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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>9:00 AM 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 12:00 p.m. to 5:00 p.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 southwesterly flow aloft continuing to feed
surges of rain into the region.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Skies are cloudy across all of western Oregon this morning
with radar showing an enhanced region of rain moving inland. Light rain was
already making it into the northern and western Willamette Valley with light to
moderate rain along the coast and over the coastal range. This area of rain
will be very slow to move eastward today, with moderate to heavy rainfall
totals likely from the coast range westward. Rainfall in the Willamette Valley
will increase this afternoon with conditions much too damp for burning.
Rainfall totals, in the Silverton Hills area, will likely range from
one-quarter to one-half inch, before the rain tapers off this evening.<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 a chance of rain this morning, then rain likely
this afternoon. After a high temperature Thursday of 75 degrees, 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> 11am 2pm 5pm
8pm <o:p></o:p></p>
<p class=MsoNormal> Temperature: 64 69 70
64 <o:p></o:p></p>
<p class=MsoNormal> Relative Humidity: 78% 71% 68%
84% <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Direction: Var 180 190
200 <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Speed: 3 3 5
3 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Direction: 040 190 190
200 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Speed: 3 5 8
7 <o:p></o:p></p>
<p class=MsoNormal> Estimated Mixing Height: 1500 2500 2000
1000<o:p></o:p></p>
<p class=MsoNormal> Ventilation Index: 5 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 a weak weather system possibly
bringing a few light showers to the north valley and then dry weather for
Wednesday. The dry weather may not last long, with computer models showing a
more active pattern late next week. It is possible that rain could hold off
long enough to create a burning opportunity Thursday or Friday, but that is
uncertain.<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. High near 75.<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 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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