[willamette-fcst] Forecast - Monday, May 18th, 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, May 18th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 10:00am until 6:30pm.
     Straw stack burning is allowed from 10:00am until 6:30pm.

Weather Discussion:
     A broad but fairly flat upper-level ridge built over Oregon this past weekend,
     with mostly sunny skies helping temperatures climb into the upper 70s and lower
     80s across the Willamette Valley.  The ridge shifted eastward, to over Idaho,
     late Sunday.  That induced an onshore flow into western Oregon Sunday
     evening...bringing cooler air into the Willamette Valley overnight.

     The ODA Surface analysis this morning showed the thermal trough had shifted into
     central Oregon with onshore flow across western Oregon.  Visible satellite imagery
     showed low clouds along the entire Washington and Oregon coastlines with some
     penetration of marine low clouds into gaps in the Oregon coast range.  East of
     the coast range skies were generally sunny across Oregon, with an increasing
     southwesterly flow aloft spreading considerable high clouds over Washington and
     northwestern Oregon.

     Mid-morning temperatures were in the 50s and low 60s across western Oregon.  Very
     warm air was still in place east of the Cascades.  Temperatures were in the 60s
     across central Oregon and already in the 70s near the Idaho border.  The thermal
     trough will continue to migrate eastward, to near the Idaho border, this afternoon.
     That will make for one more very warm day over eastern Oregon with increasing onshore
     flow moderating temperatures west of the Cascades.
 
Surface Winds:
     W 5-10 this morning, NW 8-15 this afternoon.
Transport Winds:
     W 5 this morning, W 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 40.
High Temperature:
     Salem\'s high temperature today will be near 76.
Humidities:
     Minimum relative humidity will be near 42%.
Sunrise/Sunset:
     Salem sunset tonight: 8:38pm; sunrise tomorrow: 5:39am.

Extended Outlook:
     An increasing southwesterly flow aloft will shift the surface thermal trough
     into Idaho Tuesday, with onshore flow bringing significantly cooler weather to
     all of Oregon.  In addition, a cold front is forecast to move onshore Tuesday
     morning, bringing light to moderate rain to western Washington and much of
     western Oregon.  A farily vigorous upper-level trough will drop snow levels in
     the northern Oregon Cascades to near 4000 feet by Tuesday evening, with scattered
     showers across much of western Oregon.  Total rainfall amounts could approach
     one-half inch from western Washington southward into the northern Willamette Valley.
     Rainfall amounts will taper off to the south, with southwestern Oregon likely
     picking up less than one-tenth of an inch.

     The shower activity should taper off Tuesday night across western Oregon, as the
     upper-level trough pushes eastward.  Scattered showers may continue east of the
     Cascades, mainly over the mountains of northeastern Oregon, through early Wednesday.
     A weak upper-level ridge is forecast to move onshore Wednesday with a drier
     northwesterly flow aloft spreading from west to east across the state.  Surface
     winds will turn northerly over western Oregon with afternoon temperatures recovering
     to near-normal.

     The flat ridge is forecast to shift east of the Cascades Thursday afternoon.  That
     will induce weak onshore flow with seasonal temperatures across western Oregon.  A
     very weak upper-level trough is forecast to move over Oregon Friday.  It will likely
     increase the onshore and cool temperatures a few degrees.  However, it does not appear
     to be strong to produce any rainfall across the state.  In stark contrast to earlier
     forecasts, the main storm track is now forecast to stay north of Oregon, over the
     Memorial Day Weekend, with weak westerly flow aloft.  That would continue to bring dry
     conditions to the region with warming temperatures.

Tue (19 May):  Rain Turning to Showers. Much Cooler. Snow Level 4000 Feet North Late. 50/59 

Wed (20 May):  Morning Clouds...Becoming Mostly Sunny.  39/68

Thu (21 May):  Mostly Sunny.  Increasing High Clouds Late.  41/75

Fri (22 May):  Partly Cloudy.  Slightly Cooler.  45/70

Sat (23 May):  Morning Clouds...Becoming Mostly Sunny.  46/70

Sun (24 May):  Mostly Sunny.  44/75

Mon (25 May):  Mostly Sunny and Warmer.  47/82

ODA Meteorologist
weather at oda.state.or.us