<pre>
<html xmlns:o="urn:schemas-microsoft-com:office:office"
xmlns:w="urn:schemas-microsoft-com:office:word"
xmlns="http://www.w3.org/TR/REC-html40">
<html>
<head>
</head>
<body>
<pre>
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT THU SEP 06 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Warm, late summer weather continues...
Late morning satellite pictures show the low clouds that had moved into the coast range
overnight have retreated to the coast. Sunshine covers the entire Willamette Valley.
The late morning ODF surface pressure analysis shows the thermal trough extending from
California, into the Willamette Valley and then northward. Low level flow is easterly and
the pressure gradient from Redmond to Salem is now 2.4 mb offshore. The Dalles to
Portland is 2.3 mb easterly.
Easterly winds will continue this afternoon and increase tomorrow for unfavorable burning
conditions.
TODAY'S FORECAST:
Sunny.
Salem's high temperature today will be near 87.
Relative humidity drops to 50% by 12pm. Minimum relative humidity 27%.
Surface winds: North to northeast 4-6 mph.
Transport winds: North to northeast 6-10 mph.
Mixing height reaches 3000 feet by about 1:30pm and maxes out at around 4900 feet.
Sunset tonight: 7:38 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 81 86 76
Relative Humidity: 37% 28% 40%
Surface Wind Direction: 350 350 360
Surface Wind Speed: 4 5 4
Transport Wind Direction: 020 020 050
Transport Wind Speed: 6 8 10
Estimated Mixing Height: 3100 4900 1500
Ventilation Index: 19 39 15
EXTENDED DISCUSSION:
An upper level low off the California will drift northward tomorrow and Saturday. This
will eventually turn upper level flow southerly over western Oregon and help produce the
shift back to onshore flow on Saturday. At this point it appears very unlikely that the
50% cloud cover threshold will be reached that would allow for weekend burning.
A modified marine push Saturday afternoon or Saturday night will bring clouds and cooler
temperatures to the region for Sunday.
The last two computer model runs have been a little more agressive with a weather system
dropping in from the northwest Sunday night and Monday and the latest GFS model run
quantitative precipitation forecast still shows about a tenth of an inch of rain
overnight
Sunday and Monday.
The National Weather Service’s digital forecast is available at:
<a
href="http://forecast.weather.gov/MapClick.php?lat=44.905&lon=-122.810">http://forecast.weather.gov/MapClick.php?lat=44.905&lon=-122.810</a>.
Notes:
1. Mixing height, as used here, is the lowest height at which the
potential temperature exceeds the equivalent potential temperature
at the surface. As a practical matter it is the approximate height
to which a smoke plume will rise assuming good ignition, dry fuels,
and winds less than about 15mph.
2. Transport winds are a layer average through the mixing height,
weighted slightly toward the winds at the top of the layer.
3. Ventilation Index is the height of the mixing layer times
the transport wind speed divided by 1000.
4. Surface wind direction is the general expected wind direction.
At a specific point surface winds are highly dependent on
local terrain conditions.
This forecast is provided under an agreement between the Oregon Department of
Agriculture and the Oregon Department of Forestry. For information contact ODA
at 503-986-4701.
Jim Little
ODF Meteorologist
jlwx:060912:1146
</pre>
</body>
</html>