[willamette-fcst] Silverton Hills Forecast - Mon, Jul 26 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00PM PDT MON JUL 26 2010

BURN ADVISORY:

     Agricultural burning burning is not recommended.
     Prep burning is allowed from 2:00pm to 5:00pm with a 50 acre limit. 
     Propane flaming is allowed from 2:00pm to 5:00pm.	
									
										
WEATHER DISCUSSION:

     Upper air charts continue to show a weak trough off the California coast this
     morning. Upper level flow over Oregon is generally southwesterly.  Low level
     flow is northerly through the valley and likely will stay northerly through most
     of the day.  There is a slight possibility of a wind shift late in the
     afternoon.  Any wind shift is dependent on pressure gradients developing in a
     favorable manner.
       
     Pressures have been fairly steady throughout the morning along the coast, 
     dropping in the Willamette Valley and dropping a little
     more rapidly in central Oregon.  Gradient stacking to the east has not been an
     issue so far today and likely will not be.  If thunderstorms again develop this
     afternoon east of the Cascades in the southwesterly flow aloft (some lightning
     has already been reported east of Bend) pressures will increase east side and we
     could lose the easterly gradient across the Cascades.  Close monitoring of
     weather conditions today will be necessary to determine if any burning is
     possible.   
      
  
     For the mid-Willamette Valley this afternoon expect
     abundant sunshine. Salem's high temperature will be near 90.  Minimum relative
     humidity drops to 26%.  Expect light northerly surface winds with a shift to
     northwesterly late.

     Sunset tonight: 8:40 pm	
										
THREE-HOURLY DATA:		

     Temperature:                     85      90      78  			
     Relative Humidity:               32%     27%     40%     			
     Surface Wind Direction:         350     340     280 		
     Surface Wind Speed:               6       7       7    			
     Transport Wind Direction:       360     360     300 
     Transport Wind Speed:             5       5       8  
     Estimated Mixing Height:       4300    4700    1000
     Ventilation Index:               22      24       8
										
EXTENDED DISCUSSION:

     The trough off the coast will help reinforce the marine layer the next couple of
     days. More marine air will make it into the valley for slowly decreasing
     temperatures through mid week.  Thunderstorms development east of the Cascades
     is likely throughout the week which will complicate the pressure gradient
     situation across the Cascades.  Again, careful monitoring will be required to
     detect burn opportunities.    

EXTENDED FORECAST:	
     
     Tuesday: Sunny, with a high near 85. Winds light becoming W 5-8.  Potential burn
        opportunity.
     Wednesday: Sunny, 83. Wind W6.  Potential burn opportunity. 
     Thursday: Partly sunny, 82.   
     Friday: Partly sunny, 81.   
     Saturday: Mostly sunny, 82.  
     Sunday: Mostly sunny, 82.  
     
										
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.
	
This forecast is provided under an agreement between the Oregon Department of
Agriculture and the Oregon Department of Forestry.  For information contact ODA
at 503-986-4701.