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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00PM PDT TUE SEP 25 2012
BURN ADVISORY:
Agricultural burning burning is allowed. North of Woodburn recommended burn times
3:00pm to 5:00pm. Woodburn south recommended burn times are now until 5:00pm.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
High pressure is building in behind a Pacific cold front that moved through overnight
last night. A thermal trough extends from northern California into SW Oregon.
This pattern normally gives northerly transport winds to the Willamette Valley and today
is no exception.
The morning Salem sounding tracked northerly winds to about 5000 feet. Above that winds
backed to westerly. The sounding showed some cooling since yesterday up to about 5000
feet as well. This means a less stable atmosphere today and better mixing conditions.
Maximum mixing height today should reach about 4200 feet versus yesterday's 2800 feet.
Pressure gradients as of 11am included: Newport to Salem, 2.4 mb onshore; Salem to
Redmond, 2.1 mb onshore. However, it is the north wind that will preclude any open
field burning today.
TODAY'S FORECAST:
Sunny.
Salem's high temperature today will be near 74.
Minimum relative humidity 35%.
Surface winds: N-NNE 5-8 mph increasing to 9-15 by evening.
Transport winds: N-NNE 9-14 mph.
Maximum mixing height: 4200 feet.
Sunset tonight: 7:02 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 71 73 65
Relative Humidity: 41% 35% 46%
Surface Wind Direction: 010 030 360
Surface Wind Speed: 7 9 15
Transport Wind Direction: 010 020 020
Transport Wind Speed: 11 13 14
Estimated Mixing Height: 3800 4000 3900
Ventilation Index: 42 52 55
EXTENDED DISCUSSION:
Ridging aloft will continue over the Pacific Northwest tomorrow and Thursday, and it now
looks like into Friday as well. This pattern suggests unfavorable northerly winds.
Latest models show the next Pacific frontal system moving in Friday night and it looks
like a near repeat of what went through last night: That is little, if any rain, and no
burn opportunity ahead of it. We will monitor this system for possible changes in speed
or intensity.
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:250912:1146
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