Mixed clouds & sun today; Severe risk Friday; “Loud thunder?”

Get set for a mixed weather bag again today across Minnesota.

They say all weather is local, and today will be one of those days. Even across the metro there may be big differences in sky cover today. It could be cloudy in Cambridge and sunny in Shakopee this afternoon.

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Surface weather maps and the morning 1km GOES visible satellite image make 2 things clear this Thursday.

1) The center of low pressure is spinning near Hibbing & the Iron Range today.

2) The back edge of the cloud line is hanging right near the metro.

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GOES 1km visible image shows low clouds. They should gradually burn off in southern Minnesota today.

Expect mostly sunny skies in southwest Minnesota…right up to the southwest edge of the metro. Cloudy skies will prevail much of the day from the metro north and east until the system slowly pulls away to the northeast, and drier air should mix in to help gradually burn off some of the low clouds near the metro.

Temperatures will recover nicely into to near 80 in the southwest, with 70s elsewhere this afternoon.

Next wave Friday:

It’s hard to string together two dry days in a row this spring it seems. Our next wave of showers and T-Storms may roll in with a warm front late Friday PM & evening.

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NAM model paints scattered rain & T-Storms late Friday PM & evening.

The system could generate a narrow line of convection Friday, and there may be just enough oomph to spawn a few severe storms.

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Summer like weekend?

After the warm front pushes through Friday night, this weekend may finally feel a bit more like summer.

Saturday and Sunday should both bring ample sunshine and temps near 80 in southern Minnesota.

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There will be a threat of a passing thunderstorm or two this weekend, but the bigger more organized storm threat appears to hold off until late Monday or Monday night.

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A mostly dry weekend with occasional rain chances?

Loud Thunder?

We got several reports of “loud thunder” Tuesday night and early Wednesday in Minnesota…including in St. Paul.

That got us thinking, is thunder sometimes louder than other times?

The answer it seems is, yes!

There are a few factors that affect the volume and duration of thunder at nay location.

1) The distance from the lighting bolt. Simply put, the closer you are to the actual lighting bolt the louder and more immediate the thunder.

Nearby bolts may cause a sharp “clap” of thunder, while more distant (or horizontal) bolts may produce less intense or rolling thunder as the sound waves form different parts of the lighting bolt’s thunder reach your ear.

2) Temperature inversions can make thunder louder, often at night. When there is colder air near the surface and a warm layer aloft (warm front) you get a temperature inversion…where temperatures increase with height above ground.

The inversion creates a discontinuity or “sound barrier” in the atmosphere which can “bounce” sound waves back to the ground. The result can be louder and more “rolling thunder” as the waves are more focused and reflected back to the ground level.

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Temperature inversions can also be the reason distant trains or highways seem louder on some nights.

Gulf of Mexico Dead Zone: Biggest ever in 2011?

Sad news from NOAA. It looks like all that record spring flooding will create the largest “hypoxic dead zone” on record in the Gulf of Mexico this year.

The massive floodwaters in 2011 swept huge amounts fo “nitrogen runoff” into the Gulf, and the subsequent algal blooms may suck the oxygen out of the Gulf Waters.

Major flooding on the Mississippi river predicted to cause largest Gulf of Mexico dead zone ever recorded

June 14, 2011

“The Gulf of Mexico’s hypoxic zone is predicted to be the largest ever recorded due to extreme flooding of the Mississippi River this spring, according to an annual forecast by a team of NOAA-supported scientists from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan. The forecast is based on Mississippi River nutrient inputs compiled annually by the U.S. Geological Survey (USGS).

Scientists are predicting the area could measure between 8,500 and 9,421 square miles, or an area roughly the size of New Hampshire. If it does reach those levels it will be the largest since mapping of the Gulf “dead zone” began in 1985. The largest hypoxic zone measured to date occurred in 2002 and encompassed more than 8,400 square miles.”

On a brighter note, enjoy the quieter weather pattern most of today and early Friday!

PH

  • Jamie

    Don’t you answer questions here? I asked these yesterday:

    I have a couple questions:

    When weather reports say “west winds at 10-15 mph” or something like that, does it mean the wind is coming FROM the west, or going TOWARD the west? In today’s weather report on another page of this site it says something like “winds changing to the west.” Does that mean winds will change to coming FROM the west or change to going TO the west?

    Also, the humidity feels REALLY high to me today, but I looked at the current report and it says the dew point is only 54 (feels 10 points higher to me), but the humidity is 90%, which sounds about right for how it feels. I haven’t been paying much attention to the humidity number for the last couple years since meteorologists mostly refer to dew points now, so I may be remembering this incorrectly, but it seems that 90% humidity would make for a higher dew point number. What’s up with that?

    Posted by Jamie | June 15, 2011 10:11 AM

  • Nick N.

    Jamie, the “90% humidity” is “relative humidity”, which measures how much water is in the air relative to how much water could be in the air. The trick is that, as the temperature increases, the amount of water that can be in the air increases. So, while a dew point of 54 degrees and air temperature of 57 degrees will give a relative humidity of 90%, a dew point of 54 degrees and an air temperature of 80 degrees will give a relative humidity of 54%.

    The dew point is the temperature that, if the amount of water in the air stayed the same, would produce 100% relative humidity. This means that the dew point cannot be higher than the air temperature, since water would precipitate out of the air in that case.

    In my experience, when dealing with temperatures below a standard house temperature of 75 F or so, relative humidity is a better indicator of how “wet” the air feels. When you have nearly 100% relative humidity, sweat will not evaporate for the most part, so even cool temperatures can leave you feeling sticky.

    On the other hand, at hotter temperatures (90+), the relative humidity is a poor indicator of comfort level — even 50% relative humidity at 90 F is almost a 70 degree dew point. Instead, dew point is a much better indicator of how stifling the heat will be (and more stable, as the air temperature changes).

  • Disco

    @Jamie:

    “west wind” means wind coming from the west.

    in fact, wind direction can sometimes be used alone to guess what the weather will be. winds from W, NW, or N often mean clear, dry and maybe cooler weather.

    E, NE, and SE winds can bring changing weather and precipitation. these winds will often be followed by W or NW winds after a cold front has passed.

  • Ed

    I was on an airline flight that departed MSP on Tuesday afternoon just after the rain began. Less than 5 minutes into the climb I saw a flash of lightning that appeared to actually hit the airplane, but there was no thunder. I did hear a sound but it was more like an air cannon or a kind of “whoop” sound. Anyway, I was wondering it is normal to have lightning without any thunder?

  • Paul Huttner

    When weather reports say “west winds at 10-15 mph” or something like that, does it mean the wind is coming FROM the west, or going TOWARD the west? In today’s weather report on another page of this site it says something like “winds changing to the west.” Does that mean winds will change to coming FROM the west or change to going TO the west?

    Also, the humidity feels REALLY high to me today, but I looked at the current report and it says the dew point is only 54 (feels 10 points higher to me), but the humidity is 90%, which sounds about right for how it feels. I haven’t been paying much attention to the humidity number for the last couple years since meteorologists mostly refer to dew points now, so I may be remembering this incorrectly, but it seems that 90% humidity would make for a higher dew point number. What’s up with that?

    Posted by Jamie | June 15, 2011 10:11 AM

    Hi Jamie:

    1) Wind direction is always listed as the direction the wind is blowing FROM.

    2) Dew point is the absolute measure of moisture in the air. Just like higher temp = warmer air, higher dew point = wetter air.

    Humidity changes with temperature and is relative to how much water the air can hold at any given temp, but if dew point is the same the total amount of moisture in the air is unchanged.

    PH

  • Paul Huttner

    I was on an airline flight that departed MSP on Tuesday afternoon just after the rain began. Less than 5 minutes into the climb I saw a flash of lightning that appeared to actually hit the airplane, but there was no thunder. I did hear a sound but it was more like an air cannon or a kind of “whoop” sound. Anyway, I was wondering it is normal to have lightning without any thunder?

    Posted by Ed | June 16, 2011 11:34 AM

    Hi Ed:

    All lighting produces thunder. But the sound waves can be affected by several atmospheric factors.

    I can’t say what happened in your case without having been there but it’s possible lighting did not actually hit the plane as it “appeared” to.

    Also if the plane had hit cruising air speed of say 400-500 mph or so, you may have partially outrun the thunder which would travel at the speed of sound (768 mph)…and planes are pretty well insulated from the sound of jet engines as you might imagine.

    Again, it’s tough to say what happened for sure without all the facts….but I’ll bet it was a cool experience!

    PH