[willamette-fcst] Forecast - Friday, December 11th, 2009
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Fri Dec 11 09:12:05 PST 2009
Daily Smoke Management Forecast
Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.
Friday, December 11th, 2009 at 9:00am.
Agricultural burning is not recommended.
Stack burning is not allowed.
A very cold and dry air mass remains entrenched across
Washington and Oregon this morning. Clear skies allowed
temperatures to drop into the teens, and locally single
digits, in the Willamette Valley this morning, with most
areas only a couple of degrees warmer than on Thursday
morning. Skies also remained clear along the northern and
central coast, with most morning temperatures dropping into
the low to mid 20s and locally into the upper teens. Many
areas east of the Cascades fell below zero again this morning.
As expected, some significant changes in the weather pattern
are taking place this morning. The flow aloft over Oregon
has become westerly, with a weather system undercutting the
offshore ridge of high pressure and moving into California.
That has continued to warm the air aloft, between 2000 and
10,000 feet, with a shallow layer of above-freeezing air
showing up on the morning soundings, over Salem and Medford,
between 2000 and about 5000 feet. The column of above
freezing air was thicker over Medford than over Salem.
Temperatures were still well below freezing from the surface
up to about 2000 feet over both locations. That will set
the stage for a wintry mix of precipitation later today
through Saturday, as the feed of moisture moves northward
across western Oregon.
Clouds spread northward, into southern Oregon, overnight,
and Doppler radar was showing precipitation also spreading
north of the California border at mid-morning. Rain was
falling in Brookings, on the southern Oregon Coast, where
temperatures had warmed into the upper 30s. Surface
temperatures in the southwestern interior were still in the
20s, where the precipitation will fall in the form of a
wintry mix as it spreads northward this morning.
Computer models differ considerably on both their timing and
intensity of the precipitation, as it moves northward,
across western Oregon today. Some begin the wintry mix, in
the southern Willamette Valley, as early as mid-afternoon,
with precipitation likely moving into the south valley by
this evening. The plume of moisture will sweep northward to
the Portland area by about midnight. High temperatures
today will, once again, struggle to climb into the low to
mid 30s. Temperatures will rapidly chill back into the 20s,
as soon as the sun sets or if precipitation begins.
The precipitation will begin mostly as snow or sleet in the
south valley, with a likely transition to sleet and freezing
rain, as the air aloft continues to warm. Light northerly
surface winds will continue to supply low-level cold air
throughout the valley. However, there may be enough surface
warming, in the south valley, to change precipitation to
just plain rain as early as Saturday morning. Further
north, precipitation will be more likely to begin as snow,
due to the deeper layer of cold air, especially in the
Portland area and in the Columbia Gorge. A transition to
sleet and/or freezing rain is possible in the north valley
during the day Saturday, with portions of the central valley
possibly changing to plain rain.
Forecast precipitation amounts vary from around one-tenth of
an inch (water equivalent) to around four-tenths of an
inch. However, even small amounts of snow, sleet, and
freezing rain can make for very hazardous travel conditions,
so be prepared for wintry travel conditions in the
Willamette Valley tonight and Saturday. It is possible that
the bands of precipitation will stall over the north valley
Saturday, which could end up producing more significant
amounts of snow and ice there.
NNE 0-6 this morning, NNE 3-6 this afternoon.
NNE 5 this morning, NNE 5 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 1500 feet. Ventilation index 8.
Salem\'s high temperature today will be near 34.
Minimum relative humidity will be near 51%.
Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:41am.
Precipitation is expected to taper off Sunday, with the
low-level flow turning onshore across most of the valley.
That should help most of the Willamette Valley transition to
just plain rain. However, there could still be enough cold
air coming out of the Columbia Gorge to keep wintry
precipitation in the immediate Portland area. Another
weather system is forecast to come onshore late Monday.
There could still be enough cold air remaining in the
Columbia Gorge, and the immediate Portland area, for a
wintry mix of precipitation, but the rest of the Willamette
Valley should get just rain. Even the Gorge should get
scoured out by Tuesday, with warmer Pacific air moving back
into the region.
Tomorrow (12 Dec): Snow, Sleet, or Freezing Rain...Likely Changing to Rain South. 28/35
Sun (13 Dec): Showers...Possible Wintry Mix Near the Gorge. Snow above 1500 feet. 32/42
Mon (14 Dec): Mostly Cloudy. Chance of Rain...Possible Wintry Mix North. 32/40
Tue (15 Dec): Rain. Possibly Starting as Freezing Rain North. 32/47
Wed (16 Dec): Mostly Cloudy and Warmer. Rain Likely Late. 37/49
Thu (17 Dec): Rain Turning to Showers. 42/49
Fri (18 Dec): Mostly Cloudy. Chance of Rain. 38/48
weather at oda.state.or.us
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