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<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>9:00 AM PDT FRI SEP 10 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from 1:00pm to 5:30pm.</div>
<div> Prep burning is not allowed due to staff unavailability. </div>
<div> Propane flaming is not allowed due to staff unavailability. </div>
<div> </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Weak upper level ridge will build into the state this morning but quickly slide</div>
<div> to the east later today and tonight as a minor trough moves in. Weather pattern</div>
<div> is fairly innocuous with little pressure gradient and little wind.</div>
<div> </div>
<div> Morning sounding shows a fairly strong surface-based temperature inversion up to</div>
<div> a few hundred feet then a modestly stable temperature sounding above. Afternoon</div>
<div> heating will gradually lift mixing levels up into the 4000 - 5000 ft range.</div>
<div> </div>
<div> Expect a mostly fair day with morning low clouds and fog slowly giving way to</div>
<div> afternoon sunshine as clouds clear from the south to north. Pressure gradients</div>
<div> are weak this morning with the Newport to Salem gradient .4 mb onshore and the</div>
<div> Salem to Redmond gradient .9 mb offshore. With surface heating today that</div>
<div> pressure gradient will become increasingly onshore with fairly even stacking</div>
<div> between the Coast Range and Cascades.</div>
<div> </div>
<div> Salem's high temperature today will be near 72. Relative humidity drops to 50%</div>
<div> by 1pm. Minimum relative humidity 39%. Wind flow will be light and variable</div>
<div> during the morning becoming northwesterly in the afternoon. Some models show a</div>
<div> nearly northerly flow. Will have to monitor with pibals this afternoon to</div>
<div> determine if there will be any usuability to the wind for burning.</div>
<div> </div>
<div> Sunset tonight: 7:27 pm </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 62 69 72 65 </div>
<div> Relative Humidity: 65% 45% 39% 54% </div>
<div> Surface Wind Direction: 190 300 340 310 </div>
<div> Surface Wind Speed: 3 5 6 5 </div>
<div> Transport Wind Direction: 230 330 320 340 </div>
<div> Transport Wind Speed: 5 7 7 7 </div>
<div> Estimated Mixing Height: 2200 4200 4800 1000</div>
<div> Ventilation Index: 11 29 34 7</div>
<div> </div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> Weak troughing moves in over the state early tomorrow as an upper level low</div>
<div> moves by to the north. Trough then moves by to the east during the afternoon.</div>
<div> This will have little effect on the weather with another pleasant warm day and</div>
<div> mostly sunny skies after some morning low clouds. Pressure gradients will be</div>
<div> mostly weak with a slight onshore flow in the afternoon.</div>
<div> </div>
<div> Another minor trough moves by to the north on Sunday with a ridge moving in</div>
<div> later Monday and Tuesday. Temperatures will gradually warm up through the</div>
<div> extended period. Upper ridge generally holds through the period as well. Pressure</div>
<div> gradients and wind flow will be rather weak with light northerly to offshore</div>
<div> flow in the morning and northerly to onshore flow in the afternoon.</div>
<div> </div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Saturday: Partly sunny, with a high near 74. North northwest wind between 3 and</div>
<div> 8 mph. </div>
<div> Saturday Night: Partly cloudy, with a low around 48. North northwest wind</div>
<div> between 4 and 7 mph becoming calm. </div>
<div> Sunday: Partly sunny, with a high near 77. Calm wind becoming north northwest</div>
<div> between 4 and 7 mph. </div>
<div> Sunday Night: Partly cloudy, with a low around 51. </div>
<div> Monday: Sunny, with a high near 77. </div>
<div> Monday Night: Mostly clear, with a low around 49. </div>
<div> Tuesday: Sunny, with a high near 80. </div>
<div> Tuesday Night: Mostly clear, with a low around 50. </div>
<div> Wednesday: Mostly sunny, with a high near 79. </div>
<div> Wednesday Night: Partly cloudy, with a low around 52. </div>
<div> Thursday: Mostly sunny, with a high near 80. </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </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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