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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON AUG 13 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from 3:00pm to 5:00pm with a 50 acre limit.
Propane flaming is allowed from 3:00pm to 5:00pm.
WEATHER DISCUSSION:
Late morning satellite pictures show sunny skies over the Oregon except for low clouds
and
fog along the immediate coastal strip and locally in some coastal valleys. Air quality
monitoring stations around the state are showing elevated readings mainly do to wildfire
smoke.
Low level flow is weak but generally northerly. Pressure gradients as of 11am included:
Newport to Salem, 2.1 mb onshore; Salem to Redmond, 0.8 mb onshore; and Portland to
Medford, 2.5 mb northerly.
Computer models indicate a continued northerly transport flow this afternoon. Afternoon
pibals will be needed to confirm the generally unfavorable wind situation.
THIS AFTERNOON'S FORECAST:
Sunny, not as hot as yesterday.
Salem's high temperature today will be near 89.
Minimum relative humidity 28%.
Surface winds: Northerly 7-10.
Transport winds: Northerly 4-6 becoming north-northwesterly mid-evening.
Maximum mixing height: 3200 feet.
Sunset tonight: 8:20 pm.
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 89 95 81
Relative Humidity: 33% 24% 37%
Surface Wind Direction: 010 010 330
Surface Wind Speed: 8 8 9
Transport Wind Direction: 360 340 330
Transport Wind Speed: 5 6 9
Estimated Mixing Height: 5600 7200 2000
Ventilation Index: 28 43 18
EXTENDED DISCUSSION:
Another upper level disturbance will move by to the north tomorrow. This will draw
additional marine air into the valley for morning clouds and cooler temperatures. Models
show a continued unfavorable northerly transport wind. High pressure will rebuild
Wednesday and begin another spell of hot weather. Transport flow will likely become
offshore or easterly and preclude any burning later in the week. In addition Fire Marshal
burn-ban conditions may come into play Thursday and Friday.
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:130812:1154
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