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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON SEP 19 2011
BURN ADVISORY:
Recommended burn times for agricultural burning are from 9:00am to 5:00pm.
Prep burning is allowed from 12:00pm to 2:00pm with a 50 acre limit.
Propane flaming is allowed from 12:00pm to 5:00pm.
WEATHER DISCUSSION:
The remains of a cold front that was off the coast yesterday is draped over the Willamette
Valley this morning but will move to the south and east this afternoon. The cold front
was re-energized overnight as an upper level short wave moved through. Rainfall amounts
have generally been in the one to two-tenths range. The Salem Airport reported .09 in 24
hours, and CoCoRaHas reports are indicating about a quarter of an inch near the Cascade
foothills.
The morning Salem sounding showed a temperature profile fairly similar to yesterdays up to
about 6000 feet. The atmosphere was farily moist - in fact the sounding showed saturation
from 2500 feet to about 7000 feet. One difference from yesterday was wind direction.
Yesterday's southerly winds have given way to light northwesterly winds this morning.
The morning surface pressure analysis shows fairly flat gradients across the valley today.
High pressure is nosing in to the north and forecast models show winds turning
north-northeasterly during the day today.
Pressure gradients as of 8am included: Newport to Salem, 0.2 mb onshore; Salem to
Redmond, 1.2 mb onshore; and Newport to Redmond, 1.4 mb onshore.
With the rainfall overnight and unfavorable winds forecast it is not likely that there
will be open field burning today.
TODAY'S FORECAST:
Salem's high temperature today will be near 76.
Relative humidity drops to 50% by 2pm. Minimum relative humidity 43%.
Surface winds: NE 4-6 mph.
Transport winds: N to N# 6-9 mph.
Maximum mixing height: 4000 feet.
Sunset tonight: 7:15 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 66 73 76 68
Relative Humidity: 73% 53% 43% 57%
Surface Wind Direction: 030 050 040 030
Surface Wind Speed: 4 4 6 5
Transport Wind Direction: 360 030 020 030
Transport Wind Speed: 6 7 9 14
Estimated Mixing Height: 2200 3500 4000 1700
Ventilation Index: 13 24 36 24
EXTENDED DISCUSSION:
Forecast models indicate high pressure rebuilding over the area overnight tongith and
tomorrow. This should give a pattern of morning clouds, afternoon sunshine to the region.
Transport winds will remain northerly on Tuesday.
The ridge axis moves east on Wednesday for southwesterly winds aloft and models indicate
that transport winds will become more southwesterly or westerly as well. Wedensday could
present a burn opportunity.
The ridge remains over the area through the end of the week for dry weather and potential
afternoon burn opportunities.
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:190911:0818
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