[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.

...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 9:00am.

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

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

     The strong temperature inversions made for considerable
     variation in afternoon temperatures Wednesday, with the
     warmest readings in the mountains and along the coast.  Some
     locations in the coast range pushed into the low 70s
     Wednesday afternoon.  It reached 61 degrees, at the
     5000-foot level near Government Camp, on Mt. Hood, and 56
     degrees at Timberline Lodge (6000 feet).  Tillamook, along
     the north coast, hit 59 degrees.  Further south, Newport hit
     55, North Bend climbed to 63 degrees and Brookings topped
     out at 68. Meanwhile, low clouds and trapped low-level cool
     air held central and southern Willamette valley highs in the
     low 40s.  The north valley saw some sunshine Wednesday
     afternoon, where temperatures managed to climb into the mid 40s.

     Fog and low clouds were also persistent in some of the
     valleys east of the Cascades Wednesday, especially in the
     Columbia Basin region of northeastern Oregon.  Pendleton
     only managed a high temperature of 37 degrees.   Baker City
     and Ontario never made it to the freezing mark Wednesday,
     both recording a high of just 30 degrees.  Meanwhile, places
     like Redmond got a tast of the warmer air aloft and climbed
     into the low 60s.

     The Salem sounding this morning revealed the strong
     low-level temperature inversion.  Readings near the surface
     were in the mid 30s and 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.  Timberline Lodge (6000-foot elevation on Mt. Hood)
     had a low temperature of a balmy 48 degrees overnight and
     was 49 degrees at mid morning.  That was in stark contrast
     to the icy fog in the western valleys, where temperatures
     ranged from the mid 20s, to the mid 30s.

     The 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.  Newport was 45 degrees at mid-morning with clear
     skies and easterly winds of 15 mph.  The drier easterly
     winds were not able to penetrate the low-level temperature
     in version in the Willamette Valley, where fog was locally
     reducing visibilities to less than one-quarter of a mile. 
     Very light winds allowed temperatures to fall into the teens
     and 20s across central and eastern Oregon.  Meacham, in
     northeastern Oregon, was one of the coldest spots in the
     state with a low of 9 degrees this morning.

     Very little change in the weather is expected today,
     compared with Wednesday.  Some high clouds will stream
     across the state at times, in the north-northwesterly flow
     aloft.  Fog and low clouds will be fairly 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 with valley
     locations considerbly cooler than mountain and coastal
     sites.  Most of the central and sotuhern Willamette Valley
     will have persistent fog and low clouds, with temperatures
     struggling to reach the mid 40s. Some afternoon sunshine
     should help north-valley temperatures climb at least the low
     50s.  Once again, mountain and coastal locations could push
     up well into the 60s, under mostly sunny skies.  

Surface Winds:
     NE 0-6 this morning, NE 3-8 this afternoon.
Transport Winds:
     NE 3 this morning, 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 45.
Humidities:
     Minimum relative humidity will be near 70%.
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
     well 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 may help to
     briefly clear fog and low clouds, even from the central and
     south valley...revealing some afternoon sunshine. 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 change in the weather paatern is forecast by some of the
     computer modles beginning late next week.  It is possible
     that some modified Arctic air may begin spilling back into
     the Columbia Basin of eastern Washington and northeastern
     Oregon by the following weekend. It is also possible that
     the upper-level ridge will rebuild directly over the region
     for a continuation of dry and stagnant conditions.  The
     upcoming potential weather pattern change is still too far
     out to call.

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