[wxqc] temperature errors

Wed Oct 18 09:56:20 CDT 2006

The inland rural Florida peninsula almost always see's it's coldest minimum temperatures when the sky is clear, the wind is calm and the atmosphere dry. This is a perfect setup for a classic radiational cooling temperature inversion. 

A small low lying meadow in my front yard is at an elevation of 208 feet AMSL and the back yard where the VP2 is set up is at 218 feet AMSL. This 10 foot elevation difference produces a minimum temperature difference of 8 deg. F. I also have a larger low lying meadow adjoining my back yard at an elevation of 210 feet. This 8 foot elevation difference produces a minimum temperature difference of 6 deg. F. At my station I have seen temperature differences of 5 deg. F vertically from ground level to 5 feet above ground level during radiational cooling conditions. This vertical gradient will vary depending on ground cover, soil type and soil moisture level.

Also one time in Pasco County, FL I measured a temperature difference between a 301 foot AMSL hill elevation and a nearby 99 foot AMSL meadow elevation of 20 deg. F. Another time I was traveling on I-10 in the Florida panhandle region on January 21, 1985. The time was near local sunrise and on top of a hill near Chipley, FL I measured a temperature of 7 deg. F and in a nearby valley I measured a temperature was -6 deg. below zero F. 

So the bottom line is that under radiational cooling conditions you can see very large temperature gradients with small elevation changes.

Take Care,
Thomas F. Giella, KN4LF
Retired Meteorologist & Space Plasma Physicist
Lakeland, FL, USA
flycylone at tampabay.rr.com

NWS Tampa Bay, FL SKYWARN Observer #POL-10A
CWOP Station #AR692/KN4LF

Live Lakeland, FL Weather Observations: http://www.kn4lf.com/index1.html
Lakeland, FL Daily Climatological Weather Data Archive: http://www.kn4lf.com/kn4lf22.htm
September 2006 Lakeland, FL Daily Climatological Weather Observations http://www.kn4lf.com/kn4lf63.htm
Florida/US Raw Weather Forecasting Resource Links: http://www.kn4lf.com/kn4lf13.htm
Man Induced Climate Change Refuted: http://www.kn4lf.com/globalwarminglie.htm
New Scientific Evidence for the Existence of God: http://www.cosmicfingerprints.com/audio/newevidence.htm 

  ----- Original Message ----- 
  From: Dan Crooks 
  To: Discussion of weather data quality issues 
  Sent: Wednesday, October 18, 2006 9:23 AM
  Subject: Re: [wxqc] temperature errors

  Same situation here at CW1789.  Nighttime temps remain higher than the valley
  and daytime highs are slightly lower.  More noticeable at night with less wind to stir 
  things up.

  I have a 1-wire station I want to put at the bottom of my driveway for the same reason, house
  is at 1309 ft and bottom of my driveway is 1000 ft.  Would be interesting to see the difference
  between the 2 locations. 

  I bought an Extech RH390 precision psychrometer (NIST traceable) to verify my Davis VP2+
  was reading correctly.  I had trouble believing my station readings and the RH390 showed that 
  my station is reporting correct data for my location.

  -Dan

  On 10/18/06, Mark Wyman <mark at markwyman.com > wrote:
    Yes. I am on a fairly decent hill, at 1300 feet or so, our driveway has a 
    240' elevation change. At night the house is typically 5 degrees warmer than
    the bottom of the driveway, especially on frosty, still nights. The
    inversion can set up fairly steep even before the sun finishes setting! Much 
    of the time I look out the window on the top and say "great, no frost this
    time", and get to the bottom of the driveway and it looks like someone
    exploded a large can of white paint.

    One of these days I will add a station to the bottom of the hill that can 
    send all the way back to the top just to see the differences in real-time.

    -Mark

    -----Original Message-----
    From: wxqc-bounces at lists.gladstonefamily.net 
    [mailto:wxqc-bounces at lists.gladstonefamily.net] On Behalf Of dbj at capital.net
    Sent: Tuesday, October 17, 2006 4:10 PM 
    To: wxqc at lists.gladstonefamily.net
    Subject: [wxqc] temperature errors

    I checked the accuracy of my temperature sensor with another thermometer
    placed on top of the rain gauge and on the other side of the house last 
    night.  Both sensors were within 1 degree F of each other.  So, assuming my
    sensor is accurate, why is my location so much warmer (up to 11 degrees
    warmer the night of October, 16) than neighboring stations most 
    nights?   Could it be caused by temperature inversion because my neighbors
    are located at lower elevations in the Hudson River valley and I am on top
    of a hill at 645 feet?  Is temperature inversion typically a night-time 
    phenomenon?

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