[willamette-fcst] Forecast - Thursday, February 26th, 2009

Thu Feb 26 12:04:26 PST 2009

Daily Smoke Management Forecast

Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

NOON UPDATE

Issued: 
     Thursday, February 26th, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 4:00pm.
     Straw stack burning is allowed from now until 4:00pm.

Weather Discussion:
     A cold upper-level low-pressure system slowly sagged
     southward, along the Washington Coast, last night.  It
     circulated cold Arctic air, from southern British Columbia,
     over the warmer ocean waters and then inland across
     Washington and Oregon.  That increased the shower activity
     with progressively lowering snow levels.  By early this
     morning, wet snow showers were falling down to sea level
     along the Oregon coast and down to the floor of the
     Willamette Valley.

     Doppler radar showed the main area of morning snow showers
     extended from just south of Portland to near Corvallis and
     stretched from the coast to the creast of the Cascades. 
     Roadways were locally covered in slush along the I5 corridor
     early this morning with some of the higher elevations on
     both sides of the valley locally picking up a few inches of
     wet snow.  Up to about 6 inches of snow fell over the
     coastal passes with up to a foot over the Cascade passes. 
     The ski areas on Mt. Hood have received almost 2 feet of new
     snow in the past 24 hours.  Timberline Lodge has received
     more than 4 feet of snow in the past 72 hours.

     The upper-level low-pressure system moved east of the
     Cascades late this morning, with showers rapidly decreasing
     across the lower elevations of western Oregon.  Snow showers
     were continuing in the Cascades, where ODOT reports showed
     rough driving conditions as far south as Willamette Pass. 
     The storm center was over extreme southeastern Washington at
     midday.  Doppler radar showed a lessening of the snow shower
     activity over the Cascades and mountains of northeastern Oregon.

     Showers all but ended west of the Cascade foothills with
     some sunbreaks appearing.  Daytime heating has lifted to
     snow level to between 1000 and 1500 feet.  Willamette Valley
     temperatures had warmed to near 40 degrees, by late this
     morning, with sections of the coast and southwestern Oregon
     in the mid 40s.  Willamette Valley temperatures should climb
     into the mid 40s this afternoon, with gradually clearing skies.

     The late-morning ODA surface analysis continued to show an
     Arcitc frontal boundary extending from just south of
     Bellingham to just north of Spokane, Washington.  North of
     that line, temperatures were well below freezing with cold
     northerly winds.  The leading edge of the cold front that
     brought the low-elevation snow to Oregon earlier this
     morning had pushed into Idaho by midday.  Winds were
     west-southwesterly, at 5-15 mph, in the Willamette Valley
     with partly sunny skies melting the morning slush.  Skies
     were clearing along with coast with drying westerly surface
     winds gusting to near 20 mph.

Surface Winds:
     WSW 5-15 this afternoon.
Transport Winds:
     W 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 80.
High Temperature:
     Salem\'s high temperature today will be near 45.
Humidities:
     Minimum relative humidity will be near 55%.
Sunrise/Sunset:
     Salem sunset tonight: 5:56pm; sunrise tomorrow: 6:53am.

Extended Outlook:
     The upper-level low-pressure system is forecast to move into
     Idaho tonight with showers ending and skies clearing across
     Oregon.  That will allow for much colder overnight
     temperatures.  Valley minimums will likely drop into the mid
     to upper 20s most areas.  Please be aware that wet road
     surfaces may freeze and create locally slick driving
     conditions through early Friday.  There may also be areas of
     morning fog.  A transitory ridge of high pressure will
     likely allow for at least partly sunny skies Friday, but
     temperatures will be well below normal.

     Mostly clear skies Friday evening will lead to areas of fog
     forming Friday night.  Valley temperatures should, once
     again, drop to near or below freezing by Saturday morning. 
     The next weather system will increase clouds over the region
     Saturday with a chance of rain by the afternoon.  Increasing
     southwesterly flow aloft should lift the snow level to near
     or slighty above the Cascade passes.  Rain is likely
     Saturday night and Sunday, as the storm moves onshore.  Snow
     levels will hover around the Cascade passes Sunday, before
     dropping to near 3000 feet Sunday night.

     An upper-level trough will slowly move onshore Monday and
     Tuesday with an ongoing threat of showers.  That trough
     should not be nearly as cold as the one that came through
     the region this morning, so snow levels should stay in the
     3-4000 foot range.  Valley temperature will be near normal. 
     A stronger and colder system is forecast to come onshore
     late Wednesday and Thursday.

Tomorrow (27 Feb):  Very Cold Start.  Partly Sunny and Cool Afternoon.  25/48

Sat (28 Feb):  Increasing Clouds.  Chance of PM Rain.  Snow Level Rising to 4000 Feet.  31/49

Sun (01 Mar):  Rain.  Snow Level 4000 Feet...Dropping to 3000 Feet Late.  39/52

Mon (02 Mar):  Showers.  Snow Level  3-4000 Feet.  37/51

Tue (03 Mar):  Mostly Cloudy.  Chance of Showers.  Snow Level near 4000 Feet.  37/52

Wed (04 Mar):  Rain Increasing.  Snow Level 3-4000 Feet.  36/51

Thu (05 Mar):  Rain Turning to Showers.  Snow Level Dropping to 2000 feet.  35/49

ODA Meteorologist
weather at oda.state.or.us