[willamette-fcst] Forecast - Monday, December 7th, 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, December 7th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 9:00am until 2:30pm.
     Straw stack burning is allowed from 9:00am until 2:30pm.

Weather Discussion:
     A strong northerly flow aloft drove a cold and dry Arctic
     air mass into Oregon over the weekend.  The morning ODA surface
     analysis showed a cold dome of high pressure centered over
     central and eastern Washington, with strong northerly flow
     across central and eastern Oregon and offshore flow across
     western Oregon.  The combination of brisk north-northeasterly
     winds, gusting to near 30 mph, and surface temperatures in the
     mid 20s dropped windchill values into the single digits in the
     northern Willamette Valley overnght.  Northerly winds of 10-15 mph
     were common in the central and southern Willamette Valley this
     morning, with temperatures in the low to mid 20s.

     Visible satellite imagery showed low clouds, due to
     upsloping northeasterly winds, covering sections of central
     Oregon.  A few middle and high clouds were streaming across
     the Willamette Valley, but the low-levels of the atmosphere
     were very dry west of the Cascades.  Cold air also moved in
     aloft over the weekend, with the freezing level crashing
     from around 10,000 feet to the surface.  Temperatures were
     near zero this morning over the Cascade passes, with brisk
     easterly winds making for dangerously cold windchill
     temperatures.  The cold and dry offshore flow extended to
     the coastline.  Temperatures along the beaches were in the
     mid to upper 20s this morning, with brisk easterly winds
     dropping windchill temperatures to around 10 degrees. 
     Temperatures were in the single digits over most of central
     and eastern Oregon, at mid-morning.  Meacham, in the
     northeast mountains, was a chilly 5 degrees below zero.

     The upper-level trough that ushered the cold air into the
     region has moved south of Oregon and will bring rain and
     snow to much of central and southern California today.  Dry
     notherly flow aloft will presist over Oregon, with
     temperatures staying below freezing all day, except for
     along the southern coast and sections of the interior of
     southwestern Oregon.  Even with plenty of sunshine, highs in
     the Willamette Valley will struggle to reach 30 degrees,
     with continued brisk north-northeasterly winds.  Mostly
     clear skies tonight will allow temperatures to quickly fall
     into the teens and possibly the single digits, in wind-sheltered areas.

Surface Winds:
     NNE 10-15 G30 North this morning, NNE 10-15 G 30 North this afternoon.
Transport Winds:
     NE 15 this morning, NE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 38.
High Temperature:
     Salem\'s high temperature today will be near 30.
Humidities:
     Minimum relative humidity will be near 27%.
Sunrise/Sunset:
     Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:38am.

Extended Outlook:
     A weak upper-level disturbance, in the cold northerly flow
     aloft, is forecast to drop southward, from British Columbia
     to just off the Oregon Coast Tuesday.  It may gather enough
     moisture to spread some clouds across western Oregon, with a
     treat of snow flurries, especially along the coast and over
     the coast range.  Offshore pressure gradients should relax
     slightly, with some decrease in the north-northeasterly
     winds across western Oregon.  After a very cold start,
     afternoon temperatures will, once again, struggle to reach
     30 degrees in the Willamette Valley.

     Cold and generally dry notherly flow aloft will continue
     Wednesday and Thursday, with only a slight moderation of
     temperatures.  By Friday, a westerly flow aloft will begin
     to undercut the offshore ridge and inject Pacific moisture
     into the cold dome of air over western Oregon.  That will
     increase the chance of snow or freezing rain, with moderating
     temperatures.  Things could get pretty messy, especially in
     the northern Willamette Valley, before an eventual changeover
     to plain old rain early next week...if not sooner.

Tomorrow (08 Dec):  Partly Cloudy.  Slight Chance of Snow Flurries.  13/28

Wed (09 Dec):  Partly Cloudy.  Slight Chance of Snow Flurries.  14/30

Thu (10 Dec):  Mostly Sunny and Continue Cold.  17/32

Fri (11 Dec):  Increasing Chance of Snow or Freezing Rain.  22/32

Sat (12 Dec):  Snow, Sleet, Freezing Rain, or Rain Likely.  28/35

Sun (13 Dec):  Snow, Sleet, Freezing Rain or Rain Likely.  30/37

Mon (14 Dec):  Chance of Snow, Sleet, Freezing Rain or Rain.  30/37

ODA Meteorologist
weather at oda.state.or.us