[willamette-fcst] Silverton Hills Forecast - Mon, Jul 19 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON JUL 19 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from now until 7:00pm.
     Prep burning is not allowed. 
     Propane flaming is not allowed.	
									
										
WEATHER DISCUSSION:


     Satellilte pictures show the clouds in the Wilamette Valley are breaking up and
     the Silverton Hills area of Marion County cloud free as of late morning.  Low
     level flow continues onshore.  Pressure gradients as of 11am included:  Newport
     to Salem, 1.0 mb onshore; Salem to Redmond, 3.7 mb onshore for a total onshore
     gradient Newport to Redmond of 4.7 millibars.  The Portland to Medford gradient
     is 5.3 mb northerly and that is causing the northerly transport winds in the
     valley.  With sunshine finally breaking out in the Salem area pressures will
     drop relative to the coast and the gradient stacking to the east issue may
     improve this afternoon, but the north to south gradient across the state will
     continue and no wind switch to westerly is likely this afternoon.  
  
     Expect sunshine today.  Salem's high temperature today will be near 78 and the
     minimum relative humidity should be 36%.
 

     Sunset tonight: 8:47 pm	
							
										
THREE-HOURLY DATA:		

                                     2pm     5pm     8pm			
     Temperature:                     71      77      72  			
     Relative Humidity:               44%     37%     44%     			
     Surface Wind Direction:         350     010     340 		
     Surface Wind Speed:               9      10      11    			
     Transport Wind Direction:       010     010     010 
     Transport Wind Speed:            10      10      13  
     Estimated Mixing Height:       2100    3500     500
     Ventilation Index:               21      35       6

                               				
										
EXTENDED DISCUSSION:

     Another upper level disturbance develops and moves in from the northwest tomorrow.
     This will serve to deepen the marine layer Tuesday makeing for a slower
     burn-off of clouds.  This disturbance pulls out Wednesday with a northwesterly
     flow aloft developing.  This should give more afternoon sun and warmer
     temperatures.  Models then indicate broad, flat ridging through the rest of the
     week for dry weather and temperatures near or slightly above average.  The
     pattern favors persistent northerly transport winds and burning opportunities are 
     not likely.


EXTENDED FORECAST:
	
     Tuesday: Morning clouds then partly sunny, high 80. NNW wind between 5 and 9 mph. 
     Tuesday Night: Mostly cloudy, low 52. Wind NNW 6-10 decreasing.
     Wednesday: Mostly sunny, with a high near 83. Light winds early, becoming NW 8-12
        with higher gusts.
     Wednesday Night: Partly cloudy, with a low around 52.  
     Thursday: Mostly sunny, with a high near 80.  
     Friday: Mostly sunny, 83.  
     Saturday: Mostly sunny, 82.  
     Sunday: Mostly sunny, 83. 			

										
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.