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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM 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.
The morning Salem sounding showed light southerly winds up to about 3000 feet but
northeasterly winds above that. However, low level winds should shift to northerly or
northeasterly during the day today.
The sounding also shows that temperatures have cooled a bit in low levels. There is
still an inversion between about 2000 and 3000 feet however. This will limit mixing
today and the maximum mixing height should top out around 3000 feet.
Satellite pictures show low clouds along the coast and pushing into coastal valleys.
There are also some patchy low clouds and areas of fog in the Willamette Valley. The
clouds and fog should burn off quickly for a mostly sunny afternoon.
Pressure gradients are flat with just 0.8mb onshore from Newport to Salem and 0.6mb
onshore from Salem to Redmond. The Portland to Medford gradient is 2.1mb northerly.
With the light northerly flow today is not a favorable day for open field burning.
TODAY'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:
11am 2pm 5pm 8pm
Temperature: 57 69 72 59
Relative Humidity: 64% 42% 37% 60%
Surface Wind Direction: 150 330 360 290
Surface Wind Speed: 3 4 4 2
Transport Wind Direction: 330 360 015 030
Transport Wind Speed: 2 7 10 11
Estimated Mixing Height: 2000 2800 3000 500
Ventilation Index: 4 20 30 6
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:091012:0833
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