[willamette-fcst] Forecast - Wednesday, July 30th, 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: 
     Wednesday, July 30th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is allowed from 11:00am until 5:00pm with a 100 acre limit.
     Propane flaming is allowed from 11:00am until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A fairly active cold front, for late July, moved across
     Western Oregon Tuesday evening and was falling apart east of
     the Cascades this morning.  Spotty light rain fell across
     the Willamette Valley with the extreme north valley locally
     picking up a few hundredths of an inch.  Generally trace
     amounts fell from Salem south to Eugene.  Up to one-quarter
     of an inch of rain fell along the Noorthern Oregon Coast
     with about one-tenth of an inch along the central coast.  A
     few light showers also fell across North-Central and NE
     Oregon with Pendleton picking up .01 inches.

     The trace of rain that fell in Salem Tuesday was not enough
     to offically end the long dry spell that has lasted for over
     a month and a half.  Today will be the 51st consecutive day
     without measurable rain in Salem.  That is not
     extraordinary, since July is typically the driest month of
     the year.  The valley normally only gets about
     three-quarters of an inch of rain in July.

     The Salem sounding this morning showed quite cool air, for
     late July, below 7000 feet.  That is not surprising, since
     high temperatures Tuesday were only in the low 70s...10-15
     degrees below normal.  Winds aloft were generally
     westerly...indication that strong onshore flow was occuring.

     Skies were mostly cloudy over the valley this morning,
     which helped to hold minimum temperatures in the low to mid
     50s (near normal).  Daytime heating will combine with cool
     air aloft and ample low-level moisture to keep a fair amount
     of clouds around through early this afternoon.

     A transitory upper-level ridge of high pressure is forecast
     to move over the region today.  That will promote sinking
     air in the mid-levels of the atmosphere with considerable
     warming aloft forecast by this afternoon.  That will help
     valley high temperatures recover into the mid to upper 70s
     today...still well below normal.  Transport winds are
     forecast to turn northerly by early this afternoon and
     north-northeasterly by late this afternoon, so open burning
     is unlikely today.

Surface Winds:
     NW 5-10 this morning, NNW 5-15 this afternoon.
Transport Winds:
     NW 8 this morning, N 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 45.
High Temperature:
     Salem\'s high temperature today will be near 77.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 36%.
Sunrise/Sunset:
     Salem sunset tonight: 8:40pm; sunrise tomorrow: 5:57am.

Extended Outlook:
     A dry westerly flow aloft is forecast through early Thursday
     with the flow becoming more southwesterly Thursday
     afternoon, in response to a system dropping down the British
     Columbia Coastline.  Transport winds are forcast to become
     west-southwesterly Thursday afternoon with mixing heights
     climbing to near or above 5000 feet.  A significant open
     burning opportunity now appears likely Thursday afternoon
     and early evening.

     The Gulf of Alaska system will move onshore across
     Washington and Northern Oregon Thursday night and Friday. 
     It will likely bring some light rain the the northern and
     central Oregon Coast Thursday night and possibly into the
     Willamette Valley by Friday morning...especially north of
     Salem.  High temperatures Friday will likely be about 10
     degrees below normal.

     The parent upper-level low pressure area will stall and
     weaken, over Southern British Columbia, with a drier
     westerly flow aloft over Oregon this weekend.  Strong
     onshore flow Saturday will turn more northerly Sunday, as
     temperatures recover to near normal.  The upper-level low
     pressure center is forecast to continue to weaken and drift
     off the coast Monday.  That would put southwesterly flow
     aloft over Washington and Oregon with only slight warming
     due to onshore surface winds.

     The upper-level trough is further weaken and move over the
     region Tueday and Wednesday of next week.  That would
     maintain onshore low-level flow and maintan near-normal
     temperatures across Western Oregon.  There is potential for
     burning opportunities with this pattern, but it it way too
     far out to be more specific at this time.

Tomorrow (31 Jul):  Mostly Sunny...Increasing Clouds with a Chance of Rain North Late.  49/79

Fri (01 Aug):  Mostly Cloudy and Cool.  Chance of Showers...Mainly North.  53/73

Sat (02 Aug):  Morning Clouds...Becoming Mostly Sunny.  51/79

Sun (03 Aug):  Mostly Sunny.  51/82

Mon (04 Aug):  Mostly Sunny.  52/85

Tue (05 Aug):  Mostly Sunny.  52/84

Wed (06 Aug):  Mostly Sunny.  53/82

ODA Meteorologist
weather at oda.state.or.us