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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON AUG 22 2011
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is allowed from now until to 5:00pm.
WEATHER DISCUSSION:
An active Pacific cold front is pushing into northwestern Washington today. Quillayute
has recorded over a half an inch of rain since the precipitation started there. So far
nothing except some coastal drizzle has been reported in Oregon.
Some middle and high level clouds out ahead of the front passed over the Willamette
Valley earlier this morning. And some marine low clouds were pushed into the valley
ahead of the front as well.
The cloudiness has held temperatures down. Temperatures are running about 10 degrees
cooler than they were yesterday at this time, and are also running cooler than forecast
earlier this morning. I have revised the high temperature today to 78 degrees for Salem.
A temperature of 76 will be required to wipe out several shallow inversions in the lower
atmosphere. Right now it looks like that should occur around 2pm.
Gradient stacking to the east remains an issue. Pressure gradients as of 11am had
Newport to Salem at 0.8 mb onshore and Salem to Redmond 3.4 mb onshore. Computer models
are not optimistic about this difference being overcome, but the key will be sunshine in
the valley. Enough heating will lower pressures here and balance the coast/valley and
valley/central Oregon gradient. Thus we will be monitoring pressures and temperatures
carefully this afternoon.
THIS AFTERNOON'S FORECAST:
Partly cloudy.
Salem's high temperature today will be near 78.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 43%.
Surface winds: SSW becoming SW 8-10 mph.
Transport winds: Generally westerly 10-13 mph.
Maximum mixing height: 3900 feet
Sunset tonight: 8:07 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 75 78 70
Relative Humidity: 55% 49% 61%
Surface Wind Direction: 200 230 240
Surface Wind Speed: 8 10 9
Transport Wind Direction: 250 270 270
Transport Wind Speed: 10 13 11
Estimated Mixing Height: 3000 3900 1000
Ventilation Index: 35 51 11
EXTENDED DISCUSSION:
The front moving into Washington should stall overnight then the remains will push
through Oregon early tomorrow. By that time it should be considerably weakened. If it
induces a strong marine push early tomorrow then tomorrow would not be a good burn day.
If its effect is minimal then tomorrow could work out as a pretty good burn day. This
will need to be monitored closely.
The remains of the front will be east of the Cascades by Wednesday and temperatures
should pop up a few degrees and skies should be sunny through the end of the week.
However this also means a return to a more northerly transport wind pattern and more
unfavorable burn conditions.
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:220811:1149
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