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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON SEP 10 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
The first Pacific cold front of the season moved into western Washington and northwest
Oregon overnight last night. Satellite pictures show the system weakening as it
continues to move east. Rainfall amounts ranged from a few hundredths to around a thrid
of an inch in the north coast range. Marion county saw from .01 to .07 inches. From
Radar it appears that any remaining rain moved into the Cascade foothills. There are
some post frontal showers visible on radar and satellite off the Washington coast but
those should remain to the north.
At the surface the thermal trough in northern California snd SW Oregon remains.
As high pressure at the surface noses into Washington and NW Oregon behind the front
winds in the Willamette Valley will shift to northerly and increase this afternoon.
The increasing winds this afternoon should promote fairly rapid drying of grass seed
fields, however the northerly and potentially north-northeasterly wind direction to
transport winds means today will not be a favorable day for open field burning.
TODAY'S FORECAST:
Cloudy this morning, gradually becoming mostly sunny this afternoon. Temperatures 8 to
10 degrees below average.
Salem's high temperature today will be near 70.
Relative humidity drops to 50% by 2pm. Minimum relative humidity 37%.
Surface winds: North to northwest 6 to 9 mph.
Transport winds: North to north-northeast 7-10 increasing to 14-20 this evening.
Maximum mixing height: 6100 feet.
Sunset tonight: 7:30 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 63 69 70 62
Relative Humidity: 67% 45% 38% 48%
Surface Wind Direction: 350 350 330 330
Surface Wind Speed: 6 9 9 9
Transport Wind Direction: 030 010 010 030
Transport Wind Speed: 7 10 14 20
Estimated Mixing Height: 3500 6100 6100 1800
Ventilation Index: 24 61 85 36
EXTENDED DISCUSSION:
The trough associated with today's cold front moves into central Canada tomorrow and high
pressure aloft builds just offshore. This should warm temperatures tomorrow and as the
ridge builds tempertures will get back above average by Wednesday. In fact by Thursday
temperatures will be pushing 90 once again. The downside is that there will be a north
or northeast flow pattern at transport levels for unfavorable burning conditions. The
next opportunity for open field burning looks to be late in the week when there is a
potential for a marine push.
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:100912:0832
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