[willamette-fcst] Forecast - Monday, August 25th, 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: 
     Monday, August 25th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     After a warm weekend, with valley highs Saturday in the mid
     to upper 80s and Sunday in the low 80s, another moist cold
     front spread rain into the Willamette Valley late Sunday
     afternoon.  The slow moving front cold front dumped between
     one-quarter and two-thirds of an inch of rain across the
     valley by 5am this morning.  The clouds and rain held valley
     temperatures up overnight with minimums in the mid to upper 50s.

     The soundings from Salem on Sunday showed a large tongue of
     warm air aloft capping mixing heights below 2000 feet all
     day.  The sounding from this morning showed considerable
     cooling from the surface all the way up to 25,000 feet. 
     That will make for higher mixing heights today, but relative
     humidtiy levels will stay over 60% for most of the day and
     fields are wet.

     The ODA surface analysis showed high pressure across Western
     Washington and Western Oregon with onshore flow west of the
     cold front that was moving into Eastern Oregon.  Satellite
     imagery showed the leading edge of the clouds from the cold
     front reaching Union County in NE Oregon and stretching
     southeastward into northern Klamath County, in South-Central
     Oregon.  The back edge of the solid clouds had moved across
     the western side of the Willamette Valley, where some
     patches of blue sky were breaking through.

     An upper-level trough will further chill the air aloft today
     and keep a few showers going across Western Oregon.  With
     strong onshore flow and cold air aloft, valley high
     temperatures should stay in the upper 60s (normal for today
     is 80 degrees).  The upper-level trough will slide east of
     the Cascades this evening with the flow aloft becoming
     northwesterly and drying out.  That will help skies to clear
     overnight, which will allow most valley temperatures to drop
     into the 40s.  With high humidity levels near the surface,
     areas of fog and low clouds are likely by Tuesday morning.


Surface Winds:
     NW 5-10 this morning, NW 8-15 this afternoon.
Transport Winds:
     NW 10 this morning, NW 13 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 59.
High Temperature:
     Salem\'s high temperature today will be near 68.
Humidities:
     Minimum relative humidity will be near 57%.
Sunrise/Sunset:
     Salem sunset tonight: 8:01pm; sunrise tomorrow: 6:28am.

Extended Outlook:
     A flat ridge of high pressure will continue the
     northwesterly flow aloft Tuesday.  Surface winds across the
     valley will turn northerly with slow drying and warming of
     the air mass across Western Oregon.  A weak cold front is
     forecast to slide across Southern British Columbia and
     Western Washington Wednesday.  The southern edge of this
     system may be strong enough to to bring some drizzle fromt
     he north coast to the extreme Northern Willamette Valley.

     Transport winds may back from northerly to northwesterly
     Wednesday, especially in the north valley.  That would
     normally present a possible burning opportunity for the
     north valley, but fields may be too damp from the recent
     rains.  Weak ridging aloft will dry the air mass Thursday
     with transport winds likely turning northerly again.

     Another weather system is forecast to swing into Southern
     British Columbia and NW Washington Friday afternoon.  The
     flow aloft is forecast to become more westerly over Oregon,
     in response to an approaching weak upper-level trough. 
     Transport winds and mixing heights could become favorable
     for open burning of dry fields.  The upper-level trough is
     forecast to move over the region Saturday with increasing
     onshore flow cooling valley temperatures back into the 70s. 
     Some morning drizle is possible...especially along the coast.

     A flat transitory ridge will turn the flow aloft
     northwesterly Sunday, for drier and warmer weather.  The
     ridge if forecast to shift east of the region Monday with
     the flow aloft becoming southwesterly.  A cold front is
     forecast to approach the coast late Monday, but that is
     getting too far out for the forecast models to time accurately.

Tue (26 Aug):  Areas of Morning Fog and Low Clouds...Mostly Sunny in the Afternoon.  47/76

Wed (27 Aug):  Partly Sunny.  Slight Chance of Sprinkles or Drizzle North.  48/78

Thu (28 Aug):  Sunny and Warmer.  48/83

Fri (29 Aug):  Mostly Sunny.  Increasing High Clouds.  52/82

Sat (30 Aug):  Morning Clouds.  Afternoon Clearing.  53/76

Sun (31 Aug):  Mostly Sunny.  50/80

Mon (01 Sep):  Mostly Sunny.  Increasing Clouds late.  51/78

ODA Meteorologist
weather at oda.state.or.us