[willamette-fcst] Forecast - Wednesday, November 18th, 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: 
     Wednesday, November 18th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 4:30pm.
     Straw stack burning is allowed from now until 4:30pm.

Weather Discussion:
     The strong cold front that moved across western Oregon
     Tuesday morning had advanced eastward into Montana and Idaho
     by this morning.  In it\'s wake, a cool upper-level trough
     produced scattered showers across western Oregon Tuesday and
     Tuesday night.  Colder air aloft had dropped the freezing
     over Salem to just 3100 feet by early this morning, with a
     few showers still falling across northwestern Oregon.  ODOT
     road cameras showed snow-packed Cascade passes but just wet
     pavement over the coastal range passes.

     Partial clearing allowed areas of valley fog to form in
     southwestern Oregon, where temperatures locally dropped to
     near the freezing mark.  There was enough instability in the
     atmosphere to keep the air stirred up over the Willamette
     Valley during the night, so fog was not able to form.  Skies
     were partly sunny at mid-morning across northwestern Oregon,
     but Doppler radar was still showing a few showers rotating
     onshore, in a southwesterly flow aloft.

     Satellite imagery showed another impressive-looking storm
     system approaching the coastline this morning.  The leading
     edge of the cloud-shield, associated with a warm front, was
     just off the Washington Coast.  Solid cloud-cover extended
     weasward, to the low-pressure center, about 500 miles west
     of Vancouver Island, British Columbia. The frontal system is
     forecast to very slowly progress eastward, as waves of
     low-pressure develop along it and rotate northeastward
     towards Vancouver Island.  That is a similar weather pattern
     to the one that brought heavy rain and strong winds to the
     coast and northwestern Oregon earlier this week.

     The bulk of the moisture, from the approaching frontal
     system, is forecast rotate into western Washington and
     southern British Columbia over the next 24 hours. However,
     the frontal boundary may sag just far enough south and east
     to bring heavy rain back to the extreme northwestern tip of
     Oregon by tonight. South-southeasterly pressure gradients
     will be increasing across western Oregon, with strong winds
     likely developing along the Oregon Coast by this evening.
 
     The National Weather Service has issued a High Wind Warning
     for later this afternoon and tonight along the Oregon Coast,
     but winds are not expected to be as strong with this system
     as they were on Monday.  Still, south winds could locally
     gust to around 70 mph over exposed headlands and along
     beaches.  A High Surf Advisory had also been issued for this
     evening through Thursday morning.

     Clouds and south-southeasterly winds will increase across
     the Willamette Valley this afternoon, but not much rainfall,
     if any, is expected until Thursday morning east of the
     coastal range.  After a lingering shower or two this
     morning, the beat chance for rain, later today, will be in
     the north valley.  Even with increasing south-southeasterly
     winds, temperatures will remain below normal across most of
     western Oregon today, due to the cool air aloft and increasing
     cloud-cover.  Willamette Valley temperatures were only in the
     upper 30s and low 40s at mid-morning and will slowly climb all
     day...likely peaking near 50 degrees around midnight.

Surface Winds:
     SSE 7-15 G20 this morning, SSE 10-15 G25 this afternoon.
Transport Winds:
     SSW 20 this morning, S 25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2000 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature this afternoon will be near 49.  Low 50s are possible tonight.
Humidities:
     Minimum relative humidity will be near 65%.
Sunrise/Sunset:
     Salem sunset tonight: 4:40pm; sunrise tomorrow: 7:15am.

Extended Outlook:
     Waves of low-perssure will continue to form along the
     offshore frontal boundary on Thursday, with the main
     precipitation zone slowly sagging south and east...likely
     making it into extreme northwestern Oregon.  Strong south
     winds will continue along the coast, where the National
     Weather Service has issued a High Wind Watch for all day
     Thursday.  Oregon will be in the warm-sector of the storm,
     with blustery south winds lifting Willamette Valley
     temperatures into the mid 50s.  The freezing level should
     climb to around 6000 feet, with just a chance of light rain
     or snow making it as far east as the Cascades.

     The cold front is forecast to finally come onshore Thursday
     night and slowly progress across western Oregon Friday. 
     Rainfall could be locally heavy, especially along the coast
     and in the coastal range.  The strong winds will continue
     until the front moves east of the region Friday afternoon,
     and the steady rain turns to showers.  The snow level will
     drop back to around 2500 feet by Friday night with
     accumulating snow over the mountain passes.

     Showers will taper off Saturday, with yet another weather
     system forecast to come onshore Saturday evening.  That will
     be a colder system, with possibly heavy snow in the
     Cascades.  Showers will taper off Sunday afternoon. 
     A weaker system is slated to spread more rain across western
     Oregon Monday...along with rising snow levels.  We may get a
     break from the rain next Tuesday and Wednesday.

Tomorrow (19 Nov):  Blustery and Warmer.  Chance of Rain...Mainly North.  44/55

Fri (20 Nov):  Rain and Windy...Turning to Showers.  Snow Level Dropping to 2500 Feet.  45/50

Sat (21 Nov):  Showers Early...Rain and Wind Late.  Snow Level 3-4000 Feet.  39/48

Sun (22 Nov):  Showers.  Snow Level near 3000 Feet. 40/49

Mon (23 Nov):  Rain.  Snow Level Rising to 5-6000 Feet.  42/53

Tue (24 Nov):  Partly Sunny.  40/53

Wed (25 Nov):  Partly Sunny.  40/53

ODA Meteorologist
weather at oda.state.or.us