<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 MON SEP 24 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Satellite pictures show mostly clear skies over northwestern Oregon this morning. A
weakening band of clouds extends from Vancouver Island to about 200 miles west of
Newport.
The morning Salem sounding is not optimistic for open field burning this morning. Winds
were measured at a light north-northeast up to about 2000 feet, then north-northwesterly
from 2500 to 5000 feet, then north to northeast up to about 14,000 feet.
Temperatures aloft have warmed since yesterday creating a more stable atmosphere. There
is an inversion from about 3000 to 3500 feet that will likely not completely mix out
today and maximum mixing heights will likely be right around 3500 feet.
Pressure gradients are not favorable this morning, showing lowest pressures in the
Willamette Valley. There is 1.7mb onshore from Newport to Salem as of 8:00am. At the
same time the Redmond to Salem gradient was 0.5mb offshore.
Computer models show a continuing northerly wind. Some models slightly north-northeast,
some slightly north-northwest. Nothing is indicating a change to a favorable transport
wind direction this afternoon.
Bottom line: Today does not look like an open field burn day.
TODAY'S FORECAST:
Sunny after patchy morning clouds or fog.
Salem's high temperature today will be near 78.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 36%.
Surface winds: Northerly 3-6 mph becoming northwesterly 3-6 this evening.
Transport winds: Northerly to north-northeasterly 5-10 mph.
Becoming northerly 10-15 this evening.
Maximum mixing height: 3500 feet.
Sunset tonight: 7:04 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 66 76 78 67
Relative Humidity: 58% 40% 36% 54%
Surface Wind Direction: 340 350 360 310
Surface Wind Speed: 3 5 6 5
Transport Wind Direction: 020 360 360 360
Transport Wind Speed: 5 7 10 15
Estimated Mixing Height: 1500 3300 3400 1400
Ventilation Index: 8 23 34 21
EXTENDED DISCUSSION:
A weak upper level disturbance moves through British Columbia overnight tonight and early
tomorrow. A cold front associated with this feature is offshore this morning, and will
push through the area overnight. It will be very weak however. Another upper ridge will
build behind during the day tomorrow keeping transport wind flow mostly northerly for
Tuesday.
A weak, flat upper ridge will then remain over the Pacific Northwest Wednesday for
another seasonal, pleasant day. Dry weather will continue Thursday with another weak
front sometime on Friday. This could present a burn opportunity, but it is too soon to
tell about timing and strength.
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:240912:0834
</pre>
</body>
</html>