[willamette-fcst] Silverton Hills Forecast - Tue, Jul 20 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 AM PDT TUE JUL 20 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from 12:00pm to 7:00pm.
     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:

     An upper level disturbance is deepening along the southern British Columbia
     coastline today.  This has produced some high clouds across portions of 
     Washington and should help turn winds in the Willamette Valley a little more 
     northwesterly late this afternoon.  
 
     Satellite pictures show most of the clouds in the Valley
     are east of the Willamette river as of late morning.  In addition, low marine
     clouds are banked up against the north coast and into some of the coastal
     valleys.  Any clouds still covering the Silverton Hills should burn off within
     the next hour or so for a sunny afternoon.  Temperatures should reach into the
     low 80's with Salem's high temperature near 82.  Minimum
     relative humidity today will be 32%. Winds will be northerly, shifting to
     northwesterly late this afternoon or early this evening.   
 
     Gradient stacking to the east has actually increased during the morning.  As
     of 11am this morning the Newport to Salem gradient was 1.3mb while the Salem
     to Redmond gradient was 3.9mb. However,  as valley temperatures warm, valley
     pressures will drop giving a more favorable west to east gradient profile this
     afternoon.  

     Today is a potential burn day if the winds do indeed shift to more
     northwesterly.  However, it appears no fields are ready to be put to flame.  We
     will monitor pressure gradients and surface winds to confirm any wind shift.   

     Sunset tonight: 8:46 pm	
										
THREE-HOURLY DATA:		

                                     2pm     5pm     8pm			
     Temperature:                     69      75      70  			
     Relative Humidity:               51%     40%     51%     			
     Surface Wind Direction:         340     340     300 		
     Surface Wind Speed:               8      10      11    			
     Transport Wind Direction:       350     340     290 
     Transport Wind Speed:             8       8      10  
     Estimated Mixing Height:       3200    4800    1000
     Ventilation Index:               26      38      10
					
EXTENDED DISCUSSION:

     The westerly or west-northwesterly flow pattern aloft will continue until about
     Friday when we will see a transition to a southwesterly flow aloft with a weak
     trough off the California coast and a ridge over the western United States. 
     This should get the Willamette Valley out of a persistent north wind regime and
     potentially open up some burn opportunities next week.  
 
EXTENDED FORECAST:	
     
     Wednesday: Cloudy early then clearing slowly. High 84. Light winds early then
         NW 5-8mph. 
     Wednesday Night: Partly cloudy, 53.
     Thursday: Mostly sunny. 80. Wind becoming WNW 8-12.  Potential burn opportunity.  
     Friday: Mostly sunny, 88.   
     Saturday: Mostly sunny, 88.  
     Sunday: Mostly sunny,  83.  
     Monday: 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.