[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
12:00 PM PDT MON JUL 12 2010

BURN ADVISORY:

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

     A fairly active upper disturbance for mid July is moving across British Columbia
     today.  This thickened the marine layer last night and brought clouds and 
     cooler air into the Willamette Valley. The morning Salem sounding showed
     temperatures about 10 degrees cooler than yesterday at the same time up to 
     about 3000 feet.  As 11am today surface temperatures were running 10 to 15 
     degrees cooler than 11am yesterday. 

     Late morning satellite pictures show a fairly solid cloud deck from about
     central Douglas County northward through the Willamette Valley and across most of
     western Washington.  The clouds extend at least 200 miles offshore to the west.
     The morning sounding showed this cloud layer to be 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.  Pressure gradients as of 11am included:  Newport to Salem, 1.1 mb onshore;
     Salem to Redmond, 7.6 mb onshore for considerable gradient stacking to the east. 

     Expect clouds through early afternoon, then partly cloudy skies late 
     afternoon, finally clearing early evening.   Salem's high temperature today will
     be in the low 70s.  Relative humidity reaches 50% shortly after noon. Minimum
     relative humidity will be near 38%  
  
     One more item from the morning sounding:  it 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.  Trajectory models 
     show 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:		

                                     2pm     5pm     8pm			
     Temperature:                     67      69      65  			
     Relative Humidity:               49%     42%     47%     			
     Surface Wind Direction:         320     330     320 		
     Surface Wind Speed:              10      12      15    			
     Transport Wind Direction:       340     330     340 
     Transport Wind Speed:             5      12       6  
     Estimated Mixing Height:       3300    3700    1300
     Ventilation Index:               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: Partly sunny, with a high near 75. North northwest wind between 5 and
     14 mph, with gusts as high as 20 mph. 
     Wednesday: Mostly sunny, with a high near 84. Calm wind becoming north northwest
     between 7 and 10  mph.  
     Thursday: Sunny, with a high near 86.  
     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.