<pre>
<!DOCTYPE HTML PUBLIC -//W3C//DTD HTML 4.0 Transitional//EN>
<html>
<head>
</head>
<body>
<pre>
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON JUL 23 2012
BURN ADVISORY:
Recommended burn times for agricultural burning are from 11:00am to 7:00pm.
Prep burning is allowed from 12:00pm to 5:00pm with a 50 acre limit.
Propane flaming is allowed from 12:00pm to 5:00pm.
WEATHER DISCUSSION:
An upper level low over northern Washington will pull out to the northeast today as higher
pressure aloft builds to give the region more sunshine than was the case the past few
days. Temperatures will warm as well, although remain a bit below average for late July.
The morning ODF surface pressure analysis shows a well developed thermal trough in the
central valley of California extending northwestward to just off the southern Oregon
coast. Higher pressure is nosing into northwestern Oregon. Pressure gradients as of 8am
included: Newport to Salem, 0.1 mb onshore; Salem to Redmond, 2.1 mb onshore for a total
Newport to Redmond gradient of 2.2 mb onshore. At the same time the Portland to Medford
gradient 4.1 mb northerly. The northerly gradient will dominate today for a generally
northerly transport flow. In fact there will likely be a slight northeasterly component
as the thermal trough strengthens over southern coastal waters.
The morning Salem sounding showed cooling aloft this morning compared to Sunday morning.
This has destabilized the atmosphere a bit and mixing heights should be quite high this
afternoon, reaching above 5000 feet. Models show warming aloft this afternoon and with
the increased sunshine surface temperatures should be significantly warmer than yesterday.
In addition, humidities will be lower.
The northerly or northeasterly transport winds make today an unfavorable day for open
field burning.
TODAY'S FORECAST:
Salem's high temperature today will be near 80. (Average is 85. Yesterday was only 70.)
Relative humidity drops to 50% by 2pm. Minimum relative humidity 30%.
Surface winds: Northerly to north-northwesterly 6-12 mph.
Transport winds: Northerly to north-northeasterly 10-15 mph.
Maximum mixing height: 5800 feet.
Sunset tonight: 8:48 pm.
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 68 76 80 70
Relative Humidity: 51% 36% 30% 47%
Surface Wind Direction: 360 350 360 340
Surface Wind Speed: 6 10 12 12
Transport Wind Direction: 020 020 020 020
Transport Wind Speed: 12 13 14 17
Estimated Mixing Height: 4100 5000 5800 4000
Ventilation Index: 49 65 81 68
EXTENDED DISCUSSION:
Computer models show dry weather through this week. A weak upper level trough will set up
offshore to give the region southwesterly flow aloft. Surface pressure patterns look to
become more favorable to an afternoon sea-breeze regime and possible open field burning
opportunities later this week.
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:230712:0850
</pre>
</body>
</html>