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<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>12:00 PM PDT WED SEP 01 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from now until 4:00pm.</div>
<div> Prep burning is not allowed. </div>
<div> Propane flaming is not allowed. </div>
<div> </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Satellite pictures show the thickest clouds have now moved into the southern</div>
<div> Willameete Valley as of late morning. Some breaks in the clouds are showing up</div>
<div> over the northern coast range and southward into Polk and Marion counties.</div>
<div> Temperatures are running 5 or 6 degrees warmer than yesterday at the same time</div>
<div> across the northern Willamette Valley. </div>
<div> </div>
<div> The late morning ODF surface analysis show higher pressure beginning to build</div>
<div> off the Washington coast, but surface wind directions is still southerly at most</div>
<div> valley locations. Surface winds will eventually shift to northerly but right now</div>
<div> that looks like it won't happen until this evening.</div>
<div> </div>
<div> The morning Salem sounding showed warming from the surface to above 14,000 feet</div>
<div> and with warmer air aloft, even with surface heating, mixing heights will be</div>
<div> suppressed today. Best estimate is maximum mixing heights not quite reaching</div>
<div> 3000 feet. </div>
<div> </div>
<div> With low mixing heights and an unfavorable southerly wind direction through the</div>
<div> afternoon conditions do not look favorable for open field burning today. </div>
<div> </div>
<div> For the mid Willamette Valley expect partly to mostly cloudy skies this</div>
<div> afternoon. Salem's high temperature today will be near 73, minimum relative</div>
<div> humidity 53%.</div>
<div> </div>
<div> Sunset tonight: 7:43 pm </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 2pm 5pm 8pm </div>
<div> Temperature: 71 73 66 </div>
<div> Relative Humidity: 61% 53% 63% </div>
<div> Surface Wind Direction: 200 140 350 </div>
<div> Surface Wind Speed: 6 4 5 </div>
<div> Transport Wind Direction: 200 190 250 </div>
<div> Transport Wind Speed: 6 6 5 </div>
<div> Estimated Mixing Height: 2500 2900 1000</div>
<div> Ventilation Index: 15 17 5</div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> *** Latest computer models now suggest a possible ***</div>
<div> *** burn opportunity Friday afternoon. ***</div>
<div> </div>
<div> This morning was the final surge of moisture into the Pacific Northwest for the</div>
<div> next couple of days. High pressure will quickly build offshore tonight and shift</div>
<div> inland later tomorrow for a quick warm-up. Temperatures tomorrow will jump on</div>
<div> the order of 15 degrees compared to today. At this point it appears that</div>
<div> transport wind directions will be northerly and thus unfavorable for burning</div>
<div> Thursday. </div>
<div> </div>
<div> By late Friday the ridge over the region begins to shift east as another upper</div>
<div> level trough approaches from the Pacific. This should bring cooler weather to</div>
<div> the mid Willamette valley once again this weekend, although not as cool as the</div>
<div> past couple of days. </div>
<div> </div>
<div> Latest computer models are suggesting a marine push ahead of the trough Friday</div>
<div> afternoon for a possible burn opportunity. This is a change from earlier</div>
<div> forecasts.</div>
<div> </div>
<div> There is a potential for some light rain over the weekend, but moisture appears</div>
<div> quite limited. Longer range models indicate a second trough aproaching early</div>
<div> next week.</div>
<div> </div>
<div>EXTENDED FORECAST:</div>
<div> </div>
<div> Thursday: Morning low clouds or fog, otherwisesunny. 85. N 5-10 mph. </div>
<div> Friday: Sunny, with a high near 87. N 5-10 g 15 mph becomming westerly in the</div>
<div> afternoon. </div>
<div> Saturday: Partly 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 75. </div>
<div> Tuesday: Partly sunny, with a high near 74. </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>
<div> </div>
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