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<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>9:00 AM PDT TUE SEP 14 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Agricultural burning burning is not recommended.</div>
<div> Prep burning is allowed from 1:00pm to 5:00pm with a 50 acre limit. </div>
<div> Propane flaming is not allowed. </div>
<div> </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> A weak upper level ridge covers western Oregon this morning. To the east a small</div>
<div> but active upper level disturbance is pulling out and to the west a strong but</div>
<div> slow moving upper level low is developing. </div>
<div> </div>
<div> Satellite pictures show low clouds over portions of the Willamette Valley, but</div>
<div> the cloud deck is not as extensive as yesterday. By afternoon the entire valley</div>
<div> should be sunny with temperatures climbing into the low 80's which is about 5</div>
<div> to 7 degrees above the seasonal average for this time of year.</div>
<div> </div>
<div> The morning Salem sounding temperature profile looked similar to yesterday's.</div>
<div> There was a weak inversion between 2200 feet and 2900 feet. Below the inversion</div>
<div> winds were light north-easterly, above light north-westerly. The inversion should</div>
<div> easily mix out and the maximum mixing height today should go above 4000 feet. </div>
<div> </div>
<div> The morning ODF surface analysis shows higher pressure to the north, lower</div>
<div> pressure to the south for northerly winds today. Unfortunately this is not a</div>
<div> favorable direction for burning. Computer models indicate a transition to</div>
<div> southerly winds early this evening, but no indication of any sustained transport</div>
<div> flow with a westerly component for a burn opportunity. Pibals this afternoon</div>
<div> will confirm or deny the modeled winds.</div>
<div> </div>
<div> For the mid Willamette Valley look for mostly sunny skies today with light north</div>
<div> to northwest winds. Salem's high temperature today will be near 81. Relative</div>
<div> humidity drops to 50% by 12pm. Minimum relative humidity 35%.</div>
<div> </div>
<div> Sunset tonight: 7:19 pm </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 69 78 81 73 </div>
<div> Relative Humidity: 61% 42% 35% 48% </div>
<div> Surface Wind Direction: 360 340 360 280 </div>
<div> Surface Wind Speed: 2 3 4 4 </div>
<div> Transport Wind Direction: 350 350 340 340 </div>
<div> Transport Wind Speed: 3 5 5 3 </div>
<div> Estimated Mixing Height: 2500 3300 4500 500</div>
<div> Ventilation Index: 8 16 22 2</div>
<div> </div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> Today may be the last of summer weather for 2010. The upper low to the west will</div>
<div> continue to spin off the coast sending surges of moisture inland until the low</div>
<div> itself finally weakens and moves across the region next Monday.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Wednesday: Mostly cloudy,rain developing by evening. 74. Wind SW 3-8</div>
<div> Thursday: Mostly cloudy, periods of light rain. 76. Wind SW 3-8 </div>
<div> Friday: A 50 percent chance of rain. Mostly cloudy, with a high near 73. </div>
<div> Saturday: A chance of rain. Mostly cloudy, with a high near 70. </div>
<div> Sunday: A chance of rain. Mostly cloudy, with a high near 71. </div>
<div> Monday: A chance of rain. Mostly cloudy, with a high near 71. </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>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
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