<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
12:00 PM PDT MON JUL 30 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from now until 2:00pm with a 50 acre limit.
Propane flaming is allowed from now until 5:00pm.
WEATHER DISCUSSION:
Satellite pictures indicate some thinning of the cloud cover over northwestern Oregon
late this morning, but a pilot report over Salem just a few minutes ago at about 10 after
11 indicated that the base of the cloud deck was at 1800 feet and the tops of the clouds
were at about 4000 feet - just about what was estimated for the 9am broadcast. Cloud
break up this afternoon will likely be on the late side – pushing 3pm.
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.
Computer models indicate northerly transports through most of the afternoon, possibly
coming around to about 330 degrees during the early evening.
Gradient stacking has not improved since this morning, if anything it has gotten worse.
As of 11am Newport to Salem was down to 0.5 mb onshore while Salem to Redmond had climbed
to 3.9 mb onshore. Sunshine in the valley later this afternoon will help to equalize
pressures, but we have low confidence that it will be enough to allow open field burning.
Bottom Line: Prospects for favorable burning conditions today are low, but it is not
impossible that a short window of opportunity could open up late this afternoon. We will
monitor pressure gradients and do a pibal when the low clouds break up.
THIS AFTERNOON'S FORECAST:
Clouds slowly giving way to sunshine.
Salem's high temperature today will be near 77.
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: 8:41 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 71 76 71
Relative Humidity: 55% 43% 51%
Surface Wind Direction: 350 350 320
Surface Wind Speed: 5 6 7
Transport Wind Direction: 350 340 330
Transport Wind Speed: 4 9 13
Estimated Mixing Height: 4000 4300 3900
Ventilation Index: 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:300712:1147
</pre>
</body>
</html>