[willamette-fcst] Forecast - Thursday, May 21st, 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: 
     Thursday, May 21st, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:30pm.
     Stack burning is not allowed.

Weather Discussion:
     A flat and weak upper-level ridge moved onshore Wednesday
     with a drier northwesterly flow aloft spreading from west to
     east across the state.  Strong onshore flow turned
     northerly, and winds became blustery Wednesday afternoon in
     the Willamette Valley and along the central and southern
     coast.  Northerly winds gusted to more than 30 mph in
     Newport to 40 mph in North Bend, along the coast.  In the
     Willamette Valley, northerly wind-gusts between 20 and 25
     mph were common Wednesday afternoon.  Some warming aloft
     helped to clear skies in the afternoon, but temperatures
     remained below normal, with highs only near 60 along the
     coast and in the mid 60s in the Willamette Valley.  Central
     and eastern Oregon saw plenty of sunshine Wednesday, but
     cool north-northwesterly winds also held temperatures there
     in the 60s.

     Mostly clear skies overnight allowed temperatures to drop
     into the upper 30s and lower 40s over most of western
     Oregon.  East of the Cascades, minimums dipped as low as the
     mid 20s, under clear skies.  Meacham was the cold spot in
     the state this morning with a low of 26 degrees.  The
     morning sounding over Salem showed weak westerly flow aloft
     with some minor warming of the air mass since Wednesday
     afternoon.  The ODA surface analysis showed generally
     northerly gradients across all of Oregon, with the
     California thermal trough being held south of Oregon due to
     the westerly flow aloft.  Satellite imagery showed mostly
     clear skies across the entire Pacific Northwest, with only a
     few patches of marine low clouds over western Oregon.

     Mid-morning temperatures had warmed into the upper 40s and
     low 50s across most of Oregon.  Winds were generally
     northerly between 5 and 15 mph on both sides of the
     Cascades.  The air mass aloft has warmed enough to prohibit
     the development of convective cloud formation today, so
     skies should remain sunny today statewide.  Some tightening
     of the northerly presure gradients is expected again the
     afternoon, so north winds will increase along the coast and
     in the Willamette Valley.  High temperatures should climb
     into the low 60s along the coast and low 70s in the
     Willamette Valley.  Cascade pass temperatures should climb
     into the 60s this afternoon, with the freezing level above
     10,000 feet.  Afternoon temperatures east of the Cascades
     should climb mostly into the 70s.

     The flat upper-level ridge over the region is forecast to
     shift eastward, to over Idaho, by tonight.  That will turn
     the flow aloft slightly southwesterly and increase the
     onshore flow into western Oregon overnight.  Marine low
     clouds will likely push onshore by Friday morning and
     locally into the Willamette Valley.  Overnight temperatures
     should remain above 40 degrees in the valley.

Surface Winds:
     N 5-12 this morning, N 10-15 G20 this afternoon.
Transport Winds:
     NNE 12 this morning, N 13 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 52.
High Temperature:
     Salem\'s high temperature today will be near 73.
Humidities:
     Minimum relative humidity will be near 33%.
Sunrise/Sunset:
     Salem sunset tonight: 8:41pm; sunrise tomorrow: 5:36am.

Extended Outlook:
     A very weak upper-level trough is forecast to move over
     Oregon Friday and Saturday, with increasing onshore flow but
     little to no rainfall.  Areas of morning low clouds should
     give way to afternoon sunshine west of the Cascades, with
     mostly sunny skies across central and eastern Oregon.
     Temperatures will likely cool a couple of degrees over
     western Oregon, due to the increased onshore flow. 
     Transport winds will back from northerly to northwesterly,
     which should improve ventilation conditions for possible
     stack burning.

     The flow aloft is forecast to turn northwesterly and dry out
     again by late Sunday.  A weak upper-level ridge is forecast
     to build over the region early next week, which should warm
     temperatures above normal with weak onshore flow. The
     upper-level flow is forecast to turn more southwesterly by
     midweek, with increasing onshore flow starting a cooling
     trend at the surface.

Tomorrow (22 May):  Partly Cloudy in the Morning.  Sunny in the Afternoon.  43/71

Sat (23 May):  Morning Clouds.  Mostly Sunny in the Afternoon.  43/71

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.  46/79

Wed (27 May):  Mostly Sunny.  49/78

Thu (28 May):  Morning Clouds.  Partly Sunny and Cooler in the Afternoon.  48/69

ODA Meteorologist
weather at oda.state.or.us