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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 22 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from 1:00pm to 5:00pm.</div>
<div> Prep burning is allowed from noon to 5:00pm with a 50 acre limit. </div>
<div> Propane flaming is allowed from noon to 5:00pm. </div>
<div> </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> An upper level trough moving mainly through California is slowly pulling east</div>
<div> with weak high pressure aloft beginning to build over the eastern Pacific Ocean.</div>
<div> Satellite pictures as of late morning show a mixture of clouds and sun over the</div>
<div> Willamette Valley with thicker cloud cover over the western Cascade foothills.</div>
<div> Temperatures are running very close to where they were yesterday at the same</div>
<div> time. </div>
<div> </div>
<div> The morning Salem sounding was very similar to the sounding yesterday morning.</div>
<div> There was an unusually persistent inversion aloft with a base that has been near</div>
<div> 7500 feet for the past couple of days. Today that inversion is between about</div>
<div> 7800 feet and 8100 feet. Below this feature winds light light but favored</div>
<div> northerly, above winds were westerly. </div>
<div> </div>
<div> The pressure gradient profile is marginally favorable at 11am. As of 11:00 am</div>
<div> gradients included: Newport to Salem, 1.2 mb onshore; Salem to Redmond, 0.2 mb</div>
<div> onshore Computer models indicate an increasing onshore gradient. We will monitor</div>
<div> the pressure pattern to see if it remains favorable this afternoon. </div>
<div> </div>
<div> Smoke trajectory forecasts from the Air Resources Lab based on this morning's</div>
<div> NAM run indicate a favorable easterly direction for smoke movement this</div>
<div> afternoon.</div>
<div> </div>
<div> A pibal sounding is scheduled for 1:00 pm this afternoon to confirm wind direction.</div>
<div> </div>
<div> For the mid Willamette Valley expect partly</div>
<div> cloudy skies this afternoon. Temperatures will be a bit below average for this</div>
<div> time of year and winds will be light westerly.</div>
<div> </div>
<div> Salem's high temperature today will be near 70.</div>
<div> Relative humidity drops to 50% by 12pm. Minimum relative humidity 41%.</div>
<div> </div>
<div> Sunset tonight: 7:04 pm </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 2pm 5pm 8pm </div>
<div> Temperature: 68 68 60 </div>
<div> Relative Humidity: 47% 45% 62% </div>
<div> Surface Wind Direction: 260 270 260 </div>
<div> Surface Wind Speed: 4 6 5 </div>
<div> Transport Wind Direction: 240 240 290 </div>
<div> Transport Wind Speed: 6 6 7 </div>
<div> Estimated Mixing Height: 7800 7800 1000</div>
<div> Ventilation Index: 47 47 7</div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> The morning runs of both the NAM and GFS showed no rain for Salem with the weak</div>
<div> cold front that will move through the area tomorrow. Models have been</div>
<div> flip-flopping on this for the past couple of days. If any rain does fall it will</div>
<div> likely be light.</div>
<div> </div>
<div> Models continue showing a strong low in the Gulf of Alaska</div>
<div> late in the weekend and into the first part of next week. But the low will be</div>
<div> far enough off the coast that moisture rotating around it will stay well west of</div>
<div> the Pacific Northwest for fair weather and temperatures near seasonal average</div>
<div> into early next week.</div>
<div> </div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Thursday: Mostly cloudy, slight chance of rain, 66. SSW 5-10. </div>
<div> Friday: Mostly sunny, with a high near 77. S 5.</div>
<div> Saturday: Mostly sunny, with a high near 80. W 5. </div>
<div> Sunday: Partly sunny, with a high near 73. W 4. </div>
<div> Monday: Partly sunny, with a high near 78. </div>
<div> Tuesday: Partly sunny, with a high near 75. </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>
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