[willamette-fcst] Forecast - Wednesday, March 24th, 2010

[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: 
     Wednesday, March 24th, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from 12:00pm until 5:30pm.
     Straw stack burning is allowed from 12:00pm until 5:00pm.

Weather Discussion:
     The upper-level ridge that brought dry and warmer conditions
     Tuesday afternoon is shifting east of the region this
     morning.  Infrared satellite imagery showed a broad band of
     mostly high clouds sweeping across Washington and Oregon, in
     response to a very weak upper-level disturbance, embedded in
     an increasing south-southwesterly flow aloft.  The ODA
     surface analysis showed southeasterly pressure gradients
     across Oregon.  Winds were mostly light across the state,
     except for easterly gusts to near 30 mph at the western end
     of the Columbia Gorge.

     The veil of high clouds helped to keep overnight
     temperatures from getting as cold as they did Tuesday
     morning.  Temperatures in the Willamette Valley stayed well
     above freezing this morning.  Although most areas east of
     the Cascades still dropped below freezing, mid-morning
     temperatures were running several degrees warmer than 24
     hours ago.

     The upper-level ridge will weaken and continue to drift
     eastward, to over Idaho, by this afternoon.  A stronger
     weather system will approach the coastline late in the day,
     with increasing south-southwesterly flow aloft.  The Salem
     sounding this morning showed a weak temperature inversion
     from the surface to about 2500 feet, where the temperature
     climbed to about 50 degrees.  That will keep mixing heights
     low this morning.

     The back edge of the veil of high clouds was moving over the
     coastline this morning and should push east of the Cascades
     this afternoon.  Mostly sunny skies will warm afternoon
     temperatures into the mid 60s across the Willamette Valley. 
     Daytime heating should combine with cooling aloft to
     significanly raise mixing heights in the mid to late
     afternoon, with increasingly southwesterly transport winds
     improving ventilation conditions for stack burning.  Cooler
     marine air will begin puring into the valley this evening,
     as clouds thicken in response to the next weather system
     moving onto the southern Oregon/northern California coast.

Surface Winds:
     S 0-6 this morning, SE 5-10 early this afternoon...becoming WSW 5-12 late this afternoon.
Transport Winds:
     S 4 this morning, SW 5 early this afternoon...becoming SW 8 late this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 25.
High Temperature:
     Salem\'s high temperature today will be near 64.
Humidities:
     Minimum relative humidity will be near 43%.
Sunrise/Sunset:
     Salem sunset tonight: 7:30pm; sunrise tomorrow: 7:06am.

Extended Outlook:
     A cold front is forecast to spread rain across western
     Oregon tonight and Thursday morning, but the main energy
     from this system will get directed at extreme southern Oregon
     and northern California.  A cool upper-level trough will
     maintain showers over all of Oregon Thursday and much of
     Friday, with the snow level dropping to below the Cascade passes.

     An upper-level ridge is forecast to bring drying conditions
     late Friday.  After a chilly start, mostly sunny skies will
     make for a very pleasant Saturday afternoon.  The next weather
     system, on Sunday, appears strong enough to bring some light
     rain and higher elevation snow back to western Oregon.  A much
     stronger system is forecast to come onshore Monday, with more
     significant rain and possibly windy conditions...especially
     along the coast.

     Snow levels will initially be fairly high, on Monday, but
     drop significantly Monday night, as a cold upper-level
     trough swings inland behind the cold front.  Tuesday and
     Wednesday look showery and cool, with possible significant
     mountain snowfall.  That would be helpful for the water supply
     outlook, since snowpacks are well below normal statewide.

Thu (25 Mar):  Rain Turning to Showers.  Cooler.  Snow Level Dropping to 3-4000 Feet.  44/55

Fri (26 Mar):  Showers Decreasing Late with Partial Clearing. Snow Level 3-4000 Feet.  40/56

Sat (27 Mar):  Chilly Start...Becoming Mostly Sunny and Warmer.  35/63

Sun (28 Mar):  Light Rain Likely.  Snow Level 5-6000 Feet.  44/58

Mon (29 Mar):  Increasing Rain and Wind.  Snow Level 5-6000 Feet.  46/59

Tue (30 Mar):  Rain Turning to Showers.  Snow Level Dropping to 3000 Feet.  43/56

Wed (31 Mar):  Showers.  Snow Level 2500 Feet.  38/55

ODA Meteorologist
weather at oda.state.or.us