhere, kids are thinking about fall classes....

Don't write off summer just yet. We had a nice intermission (all of July) but Part II may have more umpfh than you thought possible. My hunch: 1-3 days of 90+ temperatures - and more severe T-storms than we experienced in July. Just a gut feel based on the latest weather maps. Could be nausea....

Paul's Outlook for the Twin Cities

Today: Sunny start, clouds slowly increase by afternoon. Winds: East 3-8 mph. High: 79

Tonight: A growing chance of showers and T-storms. Low: 63

Friday: Unsettled, more clouds than sun, more wind and humidity. A few hours of showers/T-storms. High: 78

Friday night: Storms, some heavy/strong. Low: 64

Saturday: Partly sunny, hot and steamy - passing T-storm likely. High: 94 (heat index may top 100 over southern Minnesota Saturday afternoon).

8Sunday: A blend of clouds and sun, another passing shower or T-storm. High: 86

Monday: Cooler and less humid with generous sunshine. High: 84

Tuesday: Still sunny, very pleasant. High: 85

Wednesday: Growing chance of bumping into a shower or T-storm. High: 88

NAM Outlook through 7 am Friday. Purple/blue/green shaded areas are regions of expected rainfall during each 12 hour period. A bubble of high pressure directly over Minnesota treats us to comfortable sunshine much of today. The approach of much hotter, stickier air from the south/west will spark a good chance of showers/T-storms tomorrow, with a nagging thunder threat (or should I say opportunity?) into Sunday.

60 Hour WRF-NMM Computer Outlook for 7 am Saturday morning. This graphic shows predicted rainfall Friday night, from 7 pm Friday through 7 am Saturday, hinting at bands of heavy thunderstorms setting up over central and southern Minnesota as a "hot front" approaches from the south. Warm fronts tend to become more active (increasing storminess) at night, so this isn't too hard to believe. The latest computer run prints out over 2" of rain for the Twin Cities, but .60" for St. Cloud. This far out it's hard to delineate which towns/counties will experience the heaviest rains - if you're CAMPING Friday night keep in mind the sky may open up at any moment - especially over the southern third of Minnesota.

WRF-NMM Predicted Temperatures for 1 pm Saturday. Check out the expanding 90s sweeping into southern Minnesota by midday. As I've been saying since the beginning of the week I'm pretty sure the 90 degree "isotherm" will reach St. Cloud, with some mid 90s possible from the Twin Cities to Mankato, Rochester and Austin. Factor in a dew point in the mid 60s and it may feel like 100-105 over southern Minnesota. I wouldn't be at all surprised if the NWS issued a Heat Advisory Saturday, best chance south of the Minnesota River Valley.

Wednesday Evening Satellite Image. Check out the "monsoon" T-storms sprouting over the desert southwest (persistent hot weather produces a semi-permanent area of low pressure over Arizona, New Mexico and parts of California - a partial vacuum that literally sucks Pacific moisture into the southwest, sparking late-day T-storms. While you're at it, go ahead and find Felicia's "eye".

NHC Forecast Track for "Felicia". As of last night Hurricane Felicia was upgraded to a violent Category 4 hurricane with sustained winds of 140 mph, gusts over 170 mph. The 5-Day track above shows significant weakening of Felicia before the soggy remnants drift into Hawaii by early next week. The reason? Felicia is expected to pass over colder Pacific Ocean water. To get the latest information on Felicia (and anything that might be brewing in the Gulf of Mexico, Caribbean or Atlantic), click here for NHC, the National Hurricane Center.
Perseid Meteor Shower. This year's Perseid meteor shower could be even better than usual. "A filament of comet dust has drifted across Earth's path and when Earth passes through it, sometime between 0800 and 0900 UT (1 - 2 am PDT) on August 12th, the Perseid meteor rate could surge to twice its normal value," says Bill Cooke of NASA's Meteoroid Environment Office. The following profile is based on the debris stream models of veteran forecasters Jeremie Vaubaillon and Mikhail Maslov:

Looks like the morning of August 12 stands the best chance of seeing the Perseids, what is historically Minnesota's best meteor shower of the year. That's next Wednesday. Circle your calendar! (or not).

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