[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
9:00 AM 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 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.
      
     Pressure gradients as of 8am included:  Newport to Salem, 2.5 mb onshore; Salem to
     Redmond, 1.1 mb onshore for a total onshore gradient of 3.6mb.   This
     is a favorable pattern.  However if thunderstorms again develop this afternoon
     east of the Cascades in the southwesterly flow aloft (which is likely)
     pressures will increase east side and the gradient pattern may become
     unfavorable.  Close monitoring of weather conditions today will be necessary to
     determine if any burning is possible.  Afternoon pibals will tell the story.  
     
 
      For the mid Willamette Valley today expect abundant sunshine. Salem's high
     temperature will be near 90. Relative humidity drops to 50% by 10am.  Minimum
     relative humidity 26%.  Expect light northerly surface winds with a shift to
     northwesterly late.
  
     Sunset tonight: 8:40 pm	
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 76       86      90      81  			
     Relative Humidity:           46%      32%     26%     37%     			
     Surface Wind Direction:     360      350     330     280 		
     Surface Wind Speed:           4        6       7       7    			
     Transport Wind Direction:   360      360     360     300 
     Transport Wind Speed:         5        5       5       8  
     Estimated Mixing Height:   2000     4300    4700    1000
     Ventilation Index:           10       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.