[willamette-fcst] Forecast - Tuesday, May 20th, 2008

[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: 
     Tuesday, May 20th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:30pm.
     Straw stack burning is allowed from now until 6:30pm.

Weather Discussion:
     A cooling trend began Sunday across Oregon and will really
     kick in today with a fairly strong cold front sweeping
     across the state.  Infrared satellite imagery showed cloudy
     skies covering Washington and Oregon at mid-morning.  A
     well-defined solid cloud-band stretched from NW Washington
     through Western Oregon with the back edge just moving
     onshore.  Doppler radar showed rain across much of Eastern
     Washington extending southward into NE Oregon with an
     enhanced zone of rain across Western Washington and Western
     Oregon, in assoication with the cold front.

     Cloudy skies helped to hold Westner Oregon temperatures in
     the low to mid 50s overnight, but they were still dropping
     at mid-morning.  Over one-quarter of an inch of rain fell
     along the northern coastal strip this morning with one-tenth
     to one-quarter of an inch falling so far across the
     Willamette Valley.  The fairly strong cold front is forecast
     to move through the Willamette Valley in the next couple of
     hours with the steady rain tapering off.  Strong onshore
     flow will keep skies generally cloudy with an upper-level
     trough helping to maiintain scattered showers through
     Wednesday and perhaps into Thursday.  Temperatures will
     struggle to reach the low 60s this afternoon...20-25 degrees
     cooler than on Monday.

     The freezing level over Western Oregon, which was above
     15,000 feet Saturday, dropped to between 12,000 and 14,000
     feet Monday to between 9000 and 12,000 feet this morning. 
     It will fall rapidly today, in the wake of the cold front,
     to near 6000 feet this afternoon.  Rain was falling over the
     Cascade passes at mid-morning with pass temperatures in the
     low 40s.  The snow level will likely drop to near 4500 feet
     later today with a couple of inches of wet snow possible
     over the Cascade Passes by tonight.

     The ODA surface analysis showed high pressure building into
     the Southern Oregon Coast, in the wake of a cold front
     moving across the western half of Washington and Oregon. 
     Onshore flow at the surface and colder air aloft will
     combine to create good ventilation condions across Western
     Oregon today, so stack burning is allow.

     Cloudy skies extend well out ahead of the surface cold front
     this morning and cover almost the entire Pacific Northwest. 
     Light rain was falling as far east as Ontario, near the
     Idaho border.  The air mass is still quite warm and somewhat
     unstable over Eastern Oregon with many areas still in the
     60s this morning.  Baker City even reported a thunderstorm
     at mid-morning.

     Rain will increase east of the Cascades this afternoon, as
     the cold front, currently over Western Oregon, pushes east
     of the Cascades.  There will continue to be a threat of 
     thunderstorms, ahead of the cold front, over much of Eastern
     Oregon this morning.  In the wake of the cold front, steady 
     rain this afternoon will turn showery as brisk and cooler west
     winds, gusting as high as 35 mph, stabilize the air mass east
     of the Cascades enough to prohibit thundershower development.

Surface Winds:
     SW 10-15 this morning, W 10-15 this afternoon.
Transport Winds:
     W 12 this morning, W 18 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 90.
High Temperature:
     Salem\'s high temperature today will be near 62.
Humidities:
     Minimum relative humidity will be near 58%.
Sunrise/Sunset:
     Salem sunset tonight: 8:40pm; sunrise tomorrow: 5:37am.

Extended Outlook:
     A cold upper-level trough will move over the Pacific
     Northwest Tonight and Wednesday for continued cool
     temperatures and the threat of showers.  High pressure will
     slowly push closer to the coastline Thursday with the flow
     aloft turning more northerly and drying out some.

     A cool upper-level trough is forecast to set up camp over the 
     Western United States through the holiday weekend with a continued
     chance of showers for Oregon...mainly over the mountains.  
     Temperatures should be near to slightly below normal.

Tomorrow (21 May):  Mostly Cloudy and Cool.  Chance of Showers.  Snow Level 5000 Feet.  46/60

Thu (22 May):  Partly Sunny.  A Little Warmer.  43/62

Fri (23 May):  Partly Cloudy.  Slight Chance of Showers.  43/65

Sat (24 May):  Partly Cloudy.  Slight Chance of Showers.  A Little Warmer.  43/69

Sun (25 May):  Partly Cloudy.  Slight Chance of Showers.  44/70

Mon (26 May):  Partly Cloudy.  44/72

Tue (27 May):  Chance of Showers.  46/71

ODA Meteorologist
weather at oda.state.or.us