February 17, 2007

6:30 to 7:30 a.m.


  Clearing skies after a previous cloudy and rainy day left the ground wet and helped produce widespread fog preceding the temperature trek hour around dawn.  Fog tops were in the 300 to 500 foot range and the fog covered most of the metro area below these levels.  A light south and easterly drift of 5 mph or less was observed above the fog.


  The most interesting feature on the map is the cool air pool at the lowest elevations near the Willamette River, where the inversion and fog was probably deepest.  The cool readings on the far SE side of the metro area are possibly due to stronger radiational cooling because the fog there was thinner and of less duration.  The warmer readings in the higher elevations are above much of the inversion.


  The higher temperatures in normally coolest areas of Clark Co. and the Tualatin Valley are interesting.  Perhaps the light SE winds above the inversion brought some heating down to the surface in these areas. North and west of Forest Grove and Hillsboro skies were mostly clear during the trek, suggesting a possible backwash flow as the light east winds hit the Coast Range foothills.  The heat island was poorly developed, confined to a small area north and east of Starbucks, in close-in NE.


  Thanks again to all that participated in the 3rd Annual Temperature Trek.  This event proved to be a lot of fun for all. See you all next time.


Charlie Feris,

Oregon-AMS member and past officer