[willamette-fcst] Silverton Hills Forecast - Mon, Sep 27 2010

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON SEP 27 2010

BURN ADVISORY:

     Agricultural burning burning is not recommended.
     Prep burning is allowed from 12:00pm to 3:00pm with a 50 acre limit. 
     Propane flaming is allowed from 12:00pm to 5:00pm.	
									
										
WEATHER DISCUSSION:

     Upper air charts show a deep low in the northern Gulf of Alaska this morning,
     while an upper ridge builds over the intermountain region. This is giving a weak
     southwesterly flow aloft the region. Embedded in that southwesterly flow is a
     Pacific warm front/cold front combination. The warm front is producing clouds
     over most of western Washington and extreme northwestern Oregon. For the most
     part those clouds should stay north of Marion County, but some clouds may drift
     over the region during the afternoon. The cold front will move northeast and
     should not affect the area. 
     
     The morning Salem sounding showed warming at most levels and a
     fairly stable atmosphere. There was an inversion from the surface to about 2800
     feet. This should mix out this afternoon. We anticipate a mixing height of 3000
     feet by about 1pm.

     Winds on the sounding were light southerly at the surface veering to light
     southwesterly by about 3500 feet. Unfortunately it does not look like this
     favorable southwesterly wind direction will be present this afternoon. Computer
     models are showing a shift to north-northeasterly by mid afternoon. Surface
     pressure gradients have already gone offshore with a pressure difference from
     Redmond to Newport of 2.5mb.
    
     Expect mostly sunny skies today. Salem's high temperature today will be near
     84. Minimum relative humidity will be near 51%.

     Sunset tonight: 6:54 pm	
							
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 73       81      83      74  			
     Relative Humidity:           71%      56%     53%     66%     			
     Surface Wind Direction:     190      240     330     330 		
     Surface Wind Speed:           4        4       5       4    			
     Transport Wind Direction:   180      220     020     350 
     Transport Wind Speed:         3        2       4       6  
     Estimated Mixing Height:   1200     3100    4000     500
     Ventilation Index:            4        6      16       3                          
										
EXTENDED DISCUSSION:

     The upper ridge centered over Nevada and Utah will remain over the western US
     much of the week. Computer models show a transport wind over northwest Oregon
     from the north or northeast through Thursday, then going back to southwest by
     Friday. Afternoon mixing heights will likely slowly deterioriate through about
     Thursday as well.

EXTENDED FORECAST:	
     
     Tuesday: Partly sunny, with a high near 77. Calm wind becoming north between 5
     and 8  mph. 
     Wednesday: Mostly sunny, with a high near 76. North northeast wind between 6 and
     9 mph.  
     Thursday: Mostly sunny, with a high near 79.  
     Friday: Mostly sunny, with a high near 79.   
     Saturday: Mostly sunny, with a high near 76.  
     Sunday: Partly sunny, with a high near 74.  
     
										
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.








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