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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE JUL 17 2012
BURN ADVISORY:
Recommended burn times for agricultural burning are from 1:00pm to 7:00pm.
Prep burning is allowed from 1:00pm to 5:00pm with a 50 acre limit.
Propane flaming is allowed from 1:00pm to 5:00pm.
WEATHER DISCUSSION:
The upper level low pressure area that dominate has been the major feature of Pacific
Northwest recently continues to meander. Just before noon it was still just offshore of
northern California, not far from the Oregon border.
The low will meander today,gradually working its way back northward. Satellite
pictures convection has decreased, but it will likely pick up again with daytime heating
this afternoon. Virtually any place in Oregon is vulnerable to a shower or a
thunderstorm, but most areas will stay dry.
Low level flow is weakly onshore. Transport winds should be southwesterly at low levels,
but the circulation around the upper low to the south means easterly flow aloft.
The complex and changeable flow pattern, together with chances for rain and relatively
high humidities make today an unfavorable burning day.
THIS AFTERNOON'S FORECAST:
Salem's high temperature today will be near 81.
Relative humidity drops to 50% by 5pm. Minimum relative humidity 49%.
Surface winds:
Transport winds:
Maximum mixing height:
Sunset tonight: 8:54 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 77 80 72
Relative Humidity: 54% 51% 61%
Surface Wind Direction: 230 250 260
Surface Wind Speed: 4 6 7
Transport Wind Direction: 250 250 250
Transport Wind Speed: 4 5 4
Estimated Mixing Height: 4800 5000 2000
Ventilation Index: 19 25 8
EXTENDED DISCUSSION:
The upper level low will still be over SW Oregon tomorrow and mid Willamette Valley
weather patterns will still be unfavorable for open field burning. In fact it won’t be
until Friday before the remains of the low lift out to the northeast and weather patterns
become more typical of summer.
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:170712:1139
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