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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON AUG 20 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Upper air charts show a broad upper ridge over the western United States with a
relatively weak upper trough to the west over the eastern Pacific. This leaves the
region in a southwesterly flow aloft.
Satellite pictures show just a few middle and high clouds over the region as well as some
low cloudiness along the coast.
Temperatures in teh central Willamette Valley are running 7 or 8 degrees warmer than
yesterday as of late morning.
Gradient stacking east continues. Pressure gradients as of 11am included: Newport to
Salem, 0.9 mb onshore; Salem to Redmond, 2.3 mb onshore; and Portland to Medford, 3.2 mb
northerly.
Models continue to show a generally northerly transport flow this afternoon, with winds
becoming a little more northwesterly late afternoon or early evening.
Chances for a burn opportunity this afternoon are low but not impossible.
THIS AFTERNOON'S FORECAST:
Salem's high temperature today will be near 82.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 35%.
Surface winds: Northerly 4-6 mph becoming northwesterly early evening.
Transport winds: Northerly 4-6 mph becoming northwesterly and increasing early evening.
Maximum mixing height: 3900 feet.
Sunset tonight: 8:09 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 76 82 74
Relative Humidity: 45% 35% 50%
Surface Wind Direction: 010 010 320
Surface Wind Speed: 5 6 5
Transport Wind Direction: 350 340 320
Transport Wind Speed: 3 5 10
Estimated Mixing Height: 3000 3900 1000
Ventilation Index: 9 20 10
EXTENDED DISCUSSION:
The upper trough off the coast moves across the region tomorrow afternoon and may present
a burn opportunity. Models are showing westerly transport winds for tomorrow. Upper
flow will be generally westerly much of the rest of the week, but models show transport
level flow back to northerly by Wednesday. Expect sunny skies and high temperatures near
80 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:200812:1155
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