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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON SEP 12 2011
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Late morning satellite pictures show the low clouds have nearly completely burned off in
the Willamette Valley. This is good news as it will allow temperatures to warm up which
will cause pressures to drop and thus even out the pressure gradient stacking that exists
now.
Pressure gradients as of 11am included: Newport to Salem, 0.8 mb onshore; Salem to
Redmond, 2.8 mb onshore; and Newport to Redmond, 3.6 mb onshore.
The surface analysis shows a trough in eastern Washington extending southwestward into
central Oregon and the California thermal trough just barely extending into SW Oregon.
Temperatures are mostly in the upper 60's and low 70's as of late morning. A temperature
of about 78 will be needed to mix out enough of the morning inversion to raise the mixing
height to above 3000 feet.
Models indicate a good westerly component to transport winds this afternoon. That will
need to be monitored with pibals.
If pressure gradients equalize then conditions will likely be marginally favorable for
open field burning this afternoon.
THIS AFTERNOON'S FORECAST:
Mostly sunny.
Salem's high temperature today will be near 82.
Relative humidity drops to 50% by 2pm. Minimum relative humidity 41%.
Surface winds: SW 8-12 mph.
Transport winds: WSW to WNW 6-9
Maximum mixing height: 3300 feet
Sunset tonight: 7:29 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 80 82 70
Relative Humidity: 48% 41% 66%
Surface Wind Direction: 230 230 230
Surface Wind Speed: 8 12 12
Transport Wind Direction: 240 270 290
Transport Wind Speed: 6 6 11
Estimated Mixing Height: 2900 3300 900
Ventilation Index: 17 20 10
EXTENDED DISCUSSION:
New model runs show a weak upper ridge remains to the north and a weak upper low meanders
over California tomorrow. Transport winds are forecast to be quite light and there is no
obvious burn opportunity, but close monitoring may allow some burning.
On Wednesday, transport winds are forecast to be northwesterly and again, close
monitoring may reveal a small window of opportunity.
The remains of a weak Pacific cold front should reach the Pacific Northwest sometime on
Thursday which, if timing is right, provide a burn opportunity for the Silverton Hills
area.
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:120911:1155
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