[willamette-fcst] Silverton Hills Forecast - Mon, Jul 19 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON JUL 19 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from 12:00pm to 7:00pm.
     Prep burning is not allowed. 
     Propane flaming is not allowed.	
									
										
WEATHER DISCUSSION:

     Typical mid-July weather is on the menu for today in the Willamette Valley. 
     Upper level flow is west-northwesterly behind an upper level disturbance that
     pushed across southern Alberta last night.  Low level flow is onshore with a
     pressure gradient of about 4.5 millibars between the coast and central Oregon. 
     Satellite pictures show marine clouds covering all of the Willamette Valley this
     morning.  Just one aircraft report available so far today from 8 miles
     north of Eugene and it indicates the top of the overcast layer there is about 2200
     feet.  The morning Salem sounding shows the tops of the clouds are at about
     2800 feet in the mid valley.  In either case the clouds shoud break up this
     afternoon for sunshine and temperatures in the mid to upper 70's - just a few
     degrees below average.  For Salem and the Silverton Hills expect morning clouds,
     afternoon sunshine and a high temperature of 78.  Minimum Relative humidity
     drops to 50% by noon and the minimum relative humidity today will be 36%. 
     Sunset tonight: 8:47 pm.

     The morning Salem sounding showed a temperature profile very similar to
     yesterday morning.  Model forecasts indicate slight warming aloft during the day
     today.  Modifying the sounding based on this warming and using a high of 78
     gives a maximum mixing height of 3500 feet by late afternoon, but it will be at
     least mid-afternoon before the mixing height gets above 3000 feet.   Transport
     winds today will stay northerly and model smoke trajectory forecasts indicate
     mid-Marion county smoke would head south toward Eugene.      
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 63       71      77      74  			
     Relative Humidity:           58%      44%     36%     43%     			
     Surface Wind Direction:     010      360     360     330 		
     Surface Wind Speed:           8        9      11      10    			
     Transport Wind Direction:   010      010     010     010 
     Transport Wind Speed:         5       10      10      13  
     Estimated Mixing Height:   1900     2100    3500     500
     Ventilation Index:           10       21      35       6

                               				
										
EXTENDED DISCUSSION:


     Another upper level disturbance develops and moves in from the northwest tomorrow.
     This will serve to deepen the marine layer Tuesday makeing for a slower
     burn-off of clouds.  This disturbance pulls out Wednesday with a northwesterly
     flow aloft developing.  This should give more afternoon sun and warmer
     temperatures.  Models then indicate broad, flat ridging through the rest of the
     week for dry weather and temperatures near or slightly above average.  The
     pattern favors persistent northerly transport winds and burning opportunities are 
     not likely.


EXTENDED FORECAST:	
     
     Tuesday: Morning clouds then partly sunny, high 80. NNW wind between 5 and 9 mph. 
     Tuesday Night: Mostly cloudy, low 52. Wind NNW 6-10 decreasing.
     Wednesday: Mostly sunny, with a high near 83. Light winds early, becoming NW 8-12
        with higher gusts.
     Wednesday Night: Partly cloudy, with a low around 52.  
     Thursday: Mostly sunny, with a high near 80.  
     Friday: Mostly sunny, 83.  
     Saturday: Mostly sunny, 82.  
     Sunday: 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.