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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 THU AUG 19, 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> Agricultural burning burning is not recommended.<o:p></o:p></p>
<p class=MsoNormal> Prep burning is allowed from now to 2:00pm with a 50
acre limit. <o:p></o:p></p>
<p class=MsoNormal> Propane flaming is allowed from now to 5:00pm. <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>A very weak upper-level impulse was moving onto the northern
Oregon Coast late this morning and helping to maintain the onshore flow across
western Oregon. Late-morning satellite imagery showing marine low clouds
persisting across most areas west of the Cascade crest and north of Douglas
County. Some drizzle even fell this morning along the north coast. Skies were
sunny, late this morning, over extreme southwestern Oregon and all areas east
of the Cascades.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Gradient-stacking has increased, since earlier this morning,
with 1.0 mb onshore from Newport to Salem and 4.1 mb onshore from Salem to
Redmond. The western valleys may not get warm enough this afternoon to
overcome that much gradient-stacking, so chances for open burning today have
lowered since the morning forecast.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The low cloud deck is being more stubborn today than
yesterday but beginning to show signs of breaking up over the north coast
range. Look for skies to clear about an hour later this afternoon than they on
Wednesday. Temperatures are running a couple of degrees cooler than 24 hours
ago, so the forecast high has been lowered accordingly.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The low clouds should give way to sunshine by around 2 p.m.
Ventilation conditions will be marginal for open burning this afternoon. Even
if the gradient-stacking is overcome, which is in doubt, transport winds are
forecast to have a significant northerly component.<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>Morning clouds, then sunny and mild. After reaching 79
degrees on Wednesday, Salem's high temperature today will be near 78 degrees.
The mixing height will climb to near 4000 feet around 5 p.m. An evening sea
breeze will drop the mixing height to near 1500 feet shortly before sunset.
Surface and transport winds will be NNW 5-10 mph today. Relative humidity will
drop to 50% around 2 p.m. and to near 40% around 5 p.m. The ventilation index
will climb to 32 this afternoon.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Silverton area sunset tonight: 8:06 pm <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: 70 77 69 <o:p></o:p></p>
<p class=MsoNormal> Relative Humidity: 51% 40% 53% <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Direction: 320 330 300 <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Speed: 6 8 9 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Direction: 340 340 320 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Speed: 6 8 10 <o:p></o:p></p>
<p class=MsoNormal> Estimated Mixing Height: 3000 4000 1500<o:p></o:p></p>
<p class=MsoNormal> Ventilation Index: 18 32 15<o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal>EXTENDED DISCUSSION (no changes from the morning forecast):<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The flow aloft is forecast to turn slightly more
southwesterly Friday with little change in the surface pattern. Morning clouds
should give way to afternoon sunshine with continued north-northwesterly
transport winds. The onshore flow will strengthen over the weekend, as an
upper-level trough moves inland. Temperatures will fall to below normal. The
marine layer will deepen significantly Saturday night with a chance of drizzle
or light showers on Sunday.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>A flat upper-level ridge is forecast to build over the
region next Monday with transport winds turning northerly and mostly sunny
skies helping temperatures recover to near normal. Increasing westerly flow
aloft may provide open burning opportunities next Tuesday and/or Wednesday, as
transport winds turn back onshore.<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> Friday: Mostly sunny, with a high near 78. Wind: N 5-10
mph. <o:p></o:p></p>
<p class=MsoNormal> Friday Night: Mostly cloudy. Low near 49. Wind: NW
5-10 mph. <o:p></o:p></p>
<p class=MsoNormal> Saturday: Partly sunny, with a high near 75. Wind: NW
5-15 mph. <o:p></o:p></p>
<p class=MsoNormal> Sunday: Mostly cloudy. Chance of light showers. High
near 72. <o:p></o:p></p>
<p class=MsoNormal> Monday: Mostly sunny, with a high near 83. <o:p></o:p></p>
<p class=MsoNormal> Tuesday: Mostly sunny, with a high near 83. <o:p></o:p></p>
<p class=MsoNormal> Wednesday: Mostly sunny. Increasing onshore flow.
High near 81.<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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