Supermoon and Start of Spring

Welcome to the weekend. Today’s high was 50 degrees. Not bad for this time of year, but felt a bit cool thanks to the 65 degrees on Thursday and 60 degrees on Wednesday. Saturday’s weather looks beautiful with plenty of sun, but temps will be held down near the lake thanks to an easterly wind. Lake temperatures are in the mid 30s right now so any easterly wind will keep it chilly near the lake. Sunday brings a round of showers, but it should not rain all day.

With the clear skies on Saturday, we have a chance to see something we have not seen in our area since March of 1993. It’s the so-called “supermoon”. The moon will be at perigee at almost the same exact time we have a full moon. Perigee is when the moon is closest to the earth. The moon’s orbit around the earth is an ellipse. This means there are times when the moon is closer to the earth. When it is farthest away, it is called apogee. The moon will appear as much as 14% bigger and 30% brighter than normal. The moonrise tomorrow night is at 7:28 PM. The weather should cooperate with mainly clear skies.  One of the great things about living along the eastern shore of Lake Michigan is that we get to see the moon rise over lake. It actually looks like the moon rises out of the lake. Enjoy the show.

With our warm weather the last few days, it is finally time to think spring. Spring officially begins at 6:21 PM Sunday. I am sharing a nice write-up the National Weather Service had today on why we don’t have exactly 12 hours of daylight on the first day of spring.

Astronomical Spring begins at 6:21 PM CDT this Sunday, March 20th. Due to the tilt of the Earth, this marks the moment when the geometric center of the Sun’s disk crosses the same horizontal plane as the Earth’s equator on its way north as the Earth orbits the sun. In the graphic below, the position of the Earth at the spring, or vernal, equinox is represented by the Earth image to the rear of the graphic that is fully illuminated.

 Most people think that there are exactly 12 hours of daylight and dark on the date of the equinoxes in the Spring and the Fall, but this is not accurate.  The following explanation is from the U.S. Naval Observatory:


“Day and night are not exactly of equal length at the time of the March and September equinoxes. The dates on which day and night are each 12 hours occur a few days before and after the equinoxes. The specific dates of this occurrence are different for different latitudes.
On the day of an equinox, the geometric center of the Sun’s disk crosses the equator, and this point is above the horizon for 12 hours everywhere on the Earth. However, the Sun is not simply a geometric point. Sunrise is defined as the instant when the leading edge of the Sun’s disk becomes visible on the horizon, whereas sunset is the instant when the trailing edge of the disk disappears below the horizon. These are the moments of first and last direct sunlight. At these times the center of the disk is below the horizon. Furthermore, atmospheric refraction causes the Sun’s disk to appear higher in the sky than it would if the Earth had no atmosphere. Thus, in the morning the upper edge of the disk is visible for several minutes before the geometric edge of the disk reaches the horizon. Similarly, in the evening the upper edge of the disk disappears several minutes after the geometric disk has passed below the horizon. The times of sunrise and sunset in almanacs are calculated for the normal atmospheric refraction of 34 minutes of arc and a semidiameter of 16 minutes of arc for the disk. Therefore, at the tabulated time the geometric center of the Sun is actually 50 minutes of arc below a regular and unobstructed horizon for an observer on the surface of the Earth in a level region.
For observers within a couple of degrees of the equator, the period from sunrise to sunset is always several minutes longer than the night. At higher latitudes in the northern hemisphere, the date of equal day and night occurs before the March equinox. Daytime continues to be longer than nighttime until after the September equinox. In the southern hemisphere, the dates of equal day and night occur before the September equinox and after the March equinox.

In the northern hemisphere, at latitude 5 degrees the dates of equal day and night occur about February 25 and October 15; at latitude 40 degrees they occur about March 17 and September 26. On the dates of the equinoxes, the day is about 7 minutes longer than the night at latitudes up to about 25 degrees, increasing to 10 minutes or more at latitude 50 degrees.”

The following tables illustrate the dates nearest the spring equinox at three locations in southern Wisconsin where the hours of day and night are nearly equal. The date where the day/night hours are closest to equal is March 17th, or three days before the equinox this year.

Date Sunrise (CDT) Sunset (CDT) Amount of Daylight
March 16th 7:08 AM 7:05 PM 11 hours 57 minutes
March 17th 7:07 AM 7:06 PM 11 hours 59 minutes
March 18th 7:05 AM 7:07 PM 12 hours 2 minutes
March 19th 7:03 AM 7:08 PM 12 hours 5 minutes
March 20th 7:01 AM 7:10 PM 12 hours 9 minutes


Date Sunrise (CDT) Sunset (CDT) Amount of Daylight
March 16th 7:03 AM 6:59 PM 11 hours 56 minutes
March 17th 7:01 AM 7:00 PM 11 hours 59 minutes
March 18th 6:59 AM 7:01 PM 12 hours 2 minutes
March 19th 6:57 AM 7:03 PM 12 hours 6 minutes
March 20th 6:56 AM 7:04 PM 12 hours 8 minutes


  Fond Du Lac    
Date Sunrise (CDT) Sunset (CDT) Amount of Daylight
March 16th 7:05 AM 7:01 PM 11 hours 56 minutes
March 17th 7:03 AM 7:02 PM 11 hours 59 minutes
March 18th 7:01 AM 7:03 PM 12 hours 2 minutes
March 19th 6:59 AM 7:05 PM 12 hours 6 minutes
March 20th 6:57 AM 7:06 PM 12 hours 9 minutes

Now, on to the storm for the middle of the week. It looks like it will be another mixed event for us. Meaning some rain, some snow, and some areas a mixture of both. Check out the GFS for Tuesday night.

I still believe there will be many changes to the track and intensity of this storm. Even though it may be turning to spring, I don’t believe our winter precipitation is over. Have a great weekend.



18 Responses

  1. Dan K, I responded to your request for a radar loop of the signature storm last cycle in the comments section from the previous post. A link is provided.

    • Thanks, Josh.

  2. Mark, looking forward to watching the moon rising over Lake Winnebago tomorrow. Thanks for the heads up!

    • My pleasure. Have a good weekend.


  3. Hi, Mark —

    About “Discovery Spring” on 3/27 — will it be a continual presentation from 1:30 to 3:00, as in something one needs to be a part of from beginning to end, or will it be in shorter segments? We don’t get done with church and education classes until Noon — {the pastor is always the last to leave — guess that’s why they gave me the keys} — so I don’t know that we’d be able to get from our place in “Dodge” to Discovery in time to get in on the beginning — and we wouldn’t want to be rude and disturb anyone by coming in late.

    Also, if we can get there, would my 7 and 12 year old grandchildren enjoy it?

    Thanks for any suggestions!

    Don {in Reeseville}

    • Don,
      I am glad you brought that up. I forgot to write about it in the blog. People will be coming and going. We will likely start the presentation closer to 1:45 and talk for about 1/2 hour -45 minutes. Then take questions, etc. Would love to meet you. Kids are more than welcome. There will be fun stuff for them as well.


  4. I just looked at the latest SPC forecast….. If this storm slides more north than it is now, could we be looking at a severe weather outbreak?

  5. Thanks, Josh! Got it 🙂

    I suppose you can never trust a model 120 hours out, but next week is looking interesting. What if the storm slides south a bit, giving us more snow? 😀 It looks like it’s been coming south more lately, eh?

    • Don’t get too excited about the spastic GFS model. The new 12z run keeps the rain/snow line near Green Bay until at least Wednesday morning and by then the precip starts winding down.

      It would seem the models are having a very difficult time tracking this storm… just like their inability to do so with the previous signature storms.

      The cure for modelitis is simply knowing how inaccurate they can be until within 36-48 hours of a storm.

      • Yeah, just saw the 12z now. Well… maybe it’ll come back south again 😀

        Would you expect that the next time around in May that it will track much further west and north? It seems that the February 1st blizzard will be as far south as the low will go, right? So we would have a very good chance of thunderstorms the next time around?

      • Daniel,

        I’m going to really look back at previous ‘signature’ storms this weekend. But my take on models now is that this resembles the December storm in some ways. That storm slid the surface low just to our south. Keep in mind on December 11 the average high was 34, by this Tuesday-Wednesday it is 45. The expectation for snow should be tempered just by this number alone. I think this should still be a good precipitation producer in our area.


      • I noticed the storm track looks similar to the December storm where the LP comes from the Dakotas and slides primarily east-southeast, whereas the late October and early February versions started out in the Texas/Oklahoma area and hooked NE towards our region.

      • Daniel,

        The pattern has been very close to late November early December over the past few weeks. So the track showing up on some models seem realistic.


      • I see what you guys mean… it even looks a little like the October system though, right? But do you think the back end of the storm will stay more in tact like the December storm, instead of hanging back by Minnesota and not making it to Milwaukee?

        I’ve also been looking at this…. anyone know what model this is from? Clicking “animate” shows this week’s system.

  6. Severe weather looks quite possible next week…for many others, lots of precipitation. Sure wish I knew this was coming in advance. 😉 Darned negatively tilted upper level low in the Northern/Central Plains.

    Time to gas up the car…

    • Haha… sorry man! So does the fact that it’s negatively tilted still correlate with the LRC? Why the difference? Is it just its development that’s slightly different, but once it rotates it will look just like the storm the previous several cycles?

      • Dan – looking at past patterns, there has been a tendency in this pattern for a bit more negatively tilted ULLs. From a chase perspective, having that tilt will further bring up the warm air and improve the environment especially with the LLJ and improved dynamics for the 0-1KM aspect.

        From an active weather enthusiast viewpoint…I would rather ALL storms be negatively tilted as they tend to be the most dynamic. Behind that, I would take the stacked ones and last the positively tilted ones. Positively tilted seems to yield more linear/embedded..and makes it less favorable to chase.

      • lrcweather: thanks for your response! Very interesting stuff….. I have a lot to learn still 🙂 Chasing sounds so great. So I guess if you want a lot of snow, you generally dont want a negatively tilted storm if you’re right by the rain/snow line like Milwaukee, huh? Although it could bring thundersnow, I suppose, if it was cold enough.

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