[willamette-fcst] Silverton Hills Forecast - Tue, Sep 28 2010
Willamette Valley Field Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Tue Sep 28 08:42:30 PDT 2010
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT TUE SEP 28 2010
BURN ADVISORY:
Recommended burn times for agricultural burning are from 1:00pm to 5:00pm.
Prep burning is allowed from 3:00pm to 5:00pm with a 50 acre limit.
Propane flaming is allowed from 2:00pm to 5:00pm.
WEATHER DISCUSSION:
A broad ridge of high pressure in the upper atmosphere covers much of the
western United States this morning. The Pacific Northwest is on the edge of this
ridge with a southwesterly flow aloft. That southwesterly flow is again pushing
some cloudiness into western Washington and portions of northwest Oregon. This
is aided by low level onshore flow from the coast to the Valley. The Newport to
Salem gradient as of 8:00am was 1.3mb.
There is an offshore gradient, however from Redmond to Salem. As of 8:00am
Redmond's pressure was 1.1mb higher than Salem's.
The morning Salem sounding showed a light westerly flow at the surface but a
moderate north-northeasterly flow from about 800 feet to 3000 feet. The
temperature trace showed a quite stable atmosphere over the Valley. Several
shallow inversions were present from the surface to about 2500 feet. Also there
was evidence of subsidence, or sinking air motion, aloft which does not allow
for good smoke ventilation.
Computer models show a northerly transport wind today. Smoke trajectory
forecasts from the Air Resources Lab show smoke from Marion County headed south
toward Lane County today.
Bottom line: It does not look favorable for open field burning this afternoon.
Expect patchy fog and low clouds this morning and mostly sunny skies this
afternoon. Salem's high temperature today will be near 82. It will remain quite
humid today with dewpoint temperatures in the low 60's. Relative humidity drops
to 50% by 3pm. Minimum relative humidity 49%.
Sunset tonight: 6:52 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 71 80 82 71
Relative Humidity: 73% 56% 49% 68%
Surface Wind Direction: 360 330 350 320
Surface Wind Speed: 4 5 7 6
Transport Wind Direction: 020 360 360 020
Transport Wind Speed: 7 6 6 5
Estimated Mixing Height: 1100 2500 3200 500
Ventilation Index: 8 15 19 2
EXTENDED DISCUSSION:
The northerly transport wind pattern will continue tomorrow for unfavorable
burning conditions. An upper disturbance embedded in the southwesterly flow
aloft will move by to the north late on Thursday which should shift the winds
over the Willamette Valley. This will need to be monitored for a possible burn
opportunity, however at this point it looks like the wind shift would come too
late for burning. Friday remains an opportunity.
EXTENDED FORECAST:
Wednesday: Mostly sunny, with a high near 81. NNE 5-9 mph
Thursday: Mostly sunny, with a high near 81. Wind Light/Variable becomming SW 3-6
mph during the evening.
Friday: Mostly sunny, with a high near 77.
Saturday: Mostly sunny, with a high near 76.
Sunday: Partly sunny, with a high near 74.
Sunday Night: Mostly cloudy, with a low around 51.
Monday: Partly sunny, with a high near 72.
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.
jlwx:280910:0842
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