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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE AUG 09 2011
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from 11:00am to 2:00pm with a 50 acre limit.
Propane flaming is allowed from 11:00am to 5:00pm.
WEATHER DISCUSSION:
Clouds are burning off sooner today than yesterday. As a result temperatures today are
running 5 to 9 degrees warmer as of late morning. With the surface warming mixing
heights
should now be above 3000, headed for a maximum of over 5000 feet.
Wind directions will be dicy for open field burning today. The latest NAM computer model
shows less westerly than the earlier model run for this afternoon and evening. University
of Washington models are also rather pesimistic about wind directions, showing transport
winds at about 340 degrees.
Pressure gradients are also not showing much improvement. As of 11am Newport to Salem
was just 0.9 mb onshore while Salem to Redmond was holding at 4.7 mb onshore - not
significantly different than earlier this morning.
Bottom line: I'm not optimistic about the chances favorable conditions for open field
burning this afternoon. We will monitor gradients and a pibal is scheduled for 1pm to
check winds.
THIS AFTERNOON'S FORECAST:
Partly cloudy to mostly Sunny. Temperatures warm but a little below average for the time
of year.
Salem's high temperature today will be near 79.
Relative humidity drops to 50% by 10am. Minimum relative humidity 32%.
Surface winds: NW 6-9 mph.
Transport winds: NNW 6-9 becoming NW this evening.
Maximum mixing height: 5200 feet.
Sunset tonight: 8:28 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 73 77 71
Relative Humidity: 38% 32% 42%
Surface Wind Direction: 330 340 310
Surface Wind Speed: 8 8 8
Transport Wind Direction: 340 340 320
Transport Wind Speed: 7 9 10
Estimated Mixing Height: 5200 5200 1000
Ventilation Index: 36 47 10
EXTENDED DISCUSSION:
Very little change in the overall weather pattern is expected tomorrow. Slightly higher
pressure aloft and an earlier burn-off to any morning low clouds are about the only
change. Computer models continue to show a northwesterly transport only marginally
favorable for open field burning. The gradient stacking to the east issue may improve by
tomorrow afternoon.
Longer range, dry weather with a generally light westerly flow aloft will close out the
week and weather looks dry into the weekend.
The National Weather Service’s digital forecast is available at:
http://forecast.weather.gov/MapClick.php?lat=44.905&lon=-122.810.
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:090811:1133
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