[willamette-fcst] Forecast - Wednesday, August 6th, 2008
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Wed Aug 6 10:28:32 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.
Wednesday, August 6th, 2008 at 9:00am.
Agricultural burning is not recommended.
Preparatory burning is not allowed.
Propane flaming is not allowed.
Stack burning is not allowed.
Increasing southerly flow aloft spread smoke, from
California wildfires, northward across most of Oregon by
Monday evening. The southerly flow aloft increased Tuesday
with more wildfire smoke making for hazy sunshine across
Western Oregon. The air mass warmed considerably Tuesday
with valley high temperatures climbing well into the 90s.
Hillsboro was the warm spot with 98 degrees, Portland and
Troutdale topped out at 97. Aurora, Salem, and Corvallis
all hit 93 and Eugene hit 94.
The Salem sounding this morning had a very similar
temperature profile to Tuesday morning, so another warm day
is on tap. Winds were light southwesterly below about 2000
feet...turning to southeasterly above 5000 feet. Warm air
aloft will, once again, lead to mixing heights below 3000
feet for much of today.
The ODA surface analysis showed the thermal trough of low
pressure over the Willamette Valley showing signs of
shifting into North-Central Oregon, in response to the
upper-level ridge axis moving east to over Idaho. Onshore
flow had brought low clouds onto both the Washington and
Oregon Coastlines. Visible satellite imagery showed some
low clouds making their way up the Columbia River.
The increasing the southerly flow aloft brought middle and
high-level moisture into Southern Oregon Tuesday night.
Thundershower activity began in the early morning hours over
South-Central Oregon with locally heavy rainfall reported in
Klamath County. The storms were moving north into Deschutes
County and extreme Eastern Lane County at mid-morning. The
moist southerly flow aloft was also starting to spread middle
and high clouds northward across the Willamette Valley with
skies becoming mostly cloudy in the south valley.
Increasing clouds will hold afternooon temperatures down a
few degrees from Tuesday...especially in the south valley.
In addition, some marine air will begin seeping through
the coastal mountain gaps this afternoon and help to cap the
daytime temperatures near 90 degrees. The increased
moisture and instability will combine with daytime heating
to trigger thundershowers this afternoon over the Cascades.
There is a good chance that some of the storms will migrate
over the Willamette Valley, this afternoon and evening, in
the southeasterly flow aloft.
Some cooing aloft may lift mixing heights over 3000 feet
later this afternoon, but south-southeasterly winds aloft
and scattered thundershower development makes open-burning
unlikely. A chance of showers or thundershowers will
continue into the night with mostly cloudy skies keeping
overnight valley temperatures near 60 degrees.
SW 3-6 this morning, NW 5-10 this afternoon.
S 5 this morning, SW 7 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 3500 feet. Ventilation index 25.
Salem\'s high temperature today will be near 91.
Relative humidity drops to 50% by 12pm.
Minimum relative humidity will be near 29%.
Salem sunset tonight: 8:31pm; sunrise tomorrow: 6:05am.
As the upper-level ridge shifts east, to over Montana, the
flow aloft over Oregon is forecast to become more
southwesterly late Thursday and Friday. The thermal trough will
shift eastward, into Eastern Oregon and Idaho, with
increasing onshore flow across Western Oregon. That will
bring increasing amounts of marine air into the Willamette
Valley with progressively cooler temperaures. Southwesterly
flow aloft will also push the moist and unstable air eastward,
with the thundershowers shifting to Eastern Oregon and Idaho by Friday.
The valley may get an open-burning opportunity Thursday
and/or Friday, depending on the timing of the cool-down, the
degree of southerly flow aloft, and the location of showers
and thundershowers. There is a good chance of showers or
thunderstorms Thursday, but they should be out of the
region Friday, with more favorable transport wind directions.
However, we may have gradient-stacking issues and too much transport
wind-speed Friday for good plume rise.
The upper-level trough is forecast to move onshore over the
weekend with the flow aloft turning westerly. Temperatures
will cool further with increasing onshore flow possibly
leading to areas of drizzle of light rain Saturday morning.
A transitory ridge of high pressure is forecast for early
next week with increasing southwesterly flow aloft by the
middle of the week.
Tomorrow (07 Aug): Mostly Cloudy and Cooler. Chance of Showers/T-storms. 60/83
Fri (08 Aug): Partly Cloudy and Cooler. 56/80
Sat (09 Aug): Morning Clouds...Chance of Drizzle. Afternoon Clearing. 54/75
Sun (10 Aug): Morning Clouds. Mostly Sunny in the Afternoon. 50/79
Mon (11 Aug): Sunny and Warmer. 50/84
Tue (12 Aug): Sunny and Warm. 52/87
Wed (13 Aug): Mostly Sunny and Very Warm. 55/90
weather at oda.state.or.us
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