Weather and Burn Advisory for Union County									
Oregon Department of Agriculture, Salem, Oregon									
10:20am Wednesday, September 30th, 2009.

     ...Last Forecast for the 2009 Field-Burning Season...

Weather Discussion:
     An autumn-like cold front and subsequent upper-level trough brought lots of clouds and wind,
     but mainly much cooler (about 30 degrees) temperatures to Union County Tuesday.  There was
     little to no rainfall recorded over NE Oregon.  The upper-level trough axis was
     over Idaho this morning with a cool northwesterly flow aloft over NE Oregon.

     Satellite imagery showed considerable clouds over Union County this morning, but Doppler
     radar was not showing much in the way of shower activity.  A weak ridge is forecast to move
     over Oregon today with the flow aloft slowly drying and warming.  That should put an end to
     the shower threat by late this afternoon, but temperatures will remain very cool.

     Cold air aloft and daytime heating will combine to lift mixing heights above 5000 feet by
     midday.  Brisk northwesterly transport winds will provide good smoke ventilation today, if
     surface winds are not too strong for burning.

Today:  Mostly Cloudy AM.  Slight Chance of a Shower.  Partly Sunny, Cool, & Breezy. High near 54.

                                11am    2pm    5pm    8pm			
     Temperature:                49      52     52     42  			
     Relative Humidity:          44%     39%    39%    55%     			
     Surface Wind Direction:    310     310    310    320 		
     Surface Wind Speed:         10      12     12      6
     1000ft AGL Wind Direction: 300     310    310    300
     1000ft AGL Wind Speed:      15      20     20     20    			
     Transport Wind Direction:  300     310    310    310 
     Transport Wind Speed:       20      20     20     15  
     Estimated Mixing Height:  5000    6500   6500   1000
     Ventilation Index:         100     130    130     15				
										
Extended Outlook:
     A Pacific frontal system is forecast to move into western Washington Thursday, with a
     continued dry and cool northwesterly flow aloft over Union County.  A cold upper-level
     trough is forecast to drop southward, over Oregon, Friday through Sunday.  That will bring
     a chance of showers and drop temperatures back to well below normal.  Temperatures should
     slowly moderate next week, as a ridge builds into the coastline.

     Tonight:  Clearing and Cold.  Freezing temperatures likely.  Low near 30.
     Thursday: Mostly sunny.  A little warmer.  High near 60.
     Friday: Mostly cloudy.  Increasing chance of showers.  High near 62.  
     Saturday: Showers likely...mainly over the mountains.  Turning cooler again.  High near 50.    
     Sunday: Mostly cloudy.  Chance of showers.  Continued cool.  High near 52.

Oregon Department of Agriculture									
Oregon Weather Center									
503-986-4701									
										
Notes:									
     1.  Mixing height, as used here, is the lowest height at which the
         potential temperature exceeds the potential temperature at the surface.  
         As a practical matter it is the approximate height to which a 
         smoke plume will rise assuming good ignition, dry fuels, and 
         winds less than about 15mph.								
     2.  Transport winds are a layer average through the mixing height, 
         weighted slightly toward the winds at the top of the layer.
     3.  Ventilation Index is the height of the mixing layer times 
         the transport wind speed divided by 1000.
     4.  Surface wind direction is the general expected wind direction.  
         At a specific point surface winds are highly dependent on 
         local terrain conditions.
     5.  1000ft AGL (Above Ground Level) wind direction and speed is for use in
         estimating smoke dispersal patterns from propane flaming.