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<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>12:00 PM PDT THU SEP 09 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from 10:00am to 5:30pm.</div>
<div> Prep burning is allowed from 1:00pm to 5:00pm with a 50 acre limit. </div>
<div> Propane flaming is allowed from 1:00pm to 5:00pm. </div>
<div> </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Upper air charts show an upper level trough beginning to pull out of the Pacific</div>
<div> Northwest and a weak upper level ridge developing to the northwest. </div>
<div> </div>
<div> The morning Salem sounding was very similar to yesterday's. The main difference</div>
<div> was that it indicated slightly drier air between 1500 and 4000 feet. It is still</div>
<div> conditionally unstable and in spite of the upper trough moving east models are</div>
<div> showing very little warming aloft for significant stabilization. Consequently</div>
<div> mixing heights will be quite high today, peaking near 6000 feet. </div>
<div> </div>
<div> Transport wind directions on the morning sounding were about 290 at 10. Computer</div>
<div> models suggest a generally westerly flow continuing in the transport region</div>
<div> during the day today. </div>
<div> </div>
<div> With rain the past few days and mostly cloudy skies this morning and high</div>
<div> humidities, dry fields will be an issue for open field burning this afternoon.</div>
<div> If any growers feel their fields are dry enough to burn today they need to make</div>
<div> that known to field burning staff. </div>
<div> </div>
<div> Gradient stacking to the east will also be an issue this afternoon. Pressure</div>
<div> gradients as of 11am included: Newport to Salem, 1.2 mb onshore; Salem to</div>
<div> Redmond, 2.6 mb onshore. The the latest RUC computer model shows the east-west</div>
<div> pressure profile becoming marginally favorable this afternoon while the NAM is</div>
<div> marginally unfavorable. We will monitor this through the day.</div>
<div> </div>
<div> For the mid Willamett Valley today expect mostly cloudy skies. There may be a</div>
<div> few showers, especially toward the Cascade foothills this morning. Winds will be</div>
<div> from the south-southwest during the morning becoming more west-southwesterly</div>
<div> during the afternoon. Salem's high temperature today will be near 68. Minimum</div>
<div> relative humidity will be near 51%.</div>
<div> </div>
<div> Sunset tonight: 7:28 pm </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 2pm 5pm 8pm </div>
<div> Temperature: 67 67 60 </div>
<div> Relative Humidity: 54% 52% 67% </div>
<div> Surface Wind Direction: 220 230 260 </div>
<div> Surface Wind Speed: 5 5 5 </div>
<div> Transport Wind Direction: 240 260 250 </div>
<div> Transport Wind Speed: 13 14 6 </div>
<div> Estimated Mixing Height: 5800 6000 500</div>
<div> Ventilation Index: 75 84 3</div>
<div> </div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> Latest computer models still show a ridge developing late this afternoon and</div>
<div> evening over the region. There will be minor disturbances moving through the</div>
<div> ridge, but at this point it still does not look like there will be any rain this</div>
<div> far south. Temperatures will remain cooler than average into the weekend. The</div>
<div> latest NAM model continues to show gradient stacking to the east both tomorrow</div>
<div> and Saturday.</div>
<div> </div>
<div> Longer range charts have turned more optimistic with ridging building the first</div>
<div> part of next week for drier weather and temperatures returning to near average</div>
<div> for mid September.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Tomorrow: Partly sunny, 72. Wind becoming NNW 5-8 mph. </div>
<div> Saturday: Partly sunny, 74. Wind becoming NW 6 mph. </div>
<div> Sunday: Mostly cloudy, with a high near 74. </div>
<div> Monday: Partly sunny, with a high near 80. </div>
<div> Tuesday: Partly sunny, with a high near 79. </div>
<div> Wednesday: Partly sunny, with a high near 77. </div>
<div> </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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