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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON SEP 19 2011
BURN ADVISORY:
Recommended burn times for agricultural burning are from now until 5:00pm.
Prep burning is allowed from now until 2:00pm with a 50 acre limit.
Propane flaming is allowed from now until 5:00pm.
WEATHER DISCUSSION:
Satellite pictures show clouds still covering the central Willamette Valley. Rainfall
has apparently ended as no new reports of precipitation are coming in. The clouds should
thin and begin to break up this afternoon for partial sunshine.
Rainfall totals in the past 24 hours generally were between .10 and .25 inches. Isolated
areas received nearly .50 inches over the course of the weekend.
Latest model runs continue to show a north or north-northeast transport flow over the
region this afternoon.
Wet fields and unfavorable wind directions this afternoon will likely preclude open field
burning.
THIS AFTERNOON'S FORECAST:
Decreasing clouds, turning partly sunny.
Salem's high temperature today will be near 76.
Relative humidity drops to 50% by 2pm. Minimum relative humidity 43%.
Surface winds: N-NE 4-7 mph
Transport winds: N-NE 7-10 mph.
Maximum mixing height: 4000 feet.
Sunset tonight: 7:15 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 72 76 69
Relative Humidity: 51% 40% 51%
Surface Wind Direction: 010 020 360
Surface Wind Speed: 5 6 5
Transport Wind Direction: 030 020 030
Transport Wind Speed: 7 9 14
Estimated Mixing Height: 3500 4000 1700
Ventilation Index: 24 36 24
EXTENDED DISCUSSION:
Latest forecast models show high pressure rebuilding over the area overnight tongiht and
tomorrow. This should give a pattern of morning clouds, afternoon sunshine to the
region. Models are now showing a north-northwest transport wind tomorrow afternoon as
opposed to the due north wind modeled by earlier runs.
The ridge axis moves east on Wednesday for southwesterly winds aloft. Latest model runs
show a northwesterly transport wind at low levels backing to westerly with height.
Wedensday could present a burn opportunity.
The ridge will remain over the area through the end of the week for dry weather and
potential afternoon burn opportunities.
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:190911:1139
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