[willamette-fcst] Silverton Hills Forecast - Tue, Jul 06 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST NOON UPDATE
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 AM PDT TUE JUL 06 2010


*** Potential Fire Marshall Conditions due to winds and humidity ***

BURN ADVISORY:

     Agricultural burning is allowed.  Suggested burn times up until 7:00pm.
     Prep burning is not allowed. 
     Propane flaming burning is not allowed.	
																			
WEATHER DISCUSSION:

     Upper air charts show a strong ridge aloft extending from about 600 miles west of
     northern California northward into the Yukon.  This gives a dry northerly or 
     northwesterly flow aloft to the region.  The ODF morning surface analysis shows
     a strong thermal trough extending from the central valley of California northward
     into southwestern Oregon.  There is a strong northerly or northeasterly surface
     pressure gradient. Pressure gradients as of 11am included:  Newport to Salem, 
     0.1 mb onshore; Salem to Redmond, 2.2 mb offshore; Newport to Redmond, 2.1 mb 
     offshore; Eugene to Medford, 4.1 mb northerly; Portland to Eugene, 1.8 mb 
     northerly; and Portland to Medford, 5.9 mb northerly.  Smoke trajectories from
     both the NAM and RUC models continue to show smoke from the Silverton Hills heading
     towards central Lane County. 

     The morning Salem sounding showed an inversion from about 1500 feet 
     to 2800 feet.  This will break with a surface temperature of about 76 degrees 
     which should be reached by 1pm.  

     The limitation on burning today will be winds and humidity.  Fire Marshal 
     burn-ban conditions will likely be met by about 2pm this afternoon.  

     Salem's high temperature today will be near 87 . 
     Relative humidity reaches 50% by 10am. Minimum relative humidity will be near 24% 
 
     Sunset: 8:55 pm	
							
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 69       79      86      82  			
     Relative Humidity:           51%      34%     24%     29%     			
     Surface Wind Direction:     010      020     020     030 		
     Surface Wind Speed:          13       16      17      12    			
     Transport Wind Direction:   020      020     030     020 
     Transport Wind Speed:        12       20      23      10  
     Estimated Mixing Height:   2500     5500    7000    1000
     Ventilation Index:           30      110     161      10
                               				
EXTENDED DISCUSSION:

     Computer models indicate the pattern tomorrow will be similar to today with a 
     dry, offshore flow.  The thermal trough shifts inland late Thursday with onshore
     flow developing but the generally dry, sunny and warm pattern continues through 
     the weekend.  

EXTENDED FORECAST:	
     
     Wednesday: Sunny, with a high near 91. East northeast wind around 9 mph. 
     Wednesday Night: Mostly clear, with a low around 62. East wind between 3 and 8
     mph. 
     Thursday: Sunny, with a high near 94. Calm wind becoming northwest between 6 and
     9  mph. 
     Thursday Night: Partly cloudy, with a low around 60.  
     Friday: Mostly sunny, with a high near 93.  
     Friday Night: Mostly clear, with a low around 57.  
     Saturday: Sunny, with a high near 91.  
     Saturday Night: Mostly clear, with a low around 58.  
     Sunday: Sunny, with a high near 89.  
 

										
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.									
										
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.