[willamette-fcst] Silverton Hills Forecast - Mon, Aug 16 2010
Willamette Valley Field Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Mon Aug 16 08:26:43 PDT 2010
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON AUG 16 2010
BURN ADVISORY:
**** Fire Marshal conditions possible this afternoon ****
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Hot weather continues over the Pacific Northwest today although there are signs
that conditions are beginning to change. A ridge of high pressure in the upper
atmosphere extends from off the Oregon coast, northward into the Yukon. The
morning ODF surface anlysis shows a thermal trough extending from central
California into SW Oregon, and a thermal low in the Columbia basin east of the
cascades. Pressure gradients are fairly flat. The Newport to Redmond pressure
difference as of 8am this morning was 0.5 mb offshore.
The morning Salem sounding showed a strong surface-based inversion extending to
about 3100 feet above the ground. This will just barely break today and the we
expect the maximum mixing height will only climb to 3200 feet.
Wind direction through the Valley will be northerly or slightly northeasterly.
The Valley will be close to Fire Marshal Burn Ban conditions this afternoon for
temperature and humidity. (Ninety-five degrees and less than 30 percent humidity is
the criterion that is reachable this afternoon.)
Expect sunny weather today. Salem's high temperature today will be near 95.
Relative humidity drops to 50% by 10am. Minimum relative humidity 22%.
Sunset tonight: 8:11 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 78 89 95 86
Relative Humidity: 43% 29% 22% 32%
Surface Wind Direction: 010 350 350 310
Surface Wind Speed: 6 6 7 6
Transport Wind Direction: 360 010 010 010
Transport Wind Speed: 4 6 8 5
Estimated Mixing Height: 1800 2800 3200 1000
Ventilation Index: 7 17 26 5
EXTENDED DISCUSSION:
The upper ridge will slowly weaken and eventually be undercut by an upper level
low moving eastward from the Pacific Ocean into northern California. As the
upper air pattern changes surface pressure patterns will change as well and a
northwesterly or west-northwesterly transport wind should develop tomorrow for a
possible burn opportunity.
Onshore flow should continue through the week with temperatures dropping to near
or slightly below average for this time of year. This will also lead to a
morning cloud-afternoon sunshine pattern.
EXTENDED FORECAST:
Tomorrow: Sunny, with a high near 92. Light winds early becoming WNW 6-8 during
the afternoon. Possible burn opportunity.
Wednesday: Sunny, with a high near 82.
Light winds becoming NW 5-8.
Thursday: Brief morning clouds then sunny, with a
high near 81.
Friday: Brief morning clouds then sunny, with a high near 76.
Saturday: Partly sunny, with a high near 76.
Sunday: Partly sunny, with a high near 77.
Notes:
1. Mixing height, as used here, is the lowest height at which the
potential temperature exceeds the 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.
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