[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
9:00 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 short wave is looking a little stronger than it did yesterday and
     moving down the BC coastline this morning.  This may be strong enough to bring
     the winds around enough to provide a burning opportunity late this afternoon. 
     (This may, however, be a moot point if there are no fields ready to burn.) 
     Growers should make sure that any fields that are ready are known to ODA.  
 
     Morning satelllite pictures show low clouds in much of the Willamette Valley but
     they are not as thick or as extensive as yesterday. The air mass is slightly
     warmer this morning and with some sunshine this afternoon after the burn-off
     look for temperatures to be up a few degrees from yesterday.  The mid Willamette
     Valley will see morning clouds, clearing by about noon and high temperatures in
     the low 80's.  Salem's high temperature today will be near 82. Relative
     humidity drops to 50% by 11am.  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 is not as strong today as past
     couple of days, and as valley temperatures warm, valley pressures will drop
     giving a more favorable west to east gradient profile this afternoon.  As of 8am
     this morning the Newport to Salem gradient was 1.4mb while the Salem to Redmond
     gradient was 2.9mb.   
 
     Careful monitoring of pibals, pressure gradients, and
     surface winds tell the story this afternoon.   

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

                                 11am     2pm     5pm     8pm			
     Temperature:                 68       77      82      75  			
     Relative Humidity:           51%      37%     32%     41%     			
     Surface Wind Direction:     010      350     340     300 		
     Surface Wind Speed:           7        7      10      10    			
     Transport Wind Direction:   360      350     340     290 
     Transport Wind Speed:         6        8       8      10  
     Estimated Mixing Height:   1800     3200    4800    1000
     Ventilation Index:           11       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.