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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE SEP 27 2011
BURN ADVISORY:
Recommended burn times for agricultural burning are from now until 5:00pm.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Late morning satellite pictures show a solid layer of clouds covering virtually all of
theWillamette Valley but a more broken cloud pattern over the north coast range. Some
sun breaks are likely in the valley later this afternoon.
Upper level flow is southwesterly on the eastern side of a broad but shallow upper level
trough that extends from the gulf of Alaska into the eastern Pacific Ocean.
Barometric pressures have been rising since yesterday afternoon and the higher pressure
that is building in should give some dry weather for the next few days.
Transport winds should be favorable for open field burning this afternoon but gradient
stacking is not. Pressure gradients as of 11am included: Newport to Salem, 0.4 mb
onshore; Salem to Redmond, 3.4 mb onshore; and Newport to Redmond, 3.8 mb onshore.
All of this is moot since wet fields will likely preclude any burning this afternoon.
THIS AFTERNOON'S FORECAST:
Turning mostly cloudy with a few sun breaks.
Salem's high temperature today will be near 67.
Minimum relative humidity 58%.
Surface winds: W 4-6 becoming NW 4-6 mid aftrenoon.
Transport winds: W 10-12 becoming NW 10-12 mid aftrenoon.
Maximum mixing height: 4800 feet.
Sunset tonight: 7:00 pm.
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 65 65 60
Relative Humidity: 65% 58% 67%
Surface Wind Direction: 220 270 300
Surface Wind Speed: 5 6 5
Transport Wind Direction: 280 300 330
Transport Wind Speed: 11 11 14
Estimated Mixing Height: 4600 4700 1500
Ventilation Index: 51 52 21
EXTENDED DISCUSSION:
High pressure builds in to the north tomorrow wtih a thermal trough building along the
coast. This will dry out the atmsosphere for mostly sunny skies tomorrow afternoon.
Winds will become northeasterly. Conditions will be unfavorable for burning but good for
drying wet fields.
There is a potential burn opportunity on Thursday afternoon as the remains of the thermal
trough shift east in advance of a weakening pacific front due in later Friday.
The Friday system looks quite weak and may not be a rain producer, although it will give
onshore flow for clouds and cooler temperatures.
The weekend looks dry with the next system due in on Monday.SCUSSION:
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:270911:1131
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