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<p class=MsoNormal>SILVERTON HILLS FIELD BURNING FORECAST<o:p></o:p></p>
<p class=MsoNormal>OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE<o:p></o:p></p>
<p class=MsoNormal>12:00 PM PDT FRI SEP 17, 2010<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>BURN ADVISORY:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal> Recommended burn times for agricultural burning are
from now to 5:00p.m.<o:p></o:p></p>
<p class=MsoNormal> Prep burning is not allowed. <o:p></o:p></p>
<p class=MsoNormal> Propane flaming is not allowed. <o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal>WEATHER DISCUSSION:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>An autumn-like weather pattern has set up across the Pacific
Northwest. A strong upper-level trough is centered about 800 miles off the
Oregon Coast with a very moist south-southwesterly flow aloft continuing to
feed surges of rain northward across the western portion of western
Oregon…mainly from the coast range westward.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Skies remain cloudy across all of western Oregon late this
morning, but radar shows that the main area of rain has not advanced eastward
since mid-morning. Only some sprinkles or very light rain has advanced
eastward into the Willamette Valley today, while the coast and coastal range
has picked up between one-tenth and one-quarter of an inch in just the past 6
hours.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>This area of rain will be very slow to move eastward today,
with locally moderate rainfall totals likely from the coast range westward. I
have downgraded how much rain I think will fall today in the Willamette
Valley. The Silverton Hills region will likely see some increase in the rain
this afternoon, but amounts may not top one-tenth of inch, before this latest
surge of moisture begins tapering off tonight.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>TODAY’S FORECAST:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Cloudy with light rain likely spreading slowly eastward
across the region this afternoon. Today’s high will only climb to 72,
which is 3 degrees below normal. The mixing height may briefly climb to near
3000 feet in the mid-afternoon, before increasing rain spreads across the
valley. With more rain moving in and with the relative humidity likely
remaining above 65% all day, fields will remain too damp for burning. The
ventilation index will only climb to about 20 this afternoon.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Silverton area sunset tonight: 7:13pm <o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal>THREE-HOURLY DATA: <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal> 2pm 5pm 8pm <o:p></o:p></p>
<p class=MsoNormal> Temperature: 69 70 64 <o:p></o:p></p>
<p class=MsoNormal> Relative Humidity: 71% 68% 84% <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Direction: 180 190 200 <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Speed: 3 5 3 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Direction: 190 190 200 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Speed: 5 8 7 <o:p></o:p></p>
<p class=MsoNormal> Estimated Mixing Height: 2500 2000 1000<o:p></o:p></p>
<p class=MsoNormal> Ventilation Index: 13 16 7<o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal>EXTENDED DISCUSSION:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Rain should be widespread across western Oregon over the weekend,
as the parent upper-level trough moves onshore. Some showers could last into
Monday. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Long-range computer models show weak weather systems
possibly bringing a few light showers to the valley Tuesday and again
Wednesday, but both days could easily remain dry. Any dry weather may not last
long, with computer models showing a more active pattern late next week. It is
possible that fields could dry out enough for a burning opportunity Thursday or
Friday, if the rain holds off. That is way too far out to call at this time.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>EXTENDED FORECAST: <o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal> Saturday: Rain likely. High near 72. <o:p></o:p></p>
<p class=MsoNormal> Sunday: Rain turning to showers. High near 70. <o:p></o:p></p>
<p class=MsoNormal> Monday: Mostly cloudy with some showers. High near
70. <o:p></o:p></p>
<p class=MsoNormal> Tuesday: Mostly cloudy. Slight chance of showers
north. High near 72.<o:p></o:p></p>
<p class=MsoNormal> Wednesday: Partly sunny. Slight chance of showers.
High near 74.<o:p></o:p></p>
<p class=MsoNormal> Thursday: Increasing clouds. Chance of rain late.
High near 75.<o:p></o:p></p>
<p class=MsoNormal> Friday: Chance of light rain. High near 70.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Notes:<o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal> 1. Mixing height, as used here, is the lowest height
at which the<o:p></o:p></p>
<p class=MsoNormal> potential temperature exceeds the potential
temperature at the<o:p></o:p></p>
<p class=MsoNormal> surface. <o:p></o:p></p>
<p class=MsoNormal> As a practical matter it is the approximate height
to which a <o:p></o:p></p>
<p class=MsoNormal> smoke plume will rise assuming good ignition, dry
fuels, and <o:p></o:p></p>
<p class=MsoNormal> winds less than about 15mph. <o:p></o:p></p>
<p class=MsoNormal> 2. Transport winds are a layer average through the
mixing height, <o:p></o:p></p>
<p class=MsoNormal> weighted slightly toward the winds at the top of
the layer. <o:p></o:p></p>
<p class=MsoNormal> 3. Ventilation Index is the height of the mixing layer
times <o:p></o:p></p>
<p class=MsoNormal> the transport wind speed divided by 1000. <o:p></o:p></p>
<p class=MsoNormal> 4. Surface wind direction is the general expected wind
direction. <o:p></o:p></p>
<p class=MsoNormal> At a specific point surface winds are highly
dependent on local<o:p></o:p></p>
<p class=MsoNormal> terrain conditions.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>This forecast is provided under an agreement between the
Oregon Department of<o:p></o:p></p>
<p class=MsoNormal>Agriculture and the Oregon Department of Forestry. For
information contact ODA at 503-986-4701.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Pete Parsons<o:p></o:p></p>
<p class=MsoNormal>ODF Meteorologist<o:p></o:p></p>
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