[willamette-fcst] Silverton Hills Forecast - Wed, Aug 11 2010

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT WED AUG 11 2010

BURN ADVISORY:

     Agricultural burning burning is not recommended.
     Prep burning is allowed from 11:00am to 2:00pm with a 50 acre limit. 
     Propane flaming is allowed from 11:00am to 5:00pm.	
									
										
WEATHER DISCUSSION:

     Upper air charts show a low pressure area, centered over about Pendleton,
     covering most of the Pacific Northwest this morning. With counter-clockwise flow
     around this low, the winds aloft over the Willamette Valley are northerly. These
     northerly winds extend to the surface as well. Early morning wind readings from
     the new Salem sodar show light north-northwest winds from the surface to 1500
     feet. 
     
     The morning ODF surface analysis shows high pressure offshore, a weak thermal
     trough in California and a weak trough in southeast Washington. Pressure
     gradients are onshore with a total of 2.8mb from Newport to Redmond. Newport to
     Salem is 1.2mb onshore and the gradient from Salem to Redmond is 1.6. Thus there
     is very little gradient stacking to the east this morning and it looks like
     there will not be a gradient stacking issue this afternoon.
     
     The limitation on burning today will be wind direction. Models show
     winds generally northerly with just a brief shift to about 330 this afternoon.
     330 degrees is not enough westerly to do much open field burning. We will
     monitor winds with both pibals and the new sodar (sound detection and ranging)
     unit temporarily installed near the intersection of Hawthorne and State street
     in Salem. If an opportunity opens up it will likely be brief with only limited
     acerage. 
     
     Expect cloudy skies this morning, breaking up by late morning, and becoming
     mostly sunny this afternoon. Salem's high temperature today will be near 80.
     Relative humidity drops to 50% by noon. Minimum relative humidity today will be
     near 34%.

     Sunset tonight: 8:19 pm	
							
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 69       76      80      74  			
     Relative Humidity:           57%      42%     34%     43%     			
     Surface Wind Direction:     350      330     340     290 		
     Surface Wind Speed:           5        6       7       6    			
     Transport Wind Direction:   350      350     330     320 
     Transport Wind Speed:         3        4       9       5  
     Estimated Mixing Height:   2800     3800    4800    1000
     Ventilation Index:            8       15      43       5

                               				
										
EXTENDED DISCUSSION:

     We are still on track for hot weather over the weekend. Temperatures will jump
     several degrees today with a similar jump tomorrow and again Friday. The upper
     level low currently centered over SE Washington and NE Oregon will shift
     eastward allowing an upper level high to build to the west. This will leave the
     region under a dry northerly or northeasterly flow through the weekend.
     Temperatures will be in the 90's by Friday and highs will remain in the 90's
     through Monday. There do not appear to be any significant burn opportunities
     through the next 5 days.

EXTENDED FORECAST:	
     
     Thursday: Mostly sunny, 86. Calm wind becoming NNW 8-11 mph. 
     Friday: Sunny, 92. Calm wind becoming NNE 5-8 mph.   
     Saturday: Sunny and hot, with a high near 96.    
     Sunday: Sunny, with a high near 92.   
     Monday: Sunny, with a high near 91.  
     Tuesday: Mostly sunny, with a high near 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.