Weather and Burn Advisory for Jefferson County									
Oregon Department of Agriculture, Salem, Oregon									
9:50am Wednesday, September 30th, 2009.

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

Weather Discussion:
     An autumn-like upper-level trough brought lots of clouds, wind, and much cooler (about 15
     degrees) temperatures to Jefferson County Tuesday...but little to no rainfall.  That made
     for good ventilation conditions for carrot-vine burning.  The upper-level trough axis was
     over Idaho this morning with a cool and drier northwesterly flow aloft over central Oregon.

     A weak ridge is forecast to move over Oregon today with continued drying and slow warming
     of the air mass.  Cold air aloft with combine with daytime heating to lift mixing heights
     above 5000 feet by midday.  Brisk northwesterly transport winds will continue to provide
     good smoke ventilation for carrot-vine burning.

Today:  Mostly Sunny, Breezy, and Cool.  High near 56.  Wind: NW 5-15 with Higher PM Gusts.	

                                11am    2pm    5pm    8pm			
     Temperature:                49      53     53     45  			
     Relative Humidity:          48%     39%    43%    64%     			
     Surface Wind Direction:    330     320    320    310 		
     Surface Wind Speed:          4      12     10      6    			
     Transport Wind Direction:  310     310    300    300 
     Transport Wind Speed:       15      20     20     10  
     Estimated Mixing Height:  5000    6500   5000    500
     Ventilation Index:          75     130    100      5				
										
Extended Outlook:
     A Pacific frontal system is forecast to move into western Washington Thursday, with a
     continued dry and cool northwesterly flow aloft over central Oregon.  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.  Ventilation conditions
     should remain good for carrot-vine burning.  Temperatures should slowly moderate next week,
     as a ridge builds into the coastline.

     Tonight:  Clearing and Cool.  Low near 32.
     Thursday: Mostly Sunny and Warmer.  High near 65.  Northwesterly transport winds.  
     Friday:  Moslty cloudy.  Increasing chance of showers.  WNW transport winds.  High near 64.
     Saturday: Mostly cloudy.  Showers likely and cool.  High near 55.
	
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.