[willamette-fcst] Silverton Hills Forecast - Mon, Jul 12 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON JUL 12 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from 11:00am to 7:00pm.
     Prep burning is allowed from 11:00am to 5:00pm with a 100 acre limit. 
     Propane flaming is allowed from 11:00am to 5:00pm.	
									
										
WEATHER DISCUSSION:

     A fairly active upper disturbance for mid July is moving across British Columbia
     today.  This has thickened the marine layer and brought clouds and cooler air into
     the Willamette Valley.  Satellite pictures show a solid cloud deck from about
     central Douglas County northward through the Willamette Valley and across all of
     western Washington.  The clouds extend at least 200 miles offshore to the west.
     The morning Salem weather balloon sounding shows the cloud layer fairly thin,
     extending from about 2200 feet to about 3000 feet. However the surface pressure
     pattern should continue strong onshore making it difficult for the clouds to burn
     off.  Expect clouds through early afternoon, then partly cloudy skies late 
     afternoon, finally clearing early evening.   Salem's high temperature today will 
     be near 75.  Relative humidity drops to 50% by 11am.  Minimum relative 
     humidity today will be about 36%.

     The morning sounding showed a strong inversion from 3200 feet to 4200 feet.
     Temperatures will not warm enough to break this inversion and the maximum mixing
     height today will be about 3700 feet.  Transport winds will be mostly north-
     northwesterly throughout the day.  With the northerly component to transport winds 
     there does not appear to be an opportunity for open field burning today.  

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

                                 11am     2pm     5pm     8pm			
     Temperature:                 68       72      75      68  			
     Relative Humidity:           53%      43%     36%     44%     			
     Surface Wind Direction:     340      320     320     310 		
     Surface Wind Speed:           9       11      16      15    			
     Transport Wind Direction:   350      340     330     340 
     Transport Wind Speed:         5        5      12       6  
     Estimated Mixing Height:   3200     3300    3700    1300
     Ventilation Index:           16       16      44       8
										
EXTENDED DISCUSSION:

    Low clouds will fill back in tonight and tomorrow morning as another upper 
    disturbance swings through to the north and maintains the moderate to strong
    onshore flow.  As this moves east a little more sunshine is likely tomorrow 
    afternoon.  A flat upper ridge moves in Wesnesday that should give more sunshine.  
    The rest of the week should see a flat westerly flow aloft with just minor upper 
    level rippels moving through - the main effect will be areas of morning low clouds
    with afternoon sunshine and temperatures near or slightly above average.  

EXTENDED FORECAST:	
     
     Tuesday: Morning clouds then partly sunny, with a high near 75. NNW wind 5 to
        15 mph, with gusts to about 20 mph. 
     Tuesday Night: Mostly cloudy, with a low around 49. 
     Wednesday: Mostly sunny, with a high near 84. Calm wind becoming north-northwest
        between 7 and 10  mph. 
     Wednesday Night: Mostly clear, with a low around 52.  
     Thursday: Sunny, high 86.  
     Thursday Night: Mostly clear, with a low around 51.  
     Friday: Sunny, high 86.  
										
										
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.