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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 02 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from 10:00am to 4:00pm.</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> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Temperatures are on track to reach the mid 80's this afternoon. </div>
<div> </div>
<div> The late morning ODF surface analysis shows that a well developed thermal trough</div>
<div> remains from California's central Valley to near Cape Blanco, then right along</div>
<div> the Oregon Coast to about Astoria. The thermal trough will shift inland later</div>
<div> today and be over the Willamette Valley by late afternoon. </div>
<div> </div>
<div> Transport winds will be generally northerly or north-northeasterly this</div>
<div> afternoon. This is an unfavorable wind direction for open field burning. </div>
<div> </div>
<div> Upper air charts show a ridge from Nevada to northwest Canada and a trough in</div>
<div> the Gulf of Alaska. Both of these features are moving steadily eastward today</div>
<div> with the trough axis forecast to be about 400 miles west of Vancouver Island by</div>
<div> this evening. </div>
<div> </div>
<div> For the mid Willamette Valley today, any cloudiness still left will dissipate</div>
<div> for nearly full sunshine this afternoon. The sun, and the dry north-northeast</div>
<div> winds should help dry fields from recent rains. Salem's high temperature today</div>
<div> will be near 87. Minimum relative humidity this afternoon will dip to 27%. </div>
<div> </div>
<div> Sunset tonight: 7:41 pm</div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 68 81 87 80 </div>
<div> Relative Humidity: 59% 35% 27% 36% </div>
<div> Surface Wind Direction: 020 020 020 020 </div>
<div> Surface Wind Speed: 8 12 12 5 </div>
<div> Transport Wind Direction: 020 040 030 360 </div>
<div> Transport Wind Speed: 8 9 11 9 </div>
<div> Estimated Mixing Height: 2000 2900 3400 5000</div>
<div> Ventilation Index: 16 26 37 45</div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> The trough in the Gulf of Alaska will help kick the thermal trough east of the</div>
<div> Cascades on Friday opening up the door for northwesterly transport flow over the</div>
<div> region. Timing is the key, but at this point it looks like northwesterly winds will</div>
<div> develop by early to mid-afternoon and this could develop into a good burn</div>
<div> opportunity. Models indicate mixing heights reaching 3000 feet by mid-afternoon</div>
<div> as well. </div>
<div> </div>
<div> An active weather pattern remains on tap for the Saturday and into the first</div>
<div> part of next week. A relative quick moving upper level trough will swing down</div>
<div> from the Gulf of Alaska and over the Pacific Northwest beginning late Saturday</div>
<div> and move east of the Rockies by early Monday. This will keep cooler temperatures</div>
<div> across the region for the Labor Day weekend with periodic showers. Models</div>
<div> indicate only a short break before another trough swings down from Alaska early</div>
<div> Tuesday.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Friday: Sunny, with a high near 87. Wind becoming west 7-10 mph. </div>
<div> Saturday: Partly sunny, but a chance of light showers. 77. SSW 5-8 becoming NNW. </div>
<div> Sunday: Partly sunny, but a chance of light showers. 75. </div>
<div> Monday: Partly sunny, with a high near 75. </div>
<div> Tuesday: Mostly cloudy periods of rain, 74. </div>
<div> Wednesday: Partly sunny, with a high near 73. </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>
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