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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 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 falling 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 continued to fall this morning along sections of the
coast and in the extreme northern Willamette Valley. After receiving around
1.50 inches of rain overnight, Astoria, on the northern coast, has picked up an
additional .40 inches this morning. Up to one-tenth of an inch of rain has
fallen in the northern Willamette Valley in the past 6 hours with trance
amounts falling as far south as the central valley.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Skies remain cloudy across western Oregon late this morning
due to a very moist southwesterly flow aloft. The cold front that has been
producing the rain is forecast to shift slightly northward this afternoon, so
not much addition rainfall is expected as far south as Marion County. However,
cloudy skies, light winds, and high humidity levels will not aid much in the
drying of damp fields.<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 near 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. 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> 2pm 5pm 8pm <o:p></o:p></p>
<p class=MsoNormal> Temperature: 73 74 67 <o:p></o:p></p>
<p class=MsoNormal> Relative Humidity: 64% 62% 75% <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Direction: 200 230 220 <o:p></o:p></p>
<p class=MsoNormal> Surface Wind Speed: 6 6 2 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Direction: 200 210 220 <o:p></o:p></p>
<p class=MsoNormal> Transport Wind Speed: 10 10 6 <o:p></o:p></p>
<p class=MsoNormal> Estimated Mixing Height: 2500 3700 1000<o:p></o:p></p>
<p class=MsoNormal> Ventilation Index: 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 early afternoon…making
the prospects for burning highly unlikely. 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 are now showing another, weaker,
weather system possibly coming onshore Tuesday with more showers…mainly
over the northern valley. The latest guidance is suggesting that a ridge will
dry things out Wednesday and Thursday, which could finally allow remaining
fields to dry out enough for burning.<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 north. High
near 70.<o:p></o:p></p>
<p class=MsoNormal> Wednesday: Partly sunny. High near 72.<o:p></o:p></p>
<p class=MsoNormal> Thursday: Partly cloudy. High near 75.<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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