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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 21 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from noon 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>WEATHER DISCUSSION:</div>
<div> </div>
<div> Satellite pictures show patchy mid and high level clouds streaming across the</div>
<div> region as of late morning. These are from an upper level disturbance now off the</div>
<div> southern Oregon coast. This will move into northern California with no further</div>
<div> effect on mid Willamette Valley weather.</div>
<div> </div>
<div> The morning Salem sounding showed a fairly unstable atmosphere up to above </div>
<div> 7000 feet. There is an inversion from 7400 to 8000 feet with stable </div>
<div> conditions above. However, daytime heating should easily push the mixing </div>
<div> height to the inversion level and maximum mixing heights this afternoon </div>
<div> should be about 7200 feet. </div>
<div> </div>
<div> Winds on the morning Salem sounding were light and variable with a tendency </div>
<div> to northerly up to about 5000 feet. Computer models today are consistent in </div>
<div> showing a northerly wind throughout the day today. Trajectory forecasts bring </div>
<div> any smoke from mid Marion County into central Lane County near Eugene and </div>
<div> Springfield. </div>
<div> </div>
<div> For the mid Willamette Valley expect mostly sunny skies with a few high clouds</div>
<div> from time to time. Winds will be light northerly becoming light northwesterly</div>
<div> later this afternoon. Salem's high temperature today will be near 70. Relative</div>
<div> humidity drops to 50% by 1pm. Minimum relative humidity 41%.</div>
<div> </div>
<div> Sunset tonight: 7:06 pm </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 2pm 5pm 8pm </div>
<div> Temperature: 64 66 60 </div>
<div> Relative Humidity: 56% 48% 62% </div>
<div> Surface Wind Direction: 350 350 310 </div>
<div> Surface Wind Speed: 5 6 5 </div>
<div> Transport Wind Direction: 360 360 330 </div>
<div> Transport Wind Speed: 10 10 10 </div>
<div> Estimated Mixing Height: 7100 7200 500</div>
<div> Ventilation Index: 71 72 5</div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> Tomorrow will be another drying day, however there likely will be areas of</div>
<div> morning fog which may deposit some dew. There has been a new run of both the NAM</div>
<div> and GFS models since the morning forecast. The NAM model is now dry for Thursday</div>
<div> while the GFS is still showing some precip. </div>
<div> </div>
<div> Friday will see minor ridging for dry weather. Longer range, models have</div>
<div> completely backed off on precip for the weekend. </div>
<div> </div>
<div> Given the flip-flops we have low confidence in forecasts from Thursday on.</div>
<div> However, if Thursday remains dry, Thursday, Friday, and Saturday all have</div>
<div> potential for some open field burning.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Wednesday: Areas of fog before 11am. Otherwise, partly sunny, with a high near</div>
<div> 72. Calm wind becoming west northwest between 5 and 8 mph. </div>
<div> Thursday: Mostly cloudy, slight chance of light rain, 67. SSW 6-8 mph. </div>
<div> Friday: Partly sunny, with a high near 74. </div>
<div> Saturday: Mostly sunny, with a high near 76. </div>
<div> Sunday: Slight chance of showers. Mostly cloudy, with a high near 72. </div>
<div> Monday: A chance of rain. Mostly cloudy, with a high near 74. </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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