Thursday, January 28, 2010

units please!

when i was in college, dr. spruill (my hydrology and petrology professor) used to harp on us constantly about including units.  even when the units cancelled... like a hydraulic gradient of 0.1 ft/ft (if you were in his class and taking his test, we had to include the ft/ft or we got it wrong).

well, the folks at NOAA needed to take a class by him.  i was just reading their forecast for 27549 zip code and i was left with questions:

Friday: A slight chance of rain and snow after 3pm. Mostly cloudy, with a high near 40. Northeast wind between 5 and 8 mph. Chance of precipitation is 20%.

Friday Night: A slight chance of rain and snow before 7pm, then snow. Low around 26. Northeast wind between 7 and 11 mph. Chance of precipitation is 100%. New precipitation amounts between a quarter and half of an inch possible.

Saturday: Snow and sleet, becoming all snow after noon. High near 28. Northeast wind around 15 mph. Chance of precipitation is 100%. New precipitation amounts between a half and three quarters of an inch possible.

half of an inch of what?  snow?  rain?  i realize they did include the units (inches), but inches of what?  chickens?  (that is what dr. spruill would have said... "chickens?")

an inch of rain is not the same as an inch of snow.

if i'm not mistaken, the rule/ratio for liquid to frozen is 1:10  (meaning 1 inch of liquid is the same as 10 inches of frozen).  so, if they were saying precipitation amounts of "liquid" or melted measurements, then, that means we should get 7.5 to 12.5 inches of snow (total).

which brings me to another question... if "they" say, for example, "rain then snow" and "precipation amount is 1 inch", do they mean 1 inch of rain or snow?  do they use different gauges for the rain and THEN measure the snow differently?  like, if it rains 1/2 inch and then it snows 5 inches, wouldn't that be the same as 1 inch of precipation (liquid)?



  1. I'm with ya, sistah! They didn't even clarify units of temperature (F or C? ;) I mean, I know, but like you said, if you don't say, then you leave it open to speculation...). And, like your unitless example, and squared inch of water over an squared inch of dirt, while still unitless, means nothing unless you know it's water on dirt... just saying ft/ft (in your gradient example) might not even be enough, sometimes!

    Too many assumptions of understanding (whether warranted or not... I believe not!) on the part of the author... I feel the same way about anyone that uses ANY sort of abbreviation in a document (even if it's considered to be common knowledge, in some cases... B/c, what is common knowledge?) without having first defined/identified it... (Like my b/c... I should have first identified it as "because"... It's lazy to do otherwise... And, F = Farhenheit (a good example of the "common knowledge" argument, but maybe there are some Kelvinists out there, who only recognize absolutes... ;) ), and C = Celsius... ;)

    Like in an argument, it's always best to be as specific as you can be, if you want someone to completely understand you...

  2. that's so funny. he always said pickles to my class.

    "10! 10 what? Pickles?"

    i miss him.

    I'm SO ready for grad school.



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