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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE AUG 07 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from now until 2:00pm with a 50 acre limit.
Propane flaming is allowed from now until 5:00pm.
WEATHER DISCUSSION:
Satellite pictures show clouds in the Willamette Valley burning off giving sunny skies to
the area. Low clouds and fog are still visible along the coastal strip however. The
scattered high clouds of earlier today have also moved away.
Latest computer model runs still indicate a favorable westerly transport wind for today.
This will need to be confirmed by pibals this afternoon.
As temperatures rise mixing heights improve to 3000 feet by about 2pm.
The limiting factor on open field burning continues to be gradient stacking and the
subsidence it implies to the east of the valley. As of 11am Newport to Salem was at 1.7
mb onshore, Salem to Redmond was up to 3.3 mb onshore for a total Newport to Redmond
onshore gradient of 5.0 mb.
With continued warming of the valley and continued low clouds along the coast pressure
gradients should balance out later this afternoon for a burn opportunity.
THIS AFTERNOON'S FORECAST:
Mostly sunny. Warm.
Salem's high temperature today will be near 83.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 38%.
Surface winds: Light winds becoming westerly 5-7 in the afternoon
Transport winds: Light westerly becoming west 5-10 in the afternoon
Maximum mixing height: 3600 feet.
Sunset tonight: 8:29 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 77 83 75
Relative Humidity: 48% 38% 48%
Surface Wind Direction: 290 310 290
Surface Wind Speed: 4 6 6
Transport Wind Direction: 260 290 290
Transport Wind Speed: 5 10 12
Estimated Mixing Height: 3000 3600 1500
Ventilation Index: 15 36 18
EXTENDED DISCUSSION:
There will be a good influx of marine air overnight tonight and tomorrow should be cloudy
and cooler with partial afternoon cooling. The first day after a marine push is usually
a poor open field burning day and tomorrow looks like no exception. Expect cloudy skies
with some afternoon clearing and temperatures limited to the upper 70’s. There will be
strong gradient stacking to the east and unfavorable northerly transport winds.
Thursday and Friday will see morning clouds, with afternoon sun and a slow warming trend
in temperatures. There may be small windows of opportunity during the afternoon hours.
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:070812:1151
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