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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 SEP 07 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are up until 5:30pm tonight.</div>
<div> Prep burning is allowed from 2:00pm to 5:00pm with a 50 acre limit. </div>
<div> Propane flaming is allowed from 2:00pm to 5:00pm. </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Satellite pictures show clouds covering much of the Willamette Valley as of late</div>
<div> morning. As of 11:15am radar showed an area of significant precipitation over</div>
<div> Benton County, moving ENE toward the Silvertion Hills grass growing region.</div>
<div> Radar estimates indicate over an inch of rain has fallen in the coast range west</div>
<div> of Corvallis during the morning hours. However, so far, the Corvallis airport</div>
<div> has picked up just .05 in the last 24 hours. It is likely that rain will</div>
<div> continue into the afternoon for much of the mid Willamette Valley. </div>
<div> </div>
<div> At 11:00am the Salem Airport was reporting a broken cloud layer at 800 feet,</div>
<div> another at 1700 feet and the base of the overcast layer was at 3000 feet.</div>
<div> </div>
<div> This morning's sounding showed some cooling aloft and a fairly unstable atmosphere.</div>
<div> Cloud cover will hold temperatures about 10-14 degrees below average for this time</div>
<div> of year however, and the cool surface temperatures will limit mixing heights</div>
<div> somewhat. Maximum mixing heights will be around 3200 feet this afternoon. </div>
<div> </div>
<div> Pressure gradients, and consequently transport winds, will be quite light today.</div>
<div> While the Newport to Salem gradient was 0.9mb onshore and the Salem to Redmond</div>
<div> gradient was 0.7mb onshore at 11:00am this morning, models indicate gradient</div>
<div> stacking to the east will increase this afternoon. </div>
<div> </div>
<div> For the mid Willamette Valley expect mostly cloudy skies today with scattered</div>
<div> light showers this afternoon. Salem's high temperature today will be near 64</div>
<div> and the minimum relative humidity will drop to about 59%</div>
<div> </div>
<div> Sunset tonight: 7:32 pm </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 2pm 5pm 8pm </div>
<div> Temperature: 63 63 62 </div>
<div> Relative Humidity: 63% 61% 72% </div>
<div> Surface Wind Direction: 200 310 320 </div>
<div> Surface Wind Speed: 6 6 4 </div>
<div> Transport Wind Direction: 250 280 290 </div>
<div> Transport Wind Speed: 5 5 3 </div>
<div> Estimated Mixing Height: 3200 3200 500</div>
<div> Ventilation Index: 16 16 2</div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> Models indicate onshore flow continuing but gradient stacking to the east for at</div>
<div> least the next two days. The upper level trough will move to the east Friday and</div>
<div> temporary ridging will set up over the region for more sunshine. Another trough</div>
<div> moves in over the weekend for cooler temperatures. The details of the trough are</div>
<div> not clear at this point but there is a potential for at least some rain at some</div>
<div> point over the weekend.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Wednesday: Mostly cloudy, a few showers. Wind SW 6 mph. Chance of precip 30%.</div>
<div> Thursday: Partly sunny, with a high near 69. Calm wind becoming west southwest</div>
<div> around 6 mph. </div>
<div> Friday: Mostly sunny, with a high near 71. </div>
<div> Saturday: Partly sunny, with a high near 71. </div>
<div> Sunday: Mostly cloudy, with a high near 70. </div>
<div> Monday: Partly sunny, with a high near 72. </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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