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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 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>WEATHER DISCUSSION:</div>
<div> </div>
<div> Temperatures should top out 10-12 degrees warmer today than yesterday. </div>
<div> </div>
<div> The morning Salem sounding showed the warming nicely. It was warmer</div>
<div> than yesterday morning at all elevations above about 1700 feet. At 5000 feet the</div>
<div> temperature had jumped from 46 degrees yesterday to 62F this morning. Two</div>
<div> distinct inversions showed up on the sounding, one from 1300 to 1800 feet and</div>
<div> another from 2500 to 3400 feet. Models show additional warming aloft for today.</div>
<div> None the less, with mostly sunny skies today surface heating should push surface </div>
<div> temperatures into the upper 80's which will help push mixing heights to</div>
<div> above 3000 feet this afternoon. </div>
<div> </div>
<div> The morning ODF surface analysis shows a well developed thermal trough extending</div>
<div> from California's central Valley to near Cape Blanco, then right along the</div>
<div> Oregon Coast to about Astoria. The thermal trough will shift inland today and be</div>
<div> over the Willamette Valley by late afternoon. Weak surface high pressure is</div>
<div> located just west of northwest Washington. With higher pressure to the north and</div>
<div> lower pressure with the thermal trough moving into the Willamette Valley</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 California to northwest Canada and a trough</div>
<div> in 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, expect any clouds this morning to quickly</div>
<div> dissipate and nearly full sunshine this afternoon. The sun, and the dry</div>
<div> north-northeast winds should help dry fields from recent rains. </div>
<div> </div>
<div> Salem's high temperature today will be near 87. Relative humidity drops to 50%</div>
<div> by 11am. Minimum relative humidity 27%.</div>
<div> </div>
<div> Sunset tonight: 7:41 pm </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 westerly transport flow over the</div>
<div> region. Timing is the key, but at this point it looks like westerly winds will</div>
<div> develop by early afternoon and this could develop into a good burn opportunity.</div>
<div> </div>
<div> An active weather pattern is on tap for the Saturday and into the first part of</div>
<div> next week. A relative quick moving upper level trough will swing down from the</div>
<div> Gulf of Alaska and over the Pacific Northwest beginning late Saturday and move</div>
<div> east of the Rockies by early Monday. This will keep cooler temperatures across</div>
<div> the region for the Labor Day weekend with periodic showers. Models indicate only</div>
<div> a short break before another trough swings down from Alaska early 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>
<div> </div>
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