[willamette-fcst] Forecast - Friday, September 19th, 2008
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Fri Sep 19 08:05:15 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.
Friday, September 19th, 2008 at 9:00am.
Agricultural burning is not recommended.
Preparatory burning is not allowed.
Propane flaming is not allowed.
Stack burning is not allowed.
An upper-level low presure system, just off the Northern
California Coast this morning, with increasing the southerly
flow aloft and sending more California and Oregon wildfire
smoke over the region...making for hazy conditions. As that
system moves onshore today, it will aid in the break-up of
the marine low clouds over the Willamette Valley. However,
even if the marine low clouds clear from the Willamette
Valley this afteroon, skies will remain mostly cloudy.
The sounding over Salem this morning showed a shallowing
marine layer, now less than 3000 feet thick, with
northeasterly transport winds. Increasing southerly winds
are present above the marine layer with continued quite warm
air aloft. A strong temperature inversion was present at
the top of the marine layer with quite warm air between 3000
and 10,000 feet. That will keep mixing heights below 3000
feet until the air mass aloft begins cooling later this
afternoon. Temperatures aloft support Willamette Valley
highs climbing into the 80s this afternoon, but the
combination of the low-level marine air and cloud-cover
should hold valley highs in the low 70s.
The ODA surface analysis showed a stalled thermal trough
extending from East-Central Washington, through Central
Oregon, to SW Oregon. It should finally progressed eastward
today in response the the upper-level system coming onshore.
Scattered showers are likely, with a possible
thundershower, from SW Oregon across Central and Eastern
Oregon later today and tonight, as the weather system slowly
pushes eastward across Southern Oregon. It does not appear
that showers will make it as far north as the Willamette
Valley, but that possibility can not be entirely ruled
out...especially for the south valley.
Cooler air aloft and northwesterly transport winds are
forecast for Western Oregon later this afternoon. If surface
temperatures warm enough this afternoon, mixing heights
could reach 4000 feet or higher. Therefore, it is possible,
although unlikely, that ventilation conditions could improve
enough to allow for limited open burning this afternoon. We
plan to monitor the changing conditions this afternoon.
Var 0-5 this morning, NW 4-8 this afternoon.
NE 9 this morning, NW 7 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 4500 feet. Ventilation index 41.
Salem\'s high temperature today will be near 72.
Relative humidity drops to 50% by 3pm.
Minimum relative humidity will be near 43%.
Salem sunset tonight: 7:14pm; sunrise tomorrow: 6:57am.
Onshore flow is likely Friday night and Saturday, as the
upper-level low pressure suystem moves across Eastern Oregon
and into Idaho. That should bring a solid deck of marine
low clouds back into the Willamette Valley Saturday morning.
A more westerly flow aloft should finally help to clear the
wildfire smoke from Western Oregon by Saturday afternoon.
Some afternoon sunshine is possible, as the marine clouds
break-up. If there is enough surface warming, mixing
heights and transport winds may be sufficient to allow for
limited open burning in the late afternoon, but that is unlikely.
A transitory ridge is forecast to move over Western Oregon
Saturday night with the next weather system, in westerly
flow aloft, forecast to approach the Sunday afternoon. That
system has the potential to create a burning opportunity
Sunday, if the air mass is able to warm enough ahead of it.
The timing of that system and the amount of marine air
already in the valley makes that questionable.
Some light showers are possible, beginning Sunday, through
Monday, as a stronger upper-level trough moves over the
state, via the westerly flow aloft. Total rainfall amounts
are forecast to be less than one-tenth of an inch with the
greatest chance of rain in the north valley near the Cascade
High pressure is forecast to build over the region Tuesday
with the onshore flow turning more northerly in the
afternoon. It appears that the upper-level ridge will
strengthen over the region Wednesday for continued warming
and drying of the air mass. Transport winds will likely be
northerly and may become offshore. The ridge is forecast to
weaken, by some of the long-range computer models, late next
week with the possibility of a weather system creating a
burning opportunity by Friday. However, that is getting
beyond the scope of the weather forecast models this time of
Tomorrow (20 Sep): Cloudy in the Morning. Partial Afternoon Clearing. 51/72
Sun (21 Sep): Mostly Cloudy. Increasing Chance of Light Showers. 51/70
Mon (22 Sep): Mostly Cloudy. Chance of Showers and Cool. 48/65
Tue (23 Sep): Becoming Partly Cloudy in the Afternoon. 45/71
Wed (24 Sep): Sunny and Warmer. 47/78
Thu (25 Sep): Sunny and Warm. 48/78
Fri (26 Sep): Increasing Clouds and Cooler. 49/72
weather at oda.state.or.us
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