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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 SEP 08 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 high humidity. </div>
<div> Propane flaming is not allowed due to high humidity. </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> An upper level low pressure area is situated over the southern Washington</div>
<div> Cascades this morning. This is making the atmosphere unstable and areas of</div>
<div> showers cover much of the Pacific Northwest. One line of showers extends from</div>
<div> the northern Washington Cascades, across the southern Puget Sound region and</div>
<div> then to about Longview, Washington. If present trajectories continue this should</div>
<div> rotate into the central Willamette Valley later this morning. As surface</div>
<div> temperatures warm instability in the atmosphere will be released and even more</div>
<div> showers will develop. Some of these showers will be quite significant with</div>
<div> locally heavy rain and possibly thunder and lightning. </div>
<div> </div>
<div> The ODF morning surface analysis shows onshore low level flow with gradient</div>
<div> stacking to the east. Gradient stacking will likely continue throughout the day.</div>
<div> </div>
<div> Wet fields will be an issue today as well. Twenty-four rainfall totals as</div>
<div> of this morning included: Salem Airport, .18; Jordan Valley, .16; Silverton,</div>
<div> .28; and Turner, .32 inches. </div>
<div> </div>
<div> The morning Salem sounding showed temperatures had cooled slightly since</div>
<div> yesterday at all levels from the surface to above 14,000 feet. The</div>
<div> temperature/moisture profile was conditionally unstable - supporting a strong</div>
<div> shower or thunderstorm forecast for this afternoon. </div>
<div> </div>
<div> For the mid Willamette Valley, expect showers, heavy at times, for this</div>
<div> afternoon with the possibility of a thunderstorm. Winds will be light westerly</div>
<div> except gusty near showers. Salem's high temperature today will be near 66.</div>
<div> Minimum relative humidity will be about 60%.</div>
<div> </div>
<div> Sunset tonight: 7:30 pm </div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 59 65 66 59 </div>
<div> Relative Humidity: 78% 60% 60% 72% </div>
<div> Surface Wind Direction: 260 210 270 270 </div>
<div> Surface Wind Speed: 2 5 5 5 </div>
<div> Transport Wind Direction: 230 220 280 270 </div>
<div> Transport Wind Speed: 4 4 9 6 </div>
<div> Estimated Mixing Height: 3500 5000 5000 500</div>
<div> Ventilation Index: 14 20 45 3</div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> The upper level low will move east of the area during the day tomorrow for a</div>
<div> decreasing chance of showers. Models indicate a continuing onshore flow for</div>
<div> mostly cloudy skies and poor field drying conditions. In addition models</div>
<div> indicate gradient stacking to the east continuing. For Friday a flat ridge</div>
<div> builds for some sun but the gradient stacking will likely continue. </div>
<div> </div>
<div> Over the weekend another upper level low will move down the coast of British</div>
<div> Columbia and help carve out a weak upper trough over the Pacific Northwest. At</div>
<div> this point it looks like most moisture should stay just north of the mid</div>
<div> Willamette Valley. Onshore flow will keep temperatures a bit below average and</div>
<div> there will be a mixture of clouds and sun.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Thursday: Mostly cloudy, with a high near 67. Wind W 6. </div>
<div> Friday: Partly sunny, with a high near 69. Wind NW 6. </div>
<div> Saturday: Partly sunny, with a high near 70. </div>
<div> Sunday: Mostly cloudy, with a high near 70. </div>
<div> Monday: Partly sunny, 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>
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