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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT TUE SEP 27 2011
BURN ADVISORY:
Recommended burn times for agricultural burning are from 11:00am to 5:00pm.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
A Pacific cold front moving through the northwest brought over an inch of rain to parts
of the northern coast range yesterday and overnight. Twenty-four hour rainfall totals
included .11 at the Salem airport, .27 at Jordan Valley and .42 at the Aurora airport.
In the upper atmosphere a broad but shallow trough covers the northwestern United States.
Flow aloft over Oregon is generally west-southwesterly.
The morning Salem sounding showed warmer temperatures than yesterday above about 2500
feet. However, cooling aloft this afternoon should increase instability and mixing
heights should reach above 4500 feet by early afternoon. Winds on the sounding were
southerly to about 1000 feet, then veered to southwesterly above.
Computer models are consistent in showing a transport winds becoming a favorable westerly
direction this afternoon.
Currently there is gradient stacking to the east, and while some equalization of
pressures is likely this afternoon gradient stacking east should continue. Pressure
gradients as of 8am included: Newport to Salem, 0.5 mb onshore; Salem to Redmond, 2.3 mb
onshore; and Newport to Redmond, 2.8 mb onshore.
The major limiting factor on open field burning today will be wet fields.
TODAY'S FORECAST:
Cloudy with showers. Showers decreasing this afternoon and skies becoming just mostly
cloudy.
Salem's high temperature today will be near 67.
Minimum relative humidity 58%.
Surface winds: S 8-12 this mornning, becoming SW 7-10 then W 7-10 by late afternoon.
Transport winds: SW 10 becoming W-NW 10 this afternoon.
Maximum mixing height: 4800 feet.
Sunset tonight: 6:59 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 60 66 66 58
Relative Humidity: 81% 63% 58% 72%
Surface Wind Direction: 180 220 260 290
Surface Wind Speed: 11 8 8 6
Transport Wind Direction: 220 280 300 330
Transport Wind Speed: 10 11 11 14
Estimated Mixing Height: 2000 4600 4700 1500
Ventilation Index: 20 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.
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:270911:0828
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