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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON AUG 20 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is not allowed.
Propane flaming is not allowed.
WEATHER DISCUSSION:
Cooler temperatures this week with highs near seasonal average.
Upper air charts show a broad upper ridge over the western United States with a
relatively weak upper trough to the west over the eastern Pacific. This leaves the
region in a southwesterly flow aloft.
Satellite pictures show areas of clouds west of the Cascades in northern Oregon, but the
cloud cover is not solid with plenty of breaks.
The Salem sounding shows a stable atmosphere this morning with inversions aloft
from 2000 to 3000 feet and from 3800 to 4300 feet. The higher of these will not mix out
today and maximum mixing heights will be around 3900 feet this afternoon. The sounding
also shows light, generally northerly, winds from the surface to around 2000 feet and
light, generally southwesterly winds from 2500 feet to around 4000 feet.
There is pressure gradient stacking to the east this morning. As of 8am Newport to Salem
was 0.2 mb onshore while Salem to Redmond was 2.1 mb onshore. Models indicate the
gradient stacking to continue through this evening, but if skies get sunny in the
Willamette Valley the gradient stacking situation will improve.
Winds and gradients are unfavorable this morning, and the greatest likelyhood is that
they will not become favorable this afternoon. However better winds and gradients cannot
be ruled out. Pibals and afternoon pressure readings will tell the story.
TODAY'S FORECAST:
Clouds decreasing late morning, becoming mostly sunny in the afternoon.
Salem's high temperature today will be near 81.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 37%.
Surface winds: Northerly 3-6 mph becoming northwesterly by evening.
Transport winds: Northerly 3-6 mph becoming northwesterly by evening.
Maximum mixing height:
Sunset tonight: 8:09 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 66 76 81 73
Relative Humidity: 68% 45% 37% 49%
Surface Wind Direction: 360 010 350 310
Surface Wind Speed: 3 4 6 6
Transport Wind Direction: 350 350 340 320
Transport Wind Speed: 3 3 5 10
Estimated Mixing Height: 1900 3000 3900 1000
Ventilation Index: 6 9 20 10
EXTENDED DISCUSSION:
The upper trough off the coast moves across the region tomorrow afternoon and may present
a burn opportunity. Models are showing westerly transport winds for tomorrow. Upper
flow will be generally westerly much of the rest of the week, but models show transport
level flow back to northerly by Wednesday. Expect sunny skies and high temperatures near
80 Thursday and Friday.
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:200812:0842
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