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<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>9:00 AM PDT WED AUG 25 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Agricultural burning burning is not recommended.</div>
<div> Prep burning is not allowed. </div>
<div> Propane flaming is not allowed. </div>
<div> </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> One more hot day is in store for the Willamette Valley then temperatures cool</div>
<div> significantly for several days. Satellite pictures this morning show low clouds</div>
<div> banked up along the coast from northern Washington to Cape Blanco Oregon.</div>
<div> Otherwise skies are clear except for smoke from wildfires. A trail of smoke from</div>
<div> the View Lake complex about 50 miles east of Estacada shows up nicely and is</div>
<div> affecting the northeast portion of the Willamette Valley. </div>
<div> </div>
<div> The morning ODF surface analysis shows a thermal trough from the central valley</div>
<div> of California northward through the Willamette Valley continuing into the Puget</div>
<div> Sound. Yesterday that trough was along the coastline and late this afternoon or</div>
<div> early this evening it will shift east of the Cascades. As the trough shifts,</div>
<div> cooler marine air will enter the valley. At 8am this morning the Newport to</div>
<div> Salem gradient was 1.0mb onshore while the Redmond to Salem gradient was 3.5mb</div>
<div> offshore. </div>
<div> </div>
<div> Also on the weather maps this morning is a weak, summer-time cold front extending</div>
<div> southwestward from the northern tip of Vancouver Island. This front is</div>
<div> associated with a fairly strong (for this time of year) upper level low in the</div>
<div> Gulf of Alaska. This front will sweep across the Willamette Valley overnight</div>
<div> tonight to further deepen the marine layer and perhaps produce some drizzle or</div>
<div> light rain by tomorrow morning. </div>
<div> </div>
<div> The morning Salem sounding shows a series of inversions from the surface to</div>
<div> abuot 2800 feet. At balloon launch time the temperature at ground level was 60F,</div>
<div> but the balloon reported that the temperature at 2800 feet was a much warmer</div>
<div> 78F. Temperatures were generally 5 to 8 degrees warmer than yesterday moorning</div>
<div> from the surface all the way to about 10,000 feet. </div>
<div> </div>
<div> With the strong inversion it will be difficult to get very high mixing heights.</div>
<div> The maximum mixing height will be around 3100 feet at about 5pm this afternoon.</div>
<div> </div>
<div> Computer models indicate that while the thermal trough will move east of the</div>
<div> valley late this afternoon finding a westerly component to the winds will be</div>
<div> difficult. The RUC model shows transport winds at 320 to 330 degrees late this</div>
<div> afternoon, while the NAM model shows transport winds between 330 and 340</div>
<div> degrees. The Portland WRF model is the most optimistic with respect to wind</div>
<div> direction showing transport winds coming around to about 310 degrees at 6pm this</div>
<div> evening. </div>
<div> </div>
<div> Pibals through the afternoon will determine if a burning opportunity develops</div>
<div> ahead of the transition to cooler weather. </div>
<div> </div>
<div> For the mid Willamette Valley expect sunny and hot weather again today. Salem's</div>
<div> high temperature will be near 94. Relative humidity drops to 50% by 9am.</div>
<div> Minimum relative humidity 20%. Sunset tonight: 7:56 pm</div>
<div> </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 80 90 94 81 </div>
<div> Relative Humidity: 35% 25% 20% 34% </div>
<div> Surface Wind Direction: 010 360 320 270 </div>
<div> Surface Wind Speed: 5 5 7 6 </div>
<div> Transport Wind Direction: 340 340 330 290 </div>
<div> Transport Wind Speed: 2 5 5 5 </div>
<div> Estimated Mixing Height: 1000 2200 3100 500</div>
<div> Ventilation Index: 2 11 16 2</div>
<div> </div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> The upper level low in the Gulf of Alaska will drop southeastward and settle in</div>
<div> over the Pacific Northwest through the weekend. This means cooler than average</div>
<div> temperatures and some unsettled weather. Low level flow will be onshore.</div>
<div> Disturbances rotating through the bottom of the trough will periodically deepen</div>
<div> the marine layer over the valley for possible drizzle or showers. Timing of</div>
<div> these disturbances is in doubt, but right now it looks like Friday will be</div>
<div> mainly dry, with a better chance of precipitation later Saturday and Sunday.</div>
<div> </div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Thursday: Mostly cloudy, a little morning drizzle. High 79. Winds NW 7-10 mph.</div>
<div> Calm wind becoming north northwest between 7 and 10 mph. </div>
<div> Friday: Partly sunny, 72. NW 5-8.</div>
<div> Saturday: Mostly cloudy, chance of showers. High 70. </div>
<div> Sunday: Mostly cloudy, chance of showers, with a high near 70. </div>
<div> Monday: Mostly cloudy, with a high near 73. </div>
<div> Tuesday: Partly sunny, 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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