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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE AUG 16 2011
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from now until 2:00pm with a 50 acre limit.
Propane flaming is allowed from now until 5:00pm.
WEATHER DISCUSSION:
Satellite pictures show cloud-free skies over the entire state at the noon hour.
Pressure gradients have now turned weakly onshore. Newport to Salem is at 0.6 mb onshore
and Salem to Redmond is 0.0 mb or flat. This is dominated by Portland to Medford which is
at 3.1 mb northerly.
Late this morning most area weather stations were showing temperatures in the upper 60's
to mid 70's with light northerly winds.
Latest computer model runs are still showing a northerly transport wind for this
afternoon. Expect northerly winds 10 to 15mph up to about 4000 feet at which point the
winds go light and variable.
THIS AFTERNOON'S FORECAST:
Sunny and warm.
Salem's high temperature today will be near 86.
Relative humidity drops a minimum of 26% later this afternoon.
Surface winds: N 5-9 mph.
Transport winds: N 10-15 mph.
Maximum mixing height: 4700 feet.
Sunset tonight: 8:17 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 81 86 78
Relative Humidity: 30% 23% 32%
Surface Wind Direction: 360 010 330
Surface Wind Speed: 7 8 8
Transport Wind Direction: 010 010 010
Transport Wind Speed: 10 10 12
Estimated Mixing Height: 3800 4700 1000
Ventilation Index: 38 47 12
EXTENDED DISCUSSION:
Dry and warm weather will continue through the week.
Computer models show a weak disturbance in the upper atmosphere moving by to the north
tomorrow but it is unlikely that this will enough to provide any significant onshore flow
or favorable transport winds. Indeed, those same models are consistent in keeping low
level winds northerly. Weather patterns through the week are conducive to a generally
northerly flow pattern and any burn opportunities would depend on an afternoon sea breeze
developing. That will need to be monitored on a day-to-day basis.
Longer range charts show the possibility of more favorable low level wind patterns
developing early next week.
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:160811:1135
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