[willamette-fcst] Forecast - Thursday, October 23rd, 2008

[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, October 23rd, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     A building ridge of high pressure brought sunny skies and
     offshore flow to western Oregon Wednesday.  That sent
     temperatures over the 70-degree mark in many locations,
     especially along the coast.  Tillamook and Newport both hit
     73 degrees, and Astoria was 71.  It took the Willamette
     Valey longer to heat up, due to steep morning temperature
     inversions and areas of fog.  Hillsboro still managed 70
     degrees.  Aurora, McMinnville, and Salem all hit 69.  Fog
     took the longest to leave Eugene, so the high was just 64.

     Satellite imagery and the ODA surface analysis showed a very
     weak cold front stretching from northeastern Washington to
     the northwest corner of Oregon at mid-morning.  It dropped
     close to a tenth of an inch of rain in northwest Washington
     but only .01 inches as far south as Astoria, Oregon.  Skies
     were mostly cloudy across Washington with a little rain still
     falling in the Seattle area.  Mostly cloudy skies extended
     south across the northern half of Oregon, but Doppler radar
     was not showing any rainfall south of the Washington/Oregon border.

     Temperatures were able to cool close to the freezing mark,
     across sections of the Willamette Valley, before clouds
     increased this morning.  McMinnville, Corvallis, and Eugene
     dipped to 32 degrees and Hillsboro hit 33.  The weak frontal
     system helped prevent fog formation this morning with only
     the Eugene area reporting some light fog.

     The cold front is forecast to continue to weaken and push
     east of the Cascades this afternoon, with skies slowly
     clearing across western Oregon.  The Salem sounding this
     morning showed several degrees of cooling aloft, so high
     temperatures will be 5-10 degrees cooler today across the
     Willamette Valley and 10-15 degrees cooler along the coast.
 
     Mixing heights will be a little higher today but still peak
     at only about 2500 feet this afternoon.  Forecast northerly
     transport winds this afternoon are not conducive to good
     ventilation for stack burning.  Clearing skies overnight
     should allow valley temperatures to drop into the low to mid
     30s again with temperature inversions and areas of fog forming.

Surface Winds:
     N 2-6 this morning, N 5-10 this afternoon.
Transport Winds:
     N 6 this morning, N 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 20.
High Temperature:
     Salem\'s high temperature today will be near 64.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 43%.
Sunrise/Sunset:
     Salem sunset tonight: 6:13pm; sunrise tomorrow: 7:40am.

Extended Outlook:
     Another cold front is forecast slide north of the regin
     Friday, maintaining some clouds with onshore flow and
     seasonal temperatures.  Rainfall should stay north or
     Oregon, except for some drizzle or sprinkles along the north
     coast and western slopes of the north coast range.

     A strong ridge of high pressure is still forecast to build
     over the region this weekend and last through the first half
     of next week.  Offshore flow will increase, beginning
     Saturday, which will send temperatures well above normal,
     again, with sunny skies statewide.  It is possible that
     western Oregon highs could locally climb into the low 70s,
     again, Sunday and Monday, which would be near-record warmth
     for late October.  

     The protective ridge of high pressure is forecast to begin
     shifting east by Tuesday afternoon with southwesterly flow
     aloft developing and the surface flow turning onshore.  That
     should cool high temperatures back into the mid 60s.  A weak
     frontal system will likely make it through the ridge late
     Wednesday and/or Thursday for further cooling.  This system
     does not appear very strong, with just a chance of some
     light rain, but it should return us to a more seasonal
     weather pattern.

Tomorrow (24 Oct):  Partly Sunny.  37/64

Sat (25 Oct):  Mostly Cloudy AM.  Afternoon Clearing.  39/65

Sun (26 Oct):  Patchy AM Fog...Mainly South.  Sunny and Very Mild.  35/70

Mon (27 Oct):  Patchy AM Fog...Mainly South.  Sunny and Very Mild.  36/70

Tue (28 Oct):  Patchy AM Fog...Mainly South.  Mostly Sunny but a Little Cooler.  38/64

Wed (29 Oct):  Increasing Clouds.  Chance of Light Rain Late.  42/61

Thu (30 Oct):  Mostly Cloudy.  Chance of Light Rain.  42/58

ODA Meteorologist
weather at oda.state.or.us