<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
9:00 AM 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:
Another sunny and warm day on tap for the Willamette Valley...
Satellite pictures this morning show sunshine throughout the Valley with low clouds or
fog along the coast and penetrating inland to near the crest of the Coast Range
mountains.
The morning ODF surface pressure analysis shows a well developed thermal trough extending
from the central valley of California northward into southwest Oregon and continuing
northward through the Willamette Valley then finally curving north-northwest to the
northern Washington Coast.
Coast to Valley gradients are onshore while central Oregon to valley gradients are
offshore. Actual values as of 8am this morning were Newport to Salem, 0.7 mb onshore and
Salem to Redmond, 1.8 mb offshore. The offshore flow will continue today producing an
unfavorable northeast transport wind.
The morning Salem sounding confirmed the easterly component to the winds showing
northeast to southeast winds from the surface to about 3000 feet. Above that level winds
were a very light southwesterly.
Computer models indicate that the offshore flow will increase today, peak tomorrow and
flow will go back onshore sometime Saturday.
Bottom line: Today does not look like an open field burning day.
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:
11am 2pm 5pm 8pm
Temperature: 71 82 87 78
Relative Humidity: 55% 35% 27% 38%
Surface Wind Direction: 030 010 360 350
Surface Wind Speed: 4 4 5 5
Transport Wind Direction: 360 020 020 050
Transport Wind Speed: 4 6 8 10
Estimated Mixing Height: 1100 3100 4900 1500
Ventilation Index: 4 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.
Latest computer models are a little more agressive with a weather system dropping in from
the northwest Sunday night and Monday and the GFS model quantitative precipitation
forecast 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:060912:0839
</pre>
</body>
</html>