Past IEM Features tagged: folklore

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Groundhog Day Forecast

02 Feb 2022 05:34 AM
It is a cruel irony that today is Groundhog Day and Saturday is Weatherperson (Meteorologists) Day as the former is the bane of the existence of the latter. For those that believe in a groundhog's forecast, the weather lore states that if an emerging groundhog sees its shadow, it will retreat back into its hole and six more weeks of winter will commence. The featured table looks into this forecast based on a theoretical groundhog here in Des Moines with the shadow metric estimated by Des Moines airport sky coverage at 7 AM. The two data columns present that year's six week total for snowfall and average temperature and if those values were a snowier/colder departure than average (more winter) or a less snowy/warmer departure (more spring). The last column grades the forecast. Of course, one may argue if these metrics are an appropriate means to grade the forecast, but we are attempting to discuss a forecast made by a groundhog here, so about anything goes!

Good: 15
Bad: 1

Tags:   groundhog   folklore  

Seven Sundays of Rain?

18 Apr 2014 05:37 AM
A saying in weather folklore is that if it rains on Easter Sunday, it will rain for the next seven Sundays after. With rain forecasted this Sunday, the featured chart investigates if this saying is true. The two series of values show the frequency of measurable precipitation after an Easter Sunday with rain and for all Easter Sundays. You can see that the frequencies for precipitation after an Easter with precipitation are no higher than for all cases and they are much less than 50%. Three years had five out of the seven Sundays with precipitation after a wet Easter. Those were 1883, 1884, and 1961.

Good: 38
Bad: 18
Abstain: 8

Tags:   folklore   easter  

Full Moon and Frost

23 Sep 2013 05:42 AM
Very cool overnight temperatures visited the state this past weekend with lows approaching freezing over northwestern Iowa on Saturday morning. This very cool weather was close to the most recent full moon late last week. There is a saying in weather folklore that the first freeze of the fall season often happens on the full moon as having a full moon impacts the profile of water vapor which allows temperatures to more rapidly cool. The featured chart looks at the first fall sub 29 degree temperature for Ames and the proximity to the nearest full moon. As you can clearly see, these events happen at about any time during the lunar cycle. The reason that this folklore gets perpetuated is that the first frost is almost always on a clear sky night with limited water vapor in the air, so any moon will appear very bright and crisp.

Good: 35
Bad: 3

Tags:   moon   folklore  

View larger image
Ames webcam used for sunsets (often facing west) and Nevada webcam used for sunrises (often facing east)

Red Sky

12 Jul 2013 05:00 AM
Most are familiar with the old adage; "Red sky at night, sailor's delight. Red sky at morning, sailor take warning." Does this saying apply for us land-locked Iowans? IEM's webcam archive contains an image every five minutes dating back to as far as 2003. For the featured analysis, webcam images approximately 10 minutes prior to sunrise and 10 minutes after sunset were analyzed for amount of red in the sky. The algorithm attempted to differentiate red sky from the red horizon that is common with everyday sun rises and sets. Of 2300 some sunrises and sunsets, 248 red sunrises and 88 red sunsets were identified by an algorithm. For these events, hourly precipitation data from Ames was queried to see if measurable precipitation fell in the 24 hours proceeding the event. The third bar is daily climatology which shows not much of a signal with these events, but there is a slight increase for red sky at morning events. Obviously, a limited sample and computer program does not prove or disprove this adage.

Good: 251
Bad: 28

Tags:   webcam   sun   folklore