[willamette-fcst] Silverton Hills Forecast - Tue, Jul 06 2010
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Tue Jul 6 08:33:29 PDT 2010
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT TUE JUL 06 2010
*** Potential Fire Marshall Conditions due to winds and humidity ***
BURN ADVISORY:
Agricultural burning is allowed. Suggested burn times are 11:00am to 7:00pm.
Prep burning is not allowed.
Propane flaming burning is not allowed.
WEATHER DISCUSSION:
Upper air charts show a strong ridge aloft extending from about 600 miles west of
northern California northward into the Yukon. This gives a dry northerly or
northwesterly flow aloft to the region. The ODF morning surface analysis shows
a strong thermal trough extending from the central valley of California northward
into southwestern Oregon. There is a strong northerly or northeasterly surface
pressure gradient. Pressure gradients as of 8am included: Newport to Salem, 0.5
mb offshore; Salem to Redmond, 2.1 mb offshore; Newport to Redmond, 2.6 mb
offshore; and Portland to Medford, 5.6 mb northerly. Smoke trajectories from
both the NAM and RUC models show smoke from the Silverton Hills heading towards
central Lane County.
The morning Salem sounding shows an inversion from about 1500 feet
to 2800 feet. This will break with a surface temperature of about 76 degrees
which should be reached by 1pm.
The limitation on burning today will be winds and humidity. Fire Marshal
burn-ban conditions will likely be met by about 2pm this afternoon.
Salem's high temperature today will be near 87 .
Relative humidity reaches 50% by 10am. Minimum relative humidity will be near 24%
Sunset: 8:55 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 69 79 86 82
Relative Humidity: 51% 34% 24% 29%
Surface Wind Direction: 010 020 020 030
Surface Wind Speed: 13 16 17 12
Transport Wind Direction: 020 020 030 020
Transport Wind Speed: 12 20 23 10
Estimated Mixing Height: 2500 5500 7000 1000
Ventilation Index: 30 110 161 10
EXTENDED DISCUSSION:
Computer models indicate the pattern tomorrow will be similar to today with a
dry, offshore flow. The thermal trough shifts inland late Thursday with onshore
flow developing but the generally dry, sunny and warm pattern continues through
the weekend.
EXTENDED FORECAST:
Wednesday: Sunny, with a high near 91. East northeast wind around 9 mph.
Wednesday Night: Mostly clear, with a low around 62. East wind between 3 and 8
mph.
Thursday: Sunny, with a high near 94. Calm wind becoming northwest between 6 and
9 mph.
Thursday Night: Partly cloudy, with a low around 60.
Friday: Mostly sunny, with a high near 93.
Friday Night: Mostly clear, with a low around 57.
Saturday: Sunny, with a high near 91.
Saturday Night: Mostly clear, with a low around 58.
Sunday: Sunny, with a high near 89.
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.
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.
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