[willamette-fcst] Silverton Hills Forecast - Wed, Jul 14 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT WED JUL 14 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from 10:00am to 7:00pm.
     Prep burning is allowed from 11:00am to 5:00pm with a 50 acre limit. 
     Propane flaming is allowed from 11:00am to 5:00pm.	
									
										
WEATHER DISCUSSION:

     Clear skies last night led to chilly temperatures this morning.  Satellite pictures
     show the Pacific Northwest is virtually cloud free this morning.  The morning Salem
     sounding showed the air mass warmer compared to yesterday at the same time at all
     levels.  In particular, temperatures are about 15 degrees warmer between 3000 and
     5000 feet.  Maximum temperatures today should be quite a bit warmer than yesterday.
     Salem's high temperature today will be near 85 with sunny skies and northerly
     surface winds.  Relative humidity drops to 50% by 11am and the minimum relative
     humidity should drop to 26%.  A surface temperature in the mid 80's will produce a
     maximum mixing height of about 5000 feet today.  

     The morning ODA surface analysis shows that the gradient stacking to the east is
     gone but a relatively strong northerly gradient has set up across the state.  The
     pressure difference from Newport to Redmond is nearly flat while the Portland to
     Medford gradient is about 4mb.  A thermal trough extends from the central Valley of
     California into extreme southwest Oregon.  This is giving a northerly transport to
     the Willamette Valley that will continue all day.  Model trajectory forecasts show
     potential smoke from the Silverton Hills area headed toward Eugene.  

     Salem sunset tonight: 8:51 pm	
							
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 68       79      85      80  			
     Relative Humidity:           51%      34%     26%     35%     			
     Surface Wind Direction:     010      360     010     360 		
     Surface Wind Speed:           8       10      14      10    			
     Transport Wind Direction:   010      360     360     360 
     Transport Wind Speed:         9       10      15       6  
     Estimated Mixing Height:   3000     4700    5000    1000
     Ventilation Index:           27       47      75       6

                               				
										
EXTENDED DISCUSSION:

     The Pacific Northwest is in a fairly normal summertime weather pattern and no
     extremes of weather are likely for the next few days.  Upper air charts show a 
     broad flat ridge today, a zonal or west-to-east flow aloft tomorrow, and a broad
     shallow trough Friday.  None of these features will have much effect on Willamette
     Valley weather other than to produce sunny skies and temperatures near or above
     average.  Maximum mixing heights will gradually lower during the rest of the week
     but should remain fairly high.  There may be a bit of a marine push Friday for a
     potential burning opportunity and long range charts are still showing a more
     westerly transport flow next Monday.  Next week looks cooler with an upper level 
     trough over the region.  

EXTENDED FORECAST:	
     
     Thursday: Sunny, with a high near 87. Calm wind becoming N 7-10 mph. 
     Thursday Night: Mostly clear, with a low around 51. NNE wind 5-10. 
     Friday: Sunny, with a high near 83. NNW wind 5-15 mph. 
     Saturday: Sunny, 85.  
     Sunday: Sunny, 82.   
     Monday: Mostly sunny, 80.    
     Tuesday: Sunny, 81.  
     
										
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.