<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="2">
<div>SILVERTON HILLS FIELD BURNING FORECAST</div>
<div>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE</div>
<div>9:00 AM PDT MON SEP 20 2010</div>
<div> </div>
<div>BURN ADVISORY:</div>
<div> </div>
<div> Recommended burn times for agricultural burning are from 11:00am to 5:00pm.</div>
<div> Prep burning is allowed from 12:00pm to 5:00pm with a 50 acre limit. </div>
<div> Propane flaming is allowed from 12:00pm to 5:00pm. </div>
<div> </div>
<div>WEATHER DISCUSSION:</div>
<div> </div>
<div> Satellite pictures this morning show solid cloud cover over western Oregon, from</div>
<div> the coast to the Cascade crest. Rainfall amounts in the past 24 hours include</div>
<div> .16 at the Salem Airport and .13 at the Oregon Gardens in Silverton. </div>
<div> </div>
<div> Upper air charts show a trough covering much of the Pacific Northwest with a</div>
<div> significant upper level disturbence just off the southern British Columbia coast</div>
<div> embedded in the through. This will rotate across northern Washington but be</div>
<div> close enough to keep some showers going as far south as the mid-Willamette</div>
<div> Valley. </div>
<div> </div>
<div> The morning Salem sounding showed an inversion from 4900 to 5500 feet. This will</div>
<div> cap mixing heights today, but at a fairly high elevation above ground level.</div>
<div> Maximum mixing height will be around 5100 feet this afternoon. The sounding also</div>
<div> showed SSW winds near the surface veering to WSW by about 2000 feet. This is a</div>
<div> favorable direction for open field burning.</div>
<div> </div>
<div> Computer models suggest smoke trajectories would be to the NE or ENE this</div>
<div> afternoon. </div>
<div> </div>
<div> Finding dry fields will be the limiting factor on open field burning this</div>
<div> afternoon.</div>
<div> </div>
<div> Salem's high temperature today will be near 69. Minimum relative humidity will</div>
<div> be down to 51%.</div>
<div> </div>
<div> Sunset tonight: 7:08 pm</div>
<div> </div>
<div>THREE-HOURLY DATA: </div>
<div> </div>
<div> 11am 2pm 5pm 8pm </div>
<div> Temperature: 63 68 68 60 </div>
<div> Relative Humidity: 72% 57% 51% 64% </div>
<div> Surface Wind Direction: 190 220 230 270 </div>
<div> Surface Wind Speed: 11 7 7 5 </div>
<div> Transport Wind Direction: 190 220 250 280 </div>
<div> Transport Wind Speed: 15 10 8 5 </div>
<div> Estimated Mixing Height: 2200 5000 5100 500</div>
<div> Ventilation Index: 33 50 41 2</div>
<div> </div>
<div>EXTENDED DISCUSSION:</div>
<div> </div>
<div> The upper level trough moves east overnight tonight and weak ridging aloft</div>
<div> develops over the region. Dry weather takes over as models show good agreement</div>
<div> on the next system out in the pacific moving toward California and weakening.</div>
<div> This may result in a few high clouds streaming across the southern Willamette</div>
<div> Valley, otherwise fair weather will dominate aside from some night and morning</div>
<div> fog due to the heavy recent rains. Temperatures will still be a little below</div>
<div> late September averages as the cool air mass aloft lingers over the Pacific</div>
<div> Northwest. </div>
<div> </div>
<div> The next frontal system will brush the Pacific Northwest sometime Thursday. This</div>
<div> will not be a major rainfall event but areas of light rain are possible in the</div>
<div> Willamette Valley. Look for drying and warming Friday into Saturday as a deep</div>
<div> upper level low develops over the Gulf of Alaska, encouraging ridging to build</div>
<div> over the Pacific Northwest. Eventually, however, a strengthing Pacific Jet will</div>
<div> break through this ridge. Timing is somewhat uncertain, but Saturday night or</div>
<div> Sunday looks like a good bet.</div>
<div> </div>
<div>EXTENDED FORECAST: </div>
<div> </div>
<div> Tuesday: Patchy morning fog then partly sunny, 72. SW 4-7 mph. </div>
<div> Wednesday: Patchy morning fog then mostly sunny, 73. SW 4-7 mph. </div>
<div> Thursday: Patchy morning fog then mostly cloudy with a chance of rain. 73.</div>
<div> Friday: Partly sunny, with a high near 74. </div>
<div> Saturday: A chance of rain late otherwise partly sunny, with a high near 73. </div>
<div> Sunday: A chance of rain. Mostly cloudy, with a high near 72. </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>
<div><font face="Calibri, sans-serif" size="2"> </font></div>
</font>
</body>
</html>