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<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>9:00 AM 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 low over north-central Washington this</div>
<div> morning with a trough extending southwest with its axis just east of the Cascade</div>
<div> crest. This will all move gradually eastward this afternoon for a slowly</div>
<div> stabilizing airmass. Radar indicates most showers are over and east of the</div>
<div> mountains this morning, but there still could be a few scattered showers in the</div>
<div> foothills through this morning. </div>
<div> </div>
<div> The morning Salem sounding looked very similar to yesterday's. The main</div>
<div> difference is that it was slightly drier 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 this morning are about 290 at 10. Computer models</div>
<div> suggest a generally westerly flow continuing in the transport region during the</div>
<div> day today.</div>
<div> </div>
<div> Impediments to open field burning are mainly the wet fields. The Salem</div>
<div> airport picked up .12 inches of rain yesterday. Cloud cover and high humidities</div>
<div> will not be conducive to much drying today. </div>
<div> </div>
<div> Gradient stacking to the east will also be an issue. Pressure gradients as of</div>
<div> 8am included: Newport to Salem, 0.8 mb onshore and Salem to Redmond, 1.9</div>
<div> onshore. The RUC computer model shows the east-west pressure profile becoming</div>
<div> favorable this afternoon while the NAM does not. We will monitor this through</div>
<div> 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> 11am 2pm 5pm 8pm </div>
<div> Temperature: 63 67 67 60 </div>
<div> Relative Humidity: 65% 54% 52% 67% </div>
<div> Surface Wind Direction: 200 220 230 260 </div>
<div> Surface Wind Speed: 5 5 5 5 </div>
<div> Transport Wind Direction: 230 240 260 250 </div>
<div> Transport Wind Speed: 10 13 14 6 </div>
<div> Estimated Mixing Height: 3500 5800 6000 500</div>
<div> Ventilation Index: 35 75 84 3</div>
<div> </div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> A weak ridge develops late this afternoon and evening over the region. There will be</div>
<div> minor disturbances moving through the ridge, but at this point it does not look</div>
<div> like there will be any rain this far south. Temperatures will remain cooler than</div>
<div> average into the weekend. The NAM model indicates gradient stacking to the east</div>
<div> both tomorrow 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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