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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT WED AUG 01 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from 12:00pm to 2:00pm with a 50 acre limit.
Propane flaming is allowed from 12:00pm to 5:00pm.
WEATHER DISCUSSION:
Weak upper level trough to zonal-like pattern remains over the Pacific Northwest today.
Marine low clouds have banked up into the Coast Range this morning with clouds moving
through the Columbia River and down into the north Willamette Valley. Upper
air sounding shows a similar pattern to yesterday with little temperature decrease going
up to 4000 ft and low level wind flow NNW to NNE at 5 - 10 mph.
Expect little change in the upper air pattern today with only a minor disturbance moving
down from the north later today and tonight. Some low clouds will continue moving down
into the Willamette Valley this morning but should burn off by noon. Mixing
heights rise to similar levels as yesterday reaching about 3000 ft around noon and 4500
ft
by late afternoon. Transport and surface winds will be mostly a light NW to N.
Pressure gradients are 1.1 mb onshore from Newport to Salem and 2.4 mb onshore from Salem
to Redmond. Portland to Medford gradient is 2.6 mb northerly.
Expect little change with gradient stacking remaining to the east.
Prospects for open field burning are questionable and will likely need to wait for
verification from pibals this afternoon.
TODAY'S FORECAST:
Salem's high temperature today will be near 81.
Relative humidity drops to 50% by 12:30 pm. Minimum relative humidity 33%.
Surface winds: NW to N at 4 - 8 mph
Transport winds: NNW to NNE at 4 - 8 mph becoming NW to NNW at 6 - 10 mph during the
afternoon
Maximum mixing height: 4500 feet
Sunset tonight: 8:37 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 70 79 81 70
Relative Humidity: 53% 36% 33% 49%
Surface Wind Direction: 360 340 350 320
Surface Wind Speed: 5 7 8 8
Transport Wind Direction: 360 350 340 320
Transport Wind Speed: 6 7 8 11
Estimated Mixing Height: 2500 3800 4500 2000
Ventilation Index: 15 27 36 22
EXTENDED DISCUSSION:
Upper level trough moves down from the north and may increase the onshore flow tomorrow
afternoon. It's still questionable, however, whether it will be enough for a burning
opportunity. This trough will move to the east Friday giving way to an upper ridge.
Expect warming conditions through the weekend with mostly northerly to offshore flow.
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.
Nick Yonker
ODF Meteorologist
jlwx:010812:0840
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