[willamette-fcst] Forecast - Monday, May 11th, 2009

Mon May 11 09:20:55 PDT 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.

Issued: 
     Monday, May 11th, 2009 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:

     ...Corrected Wording to Weather Discussion...

     ...The Next Scheduled Forecast Update is not until Thursday,
     May 14th, at 9am...

     A weak upper-level ridge of high pressure brought dry
     weather with seasonal temperatures over the weekend. 
     Willamette Valley highs ranged from the mid 60s to the low
     70s both Saturday and Sunday.  The ridge shifted east, to
     over Idaho, on Sunday with increasing westerly flow aloft
     spreading clouds back across western Oregon during the day. 
     A few light showers made their way onto the coast and across
     the northwest interior late Sunday through this morning. 
     Only a couple of hundredths of an inch of rain fell on the
     coast and as far south as about Salem in the Willamette Valley.

     The mid-morning ODA surface analysis showed high pressure
     nosing into the central and southern Oregon Coast, with
     onshore flow across western Oregon.  A weak offshore trough
     was acting to turn gradients southerly across the Willamette
     Valley.   Southerly winds had increased to between 5 and 15
     mph in the Willamette Valley with gusts to near 25 mph along
     the north coast.  Winds were generally 10 mph or lower east
     of the Cascades.

     Visible satellite imagery showed considerable marine low
     cloudiness covering all of western Washington and all but
     the extreme southwest interior of western Oregon.  A weak
     upper-level trough was also producing mostly cloudy skies
     across the eastern third of Washington and extreme northeastern
     Oregon.  Downsloping westery flow off the Cascades was
     bringing mostly sunny skies to the central sections
     Washington and Oregon.  Skies were also mostly clear from
     the southwestern interior of Oregon eastward across
     south-central and southeastern Oregon.

     Doppler radar showed only very light shower activity over
     the Washington and northern Oregon Cascades with more
     vigorous showers over northeastern Washington, extending
     south into the mountains of northeastern Oregon. 
     Mid-morning temperatures were mostly in the low to mid 50s
     across western Oregon.  East of the Cascades, readings
     ranged from the mid 40s, with rain showers, in Meacham, to
     near 60, under sunny skies, in Rome.

     A vigorous upper-level trough, dropping south from the Gulf
     of Alaska, will continue to increase the westerly flow aloft
     over Oregon today.  The air aloft will continue to cool and
     become increasingly unstable.  The freezing level was
     measured over Salem at 5900 feet early this morning and
     should hold steady or fall another 500-1000 feet by this
     evening.  Cooling aloft and daytime heating should trigger
     at least widely scattered showers today across much of
     western Oregon.  Westerly flow aloft will act to focus the
     shower activity over the western slopes of the coast range
     and the Cascades, but a few showers are possible across the
     Willamette Valley.

     Temperatures will struggle into the upper 50s this
     afternoon, across western Oregon, with a few valley
     locations possibly hitting 60.  Southerly winds will turn
     more southwesterly and increase this afternoon, resulting in
     good ventilation conditions.  Increasing onshore flow will
     bring brisk westerly winds to much of central and eastern
     Oregon later today and tonight, but showers will be limited
     to the mountains.

     As the strong upper-level trough appraoches the Washington
     and northern Oregon coastline tonight, shower activity
     should increase across western Washington and northwestern
     Oregon.  The snow level will likely drop below the passes in
     the northern Cascades, where a few inches of snow are
     possible overnight.  Cloudy skies and increasing showers
     will hold overngiht valley temperatures in the low to mid 40s. 

Surface Winds:
     S 5-15 this morning, SW 5-15 G20 this afternoon.
Transport Winds:
     SW 20 this morning, WSW 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3300 feet.  Ventilation index 66.
High Temperature:
     Salem\'s high temperature today will be near 59.
Humidities:
     Minimum relative humidity will be near 60%.
Sunrise/Sunset:
     Salem sunset tonight: 8:30pm; sunrise tomorrow: 5:46am.

Extended Outlook:
     The upper-level trough is forecast swing inland across
     Washington and northern Oregon Tuesday with scatter showers
     developing from northwestern Oregon across the Cascades into
     northeastern Oregon.  There is even a slight chance of a
     valley thunderstorm.  Snow levels in the northern mountains
     will drop to about 3500 feet with strong onshore flow
     continuing to bring breezy conditions to much of central and
     eastern Oregon.

     A transitory ridge will briefly decrease the shower activity
     Tuesday night.  Another cool upper-level trough is forecast
     drop into the region late Wednesday.  It will have a better
     moisture tap than the system on Tuesday, so more significant
     rain is expected across western Oregon.  Snow levels will
     likely rise to around 6000 feet by Wednesday evening. The
     upper-level trough will move over Oregon Thursday with
     showers and snow levels dropping to about 5000 feet.

     The long-range computer models are all indicating that a
     strong ridge of high pressure will bring much warmer and dry
     weather to the Pacific Northwest by this weekend and early
     next week.

Tue (12 May):  Showers...Mainly North.  Slight Chance T-Storm.  Snow Level 3500 Feet.  43/56

Wed (13 May):  A break early.  Rain increasing Late.  Snow Level 6000 Feet.  43/61

Thu (14 May):  Showers.  Snow Level 5000 Feet.  46/61

Fri (15 May):  Showers Ending.  Becoming Partly Cloudy.  44/66

Sat (16 May):  Becoming Mostly Sunny and Warmer.  44/72

Sun (17 May):  Sunny and Warm.  45/78

Mon (18 May):  Sunny and Warm.  47/80

ODA Meteorologist
weather at oda.state.or.us