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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE JUL 10 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
A southwesterly flow pattern in the upper atmosphere continues over the Pacific Northwest.
This is likely to continue for another few days.
At the surface a thermal trough extends from thecentral valley of California into
southwest Oregon similar to yesterday. A lee-sidetrough is again evident in the pressure
pattern over east central Washington. Low level flow has been mostly northerly in the
Willamette Valley and this should continue through the afternoon.
Pressure gradients are onshore with gradient stacking to the east. Pressure gradients as
of 11am included: Newport to Salem, 0.6 mb onshore; Salem to Redmond, 3.6 mb onshore;
Newport to Redmond, 4.2 mb onshore; Eugene to Medford, 4.3 mb northerly; Portland to
Eugene, 1.0 mb northerly; and Portland to Medford, 5.3 mb northerly.
The morning Salem sounding showed stable conditions to about 5000 feet. Temperatures had
cooled slightly since the same time yesterday morning at all levels below 12000 feet.
Temperatures climbing into the low to mid 80’s today should push mixing heights to a
little above 4100 feet, but northerly transport winds mean conditions unfavorable for
open
field burning.
TODAY'S FORECAST:
Sunny and warm.
Salem's high temperature today will be near 83.
Minimum relative humidity 38%.
Surface winds: Northerly 8-10
Transport winds: Northerly 8-10
Maximum mixing height: 4100 feet.
Sunset tonight: 8:59 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 76 84 79
Relative Humidity: 45% 36% 44%
Surface Wind Direction: 020 020 340
Surface Wind Speed: 7 7 7
Transport Wind Direction: 010 010 030
Transport Wind Speed: 9 8 8
Estimated Mixing Height: 3900 4100 1200
Ventilation Index: 35 33 10
EXTENDED DISCUSSION:
Computer models are still uncertain with respect to weather later in the week. It does
look like some sort of upper level trough or closed low will affect the Pacific Northwest
late in the week and heading into the weekend. While the chances for precipitation are
low it can’t be ruled out. In the meantime dry weather will continue but unfavorable
northerly transport winds are likely Wednesday and Thursday.
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:100712:1143
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