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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT TUE JUL 31 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from now until 2:00pm with a 50 acre limit.
Propane flaming is allowed from now until 5:00pm.
WEATHER DISCUSSION:
Most of the low cloudiness in the Willamette Valley has evaporated by late morning and
temperatures are running 3 to 5 degrees warmer than yesterday. There is still
considerable gradient stacking to the east, but quite as much as 24 hours ago.
Pressure gradients as of 11am included: Newport to Salem, 0.9 mb onshore; Salem to
Redmond, 3.3 mb onshore; and Portland to Medford, 3.8 mb northerly.
Latest trajectory models are still showing any smoke from the Silverton Hills heading to
the south our south-southeast.
An upper level disturbance is now moving into the Washington Cascades but appears to be
having little impact on Willamette Valley weather other than producing some scattered
high clouds to the north.
Unless pressure gradients make a dramatic change by later this afternoon the prospects
for open field burning look quite dim today.
THIS AFTERNOON'S FORECAST:
Sunny
Salem's high temperature today will be near 80.
Relative humidity drops to 50% by 2pm. Minimum relative humidity 34%.
Surface winds: Northerly increasing to 7-10 mph this afternoon
Transport winds: Northerly around 10 mph.
Maximum mixing height: 4300 feet.
Sunset tonight: 8:39 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 76 80 74
Relative Humidity: 40% 34% 43%
Surface Wind Direction: 010 010 330
Surface Wind Speed: 7 9 9
Transport Wind Direction: 010 360 350
Transport Wind Speed: 10 11 11
Estimated Mixing Height: 3800 4300 2000
Ventilation Index: 38 47 22
EXTENDED DISCUSSION:
The basic pattern of morning clouds/afternoon sunshine should continue with a slow
warming trend through the week. A weak upper disturbance moving down from BC into the
northern Rockies will alter upper level winds tomorrow night and Thursday, but right now
there are no indications that this will produce a significant burn opportunity. Later in
the week there is potential for weak offshore flow which is not favorable for open field
burning in the Silverton Hills.
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:310712:1152
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