[willamette-fcst] Silverton Hills Forecast - Wed, Jul 28 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT WED JUL 28 2010

BURN ADVISORY:

     Agricultural burning burning is not recommended.
     Prep burning is not allowed. 
     Propane flaming is allowed from 12:00pm to 5:00pm.	
									
										
WEATHER DISCUSSION:

Upper level trough remains off the coast today ever so slowly moving eastward. 
Thundershowers will again build over the Cascades as the upper level flow remains mostly
southerly.  Equipment problems prevented receiving an upper air sounding out of Salem so
we're operating a little in the blind.  However surface pattern shows variable to
northerly wind flow this morning.  Low clouds have again banked up against the Coast
Range
with some clouds moving through the Columbia River corridor and down the north valley.
Above mid level clouds are from some of the thunderstorm blowoff to the east.

Expect low clouds to dissipate with mid clouds to remain somewhat throughout the day. 
Thus temperatures will be a little cooler than yesterday with the high temperature today
in the mid 80s.  With slightly cooler temperatures and some cloud cover, humidities will
be somewhat higher.  Humidity will drop below 50 percent by noon with a minimum around 37
percent around 5 p.m.  Wind flow will be light through the morning, gradually showing a
tendency toward northwesterly this afternoon as the inland temperatures warm up.  With
continuing thunderstorms over the Cascades and not a big increase in onshore pressure
gradients, burning conditions will be somewhat marginal and will need pibals to determine
the strength of onshore flow later today.
     
Sunset tonight: 8:38 pm	
							
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 71       80      84      76  			
     Relative Humidity:           53%      41%     37%     46%     			
     Surface Wind Direction:     350      310     290     270 		
     Surface Wind Speed:           2        5       8       7    			
     Transport Wind Direction:   360      340     300     290 
     Transport Wind Speed:         2        6       8      11  
     Estimated Mixing Height:   2000     3000    4000    1000
     Ventilation Index:            4       18      32      11

EXTENDED DISCUSSION:

Upper level low will gradually move eastward through the remainder of the week and
weekend.  Thunderstorm threat will continue over the Cascades through Friday but as the
low approaches, thunderstorms should move eastward and allow surface pressure gradients
to
increase, giving an improved chance for open burning on Friday.  Eventually the trough
moves to the east over the weekend and gives way to northwesterly flow aloft early next
week.  Temperatures will continue to cool toward the weekend with marine low clouds
likely
moving in over the weekend.



EXTENDED FORECAST:	
     
     Thursday: Mostly sunny, with a high near 82. Calm wind becoming north between 4
     and 7  mph. 
     Thursday Night: Partly cloudy, with a low around 51. North wind around 6 mph
     becoming calm. 
     Friday: Mostly sunny, with a high near 82. Calm wind becoming north northwest
     around 6 mph. 
     Friday Night: Mostly cloudy, with a low around 50.  
     Saturday: Mostly sunny, with a high near 76.  
     Saturday Night: Partly cloudy, with a low around 52.  
     Sunday: Mostly sunny, with a high near 78.  
     Sunday Night: Mostly cloudy, with a low around 52.  
     Monday: Mostly sunny, with a high near 82.  
     Monday Night: Partly cloudy, with a low around 52.  
     Tuesday: Mostly sunny, with a high near 84.  
     
     
     
      
								
				

 
  


										
										
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.