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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON OCT 01 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
The late morning ODF surface pressure analysis shows high pressure centered over the
northern Puget Sound area with a thermal trough from Central California extending to off
the SW Oregon coast. With higher pressure to the north and lower pressure to the south
winds have been northerly overnight and this should continue during the day today.
The morning Salem sounding had a slightly northeasterly wind. Speeds were near 15 mph
from about 500 feet to around 5000 feet.
The sounding also showed warmer temperatures aloft compared to yesterday morning at the
same time. There was a strong inversion from from about 1800 to 2500 feet with stable
conditions above. This should limit mixing heights today.
Pressure gradients as of 8am: Newport to Salem, 0.8 mb onshore; Salem to Redmond, 1.6 mb
offshore
While surface winds will become light northwesterly after 5pm this evening the
northwesterly flow will be shallow with north or northeasterly transport winds continuing
above. Latest smoke trajectory forecasts indicate that smoke from any burning this
afternoon would head right to Eugene.
THIS AFTERNOON'S FORECAST:
Salem's high temperature today will be near 80.
Minimum relative humidity drops to 30%.
Surface winds: Northherly 5-10mph. Becoming northwesterly late.
Transport winds: Northerly 16-22 mph.
Maximum mixing height: 2500 feet.
Sunset tonight: 6:50 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 76 80 68
Relative Humidity: 31% 29% 49%
Surface Wind Direction: 350 360 330
Surface Wind Speed: 6 8 4
Transport Wind Direction: 020 010 010
Transport Wind Speed: 20 22 21
Estimated Mixing Height: 2200 2500 200
Ventilation Index: 44 55 4
EXTENDED DISCUSSION:
Latest computer model runs are consistent with earlier runs.
A dry cold front will move across the region tonight to bring cooler temperatures to the
Willamette Valley for Tuesday. Behind the front high pressure will rebuild over eastern
Washington. The thermal trough will continue off the southern Oregon coast and possibly
build northward a bit. This will give a dry, offshore, northeasterly wind pattern to the
region at least through Thursday.
Weather conditions do not look conductive to open field burning much of this 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:011012:1141
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