[willamette-fcst] Forecast - Thursday, February 25th, 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: 
     Thursday, February 25th, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from now to 4:00pm.
     Straw stack burning is allowed from now until 4:00pm.

Weather Discussion:
     A moist and somewhat unstable southwesterly flow aloft kept
     lots of clouds across western Oregon Wednesday, with some
     locally intense showers developing Wednesday afternoon,
     especially over the northern Cascades.  Snow levels dropped
     just below the Cascades passes, where a few inches of wet
     snow fell.  The higher ski resorts received a much-needed
     6-11 inches of snow Wednesday.  Oregon mountain snowpacks
     are running only 50-80 percent of normal, with the greatest
     deficits in the northwestern portion of the state.  Doppler
     radar showed a few lingering showers across western
     Washington and northwestern Oregon this morning, with a
     heavy shower being reported at Astoria.

     Mostly cloudy skies held overnight temperatures mostly in
     the low to mid 40s across western Oregon.  Partial clearing
     locally allowed areas, like McMinnville, to drop into the
     upper 30s, but that also led to fog formation.  Mid-morning
     visible satellite imgery showed mostly cloudy skies across
     western Oregon with some breaks in the overcast...especially
     over southwestern Oregon.  Mid-morning temperatures ranged
     from the mid 30s, with some clearing in Medford, to near 50
     in sections of the Willamette Valley and along the coast.

     The ODA surface analysis showed weak southeasterly pressure
     gradients beginning to develop, in response to an
     approaching warm front, about 300 miles off the northern
     California/southern Oregon coast.  Winds statewide were less
     than 10 mph.  The freezing levels were measured over Salem
     and Medford early this morning at 4400 and 5200 feet
     respectively.  ODOT road cameras showed packed snow over the
     higher mountain passes, with pass temperatures near freezing.

     Showers should continue to taper off across northwestern
     Oregon this morning, as a transitory upper-level ridge of
     high pressure builds over the west coast.  Slow warming
     aloft should lift the freezing levels to near 6000 feet this
     afternoon.  Some sunbreaks will combine with the warming
     aloft to help temperatures climb into the mid 50s across the
     Willamette Valley this afternoon, with continued light
     southeastery winds.

     An active warm front will begin spreading high and mid-level
     clouds, from southwest to northeast, across western Oregon
     later this morning.  Clouds should lower and thicken along
     the south coast by midday with rain coming onshore there in
     the early afternoon.  Rain will spread north and east during
     the afternoon and likely into the southern Willamette Valley
     by sundown.  Rain and southeasterly winds will increase
     tonight across all of western Oregon, with rainfall amounts
     of one-quarter of an inch, or more, likely across the
     Willamette Valley by sunrise Friday.

Surface Winds:
     SE 5-10 this morning, SE 5-10 this afternoon.
Transport Winds:
     S 12 this morning, S 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 36.
High Temperature:
     Salem\'s high temperature today will be near 56.
Humidities:
     Minimum relative humidity will be near 57%.
Sunrise/Sunset:
     Salem sunset tonight: 5:54pm; sunrise tomorrow: 6:55am.

Extended Outlook:
     A cold front is forecast to continue the steady rainfall
     across western Oregon on Friday.  However, it will encounter
     a split-flow jet stream pattern, with the bulk of its
     strength forecast to dive southeastward, into California. 
     Additional rainfall amounts of one-quarter to one-half of an
     inch are likely across the Willamette Valley Friday.  Clouds
     and rain will hold valley minimums in the low to mid 40s,
     but afternoon highs will struggle into the lower 50s.  Snow
     levels will climb to 5-6000 feet, with mostly rain over the
     passes.  The higher elevations, including the ski areas,
     should pick up about a foot of much-needed snowfall.

     A cool (not cold) upper-level trough will drop snow levels
     only to near the Cascade passes Saturday, as showers taper
     off across western Oregon.  Valley highs will climb above
     normal with some afternoon sunbreaks.  A ridge of high
     pressure is forecast to rebuild over the west coast late in
     the weekend, with mostly sunny and very mild conditions
     likely returning to western Oregon Sunday and Monday.
     Increasing south-southwesterly flow aloft will likely bring
     a weakening weather system onshore by late Monday, with rain
     and much cooler temperatures Tuesday. Showers will taper off
     Wednesday with a break in the weather possible on Thursday.

Tomorrow (26 Feb):  Rain Likely.  Snow Level Near 5000 Feet.  45/52

Sat (27 Feb):  Mostly Cloudy.  Showers Ending.  Snow Level 4000 Feet.  38/57

Sun (28 Feb):  Partly to Mostly Sunny and Very Mild.  37/60

Mon (01 Mar):  Increasing Clouds. Continued Mild.  Freezing Level Near 7000 feet.  38/62

Tue (02 Mar):  Rain Likely.  Snow Level 5-6000 Feet.  44/53

Wed (03 Mar):  Mostly Cloudy.  Decreasing Showers.  Snow Level 4-5000 Feet.  38/54

Thu (04 Mar):  Partly Sunny.  39/57

ODA Meteorologist
weather at oda.state.or.us