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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT MON JUL 23 2012
BURN ADVISORY:
Recommended burn times for agricultural burning are from now until 7:00pm.
Prep burning is allowed from now until 5:00pm with a 50 acre limit.
Propane flaming is allowed from now until 5:00pm.
WEATHER DISCUSSION:
An upper level low over northern Washington is pulling out to the northeast today as
higher pressure aloft builds to give the region more sunshine than was the case the past
few days. Temperatures will warm as well, although remain a bit below average for late
July.
Surface pressure charts show a well developed thermal trough in the
central valley of California extending northwestward to just off the southern Oregon
coast. Higher pressure is nosing into northwestern Oregon. Pressure gradients as of
11am
included: Newport to Salem, 0.3 mb onshore; Salem to Redmond, 2.3 mb onshore; Newport to
Redmond, 2.6 mb onshore and Portland to Medford, 5.9 mb northerly. The northerly gradient
will dominate today for a generally northerly transport flow. In fact there will likely
be a slight northeasterly component as the thermal trough strengthens over southern
coastal waters.
The morning Salem sounding showed cooling aloft this morning compared to Sunday morning.
Mixing heights should be quite high this afternoon, reaching above 5000 feet. Models
show
warming aloft this afternoon and with the increased sunshine surface temperatures should
be significantly warmer than yesterday. In addition, humidities will be lower.
The northerly or northeasterly transport winds make today an unfavorable day for open
field burning.
THIS AFTERNOON'S FORECAST:
Salem's high temperature today will be near 80.
Relative humidity drops to 50% by 2pm. Minimum relative humidity 30%.
Surface winds:
Transport winds:
Maximum mixing height:
Sunset tonight: 8:49 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 72 76 73
Relative Humidity: 39% 36% 44%
Surface Wind Direction: 360 010 360
Surface Wind Speed: 10 12 9
Transport Wind Direction: 020 020 020
Transport Wind Speed: 13 14 17
Estimated Mixing Height: 5000 5800 4000
Ventilation Index: 65 81 68
EXTENDED DISCUSSION:
Computer models continue to show dry weather through this week. A weak upper level trough
will set up offshore to give the region southwesterly flow aloft. Surface pressure
patterns look to become more favorable to an afternoon sea-breeze regime and possible open
field burning opportunities later 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:230712:0159
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