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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 03 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Agricultural burning burning is not recommended.</div>
<div> Prep burning is allowed from 12:30pm to 5:00pm with a 50 acre limit. </div>
<div> Propane flaming is allowed from 12:30pm to 5:00pm. </div>
<div> </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Upper level ridge has moved off to the east with the upper trough moving in this</div>
<div> morning. Surface pressure pattern shows the thermal trough in the Willamette</div>
<div> Valley this morning. The Newport to Salem gradient is .9 mb onshore while the</div>
<div> Salem to Redmond gradient is 3.6 mb offshore. As the upper level trough</div>
<div> continues marching in today, onshore pressure gradients will increase as the</div>
<div> surface thermal trough shifts east of the Cascades late this morning to early</div>
<div> afternoon. This will set up a decent marine push this afternoon.</div>
<div> </div>
<div> The morning sounding from Salem showed a strong surface and subsidence inversion</div>
<div> to nearly 4000 ft, which demonstrates the remaining strength of the exiting upper</div>
<div> level ridge. Winds up to 1500 ft are generally light and variable but show a</div>
<div> distinct light SW'erly flow above. </div>
<div> </div>
<div> Weather conditions for today will again be mostly sunny with the high</div>
<div> temperature a little cooler than yesterday's high of 90. Expect the temperature</div>
<div> to top out around 85 a little earlier this afternoon as the cooler marine air</div>
<div> starts pushing into the region. Mixing heights will remain fairly low this</div>
<div> morning but as cooler air moves in aloft this afternoon combined with surface</div>
<div> heating, mixing will rapidly improve during the early afternoon. Relative</div>
<div> humidity will drop below 50 percent by 11 a.m. with the minimum humidity nearly</div>
<div> 32 percent. SW'erly flow aloft will continue and increase today with westerly</div>
<div> surface winds starting to show up in the valley by early to mid afternoon. All</div>
<div> indications point to a good burning opportunity today.</div>
<div> </div>
<div> </div>
<div> Sunset tonight: 7:40 pm </div>
<div> </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 75 82 84 73 </div>
<div> Relative Humidity: 48% 37% 33% 49% </div>
<div> Surface Wind Direction: 230 270 270 290 </div>
<div> Surface Wind Speed: 4 5 10 8 </div>
<div> Transport Wind Direction: 220 240 260 290 </div>
<div> Transport Wind Speed: 7 10 12 10 </div>
<div> Estimated Mixing Height: 1800 4200 5000 1500</div>
<div> Ventilation Index: 13 42 60 15</div>
<div> </div>
<div> </div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> Upper level trough moves into the state on Saturday ushering in much cooler</div>
<div> conditions. Expect mostly cloudy skies with breezy onshore, NW'erly winds</div>
<div> during the afternoon. Mixing will be good but the more gradient stacking will be</div>
<div> to the east. </div>
<div> </div>
<div> Trough moves off to the east Sunday with a minor ridge building in. This will be</div>
<div> very temporary as another trough forms in the eastern Pacific Monday and moves</div>
<div> in Monday night. This trough will likely be a little stronger and bring some</div>
<div> light rain to the region on Tuesday. Trough exits to the east Wednesday.</div>
<div> Overall, expect a considerably cooler, fall-like air mass over the region over</div>
<div> the weekend and into next week.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Saturday: Partly sunny, with a high near 72. Northwest wind between 5 and</div>
<div> 10 mph. </div>
<div> Saturday Night: A 30 percent chance of showers after 11pm. Mostly cloudy, with a</div>
<div> low around 46. North northwest wind between 5 and 8 mph becoming calm. </div>
<div> Sunday: A 30 percent chance of showers before 11am. Partly sunny, with a high</div>
<div> near 68. Southwest wind 5 to 7 mph becoming west northwest. </div>
<div> Sunday Night: Mostly cloudy, with a low around 47. </div>
<div> Monday: Mostly cloudy, with a high near 72. </div>
<div> Monday Night: Mostly cloudy, with a low around 48. </div>
<div> Tuesday: Mostly cloudy with occasional light rain, with a high near 67. </div>
<div> Tuesday Night: Mostly cloudy with occasional light rain, with a low around 48. </div>
<div> Wednesday: Mostly cloudy early then partly sunny, with a high near 70. </div>
<div> Wednesday Night: Mostly cloudy, with a low around 50. </div>
<div> Thursday: Partly sunny, with a high near 72. </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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