[willamette-fcst] Forecast - Friday, January 23rd, 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: 
     Friday, January 23rd, 2009 at 12:00pm.

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

Weather Discussion:
     A dry and cold north-northwesterly flow aloft is developing across British Columbia with a
     mild and relatively moist southerly flow aloft over California today.  The, very different,
     upper-level flow patterns converge over Washington and Oregon with lots of clouds but no
     precipitation across either state.  Mostly cloudy skies kept temperatures warmer overnight
     across Oregon, with Willamette Valley minimums generally in the low 30s.  Hillsboro was one
     of the coldest spots with a low of 28 degrees.  The warmer overnight temperatures and
     fairly dry air mass kept fog from forming west of the Cascades, but fog and low clouds
     blanketed many of the valleys in central and eastern Oregon. Temperatures east of the
     Cascades were more moderate overnight, with morning minumums mostly in the 20s and low 30s.

     Infrared satellite imagery showed lots of middle and  high clouds hanging out over Oregon,
     with weak upper-level winds not moving the clouds anywhere quickly.  The ODA surface
     analysis showed cold Canadian air beginning to spill into eastern Washington, which was
     increasing pressures east of the Cascades and generating more of an offshore flow.  Easterly
     winds were gusting over 30 mph at Troutdale, and to 60 mph in Corbett, at the western end
     of the Columbia Gorge. Northeasterly winds were blowing at near 10 mph along the coast with 
     north-northesterly winds of 5-10 mph in the Willamette Valley.

     The Salem sounding this morning continued to show a fairly strong temperature inversion from
     the surface up to about 2000 feet with the temperature remaining fairly constant between 2000
     and 5000 feet (indicating a deep stable layer of air).  The freezing level held fairly steady
     over the past 24 hours and was at 7600 feet.  There was some cooling of the air mass below
     5000 feet, compared with Thursday, which will promoteslightly better mixing today.  However,
     conditions remain too stagnant to allow for stack burning.

     Midday temperatures were in the upper 30s and low 40s across the Willamette Valley, with the
     coldest readings near the Columbia Gorge.  Coattal temperatures ranged from near 40 at
     Astoria to the low 50s at Brookings, on the south coast.  Considerable middle and high clouds
     will remain over Oregon today but little or no precipitation.  High temperatures will climb
     into the mid to upper 40s across the Willamette Valley this afternoon.  Increasing cool
     outflow, from the Columbia Gorge, should keep north valley temperatures from climbing above
     the mid 40s.  Downsloping easterly winds will help the coastline shoot into the 50s this
     afternoon, except near Astoria, where cold easterly winds will keep highs in the 40s.

Surface Winds:
     N 5-10 this afternoon.
Transport Winds:
     N 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1200 feet.  Ventilation index 12.
High Temperature:
     Salem\'s high temperature today will be near 47.
Humidities:
     Minimum relative humidity will be near 46%.
Sunrise/Sunset:
     Salem sunset tonight: 5:08pm; sunrise tomorrow: 7:40am.

Extended Outlook:
     The cold northerly flow over British Columbia will sag south over Washington and Oregon this
     weekend. That will lower snow levels to 4000 feet Saturday and to near 2000 feet Saturday
     night.  Moisture will be limited, with the best chance of rain and snow across southern and
     eastern Oregon.  Colder Arctic air will spill into Washington late Saturday and into
     northern Oregon Sunday.  The air mass will rapidly dry out, as the colder air moves south
     across the Willamette Valley Sunday afternoon and evening.  There may be a brief period of
     flurries of light snow with the onset of the colder air.  However, with limited moisture,
     no significant snow accumulations are expected in the Willamette Valley, but a light dusting
     is possible before the precipitation shuts off Sunday night. 

     Temperatures should start out in the upper 30s or low 40s Sunday, then hold steady or fall
     during the afternoon and evening, as modified Arctic air moves south across the Willamette
     Valley.  Skies should begin to clear Sunday night, with dry and cold northerly winds dropping
     valley temperatures well into the 20s (perhaps the upper teens).  Monday should become mostly
     sunny, as cold Canadian high pressure settles over the area.  High temperatures will struggle
     into the low to mid 30s, with temperatures in the Columbia Gorge staying near of below
     freezing.  Brisk easterly winds will continue at the western end of the Gorge with cold
     northerly winds in the Willamette Valley.

     After a cold night Monday night, with valley minimums dropping well into the 20s, clouds will
     increase Tuesday in response to a weak weather system sliding mainly into southern British
     Columbia.  Some light precipitation could spread as far south as northern Oregon late Tuesday. 
     Precipitation from this system would likely fall as snow in the Columbia Gorge, and perhaps
     briefly in the northern Willamette Valley, before changing to rain.  Precipitation
     totals should be very light, but some minor snow accumulations are possible in the mountains
     and in the Columbia Gorge.

     A building upper-level ridge of high pressure will warm the air aloft, and also moderate
     surface temperatures, during the second half of next week.  A few sprinkles or very light
     rain is possible in the northern half of the state.  High pressure may dry things briefly
     Thursday and early Friday.  However, a strong westerly jet stream is forecast to bring a
     series of wet weather systems onshore, beginning late Friday, with frequent valley rain
     and mountain snow expected during the first week of February.

Tomorrow (24 Jan):  Chance of Showers.  Snow Level dropping to 2000 Feet Late.  32/45

Sun (25 Jan):  Light Rain Turning to Light Snow...Colder.  Little or No Accumulations.  33/38

Mon (26 Jan):  Mostly Sunny and Cold.  23/35

Tue (27 Jan):  Increasing Clouds.  Chance of Light Rain of Snow Late.  22/38

Wed (28 Jan):  Mostly Cloudy.  Chance of Sprinkles.  35/45

Thu (29 Jan):  Areas of AM Fog.  Mostly Cloudy.  Chance of Sprinkles North.  35/47

Fri (30 Jan):  Increasing Clouds.  Chance of Rain Late.  35/50

ODA Meteorologist
weather at oda.state.or.us