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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE OCT 02 2012
BURN ADVISORY:
Agricultural burning burning is allowed. Recommended burn times now until 5:00pm.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Cooler weather has settled in over the Willamette Valley following passage of a dry cold
front last night. Temperatures as of late morning are running anywhere from 5 to 10
degrees cooler than yesterday at the same time.
Cooler temperatures aloft were noted on the morning Salem sounding. The atmosphere is
less stable today than yesterday and mixing heights should climb to about 3500 feet this
afternoon versus only 2500 feet yesterday.
The ODF surface pressure analysis shows higher pressure to the north and a continuing
thermal trough in the central valley of California extending north into SW Oregon then
along the Oregon coastline.
Pressure gradients as of 11am included: Newport to Salem, 2.0 mb onshore; Salem to
Redmond, 3.6 mb onshore for gradient stacking east. Meanwhile Portland to Medford had
increased to 4.4 mb northerly.
Winds have been generally northerly, and latest computer models show northerly winds
continuing.
THIS AFTERNOON'S FORECAST:
Sunny, breezy and cooler.
Salem's high temperature today will be near 72.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 33%.
Surface winds: Northerly 6-12 mph. Higher gusts.
Transport winds: Northerly 10-20 mph.
Maximum mixing height: 3500 feet.
Sunset tonight: 6:49 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 69 73 59
Relative Humidity: 42% 29% 47%
Surface Wind Direction: 360 020 350
Surface Wind Speed: 8 12 5
Transport Wind Direction: 020 010 020
Transport Wind Speed: 15 14 18
Estimated Mixing Height: 3200 3500 1700
Ventilation Index: 48 49 31
EXTENDED DISCUSSION:
Latest computer model runs are showing a strong east wind event coming up for
the latter portion of the week. Easterly winds will slacken but continue over the
weekend as well. This, of course, is not a favorable wind direction for open field
burning.
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:021012:1145
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