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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNoSpacing>SILVERTON HILLS FIELD BURNING FORECAST<o:p></o:p></p><p class=MsoNoSpacing>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE<o:p></o:p></p><p class=MsoNoSpacing>12:08 PM PDT THU SEP 29, 2011<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Corrected Discussion wording: “south-southeasterly” to “south-southwesterly”<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>BURN ADVISORY:<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Agricultural burning is not recommended.<o:p></o:p></p><p class=MsoNoSpacing>Prep burning is not allowed. <o:p></o:p></p><p class=MsoNoSpacing>Propane flaming is allowed from 2:00 p.m. until 5:00 p.m. <o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing>WEATHER DISCUSSION:<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>A strong upper-level ridge of high pressure remains centered over the Rockies with a warm and dry southwesterly flow aloft over Oregon. The surface thermal trough was still centered just west of the coastline late this morning. Offshore pressure-gradients were slowly weakening, but easterly winds were still gusting to around 30 mph at the western end of the Columbia Gorge, with light easterly winds making it all the way to the coast.<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Offshore flow has significantly warmed the low-level air mass since yesterday. 5000-foot temperatures over Salem early this morning were in the mid 60s. That will suppress mixing heights today. ODF Sodar, located in the central coast range, was showing offshore flow from near the surface up to 3500 feet late this morning, with south-southwesterly flow above 3500 feet.<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>The upper-level ridge is forecast to shift only slightly eastward today. A reversal of the low-level offshore flow, to onshore, is looking less likely this afternoon, with the thermal trough staying over western Oregon. Winds at the top of the mixing layer are forecast to be south-southwesterly, but persistent low-level offshore flow would decrease the chances for open field-burning this afternoon. Pibals are scheduled to begin at 2 p.m.<o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing>TODAY’S FORECAST:<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Sunny and unseasonably warm. <o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Salem's high temperature today will be near 84 degrees (normal is 72).<o:p></o:p></p><p class=MsoNoSpacing>Relative humidity drops below to near 30% by 5 p.m.<o:p></o:p></p><p class=MsoNoSpacing>Surface winds: Variable 3-7 mph this afternoon.<o:p></o:p></p><p class=MsoNoSpacing>Transport winds: ESE 3-6 mph; becoming SSW 6-10 mph this afternoon.<o:p></o:p></p><p class=MsoNoSpacing>Mixing height: Rising to 3000 feet by 3 p.m. and to near 3500 feet by 5 p.m.<o:p></o:p></p><p class=MsoNoSpacing>Salem’s sunset tonight: 6:57 p.m. <o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing>THREE-HOURLY DATA: <o:p></o:p></p><p class=MsoNoSpacing> 2 p.m. 5 p.m. 8 p.m. <o:p></o:p></p><p class=MsoNoSpacing> Temperature: 78 83 68 <o:p></o:p></p><p class=MsoNoSpacing> Relative Humidity: 33% 30% 52%<o:p></o:p></p><p class=MsoNoSpacing> Surface Wind Direction: 360 Var 230<o:p></o:p></p><p class=MsoNoSpacing> Surface Wind Speed: 5 5 5 <o:p></o:p></p><p class=MsoNoSpacing> Transport Wind Direction: 200 210 180 <o:p></o:p></p><p class=MsoNoSpacing> Transport Wind Speed: 6 10 7<o:p></o:p></p><p class=MsoNoSpacing> Mixing Height: 2500 3500 1000<o:p></o:p></p><p class=MsoNoSpacing> Ventilation Index: 15 35 7 <o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing>EXTENDED DISCUSSION:<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>The upper-level ridge is forecast to weaken and shift eastward on Friday. Increasing southwesterly flow aloft will force the surface thermal trough into eastern Oregon. Onshore flow will cool temperatures back close to normal with increasing clouds. Dry conditions should prevail, with southwesterly transport winds likely allowing for the burning of any remaining fields.<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Computer models show the first in a series of weather systems coming onshore Saturday. This first system should weaken, as it moves inland, but still bring around one-tenth of an inch of rain. Sunday looks like a mostly dry day, ahead of a much more potent system forecast to come onshore Sunday night. That storm could dump more than one-half inch of rain by Monday evening. An even stronger system is forecast to come onshore late Tuesday.<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>The National Weather Service’s digital forecast is available at:<o:p></o:p></p><p class=MsoNoSpacing><a href="http://forecast.weather.gov/MapClick.php?lat=44.90549606158295&lon=-122.8106689453125&site=pqr&unit=0&lg=en&FcstType=text">http://forecast.weather.gov/MapClick.php?lat=44.90549606158295&lon=-122.8106689453125&site=pqr&unit=0&lg=en&FcstType=text</a><o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Notes:<o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing> 1. Mixing height, as used here, is the lowest height at which the<o:p></o:p></p><p class=MsoNoSpacing> potential temperature exceeds the potential temperature at the<o:p></o:p></p><p class=MsoNoSpacing> surface. As a practical matter it is the approximate height to<o:p></o:p></p><p class=MsoNoSpacing> which a smoke plume will rise assuming good ignition, dry fuels, and <o:p></o:p></p><p class=MsoNoSpacing> winds less than about 15mph.<o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing> 2. Transport winds are a layer average through the mixing height, <o:p></o:p></p><p class=MsoNoSpacing> weighted slightly toward the winds at the top of the layer.<o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing> 3. Ventilation Index is the height of the mixing layer times <o:p></o:p></p><p class=MsoNoSpacing> the transport wind speed divided by 1000.<o:p></o:p></p><p class=MsoNoSpacing> <o:p></o:p></p><p class=MsoNoSpacing> 4. Surface wind direction is the general expected wind direction. <o:p></o:p></p><p class=MsoNoSpacing> At a specific point surface winds are highly dependent on local<o:p></o:p></p><p class=MsoNoSpacing> terrain conditions.<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>This forecast is provided under an agreement between the Oregon Department of<o:p></o:p></p><p class=MsoNoSpacing>Agriculture and the Oregon Department of Forestry. For information contact ODA at 503-986-4701.<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNoSpacing>Pete Parsons<o:p></o:p></p><p class=MsoNoSpacing>ODF Meteorologist<o:p></o:p></p><p class=MsoNoSpacing><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>