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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 AUG 6 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<o:p></o:p></p>
<p class=MsoNormal> 1:00pm to 6:30pm.<o:p></o:p></p>
<p class=MsoNormal> Prep burning is allowed from 1:00pm to 3:00pm with a 50
acre limit. <o:p></o:p></p>
<p class=MsoNormal> Propane flaming is allowed from 1:00pm 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>An upper-level trough stretches from western Washington,
across western Oregon, to northern California this morning. Wildfire smoke
from both the Rooster Rock Fire, in central Oregon, and from fires in southern
British Columbia is still making skies hazy over western Oregon. Nephelometer
readings remain slightly elevated this morning in the northern Cascades and in
the Willamette Valley. Some improvement in air quality is likely today, as the
upper-level trough slowly migrates eastward and the winds aloft turn onshore.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The Salem sounding this morning still showed easterly winds
between 2000 and 3000 feet, but all other levels had turned onshore. However,
the onshore flow is still fairly weak this morning with just 1.6 mb from
Newport to salem and 1.6 mb from Salem to Redmond. Visible satellite imagery
shows low clouds along the coast with some inland penetration up the Columbia
River into the extreme northern Willamette Valley. The remainder of the valley
had hazy sunshine. Temperatures were generally running only a degree or two
cooler than 24 hours ago.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The flow aloft is forecast to turn onshore, at all levels,
by this afternoon with very slight cooling aloft likely taking a few degrees
off of valley high temperatures. Since the smoke plumes from area wildfire
extend close to 100 miles offshore, expect the increasing westerly flow aloft
to only slowly clear the hazy conditions across western Oregon. Transport
winds will need monitoring this afternoon for the possibility of ventilation
conditions improving enough for limited open burning.<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>Mostly sunny and hazy. A touch cooler. After reaching 88
degrees on Thursday, Salem's high temperature today will be near 84 degrees.
The mixing height will climb to 3000 feet about 2 p.m. and likely top out near
4000 feet around 5 p.m. An evening sea breeze should drop the mixing height to
near 2000 feet by 8 p.m. Surface and transport winds will be NW 3-6 mph this
morning, then increase to NW 5-10 this afternoon and NW 7-12 this evening.
Relative humidity is forecast to drop to 50% by 1 p.m. and to near 34% by 5
p.m. The ventilation index will climb to about 32 late this afternoon.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Silverton area sunset tonight: 8:26 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> 11am 2pm 5pm
8pm <o:p></o:p></p>
<p class=MsoNormal> Temperature: 71 80 84
75 <o:p></o:p></p>
<p class=MsoNormal> Relative Humidity: 55% 41% 34%
48% <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Direction: 320 310 320
290 <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Speed: 5 6 8
9 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Direction: 310 320 320 310
<o:p></o:p></p>
<p class=MsoNormal> Transport Wind Speed: 4 6 8
10 <o:p></o:p></p>
<p class=MsoNormal> Estimated Mixing Height: 2200 3000 4000
2000<o:p></o:p></p>
<p class=MsoNormal> Ventilation Index: 9 18 32
20<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>Stronger onshore flow will bring further cooling over the
weekend, with a weak cold front forecast to come onshore Saturday evening.
Marine clouds will be extensive by Sunday morning with local drizzle possible.
High temperatures should fall to about 10 degrees below normal by Sunday.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Another upper-level trough is forecast to drop into the
region Monday for continued cooler than normal conditions and moderate to
strong onshore flow. That may create an open burning opportunity and will
need to be monitored closely. The trough is forecast to weaken on Tuesday with
decreasing onshore flow leading warmer temperatures and decreasing the chances
for open burning opportunities. Long-range computer models are inconsistent.
Some are showing a cool northwesterly flow aloft for later next week, while
others have temperatures warming to above normal. <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: Morning clouds, then partly cloudy. 55/79<o:p></o:p></p>
<p class=MsoNormal>Sunday: Chance of morning drizzle. Partly sunny in the
afternoon. 54/75<o:p></o:p></p>
<p class=MsoNormal>Monday: Morning clouds, then mostly sunny. 54/79<o:p></o:p></p>
<p class=MsoNormal>Tuesday: Morning clouds, then mostly sunny. 53/84 <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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