[willamette-fcst] Forecast - Friday, November 14th, 2008

[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.

Issued: 
     Friday, November 14th, 2008 at 9:00am.

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

Weather Discussion:
     A building upper-level ridge of high pressure cut off the
     tropical moisture feed into the Pacific Northwest and
     brought a little sunshine to western Oregon Thursday.  Mild
     southerly winds turned northerly, which capped high
     temperatures in the 55-60 degree range across the Willamette
     Valley.  The ridge strengthen overnight with the Salem
     sounding this morning showing considerble warming aloft
     since Thursday afternoon.

     The freezing level had jumped back to near 12,000 feet over
     western Oregon.  Meanwhile, fair skies and light winds
     allowed surface temperatures to drop into the mid 30s across
     the valley, by early this morning, with areas of fog
     forming.  A strengthening low-level temperature inversion
     will keep mixing heights below 1500 feet today with light
     northeasterly transport winds this morning turning more
     southeasterly this afternoon.

     Satellite imagery showed clouds streaming over the top of
     the ridge of high pressure across Washington with only a few
     high clouds slipping south of the Washington/Oregon border. 
     Areas of fog and low clouds formed overnight in the valleys
     of southwestern Oregon and in the southern Willamette
     Valley.  The remainder of the state had sunshine this
     morning.

     The ODA surface analysis showed high pressure over eastern
     Washington and northeast Oregon with a building thermal
     trough along the southern Oregon Coast.  Offshore gradients
     were generating brisk easterly winds at the western end of
     the Columbia Gorge.  Troutdale was getting east winds
     gusting to near 25 mph.  Dry easterly flow helped the north
     valley stay clear of the fog and low clouds this morning,
     but there was a considerable amount of fog and low
     cloudiness, showing up on visible satellite imagery, across
     Linn and Lane Counties.

     Valley temperatures ranged from the mid 30s, in clear areas,
     to the low 40s in foggy zones at mid-morning.  Dry easterly
     flow was dropping off the coast range and keeping skies
     clear along the Oregon Coast.  Newport had easterly winds,
     sunny skies, and temperatures in the mid 40s this morning. 
     Continued offshore flow will help to clear the fog and low
     clouds from the southern valleys this afternoon, with
     sunshine over the remainder of the state.  Valley highs will
     range from near 50, where fog is more persistent in the
     south valley, to near 60 along the northern Cascade and
     coastal range foothills and along the coast.

     Fair skies and continued light offshore flow will allow
     areas of fog and low clouds to reform overnight...especially
     in the southern Willamette Valley.  Gorge winds will help
     the north valley stay more clear.  Minimum temperatures will
     dip locally to near freezing in clear areas and into the mid
     to upper 30s where fog forms.

Surface Winds:
     NE 0-4 this morning, SE 0-4 this afternoon.
Transport Winds:
     NE 4 this morning, SE 4 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 6.
High Temperature:
     Salem\'s high temperature today will be near 55.
Humidities:
     Minimum relative humidity will be near 57%.
Sunrise/Sunset:
     Salem sunset tonight: 4:44pm; sunrise tomorrow: 7:10am.

Extended Outlook:
     The strong and broad upper-level ridge is forecast to remain
     over Oregon through Monday.  Weak weather systems riding
     over the top of the ridge will spread some middle and high
     clouds over Washington and southern British Columbia.  Light
     offshore flow will aid in drying the air mass.     The
     freezing level will remain well over 10,000 feet, with the
     low sun-angle this time of year leading to the development
     of strong low-level temperature inversions.  Light easterly
     winds, near the Columbia Gorge, will help to clear morning
     fog from the north valley, but valley fog could be fairly
     persistent south of about Salem.

     Weekend temperatures will vary considerably, depending on
     the extent and duration of valley fog. The Cascade
     foothills, coast range, and sections of the coast could
     climb into the low to mid 60s, while sections of the
     Willamette Valley stay in the low to mid 50s with persistent
     fog.  Fair skies and light winds will drop overnight
     temperatures into the 30s the next few nights.  The ridge is
     forecast to flatten and beging shifting east Monday.  A
     weakening cold front may make it onshore about Tuesday but
     will not likely produce much, if any, rainfall.

     The ridge is forecast to rebuild Wednesday, with increasing
     offshore flow at the surface providing a little sunshine. 
     By Thursday, the ridge will likely give way to what will
     appears to be a series of Pacific stroms, which would
     improve ventilation conditions for stack burning.  Snow
     levels may drop to the Cascade passes by Friday.  That would
     be welcome news for the ski industry but initiate winter
     driving conditions, for travelers, over the mountain passes.

Tomorrow (15 Nov):  Morning Fog...Mainly South.  Becoming Mostly Sunny.  34/57

Sun (16 Nov):  Morning Fog.  Afternoon Clearing...Mainly North.  36/58

Mon (17 Nov):  Morning Fog.  Afternoon Clearing...Mainly North.  39/57

Tue (18 Nov):  Areas of AM Fog.  Partly Cloudy.  40/56

Wed (19 Nov):  Partly Cloudy.   39/56

Thu (20 Nov):  Chance of Rain.  39/54

Fri (21 Nov):  Rain Likely.  Snow Level Dropping to 4000 Feet.  38/48

ODA Meteorologist
weather at oda.state.or.us