[willamette-fcst] Forecast - Thursday, January 15th, 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.

NOON UPDATE

...An Air Stagnation Advisory is in effect for the Willamette Valley through Saturday. Warm air
   aloft is trapping colder air near the surface, resulting in very poor ventilation conditions...

Issued: 
     Thursday, January 15th, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     A very strong upper-level ridge of high pressure remains
     along the west coast today with light north-northwesterly
     winds and unsesonably warm air aloft.  Cooler air trapped
     near the surface, expecially in the valleys, is resulting in
     steep low-level temperature inversions and very stagnant
     ventilation conditions across the region.

     Strong temperature inversions are resulting in a wide range
     of temperatures around the state today.  The warmest
     readings are in the mountains and along the coast, with some
     very cool valley readings...especially east of the
     Cascacdes.  Sunny skies warmed some locations in the coast
     range into the low 70s Wednesday afternoon, with midday
     readings today already topping 60 degrees.  It is also sunny
     and warm again today in the Cascades.   The midday
     temperature was 50 degrees, at Government Camp (5000-foot
     level), and Timberline Lodge (6000 feet) was 53.  The entire
     coastline was also sunny late this morning with temperatures
     ranging from 48 degrees at Astoria to 54 at Newport and 58
     degrees at Brookings.  Meanwhile, visible satellite imagery
     showed low clouds blanketing most of the Willamette Valley,
     where temperatures were still in the 30s.  East of the
     Cascades, Redmond had warmed into the 40s with some
     sunshine, but some valley locations, like Baker City,
     Pendleton, and Klamath Falls, were still in the upper 20s
     with low clouds and fog.

     The Salem sounding this morning also refected the strong
     low-level temperature inversion.  Readings near the surface
     were in the mid 30s but rapidly warmed to 50 degrees just
     above 1500 feet, and to 65 degrees at 2500 feet. 
     Temperatures remained above 50 degrees all the way up to
     8000 feet, and the freezing level was clear up at 12,800 feet.

     The late-morning ODA surface analysis showed a thermal
     trough building just off the Oregon and Washington Coast and
     high pressure over eastern Washington and Oregon.  Offshore
     flow was increasing across western Oregon with easterly
     winds gusting between 20 and 40 mph at the western end of
     the Columbia Gorge.  East winds were also making it over the
     coastal range and helping to keep skies clear along the
     beaches, with gusts to nearly 20 mph at Newport.  

     The drier easterly winds have not been able to penetrate the
     low-level temperature inversion in the Willamette Valley,
     where fog was still locally reducing visibilities to less
     than one-quarter of a mile.  Fog and low clouds will be
     persistent in the western valleys and in the Columbia Basin
     of northeastern Oregon, while much of the state enjoys
     mostly sunny skies.  Increasing drier outflow from the
     Columbia Gorge may help to clear the fog from the northern
     Willamette Valley this afternoon.

     Temperatures will have a wide range this afternoon with
     valley locations considerably cooler than mountain and
     coastal sites.  Most of the central and sotuhern Willamette
     Valley will have persistent fog and low clouds, with
     temperatures struggling into the low 40s. Some afternoon
     sunshine should help north-valley temperatures climb at
     least the upper 40s and perhaps the low 50s.  Once again,
     mountain and coastal locations could push up well into the
     50s and 60s, under mostly sunny skies.  

Surface Winds:
     NE 3-8 this afternoon.
Transport Winds:
     NE 5 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 500 feet.  Ventilation index 3.
High Temperature:
     Salem\'s high temperature today will be near 42.
Humidities:
     Minimum relative humidity will be near 79%.
Sunrise/Sunset:
     Salem sunset tonight: 4:57pm; sunrise tomorrow: 7:46am.

Extended Outlook:
     The protective ridge of high pressure is expected to last at
     least through this weekend. Stagnant ventilation conditions
     will continue with Willamette Valley fog and low clouds
     locally giving way to partly sunny skies in the
     afternoons...mainly north.  Temperatures will be well above
     normal along the coast, in the coastal range, and in the
     Cascades, with mostly sunny skies.  Valley temperatures will
     range from slightly below normal, in cloudy/fogy areas, to
     slightly above normal, where the sunshine is able to break through.

     Long-range computer models show the upper-level ridge
     shifting east, to over the Rockies, early next week, with
     the flow aloft becoming southerly over Oregon.  Surface
     winds will remain strongly offshore, which could provide
     some afternoon clearing in the valleys, with mostly sunny
     skies elsewhere across the state. The first threat of rain
     comes late on Tuesday, but that system is likely to weaken
     and may head mostly south of Oregon.

     An upper-level ridge is forecast to begin developing, just
     offshore, during the second half of next week.  There will
     also be an undercutting jet westerly jet stream movning into
     California. Depending on the location of the developing
     ridge aloft, ventilation conditions may begin to improve by
     late next week.  A possible change in the weather paatern is
     forecast by computer models beginning late next week, but it
     is too soon to tell what the new pattern will be.

Tomorrow (16 Jan):  AM Clouds/Fog.  Afternoon Clearing...Mainly North.  33/48

Sat (17 Jan):  AM Clouds/Fog.  Afternoon Clearing...Mainly North.  33/50

Sun (18 Jan):  AM Clouds/Fog.  Afternoon Clearing...Mainly North.  33/51

Mon (19 Jan):  AM Clouds/Fog.  Afternoon Clearing...Mainly North.  33/51

Tue (20 Jan):  Increasing Clouds.  Slight Chance of Light Rain Late.  35/50

Wed (21 Jan):  Areas of Fog/Low Clouds.  Partly Cloudy.  34/49

Thu (22 Jan):  Areas of Fog/Low Clouds.  Partly Cloudy.  33/48

ODA Meteorologist
weather at oda.state.or.us