[willamette-fcst] Silverton Hills Forecast - Tue, Jul 13 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE JUL 13 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are now until 7:00pm.
     Prep burning is allowed up until 5:00pm with a 50 acre limit. 
     Propane flaming is allowed up until to 5:00pm.	
									
										
WEATHER DISCUSSION:

     A fairly deep upper level low is moving eastward across southwest Canada today.
     A trailing upper level trough sweeping across Washington and Oregon has 
     brought some cloudiness to the northern Willamette Valley.  Temperatures will be
     cooler than average for this time of year by several degrees.

     The morning Salem sounding showed an inversion aloft from about 4500 to 6300 feet.
     This inversion will not break today and the maximum mixing height this afternoon
     will be about 5300 feet. While the morning sounding showed temperatures in the 
     lower atmosphere had cooled another 5 degrees since yesterday morning,     
     increased sunshine today should push maximum temperatures a couple of degrees
     higher today. Salem is still on track for a high temperature near 76 with mostly
     sunny skies. Minimum relative humidity today will be 33%.

     The ODF late morning surface analysis continues to show high pressure nosing 
     into NW Oregon and a thermal trough in the central valley of California.  Pressure
     gradients as of 11am included:  Newport to Salem, 0.9 mb onshore; Salem to Redmond,
     4.8 mb onshore; for a total of 5.7mb on shore.  There is considerable
     gradient stacking to the east.  This is all showing up as an unfavorable 
     northerly transport wind.  Both the RUC and NAM model trajectory forecasts continue
     to show any smoke from the Silverton Hills region headed toward central Lane
     County.  Open field burning opportunities are not likely this afternoon.  

     Sunset tonight: 8:52 pm	
										
THREE-HOURLY DATA:		

                                     2pm     5pm     8pm			
     Temperature:                     68      71      70  			
     Relative Humidity:               39%     36%     41%     			
     Surface Wind Direction:         330     340     330 		
     Surface Wind Speed:               8      11      11    			
     Transport Wind Direction:       010     010     350 
     Transport Wind Speed:             7       9       4  
     Estimated Mixing Height:       5000    5300    1000
     Ventilation Index:               35      48       4

										
EXTENDED DISCUSSION:

     Weak ridging aloft will develop on Wednesday, replaced by a weak trough aloft late
     in the week.  The net effect should be almost nil in the Willamette Valley with
     mostly sunny weather and temperatures a few degrees above average.  Transport winds
     will be generally northerly with occasional shifts to northwesterly in the 
     afternoon but prospects for favorable transport winds are small through the
     weekend.  Long range charts do show more westerly flow in the transport region 
     next Monday.  

EXTENDED FORECAST:	
     
     Wednesday: Sunny and warmer. 84. Calm wind becoming N 8-12 mph. 
     Wednesday Night: Mostly clear, low 52.
     Thursday: Sunny. 86. Wind becoming NW 6-9 mph.  
     Friday: Sunny, with a high near 86.    
     Saturday: Sunny, with a high near 87.    
     Sunday: Sunny, with a high near 85.  
     Monday: Sunny, with a high near 85. 
										
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.