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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT WED AUG 10 2011
BURN ADVISORY:
Agricultural 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 cloud-free skies over virtually all of Oregon. Temperatures are
running close to where they were yesterday in the immediate Willamette Valley, but most of
the rest of western Oregon has warmed several degrees in past 24 hours.
Pressure gradient stacking to the east continues as of late morning. However gradients
have relaxed condiserably since yesterday and at last report are headed the right
direction to even out the coast-to-valley and valley-to_Redmond gradients. At 11am
Newport to Salem was at 0.7 mb onshore; Salem to Redmond, 2.8 mb onshore.
The latest run of the NAM computer model shows more northerly in the transport winds than
the earlier runs were showing. Meanwhile the latest University of Washington Models are
showing transport winds around 330 or 340 degrees - marginal at best. Pibals will tell
the story.
THIS AFTERNOON'S FORECAST:
Sunny, temperatures a few degrees below average for this time of year.
Salem's high temperature today will be near 79 (Average: 85).
Minimum relative humidity today: 31%.
Surface winds: NW 5-8mph
Transport winds: NNW to NW 5-9 mph
Maximum mixing height: 4800 feet
Sunset tonight: 8:26 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 75 78 72
Relative Humidity: 37% 32% 44%
Surface Wind Direction: 320 320 300
Surface Wind Speed: 5 7 7
Transport Wind Direction: 340 330 330
Transport Wind Speed: 5 6 9
Estimated Mixing Height: 4600 4800 1000
Ventilation Index: 23 35 9
EXTENDED DISCUSSION:
An upper level low developing over Alaska today will deepen and drop into the Gulf of
Alaska the next few days. By late Friday this should shift upper level winds to more
southwesterly and should give more of a westerly component to transport level flow.
Longer range charts still indicate a possibility of cooler weather and a chance for some
precipitation beginning Monday of 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:100811:1145
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