[willamette-fcst] Forecast - Thursday, May 15th, 2008
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Thu May 15 08:09:01 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.
Thursday, May 15th, 2008 at 9:00am.
Agricultural burning is allowed. Suggested burn times are from 12:00pm until 6:30pm.
Stack burning is not allowed.
A building upper-level ridge of high pressure, just off the
west coast, turned the flow aloft from westerly to northerly
over Washington and Oregon on Wednesday. Skies slowly
cleared, from west to east, across Oregon Wednesday
afternoon and evening. Very warm air aloft acted like a
lid...trapping low-level cooler and moist air near the
surface in the Willamette Valley overnight. That lead to
the formation of extensive low clouds over the valley early
this morning. The Salem sounding this morning showed a
strong temperature inversion from near the surface up to
about 3000 feet with relatively cool and very moist air
trapped below 2000 feet. Winds aloft were northeasterly, in
the 15-20 mph range, from just above the surface to more
than 10,000 feet.
Visible satellite imagery this morning showed extensive low
clouds covering much of Western Washington and the
Willamette Valley in Oregon, with generally clear skies over
the remainder of both states. Areas of early morning fog
and low clouds had even cleared from the Oregon Coast. It
was a mild night across the region. Morning minimums were in
the low to mid 50s across Western Oregon with 40s and 50s
east of the Cascades. It was a balmy night in the mountains
with Timberline Lodge recording a low temperature this
morning of 49 degrees.
Daytime heating will start the process of mixing the air
mass over the Willamette Valley with the much warmer and dry
air mass aloft. That should act to evaporting the low
clouds within a couple of hours with skies becoming sunny by
midday. A building surface thermal trough, just off the
Southern Oregon Coastline, will combine with high pressure
over Washington and NE Oregon to turn the surface winds
slightly offshore this afternoon across Western Oregon. The
offshore flow will combine with ample sunshine and very warm
air aloft to send Western Oregon temperatures into the 80s
this afternoon...even along the beaches. The southwestern
valleys will likely see the mid to upper 90s this afternoon.
Highs in the Willamette Valley could easily reach the mid
80s (15 degrees above normal).
Very warm air aloft will cap mixing heights at about 3000
feet this afternoon, but that will provide enough
ventilation for agricultural burning. However,
northeasterly transport winds are not favorable for
evacuation of smoke from the valley from stack burns, so
they are not allowed today. It will be another mild night
with fair skies and valley minimums in the mid to upper 50s.
N 5-15 (G20 south valley) this morning, NNE 10-20 (G25 south valley) this afternoon.
NE 18 this morning, NE 22 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 3000 feet. Ventilation index 66.
Salem\'s high temperature today will be near 86.
Minimum relative humidity will be near 37%.
Salem sunset tonight: 8:35pm; sunrise tomorrow: 5:42am.
The upper-level ridge is forecast to continue to build over
the Pacific Northwest Friday with the surface thermal trough
remaining along the coastline for offshore flow across
Western Oregon. That will push Willamette Valley high
temperatures to daily record values...in the low to mid 90s.
Onshore flow will likely kick in along the southern and
central coast Friday afternoon, as the center of the thermal
low-pressure area moves up the coast.
It appears that Friday will be the warmest day west of the
Cascades. the upper-level ridge is forecast to shift east
of the Cascades Saturday, along with the associated surface
thermal trough. That should bring cooler onshore winds into
the Willamette Valley Saturday afternooon, in time to cap
tempertures in the mid 80s. That will shift the record hot
weather into Central and Eastern Oregon Saturday afternoon.
Cooler ocean air begin filtering into Central and much of
Eastern Oregon Sunday, with increasing onshore flow west of
the Cascades cooling temperatures back into the upper 70s
and perhaps low 80s.
A increasing southwesterly flow aloft will eventually bring
even cooler temperatures and a chance of rain back to
western Oregon next week.
Tomorrow (16 May): Sunny with Record High Temperatures. 55/94
Sat (17 May): Sunny and Very Warm. 57/87
Sun (18 May): Partly Cloudy and Cooler. 52/77
Mon (19 May): Mostly Cloudy. Chance of Rain Late. 50/70
Tue (20 May): Chance of Rain and Cooler. 46/65
Wed (21 May): Partly Sunny. 42/69
Thu (22 May): Partly Sunny. 43/72
weather at oda.state.or.us
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