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<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>12:00 PM PDT TUE AUG 31 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are now until 6:00pm.</div>
<div> Prep burning is not allowed. </div>
<div> Propane flaming is not allowed. </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Upper air charts show a broad trough covering the western US today. The axis of</div>
<div> the trough remains along the Canadian Rockies, through central Idaho then</div>
<div> curving southwestward to southern California. This leaves the Pacific Northwest</div>
<div> in a generally west-northwesterly flow aloft. This flow is steering a Pacific</div>
<div> weather system at Washington and northwest Oregon.</div>
<div> </div>
<div> Rain began falling early this morning along the northern Oregon coast, and by</div>
<div> late morning had spread to a line from Portland to McMinnville to Pacific City</div>
<div> on the coast. Rain will likely continue to slowly spread southeastward this</div>
<div> afternoon. </div>
<div> </div>
<div> The morning Salem sounding showed that the air mass had warmed somewhat in the</div>
<div> past 24 hours. This will keep mixing heights lower than yesterday when the</div>
<div> maximum mixing height was about 4000 feet. Look for a maximum today of about</div>
<div> 3500 feet. Low level winds measured this morning were southwesterly, veering to</div>
<div> westerly by about 6000 feet above ground level. Computer models suggest that the</div>
<div> a WSW wind direction will continue through this afternoon. Winds and</div>
<div> mixing heights today will be favorable for burning.</div>
<div> </div>
<div> If the rain holds off long enough there may be a window of opportunity between</div>
<div> the time that the mixing heights reach a favorable level and the time that the</div>
<div> rain moves in for some open field burning.</div>
<div> </div>
<div> As of noon the estimated mixing height is 2000 feet with the mixing height</div>
<div> reaching 3000 feet about 3pm. </div>
<div> </div>
<div> Afternoon forecast for the mid-Willamette valley: expect mostly cloudy skies, an</div>
<div> increasing chance of light rain, mainly northern sections. Salem's high</div>
<div> temperature today will be near 69. Minimum relative humidity 55%.</div>
<div> </div>
<div> Sunset tonight: 7:45 pm </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 2pm 5pm 8pm </div>
<div> Temperature: 64 64 60 </div>
<div> Relative Humidity: 60% 67% 81% </div>
<div> Surface Wind Direction: 190 190 220 </div>
<div> Surface Wind Speed: 11 8 8 </div>
<div> Transport Wind Direction: 220 240 200 </div>
<div> Transport Wind Speed: 15 18 11 </div>
<div> Estimated Mixing Height: 2800 3500 1000</div>
<div> Ventilation Index: 42 63 11</div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> After Wednesday expect drier and warmer conditions as a flat upper level ridge</div>
<div> builds over the area. Temperatures should climb to near or slightly above</div>
<div> average for the time of year. Computer models suggest that another upper level</div>
<div> trough will move over the area sometime early in the weekend. Moisture looks</div>
<div> limited but temperatures will likely fall back below average for Saturday,</div>
<div> Sunday and the Labor Day holiday.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Wednesday: Mostly cloudy, showers decreasing. High 74. Wind S 5-9 becomming WNW. </div>
<div> Thursday: Mostly sunny, with a high near 85. North wind between 3 and 10 mph. </div>
<div> Friday: Sunny, with a high near 86. </div>
<div> Saturday: Mostly sunny, with a high near 78. </div>
<div> Sunday: Partly sunny, with a high near 75. </div>
<div> Monday: Partly sunny, with a high near 76. </div>
<div> </div>
<div>Notes: </div>
<div> 1. Mixing height, as used here, is the lowest height at which the</div>
<div> potential temperature exceeds the potential temperature at the surface. </div>
<div> As a practical matter it is the approximate height to which a </div>
<div> smoke plume will rise assuming good ignition, dry fuels, and </div>
<div> winds less than about 15mph. </div>
<div> 2. Transport winds are a layer average through the mixing height, </div>
<div> weighted slightly toward the winds at the top of the layer. </div>
<div> 3. Ventilation Index is the height of the mixing layer times </div>
<div> the transport wind speed divided by 1000. </div>
<div> 4. Surface wind direction is the general expected wind direction. </div>
<div> At a specific point surface winds are highly dependent on </div>
<div> local terrain conditions.</div>
<div> </div>
<div>This forecast is provided under an agreement between the Oregon Department of</div>
<div>Agriculture and the Oregon Department of Forestry. For information contact ODA</div>
<div>at 503-986-4701.</div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
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