[willamette-fcst] Forecast - Monday, January 26th, 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.

Issued: 
     Monday, January 26th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 9:00am until 3:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A strengthening northerly flow aloft drove a modified Arctic
     cold front southward, across Washington and Oregon over the
     weekend, bringing light rain and snow to much of the region.
     Light snow started falling in the higher elevations of the
     north valley Saturday with local accumulations up to an inch
     Saturday night.  Lower elevations of western Oregon generally
     saw no significant snow accumulation, but light snow did fall,
     on the valley floors, at least as far south as Salem on Sunday,
     with the passage of the modified Arctic front.

     The frontal system also dramatically cooled the air aloft,
     which wiped out the strong low-level temperature inversion
     that had brought stagnant ventilation conditions to the
     region for more than a week.  The Salem sonding this morning
     showed significant cooling from the surface up to 11,000
     feet, compared with Sunday afternoon.  The freezing level
     was at the surface.  Transport wind had turned
     north-northeasterly with the air mass rapidly drying out.

     The mid-morning ODA surface analysis showed the modified
     Arctic front near the southern Oregon border.  Some snow
     flurries were being reported along the frontal boundary, in
     the Klamath Falls area.  Satellite imagery showed clearing
     skies, in the cold and drier air, north of the front.
     Temperatures were quite cold this morning across the state. 
     Most of central and eastern Oregon was below 20 degrees,
     with Redmond dropping down to at least 2 degrees and
     Hermiston dipping to 2 degrees below zero.  Brisk
     northwesterly winds, combined with temperatures in the
     teens, dropped wind-chill values below zero from La Grande
     to Baker City, in northeastern Oregon.  Clear skies allowed
     temperatures to drop into the mid and upper 20s in the
     Willamette Valley, with northerly winds, around 10 mph,
     dropping wind-chill temperatures to about 15 degrees. 
     Cascade pass temperatures were about 10 degrees with a fresh
     layer of snow on the roadways.

     An upper-level ridge of high pressure will build over the
     region today with the flow aloft remaining dry and
     northerly.  That will allow for a full day of sunshine
     across western Oregon and clearing skies east of the
     Cascades.  Brisk northerly winds should hold Willamette
     Valley temperatures below 40 degrees today with highs on the
     coast in the low to mid 40s.  Temperatures will remain below
     freezing east of the Cascades.

     Infrared satellite imagery showed a weather weather system
     moving onto the northern British Columbia coastline this
     morning.  Some high clouds will being to increase across
     Washington and northern Oregon by this evening.  Willamette
     Valley temperatures should easily fall well into the 20s by
     Tuesday morning, with increasing clouds.

Surface Winds:
     NNE 5-15 this morning, NNE 5-15 this afternoon.
Transport Winds:
     NNE 13 this morning, NNE 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 20.
High Temperature:
     Salem\'s high temperature today will be near 39.
Humidities:
     Minimum relative humidity will be near 39%.
Sunrise/Sunset:
     Salem sunset tonight: 5:12pm; sunrise tomorrow: 7:37am.

Extended Outlook:
     Computer models forecast precipitation to move into western
     Washington early Tuesday morning and spread south into
     northwestern Oregon by late Tuesday morning.  The air mass
     will initially be cold enough for the precipitation to begin
     as snow, even at very low elevations, before southerly winds
     lift the snow level to around 2-3000 feet during the
     afternoon.  No significant snow accumulations are likely, in
     the Willamette Valley, before the transition to rain occurs
     Tuesday afternoon.  Cold air will last longer in the
     Columbia Gorge, where a couple of inches of snow is possible
     on Tuesday, before temperatures moderate and turn the
     precipitation there to rain.

     Rain will taper off to a few showers Tuesday night, along
     the coast and across the Willamette Valley, with snow in the
     mountains above 4000 feet.  Overnight temperatures will be
     much warmer and should stay well above freezing.  A few
     showers may linger into Wednesday, as high pressure builds
     back over the region. Warmer air near the surface and cool
     air aloft should improve ventilation conditions across the
     valley. Thursday looks dry, with areas of morning fog, as a
     strong upper-level ridge builds over the region.  Warmer air
     aloft will deteriorate ventilation conditions.

     A weak weather system is forecast to flatten the upper-level
     ridge, as it brushes the region Friday.  It may be strong
     enough to bring some light rain to the extreme northern
     portions of the statepass.  Snow levels will remain near
     4000 feet.  The long-range models have not been consistent
     beyond Friday, but there is some indication that the
     upper-level ridge will rebuild over the region enough to
     keep the weather dry over the weekend for most of the state.
     There could be some sprinkles or very light rain near the
     northern border.  Monday now appears dry, but that is
     getting beyond my current range of confidence.

Tomorrow (27 Jan):  Light Rain or Snow Developing...Turning to Rain.  22/44

Wed (28 Jan):  Partly Cloudy.  36/46

Thu (29 Jan):  Areas of AM Fog.  Partly Sunny.  34/47

Fri (30 Jan):  Areas of AM Fog.  Increasing Clouds.  Chance of Light Rain.  35/50

Sat (31 Jan):  Mostly Cloudy.  Chance of Sprinkles or Light Rain...Mainly North.  35/48

Sun (01 Feb):  Mostly Cloudy.  Chance of Sprinkles or Light Rain...Mainly North.  36/50

Mon (02 Feb):  Partly Sunny.  36/50

ODA Meteorologist
weather at oda.state.or.us