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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT TUE AUG 16 2011
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:
Upper air charts show a weak trough about 300 miles west of Oregon with generally light
west-southwest flow in the upper atmosphere. At the surface high pressure is centered
over the northern Washington Cascades and a well developed thermal trough extends from
central California into southwest Oregon and then northward along the Oregon coast.
Low level flow is slightly offshore with the 8am pressure gradient from Redmond to Salem
at 0.4 mb and a flat gradient from Salem to Newport. Portland to Medford was 2.7mb
northerly.
The morning Salem sounding showed temperatures had warmed since yesterday at all levels
up
to 14,000 feet. While this makes the atmosphere more stable, sunshine and warm surface
temperatures this afternoon will push mixing heights to over 4500 feet.
The sounding also showed northeast winds averaging around 10mph from just above ground
level to about 6000 feet.
Computer models show continued northerly winds in the transport region through the day.
Thus there appears to be no chance for open field burning this afternoon.
TODAY'S FORECAST:
Sunny.
Salem's high temperature today will be near 85.
Relative humidity drops to 50% by 10am. Minimum relative humidity 26%.
Surface winds: N 5-9 mph.
Transport winds: N 10-15 mph.
Maximum mixing height: 4700 feet.
Sunset tonight: 8:16 pm.
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 73 81 84 77
Relative Humidity: 46% 32% 26% 35%
Surface Wind Direction: 010 010 360 330
Surface Wind Speed: 7 7 8 6
Transport Wind Direction: 360 010 010 010
Transport Wind Speed: 10 10 10 12
Estimated Mixing Height: 2500 010 4700 1000
Ventilation Index: 25 0 47 12
EXTENDED DISCUSSION:
Dry and warm weather will continue through the week.
Computer models show a weak disturbance in the upper atmosphere moving by to the north
tomorrow but it is unlikely that this will enough to provide any significant onshore flow
or favorable transport winds. Indeed, those same models are consistent in keeping low
level winds northerly. Weather patterns through the week are conducive to a generally
northerly flow pattern and any burn opportunities would depend on an afternoon sea breeze
developing. That will need to be monitored on a day-to-day basis.
Longer range charts show the possibility of more favorable low level wind patterns
developing early 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:160811:0821
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