<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Exchange Server">
<!-- converted from rtf -->
<style><!-- .EmailQuote { margin-left: 1pt; padding-left: 4pt; border-left: #800000 2px solid; } --></style>
</head>
<body>
<font face="Courier New, monospace" size="3">
<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>9:00 AM PDT TUE AUG 24 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> **** Fire Marshal Burn Ban Conditions Likely This Afternoon ****</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from 1:00pm to 4:00pm.</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> An upper level ridge covers the Pacific Northwest this morning. The axis of the</div>
<div> ridge runs from NE British Columbia, through central Oregon to near Lake Tahoe.</div>
<div> At the surface, our morning ODF surface analysis shows a thermal trough from the</div>
<div> central valley of California into NW California, then just offshore along the</div>
<div> Oregon and Washington coast. There is a strong offshore pressure gradient today.</div>
<div> The Dalles to North Bend pressure difference is about 10mb and this will produce</div>
<div> gusty north east winds today.</div>
<div> </div>
<div> The morning Salem sounding showed dramatic warming at all levels. At about 3500</div>
<div> feet the temperature jumped from 49F yesterday morning to 71F today. Some</div>
<div> additional warming will occur this afternoon. There was a shallow, surface</div>
<div> based inversion to about 200 feet that will easily mix out. The sounding also</div>
<div> showed a more significant, subsidence inversion from about 1300 feet to about</div>
<div> 2200 feet that will not mix out. Maximum mixing heights today will likely stay</div>
<div> below 2000 feet. </div>
<div> </div>
<div> The air mass is very dry and relative humidities will drop into the teens later</div>
<div> today. It is likely that Fire Marshal conditions will be met by early</div>
<div> afternoon.</div>
<div> </div>
<div> The probability of open field burning today is nil. </div>
<div> </div>
<div> For the mid Willamette Valley today expect sunny skies and gusty northeast</div>
<div> winds. Salem's high temperature today will be near 95. Relative humidity drops</div>
<div> to 50% by 9am. Minimum relative humidity this afternoon will be near 15%.</div>
<div> </div>
<div> Sunset tonight: 7:58 pm</div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 76 89 95 87 </div>
<div> Relative Humidity: 33% 20% 15% 22% </div>
<div> Surface Wind Direction: 360 360 010 340 </div>
<div> Surface Wind Speed: 6 10-15 10-15 6 </div>
<div> Transport Wind Direction: 360 360 350 340 </div>
<div> Transport Wind Speed: 11 11 12 5 </div>
<div> Estimated Mixing Height: 900 1900 1900 500</div>
<div> Ventilation Index: 10 21 23 2</div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> The thermal trough will shift inland tomorrow then east of the Cascades late</div>
<div> tomorrow. Timing of this shift will determine if there is a burn opportunity. </div>
<div> Computer models suggest that this will be a late afternoon or early</div>
<div> evening event. Of the three computer models to which we have access two show</div>
<div> favorable winds beginning about 5pm and one shows a wind shift around 6pm.</div>
<div> Pibals and careful monitoring of pressure gradients will be necessary tomorrow.</div>
<div> </div>
<div> Thursday will likely see a deep marine layer covering the valley with the</div>
<div> possibility of some drizzle or light rain. This will be the first day after a</div>
<div> marine push - days which generally do not produce good burning conditions.</div>
<div> </div>
<div> A deepening trough, now in the Gulf of Alaska will settle over the area late in</div>
<div> the week and over the weekend. This should result in onshore flow, along with</div>
<div> increased cloud cover and much cooler temperatures. Shortwaves will periodically</div>
<div> swing around the base of the trough, helping to dig the trough further south and</div>
<div> increase the thickness of the marine layer. Models suggest that the potential</div>
<div> exists for a few rain showers over the weekend, but the timing on these would</div>
<div> depend on when the shortwaves pass through.</div>
<div> </div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Wednesday: Sunny, with a high near 94. E 5-10 mph becoming NW 5-15 late.</div>
<div> Thursday: A chance of morning drizzle then partly sunny, 75. NW 5-10 mph. </div>
<div> Friday: Partly sunny, with a high near 73. </div>
<div> Friday Night: Mostly cloudy, with a low around 46. </div>
<div> Saturday: Partly sunny, with a high near 72. </div>
<div> Sunday: Partly sunny, with a high near 70. </div>
<div> Monday: Mostly cloudy, with a high near 73. </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>
<div><font face="Calibri, sans-serif" size="2"> </font></div>
</font>
</body>
</html>