<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 TUE JUL 24 2012
BURN ADVISORY:
Recommended burn times for agricultural burning are from now until 7:00pm.
Prep burning is allowed from now until 2:00pm with a 50 acre limit.
Propane flaming is allowed from now until 2:00pm.
WEATHER DISCUSSION:
Late morning satellite pictures show the cloud deck over portions of the Willamette
Valley thinning. Clouds were confined to east of the Willamette River itself. A pilot
report from north of Eugene at 11:07 this morning indicated the clouds were between 2000
and 3000 feet and some breaks are visible at the ODF office in Salem. Thus we are still
on track for sunshine this afternoon.
Temperatures, however, have been running cooler than earlier anticipated and I have
revised the high temperature forecast for today down a couple of degrees.
Winds in the valley are light with a generally northerly direction. Remote stations in
the higher coast range show variable directions but the majority do have an easterly
component and thus the unfavorable transport wind forecast still holds.
The surface pressure pattern shows gradient stacking to the east. Pressure gradients as
of 11am included: Newport to Salem, 0.5 mb onshore; Salem to Redmond, 1.9 mb onshore for
a total Newport to Redmond gradient of 2.4 mb onshore. This compares to a Portland to
Medford gradient of 3.3 mb northerly.
THIS AFTERNOON'S FORECAST:
Turning sunny. Temperatures still below average, but warmer than yesterday...topping out
around 80 degrees. Northerly winds.
Salem's high temperature today will be near 80.
Relative humidity drops to 50% by 1pm. Minimum relative humidity 32%.
Surface winds: Northerly 7-9 mph.
Transport winds: North to north-northeasterly 10-15 mph
Maximum mixing height: 3600 feet.
Sunset tonight: 8:48 pm
THREE-HOURLY DATA:
2pm 5pm 8pm
Temperature: 71 79 76
Relative Humidity: 53% 42% 48%
Surface Wind Direction: 350 350 330
Surface Wind Speed: 7 8 7
Transport Wind Direction: 010 010 010
Transport Wind Speed: 10 11 13
Estimated Mixing Height: 3200 3600 1500
Ventilation Index: 32 40 20
EXTENDED DISCUSSION:
The Pacific Northwest will be underthe influence of a dry southwesterly flow aloft for the
rest of the week. This pattern will likely keep low level flow onshore for morning
clouds. Conditions look dry, however, and temperatures should be fairly close to average
the next few days. Weather patterns look more favorable for a westerly component to
transport flow (and better open field burning prospects) possibly as soon as tomorrow
afternoon.
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:240712:1135
</pre>
</body>
</html>