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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON AUG 27 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is allowed from 11:00am to 5:00pm.
WEATHER DISCUSSION:
Upper air charts show a strong low pressure area just west of Vancouver Island this
morning. This supported a weak cold front that moved through the region overnight last
night. Precipitation was light except along the coast. Weather stations in the
Silverton Hills generaly showed two to three hundredths of an inch this morning.
The front ushered in much cooler air aloft. At 5000 feet the morning Salem sounding
showed temperatures had cooled about 13 degrees (F) since yesterday. This has
destabilized the atmosphere and mixing heights should climb to well above 5000 feet this
afternoon. The 3000 foot threshold should be reached by late morning.
The morning sounding also showed brisk southwesterly winds over the central Willamette
Valley.
Winds at 5000 feet were southwesterly around 30mph. The winds in the lower atmosphere
should decrease today but still be in a favorable with respect to direction and speed for
field burning this afternoon.
Gradient stacking could become an issue today but as of 8am gradients are quite flat.
Newport to Salem 0.3mb onshore and Salem to Redmond 0.4mb onshore.
Bottom line: If gradient stacking east does not become an issue this afternoon and
fields are not too damp today could develop into a good burn opportunity.
TODAY'S FORECAST:
Partly sunny.
Salem's high temperature today will be near 77.
Relative humidity drops to 50% by 1pm and reaches 36% by late afternoon.
Surface winds: Light and variable becoming SW to W 5-7 mph in the afternoon.
Transport winds: SW to W 8-10 mph.
Mixing height: reaches 3000 feet by 10am and peaks around 6000 feet today.
Sunset tonight: 7:56 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 68 76 77 70
Relative Humidity: 63% 40% 36% 49%
Surface Wind Direction: 140 220 260 280
Surface Wind Speed: 5 6 6 5
Transport Wind Direction: 230 250 270 270
Transport Wind Speed: 10 9 8 7
Estimated Mixing Height: 4200 5000 6000 1000
Ventilation Index: 42 45 48 7
EXTENDED DISCUSSION:
The offshore upper low will continue over the northeast Pacific Ocean into early Tuesday
with little push to bring any precipitation onshore. Models indicate that a short wave
will swing around the base of the low and cause it to swing onshore and lift out later
Tuesday and into Wednesday. It looks like Tuessday night and Wednesday morning will be
the main time frame for a better chance of showers.
Models indicate troughiness remaining over the eastern Pacific and Pacific northwest
through the week. An impulse swings through the base of this trough late Thursday for
another slight chance of showers. Beginning Friday and through the weekend temperatures
warm and dry weather is likely.
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:270812:0828
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