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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE OCT 09 2012
BURN ADVISORY:
Recommended burn times for agricultural burning are from 2:00pm to 4:30pm.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Upper air charts show a low aloft spinning off the northern California coast while the
upper level high pressure area that has provided the sunny warm weather to the Pacific
Northwest is now retreating into the northern Gulf of Alaska. Most of Oregon is in a
region of easterly winds aloft in the counter-clockwise flow around the California low.
Latest computer models show northerly transport winds this afternoon, and the relatively
large north to south pressure gradient compared to the west to east gradient supports
this.
Pressure gradients as of 11am included: Newport to Salem, 0.8 mb onshore; Salem to
Redmond, 0.6 mb onshore; and Portland to Medford, 2.4 mb northerly.
Northern Willamette Valley air quality measuring stations have been showing elevated
readings, likely due to fires in Washington. Some smoke from the Pole Creek fire near
Sisters may be making it into the Valley as well.
With the northerly transport pattern today is not a good candidate for open field
burning.
THIS AFTERNOON'S FORECAST:
Mostly Sunny.
Salem's high temperature today will be near 72.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 37%.
Surface winds: Light and variable with a tendency toward NNW.
Transport winds: Light and variable becoming NNE this afternoon.
Maximum mixing height: 3000 feet.
Sunset tonight: 6:36 pm.
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 64 67 55
Relative Humidity: 48% 42% 69%
Surface Wind Direction: 330 340 320
Surface Wind Speed: 5 5 3
Transport Wind Direction: 360 015 030
Transport Wind Speed: 7 10 11
Estimated Mixing Height: 2800 3000 500
Ventilation Index: 0 0 0
EXTENDED DISCUSSION:
Low level flow goes back to light westerly tomorrow and Thursday for possible burn
opportunities.
The weather pattern continues to evolve toward a wet, more fall-like regiem later this
week. Rain should reach the Valley by mid-morning Friday. Another surge of moisture
moves in on Saturday and another, what is now looking like a fairly active system, moves
in Sunday night and early Monday. This weekend should mark the end of the 2012 open
field burning season as long range charts indicate additional periods of rain next week.
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:091012:1152
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