[willamette-fcst] Forecast - Wednesday, June 24th, 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: 
     Wednesday, June 24th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Straw stack burning is allowed from 11:00am until 8:00pm.

Weather Discussion:
     A weak and transitory upper-level ridge is shifting east of
     the region in response to a well developed frontal system
     moving onto the the southern British Columbia coastline this
     morning.  The real punch of this system is being directed
     north into Canada.  However, the trailing cold front did
     show up well on infrared satellite imagery this morning and
     had moved within 200 miles of the Washington and Oregon
     coastlines.  The cloud-band associated with the cold front
     was quite impressive over southwestern British Columbia,
     including over Vancouer Island, but rapidly narrowed, as it
     stretched south to off the Oregon Coast.

     High and mid-level clouds extended well out ahead of the
     system...covering the northern half of Washington.  The
     clouds lowered and thickened over northwestern Washington
     with light to moderate rain falling on the northern
     Washington coast.  Meanwhile, skies were mostly sunny over
     Oregon this morning, with the exception of a narrow zone of
     low clouds and fog along the coast and locally into the
     coastal gaps in the coast range.

     Fair skies overnight allowed Willamette Valley temperatures
     to fall into the upper 40s and low 50s, which is near-normal
     for late June.  Minimum temperatures east of the Cascades
     were mostly in the 40s and 50s.  Lakeview was the cold spot
     with a low of 39.  Mid-morning temperaturse were in the low
     to mid 50s along the coast and upper 50s to mid 60s across
     the remainder of the state.  The Salem sounding this morning
     showed further warming aloft, since Tuesday morning.  The
     freezing level had risen to near 13,000 feet.  The winds
     aloft had turned southwesterly and were increasing in
     response to the approaching weather system.

     The mid-morning ODA surface analysis showed high pressure
     over the southern Oregon Coast with a low-pressure trough
     approaching northwestern Washington.  That was producing
     southerly gradients over western Oregon.  Winds in the
     Willamette Valley were generally southerly at about 5 mph. 
     As the offshore cold front approaches the Oregon Coast,
     clouds will increase today, from northwest to southeast,
     across Oregon.  The air aloft will begin cooling with
     increasing southwesterly transport winds.  The combination
     of daytime surface heating and cooling aloft should lift
     mixing heights above 4000 feet later this afternoon...making
     for good ventilation conditions for agricultural and stack burning.

     The cold front will likely be strong enough to bring some
     light showers to extreme northwestern Oregon later this
     afternoon through Thursday morning.  Rainfall amounts will
     be greatest along the north coast, with only a trace to a
     couple of hundredths expected in the Willamette Valley. 
     Sections of the valley, especially south, may not see any
     rain at all from this system.  However, it will generate
     locally blustery southwesterly winds across western Oregon
     later today and tonight, as it sends a surge of cooler
     marine air onshore and across Oregon.

Surface Winds:
     S 5-10 this morning, SW 10-15 G25 this afternoon.
Transport Winds:
     SSW 10 this morning, SW 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 90.
High Temperature:
     Salem\'s high temperature today will be near 79.
Humidities:
     Relative humidity drops to 50% by 10am.
     Minimum relative humidity will be near 41%.
Sunrise/Sunset:
     Salem sunset tonight: 9:03pm; sunrise tomorrow: 5:27am.

Extended Outlook:
     Temperatures will likely cool to below normal on Thursday,
     with considerable marine low clouds and a chance of morning
     drizzle or light showers. A weak ridge will shift the jet
     stream northward, to over southern British Columbia, on
     Friday.  However, continued onshore flow will keep some
     morning clouds over western Oregon with afternoon sunshine
     lifting temperatures close to normal.

     The jet stream is forecast to sag southward on Saturday,
     with another weak cold front possibly spreading light
     showers as far south as northwestern Oregon by late in the
     day.  The chance of showers will continue into Sunday with
     another weak ridge drying out the atmosphere a bit on
     Monday.  A little stronger system is forecast to move into
     Washington next Tuesday and may also be strong enough to
     bring some light showers to the northwestern corner of Oregon.

Tomorrow (25 Jun):  Chance of AM Showers...Afternoon Clearing and Cooler.  54/72

Fri (26 Jun):  AM Clouds...Becoming Mostly Sunny.  48/76

Sat (27 Jun):  Increasing Clouds.  Slight Chance of Showers North late.  52/80

Sun (28 Jun):  Mostly Cloudy.  Slight Chance of Showers North.  51/75

Mon (29 Jun):  Morning Clouds.  Partly Sunny in the Afternoon.  50/77

Tue (30 Jun):  Increasing Clouds.  Slight Chance of Showers North Late.  50/75

Wed (01 Jul):  Mostly Cloudy.  Slight Chance of Showers.  50/75

ODA Meteorologist
weather at oda.state.or.us