[willamette-fcst] Forecast - Monday, August 4th, 2008
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Mon Aug 4 08:16:47 PDT 2008
Daily Smoke Management Forecast
Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.
...Corrected wording in the extended forecast...
...Fire Marshal conditions may be met this afternoon due to low humidity and wind...
Monday, August 4th, 2008 at 9:00am.
Agricultural burning is not recommended.
Preparatory burning is not allowed.
Propane flaming is not allowed.
Stack burning is not allowed.
A 52-day dry spell in Salem was broken Friday, as a weak
cold front moved south across the Willamette Valley and
dropped .03 inches of rain at the Salem Airport. The storm
produced much greater precipitation totals in the
Northeastern Willamette Valley, where upslope winds enhanced
that rainfall. Up to .70 inches of rain fell, in the
Corbett area, at the western end of the Columbia Gorge, and
troutdale picked up about one-tenth of an inch.
A weak upper-level trough, over Southern British Columbia,
provided onshore flow and moderate temperatures across
Western Oregon this past weekend. Valley highs were in the
70s both days with morning clouds and afternoon sunshine.
The upper-level low pressure area had slid eastward this
morning, and high pressure was rapidly building over the
Weak onshore flow continued to push a shallow layer of low
clouds onto the coastline, and locally into the coastal
mountain gaps, this morning. Some low clouds made it up the
Columiba River into the Portland area, while the remainder
of the valley had clear skies this morning. Valley minimums
were mostly near 50 degrees this morning. Hillsboro was one
of the colder spots with a low of 47...followed closely by
Eugene at 48. The Portland Airport was the warm spot with a
minimum of 56.
Visible satellite imagery this morning showed a blanket of
low clouds west of the coast range with patchy low clouds
along the Columbia River into the Portland area. The
remainder of the state had cloud-free skies. California
wildfire smoke was streaming over SW Oregon and
northeastward across the southern half of Central and
The ODA surface analysis showed a thermal trough forming in
the Willamette Valley with weak northerly gradients across
Western Oregon. Northerly surface winds will prevail and
increase this afternoon across the western valleys.
Increasing offshore flow will drop relative humidities below
30 percent this afternoon, so Fire Marshal conditions may
locally be met, if north winds increase to 15 mph or greater.
The north winds should be strongest in the south valley.
With the air aloft rapidly warming today, mixing heights
will struggle to reach 3000 feet. A full day of sunshine
and the lack of onshore flow will combine to lift valley
temperatures into the upper 80s.
N 5-10 this morning, N 7-15 this afternoon.
NNE 10 this morning, NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 3000 feet. Ventilation index 30.
Salem\'s high temperature today will be near 88.
Relative humidity drops to 50% by 11am.
Minimum relative humidity will be near 26%.
Salem sunset tonight: 8:34pm; sunrise tomorrow: 6:03am.
The upper-level ridge axis will be from SW Idaho through
Central Washington Tuesday with weak southerly flow aloft
over Oregon. That will increase the warming over the state
and introduce a thundershower threat to Southern Oregon as
early as Tuesday evening. Southerly flow aloft will
increase Wednesday, as the upper-level ridge shifts eastward
to over Western Montana. That will likely result in scattered
thunderstorm development along most of the Cascade Range.
If the flow aloft becomes southeasterly, thunderstorms could
also make their way over the Willamette Valley Wednesday
afternoon and evening. The surface flow will turn weakly
onshore Wednesday, as the thermal trough shifts east of the
Cascades. That will bring some cooling to Western Oregon
and could create a burning opportunity, if the flow aloft is
not too southerly.
The upper-level winds are forecast to become more
southwesterly Thursday and Friday, which will increase the
onshore flow across Western Oregon with the bulk of the
thundershower activity from the Cascades eastward Thursday
and well east of the region Friday. That would also create
another potential burning opportunity. An upper-level
trough is forecast to move onshore over the weekend for even
cooler conditions and increased onshore flow.
Tomorrow (05 Aug): Sunny and Hot. 55/95
Wed (06 Aug): Mostly Sunny. Slight Chance of PM T-storm. 56/91
Thu (07 Aug): Partly Cloudy and Cooler. Slight Chance of T-storms near the Cascades. 57/85
Fri (08 Aug): Mostly Sunny and Cooler. 57/83
Sat (09 Aug): Partly Sunny with Continued Cooling. 54/79
Sun (10 Aug): Morning Clouds. Afternoon Clearing. 53/80
Mon (11 Aug): Mostly Sunny. 52/83
weather at oda.state.or.us
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