[willamette-fcst] Forecast - Wednesday, September 17th, 2008
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Wed Sep 17 08:04:26 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.
Issued:
Wednesday, September 17th, 2008 at 9:00am.
Burn Advisory:
Agricultural burning is not recommended.
Preparatory burning is not allowed.
Propane flaming is not allowed.
Stack burning is not allowed.
Weather Discussion:
The strong ridge of high pressure that has been giving
Oregon a late-summer hot spell is moving to the east and
will allow a weak upper-level trough to move northward,
across Oregon, today. That will destabilize the atmosphere
and lead to thunderstorm development today...mainly from the
Cascades eastward. South-southeasterly flow aloft is
continuing to circulate California wildfire smoke over
Oregon, so we will see a mix of clouds and hazy sunshine
over the state today.
The ODA surface analysis showed the surface thermal trough
still over Western Oregon at mid-morning, but it is forecast
to shift east of the Cascades by this afternoon. Increasing
onshore flow should cap Willamette Valley temperatures in
the low 80s this afternoon. The air aloft has cooled some
since Tuesday morning, but mixing heights are forecast to
remain below 2000 feet this morning and below 3000 feet
until mid-afternoon. The upper-level trough will continue
to cool the air aloft this afternoon with transport winds
veering from southeasterly to southwesterly. Mixing heights
should climb to near 4000 feet by late this afternoon.
This transition may create an open burning opportunity for
the mid-to-late afternoon period. However, there are some
potential limiting factors. Southerly flow aloft may keep
mixing heights suppressed below 3000 feet, and thundershower
development over and east of the Cascades may not allow for
good evacuation of smoke over the Cascades (poor
gradient-stacking conditions). There is also a slight
chance of a thundershower rolling off the Cascades into the
Willamette Valley, because the flow above 10,000 feet is
forecast to remain southeasterly today.
Surface Winds:
SW 5 this morning, SW 5-12 this afternoon.
Transport Winds:
SE 6 this morning, SW 9 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 4000 feet. Ventilation index 36.
High Temperature:
Salem\'s high temperature today will be near 83.
Humidities:
Relative humidity drops to 50% by 12pm.
Minimum relative humidity will be near 35%.
Sunrise/Sunset:
Salem sunset tonight: 7:18pm; sunrise tomorrow: 6:55am.
Extended Outlook:
Another upper-level low pressure system is forecast to
approach the Northern California Coastline Thursday
afternoon with increasing south-southwesterly flow aloft and
continued onshore flow at the surface. This system should
bring a little more cooling to Western Oregon with a slight
chance of showers, as it comes onshore late Thursday and
Friday. This system will likely bring showers to Southern
and Eastern Oregon. It may also create favorable conditions
for burning.
A split-flow jet stream pattern is forecast by Saturday,
with one branch to our south and the other to our north,
leaving Oregon in a dry weather pattern with weak onshore
flow making for seasonal temperatures. That could create
burning opportunities over the weekend. The next weather
system is forecast to approach the coast late Sunday and may
bring some light rain to the valley by Monday afternoon. A
ridge is forecast to begin building back over the region
next Wednesday.
Tomorrow (18 Sep): AM Clouds...Mostly Sunny. 52/78
Fri (19 Sep): Mostly Cloudy. Slight Chance of a Shower...Mainly South. 50/75
Sat (20 Sep): Partly Cloudy. 50/75
Sun (21 Sep): Mostly Sunny. Increasing Clouds Late. 49/75
Mon (22 Sep): Increasing Chance of Light Rain and Cooler. 48/68
Tue (23 Sep): Partly Cloudy. Slight Chance of Showers. 48/70
Wed (24 Sep): Mostly Sunny. 47/72
ODA Meteorologist
weather at oda.state.or.us
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