[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
12:00 PM PDT WED AUG 11 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from 1:00pm to 6:30pm.
     Prep burning is allowed up until 2:00pm with a 50 acre limit. 
     Propane flaming is allowed up until 5:00pm.	
									
										
WEATHER DISCUSSION:

     An upper level low pressure area, centered over about Pendleton, covers most of
     the Pacific Northwest late this morning. With counter-clockwise flow around this
     low, the winds aloft over the Willamette Valley are northerly. 
     
     Morning sodar soundings have shown some variability with winds above 2000 feet
     occasionally showing a westerly component but also occasionally showing an
     easterly component. Surface to around 2000 feet the sodar has been consistent in
     showing a nearly due northerly wind. 
     
     The morning ODF surface analysis shows high pressure offshore, a weak thermal
     trough in California and a weak trough in southeast Washington. Pressure
     gradients as of 11am included: Newport to Salem, 2.0 mb onshore; Salem to
     Redmond, 2.1 mb onshore; and total onshore gradient Newport to Redmond, 4.1 mb
     onshore. Thus there is no issue today with "gradient stacking" to the east. 
     
     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. A pibal sounding
     is scheduled for around 1pm near Stayton to establish a baseline to monitor any
     wind shift. Skies should become mostly sunny this afternoon and the high in
     Salem will be near 80. Minimum relative humidity today will be near 34%. Sunset
     tonight: 8:19 pm

					
										
THREE-HOURLY DATA:		

                                     2pm     5pm     8pm			
     Temperature:                     75      78      72  			
     Relative Humidity:               45%     39%     48%     			
     Surface Wind Direction:         340     340     290 		
     Surface Wind Speed:               7       7       7    			
     Transport Wind Direction:       350     330     320 
     Transport Wind Speed:             4       9       5  
     Estimated Mixing Height:       3800    4800    1000
     Ventilation Index:               15      43       5
                         				
										
EXTENDED DISCUSSION:

     The Willamette Valley will see some hot weather this weekend. Temperatures today
     will be several degrees warmer than yesterday and there will be 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.