[willamette-fcst] Forecast - Monday, June 29th, 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: 
     Friday, June 26th, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     Marine low clouds were persistent across most of western Oregon
     on Thursday with strong onshore flow.  High temperatures only
     reached the upper 60s in the Willamette Valley, with low to mid
     60s for highs along the coast.  Skies did clear over southwestern
     Oregon Thursday, with sunny skies helping warm temperatures into
     the mid 70s to low 80s.  Central and eastern Oregon basked in sunshine
     Thursday with highs generally in the comfortable 70s and 80s.
     Ontario, near the Idaho border, was the warm spot in the state at 92.

     Skies began clearing over northwestern Oregon Thursday evening, as
     the flow aloft, and at the surface turned more northerly and began
     to dry out.  That allowed temperatures to drop into the mid 40s
     across sections of the Willamette Valley by early this morning.
     McMinnville and Eugene dipped to 44 degrees, and Eugene recorded
     a minimum of 45.  Portland, Aurora, and Salem all had a low of 51.

     Visible satellite imagery showed widespread low clouds across western
     Washington through mid-morning, but the clouds were breaking up there
     at midday.  There were only pockets of low clouds over mainly the
     southern Willamette Valley earlier this morning, but skies were mostly
     sunny across all but the extreme northwest tip of Oregon at midday.

     The late-morning ODA surface analysis showed high pressure had strongly
     built into the Washington and Oregon coastlines with a tongue of high
     pressure also extending into northeastern Oregon.  The strongest onshore
     gradients had shifted east to near the Idaho border, with gradients
     turning northerly across the western two-thirds of Oregon.  The strongest
     midday winds were at The Dalles and North Bend, with both of those areas
     getting gusts to near 30 mph.  North winds in the Willamette Valley had
     increased to between 5 and 15 mph.

     The Salem sounding this morning showed northwesterly winds and warming
     aloft, compared with Thursday morning, both associated with a building
     ridge of high pressure. Northerly surface winds will continue to increase
     this afternoon, as a thermal trough pushes northward into southwestern
     Oregon and tightens the pressure gradients across western Oregon.  The
     strongest winds west of the cascades will be in the southern Willamette
     Valley and along the central and southern coast.

     With increasing northerly winds and fairly high mixing heights,
     ventilation conditions are expected to be good for agricultural burning
     this afternoon.  Northerly transport winds are not good for stack burning.
     Warming aloft and plenty of sunshine will combine to lift valley temperatures
     into the mid 70s this afternoon (near-normal).  Mostly clear skies and a
     dry air mass tonight will allow temperatures to drop below normal across
     Oregon overnight, with Willamette Valley minimums dipping into the 40s.

Surface Winds:
     N 10-17 G25 south this afternoon.
Transport Winds:
     N 14 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5200 feet.  Ventilation index 73.
High Temperature:
     Salem\'s high temperature today will be near 75.
Humidities:
     Minimum relative humidity will be near 31%.
Sunrise/Sunset:
     Salem sunset tonight: 9:03pm; sunrise tomorrow: 5:28am.

Extended Outlook:
     A fairly strong upper-level trough is forecast to drop southeastward,
     from the northern Gulf of Alaska, on Saturday.  That will back the flow
     aloft over Oregon from northwesterly to southwesterly by Saturday evening.
     Initially, that will warm the air mass over the state, with sunny skies
     lifting temperatures into the low to mid 80s across the Willamette Valley
     Saturday afternoon.

     The trailing end of a cold front is forecast to move onto the Washington
     coast Saturday night and across northwestern Oregon Sunday morning.  It
     may not be strong enough to produce much shower activity this far south,
     but it will usher a strong surge of cool and moist marine air into
     western Washington and northwestern Oregon Sunday and Monday. Some marine
     low clouds will invade the western valleys with near-normal temperatures.

     The trough will pass to the east by Monday afternoon with the flow aloft
     turning northwesterly and drying out.  The jet stream will migrate slightly
     northward, to over southern British Columbia, Tuesday and Wednesday, with 
     weak westerly flow aloft.  That will decrease the onshore flow and allow
     temperatures to warm above normal.  A weak weather system may turn the flow
     aloft southwesterly by Thursday with increasing onshore flow beginning a
     cooling trend by Friday.  That system may be strong enough to end the dry
     stretch and bring in showers on the 4th of July (next Saturday).

Tomorrow (27 Jun):  Sunny and Warmer.  48/82

Sun (28 Jun):  Mostly Cloudy and Cooler.  Slight Chance of Sprinkles North.  53/76

Mon (29 Jun):  AM Clouds.  Partly Sunny in the Afternoon.  52/78

Tue (30 Jun):  AM Clouds.  Mostly Sunny in the Afternoon.  52/81

Wed (01 Jul):  Mostly Sunny.  53/84

Thu (02 Jul):  Mostly Sunny.  54/82

Fri (03 Jul):  Partly Sunny and Cooler.  52/78

ODA Meteorologist
weather at oda.state.or.us