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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 THU SEP 16, 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 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 cold front dropped up to one-half inch of
rain in the northern Willamette Valley overnight with around one-third of an
inch common as far south as Marion County. Rainfall amounts tapered off to
between one-tenth and one-quarter of an inch in Linn County with less than
one-tenth of an inch falling in Lane County.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Rain is continuing to fall this morning along the coast and
in the extreme northern Willamette Valley. Skies are cloudy across all of
western Oregon. The cold front will weaken and shift slightly northward today,
as a weak ridge of high pressure builds over Oregon. Not much addition
rainfall is expected as far south as Marion County, but skies should remain
generally cloudy with high humidity levels.<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…mainly in the morning.
Today’s high temperature should be close to yesterday’s high of 74
degrees. The mixing height will climb to near 3000 feet in the mid-afternoon
and top out below 4000 feet around 5 p.m. Relative humidity will likely remain
above 60% all day, so damp fields will have a difficult time drying out. The
ventilation index will climb to 37 by late this afternoon.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Silverton area sunset tonight: 7:15pm <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: 66 73 74
67 <o:p></o:p></p>
<p class=MsoNormal> Relative Humidity: 81% 64% 62%
75% <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Direction: 160 200 230
220 <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Speed: 5 6 6
2 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Direction: 170 200 210
220 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Speed: 4 10 10
6 <o:p></o:p></p>
<p class=MsoNormal> Estimated Mixing Height: 1800 2500 3700
1000<o:p></o:p></p>
<p class=MsoNormal> Ventilation Index: 7 25 37
6<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>Another weather system is slated to come onshore Friday with
rain projected to move back into the Willamette valley by midday. That makes
the prospect for burning highly unlikely. Wet weather is forecast this
weekend…perhaps lasting into Monday. Long-range computer models are now
showing additional weather systems possibly bringing rain to the valley again
Tuesday and Thursday of next week, but confidence in the forecast beyond Monday
is low.<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: Rain likely by the afternoon. High near 72. <o:p></o:p></p>
<p class=MsoNormal> Saturday: Rain likely. High near 69. <o:p></o:p></p>
<p class=MsoNormal> Sunday: Showers likely. High near 68. <o:p></o:p></p>
<p class=MsoNormal> Monday: Mostly cloudy. Chance of showers. High near
70. <o:p></o:p></p>
<p class=MsoNormal> Tuesday: Mostly cloudy. Chance of rain. High near 68.<o:p></o:p></p>
<p class=MsoNormal> Wednesday: Partly sunny. Slight chance of showers.
High near 71.<o:p></o:p></p>
<p class=MsoNormal> Thursday: Mostly cloudy. 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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