<pre>
<html xmlns:o="urn:schemas-microsoft-com:office:office"
xmlns:w="urn:schemas-microsoft-com:office:word"
xmlns="http://www.w3.org/TR/REC-html40">
<html>
<head>
</head>
<body>
<pre>
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON AUG 13 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from 3:00pm to 5:00pm with a 50 acre limit.
Propane flaming is allowed from 3:00pm to 5:00pm.
WEATHER DISCUSSION:
Satellite pictures show low marine clouds penetrating coastal valleys this morning - an
indication of onshore flow. The morning ODF surface pressure analysis shows the thermal
trough has retreated into northern California and southwest Oregon. Thus temperatures
should be down a few degrees from yesterday. All of this is related to a weak upper
level disturbance that moved into British Columbia overnight.
Gradient stacking is not an issue this morning. Pressure gradients as of 8am included:
Newport to Salem, 1.9 mb onshore; Salem to Redmond, 0.2 mb onshore; while the Portland to
Medford gradient was 2.0 mb northerly.
The morning Salem sounding showed slight cooling from about 2500 feet to about 7500 feet
compared to yesterday morning. There is still an inversion from 2800 to 5300 feet that
likely will not mix out today and the maximum mixing height will be limited to just a
little over 3000 feet.
Winds on the sounding are northerly up to about 6000 feet and computer models indicate
that northerly transport winds will continue throughout the day with little possiblity of
any westerly flow developing.
Bottom line: Today does not look like an open field burning day.
TODAY'S FORECAST:
Sunny, not as hot as Sunday.
Salem's high temperature today will be near 89.
Relative humidity drops to 50% by 12pm. Minimum relative humidity 28%.
Surface winds: Northerly 7-10.
Transport winds: Northerly 4-6 becoming north-northwesterly mid-evening.
Maximum mixing height: 3200 feet.
Sunset tonight: 8:20 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 74 84 87 79
Relative Humidity: 55% 37% 28% 39%
Surface Wind Direction: 360 010 010 330
Surface Wind Speed: 7 8 9 10
Transport Wind Direction: 010 360 340 330
Transport Wind Speed: 4 5 6 9
Estimated Mixing Height: 900 2800 3200 2000
Ventilation Index: 4 14 19 18
EXTENDED DISCUSSION:
Another upper level disturbance will move by to the north tomorrow. This will draw
additional marine air into the valley for morning clouds and cooler temperatures. Models
show a continued unfavorable northerly transport wind. High pressure will rebuild
Wednesday and begin another spell of hot weather. Transport flow will likely become
offshore or easterly and preclude any burning later in the week. In addition Fire Marshal
burn-ban conditions may come into play 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:130812:0835
</pre>
</body>
</html>