[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.

...Corrected temperature forecast for Wednesday, January 28th...

Issued: 
     Friday, January 23rd, 2009 at 9:00am.

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

Weather Discussion:
     A dry and cold northerly flow aloft is developing across
     British Columbia with a mild and moist southerly flow aloft
     over California this morning.  The two, very different,
     upper-level flow patterns converge over Washington and
     Oregon with lots of clouds but really nothing in the way of
     precipitation across the region.  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 29 degrees.  Cloudy skies
     helped to keep fog from forming west of the Cascades, but
     fog covered many of the valleys in central and eastern Oregon.
     Temperatures east of the Cascades were also more moderate
     overnight, where minumums were mostly in the 20s and low 30s.

     Infrared satellite imagery showed lots of mid-level and some
     high clouds hanging out over Oregon, with weak flow aloft
     not moving the clouds anywhere quickly.  The ODA surface
     analysis showed cold Canadian air beginning to spill into
     eastern Washington, which was increasing the offshore
     pressure gradients through the Columbia Gorge.  Easterly
     winds were gusting over 30 mph at Troutdale and to 60 mph in
     Corbett. Easterly winds had also increased slightly along
     the coast, compared with yesterday morning.  Light northerly
     winds were developing 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
     from 2000 feet up to about 5000 feet.  The freezing level
     held fairly steady over the past 24 hours and was at 7600
     feet.  However, the air mass did cool a few more degrees
     below 5000 feet, compared with Thursday, so mixing heights
     should be slightly higher today.  However, conditions remain
     too stagnant to allow for stack burning.

     Considerable middle and high clouds will remain over the
     region today, with not much of a chance of any precipitation
     statewide.  With a lack of fog across western Oregon, there
     will also be some sunbreaks today.  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 low-level easterly winds may keep temperatures in the 40s.

Surface Winds:
     N 0-8 this morning, N 5-10 this afternoon.
Transport Winds:
     N 8 this morning, 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 56%.
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, but moisture will be very limited.  Colder
     Arctic air will spill into Washington late Saturday and into
     northern Oregon Sunday morning, lowering the snow level to
     the valley floors west of the Cascades.  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, but significant accumulations are unlikely.

     Temperatures should start out in the upper 30s or low 40s
     Sunday, then hold steady or fall during the day, as the
     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, and 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 back well into the 20s, clouds will increase
     Tuesday in response to a weak weather system sliding by
     mainly to our north.  It could be storng enough to bring
     some light precipitation to 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 shouuld be very light, but some minor snow accumulations
     are possible in the mountains and in the Columbia Gorge.

     A few sprinkles may persist across northwestern Oregon, as
     high pressure builds back over the region Wednesday
     afternoon through Thursday.  A more westerly jet stream is
     forecast to bring a series of wet weather systems onshore
     beginning late Friday.  These systems should bring rain to
     the lowlands and snow to the mountains.

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.  32/38

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