[willamette-fcst] Silverton Hills Forecast - Thu, Jul 15 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT THU JUL 15 2010

BURN ADVISORY:

Recommended burn times for agricultural burning are from 12:00pm to 7:00pm.
Prep burning is allowed from 12:00pm to 2:00pm with a 50 acre limit. 
Propane flaming is allowed from 12:00pm to 5:00pm.	
										
WEATHER DISCUSSION:

Skies were sunny this morning across the interior of Oregon and Washington with high
pressure still in control of the weather pattern.  Visible satellite imagery showed low
clouds along the entire coastal strip, with pressure gradients beginning to turn more
onshore.  Temperatures across the Willamette Valley are running about 5-10 degrees warmer
than 24 hours ago.  The air aloft is also warmer than yesterday, so mixing heights will
likely not reach 3000 feet until the afternoon.

A weak upper-level trough is forecast to move across southern British Columbia today and
flatten the broad ridge of high pressure over the Pacific Northwest.  That will shift the
surface thermal trough, which stretched from central Washington to southwestern Oregon
this morning, east of the Oregon Cascades.  A northwesterly marine push is forecast this
evening, which should cap high temperatures in the northern Willamette Valley in the mid
to upper 80s (similar to Wednesday).  Highs in the south valley will likely approach 90
degrees.

TODAY’S FORECAST:

Sunny and warm.  Light north winds turning northwesterly and increasing by this evening to
5-15 mph.  Salem's high temperature today will be near 86 degrees.  Relative humidity
drops to 50% by 10am with a minimum of 29%.

Sunset tonight: 8:56 pm
	
										
THREE-HOURLY DATA:		

                                 11am     2pm     5pm     8pm			
     Temperature:                 76       83      86      78  			
     Relative Humidity:           45%      36%     29%     39%     			
     Surface Wind Direction:     010      360     360     320 		
     Surface Wind Speed:           7        7       8       9    			
     Transport Wind Direction:   010      360     340     330 
     Transport Wind Speed:         8        8       8      12  
     Estimated Mixing Height:   2000     3000    4000    1500
     Ventilation Index:           16       24      32      18
                           				
										
EXTENDED DISCUSSION:

A weak upper-level trough is forecast to carve out over the Pacific Northwest with
increasing onshore flow and cooler temperatures.  Conditions appear as if they will remain
dry with the exception of possible morning drizzle, mainly from the coast range westward.

EXTENDED FORECAST:	
     
Friday: Sunny but cooler.  High near 83. Wind: NW 5-15 mph. 
Friday Night: Increasing clouds.  Low near 51. Evening NW wind 5-15 mph
              decreasing overnight.
Saturday: Mostly sunny.  High near 80. Wind: NW 5-15 mph in the afternoon. 
Saturday Night: Mostly cloudy.  Low near 51.  
Sunday: Morning clouds, then mostly sunny.  High near 79.  
Monday: Morning clouds, then partly sunny.  High near 77.  
Tuesday: Morning clouds, then partly sunny.  High near 77.  
Wednesday: Morning clouds, then partly sunny.  High near 78.  
										
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.