[willamette-fcst] Forecast - Friday, May 22nd, 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: 
     Friday, May 22nd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 6:30pm.
     Straw stack burning is allowed from 11:00am until 6:30pm.

Weather Discussion:
     Skies stayed clear over most of the Willamette Valley
     overnight, while increasing onshore flow brough marine low
     clouds onto the coast and into the western slopes of the
     coast range.  Visible satellite imagery showed a solid
     balnket of low clouds over the northern and central coast
     with some penetration of low clouds into the southern
     Willamette Valley and the Umqua River Basin.  Skies remained
     clear, at mid-morning, from Portland southward through
     Marion County, but low clouds were forming along the western
     slopws of the Cascades in Linn County with more extensive
     low clouds in western Lane and Douglas Counties.

     Temperatures stayed mostly above 40 degrees overnight across
     western Oregon.  Eugene was one the coldest spots, with a
     minimum of 39 degrees.  Some low clouds formed in the Eugene
     area around daybreak and remained there at mid-morning.  By
     8am most of western Oregon had warmed into the low 50s. 
     Under clear skies, most of central and eastern Oregon had
     also warmed into the 50s.  The ODA surface analysis showed
     the pressure gradients had shifted from northerly to more
     northwesterly across Oregon...indicating an increase in the
     onshore flow.  Northerly winds were already gusting over 20
     mph along the central and southern coast but were generally
     less than 10 mph across the interiof of the state.

     The morning sounding over Salem showed that the flow aloft
     had become light southwesterly, in response to a weak
     upper-level trough approaching the coast.  The air aloft was
     still warm, with the freezing level measured at 10,300 feet.
     That will, once again, prohibit the development of
     convective clouds this afternoon, so skies should stay
     sunny, except for the areas of marine low clouds in the
     southern valleys and along the coast.

     Some tightening of  the northwesterly pressure gradients is 
     expected today, so north-northwesterly winds should increase
     this afternoon across the state.  Afternoon temperatures will
     be similar to  Thursday with highs near 60 along the coast and
     in the low 70s in the Willamette Valley.  Cascade pass temperatures
     should climb into the 60s this afternoon, with 70s across most of
     central and eastern Oregon.

Surface Winds:
     N 5-15 this morning, NNW  8-15 G20 this afternoon.
Transport Winds:
     N 13 this morning, NNW 16 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 80.
High Temperature:
     Salem\'s high temperature today will be near 72.
Humidities:
     Minimum relative humidity will be near 39%.
Sunrise/Sunset:
     Salem sunset tonight: 8:42pm; sunrise tomorrow: 5:35am.

Extended Outlook:
     A very weak upper-level trough is forecast to remain over
     Oregon Saturday, with continued onshore flow keeping
     temperatures near normal with plenty of afternoon sunshine
     across western Oregon. Skies should be mostly sunny across
     central and eastern Oregon. Transport winds should maintain
     enough of a northwesterly component to make for good
     ventilation for possible stack burning.

     The flow aloft is forecast to turn northwesterly and dry out
     again by late Sunday.  Slight warming aloft and decreased
     onshore flow will help temperatures climb a few degrees. A
     flat upper-level ridge is forecast to build over the region
     early next week, which should warm temperatures a few more
     degrees.  However, very weak onshore flow will keep
     temperatures from getting too much above average west of the
     Cascades. The upper-level flow is forecast to turn more
     southwesterly by midweek, but onshore flow is forecast to
     remain weak.

Tomorrow (23 May):  Morning Clouds.  Mostly Sunny in the Afternoon.  41/70

Sun (24 May):  Morning Clouds.  Mostly Sunny in the Afternoon.  43/73

Mon (25 May):  Brief Morning Clouds...Sunny and a Little Warmer in the Afternoon.  43/76

Tue (26 May):  Mostly Sunny and Warm.  46/79

Wed (27 May):  Mostly Sunny and Warm.  48/78

Thu (28 May):  Mostly Sunny.  48/75

Fri (29 May):  Mostly Sunny.  48/75

ODA Meteorologist
weather at oda.state.or.us