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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT WED AUG 15 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
A small but very persistent patch of clouds is still showing up on satellite pictures
covering a portion of Marion County. Otherwise the Willamette Valley is seeing sunny
skies. Temperatures are generally running a degree or two warmer than yesterday at the
same time, except where this small patch of clouds is hanging tough. Temperatures there
are about 4-6 degrees cooler. I have revised the high temperature forecast downward for
Salem.
Otherwise the forecast is verifying nicely. There is an easterly pressure gradient across
the Cascades with Redmond's pressure 2.0 millibars higher than Salem's as of 11am. There
is a weak onshore gradient between the coast and the Valley. Our late morning surface
pressure analysis shows the thermal trough running north-south through the valley with the
axis on the west side of I5. This will give generally north-northeasterly transport winds
to the grass-seed growing areas of the Silverton Hills.
THIS AFTERNOON'S FORECAST:
Salem's high temperature today will be near 90.
Relative humidity drops to 50% by 12pm. Minimum relative humidity 26%.
Surface winds: North-northeast 5-8 mph.
Transport winds: North-northeast incresing to 12-18 mph.
Maximum mixing height: 4000 feet.
Sunset tonight: 8:17 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 82 90 85
Relative Humidity: 49% 34% 40%
Surface Wind Direction: 010 020 360
Surface Wind Speed: 7 7 6
Transport Wind Direction: 020 030 030
Transport Wind Speed: 10 12 18
Estimated Mixing Height: 3200 4000 2000
Ventilation Index: 32 48 36
EXTENDED DISCUSSION:
Temperatures warm up tomorrow with highs likely near 100 degrees. Temperatures will stay
warm Friday but cool some Saturday as upper flow turns southerly bringing some mid-level
moisture northward. Fire Marshal burn-ban conditions will likely be reached Thursday and
Friday. Thunderstorms will work their way northward Saturday and temperatures will cool
further Sunday.
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:150812:1148
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