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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON JUL 30 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
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:
Satellite pictures show solid cloud-cover over northwestern Oregon from the coast to near
the crest of the Cascades. Surface observations show the cloud base is slightly below
2000 feet and pilot reports indicate the cloud tops are at around 4000 feet. The clouds
should begin to break up around 2:30 this afternoon, and by late afternoon skies will be
mostly sunny.
The morning Salem sounding showed light and variable winds this morning up to about 6000
feet. Wind flow from about 10,000 feet to above 30,000 feet is a dry southwesterly.
There may have been some very light drizzle out of the low clouds this morning otherwise
no precipitation is likely.
Gradient stacking to the east is evident this morning. As of 8am Newport to Salem was
0.8 mb onshore while Salem to Redmond was 2.8 mb onshore. This should tend towards
equalization late today but will probably not reach favorable conditions. Gradients will
be monitored closely.
Prospects for favorable burning conditions today are not good, but it is not impossible
that a short window of opportunity could open up this afternoon. Pibals and pressure
gradients will tell the story.
TODAY'S FORECAST:
Cloudy, then gradually becoming mostly sunny this afternoon,
Salem's high temperature today will be near 77. (Average is 84)
Relative humidity drops to 50% by 2pm. Minimum relative humidity 40%.
Surface winds: North to north-northwest 5-8 mph.
Transport winds: Light northerly, becoming north to north-northwest 9-13 mph.
Maximum mixing height: 4300
Sunset tonight: 8:40 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 70 75 76 67
Relative Humidity: 55% 45% 42% 56%
Surface Wind Direction: 340 330 330 320
Surface Wind Speed: 5 5 7 8
Transport Wind Direction: 360 350 340 330
Transport Wind Speed: 4 4 9 13
Estimated Mixing Height: 2200 4000 4300 3900
Ventilation Index: 9 16 39 51
EXTENDED DISCUSSION:
Overall the general weather pattern changes little through the next couple of days.
Southwesterly flow aloft will continue with occasional impulses modulating the amount of
morning cloudiness. Conditions should be dry except for the possibility of local morning
drizzle from the low clouds. This is a pattern that occasionally offers brief burn
opportunities and growers should closely monitor the forecasts for the latest
information.
Later in the week high pressure amplifies over the region alowing for warmer
temperatures but limiting mixing heights.
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:300712:0847
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