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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 MON AUG 2 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>Visible satellite imagery shows marine low clouds still
covering much of western Washington and extending along the Washington coast
and most of the northern and central Oregon coast. Patches of low clouds made
it inland into the extreme northern Willamette Valley this morning but were
evaporating at midday.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Satellite imagery also shows elevated wildfire smoke
continuing to cover much of central and eastern Washington. Some of that smoke
got rotated south and west, to over northwestern and north-central Oregon, by
the upper-level trough over the region. Skies were mostly sunny over the
remainder of the state, at midday. Temperatures in the Willamette Valley are
generally running 5-8 degrees warmer than 24 hours ago.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The morning sounding over Salem showed several degrees of
warming aloft, since Sunday morning. The marine air is very shallow with quite
dry conditions above 2500 feet. The low-level temperature profile is stable,
with a temperature inversion at about 4700 feet that should cap maximum mixing
heights this afternoon.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>A weak upper-level disturbance that was over northwestern
Oregon this morning is forecast to continue eastward into central Oregon this afternoon.
Daytime heating is already triggering some minor cumulus cloud development over
the southern Cascades and over central Oregon, but the very dry air mass will
limit afternoon thunderstorm development. Northwesterly flow aloft should
promote an afternoon sea breeze into the Willamette Valley. Transport winds
and pressure gradients will need to be monitored for the possibility of limited
open burning later this afternoon.<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>Smoke and haze aloft, otherwise mostly sunny. Salem's high
temperature today will be near 84 degrees. The mixing height will climb to
around 4700 feet later this afternoon. A cooling sea breeze will drop the
mixing height to 1500 feet by shortly before sunset. Surface and transport
winds become NW 6-10 this afternoon. Relative humidity will drop to 50% by 1
p.m. and to near 36% by late this afternoon. The ventilation index will climb
to about 36 late this afternoon.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Silverton area sunset tonight: 8:32 pm <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>Little change to the overall weather pattern is expected
through Friday, with a weak upper-level trough remaining over the Pacific
Northwest. Varying degrees of onshore flow will maintain at least a chance of
open burning each afternoon. The onshore flow may weaken a bit on Wednesday,
as the upper-level flow turns southwesterly, and then strengthen late Thursday
and Friday. The best chances for open burning opportunities later this week
appear to be Tuesday and Thursday afternoons, but that may change. <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>Tuesday: Patchy morning clouds, then mostly sunny. Wind: NW
5-12 mph. 55/84 <o:p></o:p></p>
<p class=MsoNormal>Wednesday: Mostly Sunny. Wind: NNW 5-12 mph. 55/86 <o:p></o:p></p>
<p class=MsoNormal>Thursday: Mostly sunny. Wind: NW 5-15 mph. 56/84<o:p></o:p></p>
<p class=MsoNormal>Friday: Morning clouds, then mostly sunny. 55/79 <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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