[willamette-fcst] Forecast - Thursday, July 16th, 2009

[Willamette Valley Ag/Burning Forecast]

Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

...State Fire Marshal Conditions may be met this afternoon due to low humidities and wind...

Issued: 
     Thursday, July 16th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 1:00pm until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     After a sunny and much warmer day, on Wednesday, with
     Willamette Valley highs climbing mostly into the upper 80s,
     clear skies overnight allowed temperatures to drop mostly
     into the 50s.  Hillsboro was the coolest spot with a minimum
     of 51 degrees.  Corvallis and Eugene both dipped to 54.  As
     usual, Portland was the warm spot...staying in the low 60s. 
     The coast was cloudy and foggy this morning with
     temperatures in the upper 40s and low 50s.  Mewanwhile,
     skies were mostly clear east of the Cascades, with minimums
     ranging from 40 degrees at Meacham to 60 at John Day.

     Visible satellite imagery showed low clouds banked up along
     the entire length of the Washington, Oregon, and California
     coastlines, with some minor penetration into the coastal
     mountain gaps along the southern Oregon Coast, south of
     Florence.  Elsewhere across the Pacific Northwest, skies
     were mostly clear, with only some high clouds over extreme
     eastern Oregon and Idaho.  The ODA surface analysis showed a
     broad thermal trough covering most of Washington and
     Oregon...resulting in weak northerly pressure gradients over
     the interior and onshore gradients along the coastal strip.

     An upper-level ridge of high pressure will remain over
     Oregon today...shifting slightly east to near the
     Oregon/Idaho border by late this afternoon. Weak
     southwesterly flow aloft will maintain onshore flow along
     the coast, where temperatures will stay cool with areas of
     afternoon clearing...mainly north.  Skies will be sunny,
     with slightly warmer temperatures, east of the coast range today.

     High today will range from the 60s on the central and south
     coast, where low clouds will be the most persistent, to the
     low 70s on the north coast. Willamette Valley highs today
     should climb into the low 90s, after peaking mostly in the
     upper 80s Wednesday afternoon. Surface and transport winds
     are forecast to remain northerly today, which is not
     conducive to good ventilation for open burning in the
     Willamette Valley.

Surface Winds:
     N 3-8 this morning, N 5-15 this afternoon.
Transport Winds:
     NNE 8 this morning, N 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 28.
High Temperature:
     Salem\'s high temperature today will be near 91.
Humidities:
     Relative humidity drops to 50% by 11am.
     Minimum relative humidity will be near 27%.
Sunrise/Sunset:
     Salem sunset tonight: 8:55pm; sunrise tomorrow: 5:42am.

Extended Outlook:
     The upper-level ridge is forecast to shift eastward, to over
     Idaho and western Montana, on Friday with the center of the
     associated broad surface thermal trough moving into central
     Oregon.  Temperatures will likely warm a couple of more
     degrees across the interior of western Oregon, with 
     transport winds forcast to stay northerly...limiting any
     onshore flow.  That makes a burning opportunity unlikely on
     Friday.  There is a slight chance that transport winds could
     shift from northerly to northwesterly late in the day, but
     that is looking less likely with each run of the computer
     models.  The region may also be flirting with State Fire
     Marshal conditions, again, due to high temperatures and low
     humidities.

     The upper-level ridge will shift further east, to over
     eastern Idaho and western Montana, on Saturday.  Increasing
     southwesterly flow aloft over Oregon will drive some mid and
     high-level miosture into central and eastern Oregon for an
     increasing threat of afternoon and evening thunderstorms.
     The surface thermal trough, and warmest temperatures, is
     forecast to shift into eastern Oregon, with increasing
     onshore flow across the interior of western Oregon.  That
     should cool temperatures back into the 80s across the
     Willamette Valley.

     A weak upper-level trough is forecast to finally move
     onshore, across southern British Columbia, Sunday
     afternoon...pushing the surface thermal trough into Idaho
     and ushering a significant surge of cooler ocean air across
     Oregon.  Willamette Valley highs should cool to near 80
     degrees (slightly below normal) with some marine low clouds
     possibly penetrating into the western valleys in the
     morning.  Precipitation west of the Cascades appears as if
     it will be limited to a chance of drizzle along the coast. 
     The thundershower threat, east of the Cascades, will get
     pushed closer to the Idaho border, as cooler and more stable
     air surges into central Oregon.

     An upper-level ridge is forecast to begin building back over
     the region Monday, for a return to sunny and warmer
     conditions.  A weak system may brush the region with some
     high clouds late Tuesday and Wednesday, with an increase in
     onshore flow keeping temperatures near normal.

Tomorrow (17 Jul):  Sunny and Very Warm.  Winds Likely Remaining Northerly.  58/93

Sat (18 Jul):  Mostly Sunny but Not As Warm.  Increasing Onshore Flow.  59/88

Sun (19 Jul):  Areas of Morning Clouds.  Mostly Sunny but Cooler.  56/79

Mon (20 Jul):  Morning Clouds.  Mostly Sunny in the Afternoon.  52/82

Tue (21 Jul):  Mostly Sunny.  52/85

Wed (22 Jul):  Patchy Morning Clouds.  Mostly Sunny.  55/83

Thu (23 Jul):  Patchy Morning Clouds.  Mostly Sunny.  54/85

ODA Meteorologist
weather at oda.state.or.us