[willamette-fcst] Forecast - Friday, August 8th, 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: 
     Friday, August 8th, 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:
     A moist and very unstable south-southwesterly flow aloft
     helped generate multiple strong thunderstorms over Central
     Oregon Thursday.  Golfball-sized hail was reported 12 miles
     NW of La Pine Thursday evening with multiple reports of
     one-half to three-quarter-inch diameter hail northwrd to the
     Washington border.

     An upper-level disturbance touched off more thundershowers
     over SW Oregon Thursday night that rolled up the Cascade
     crest and into Hood River about midnight.  More storms
     developed early this morning over the Northern Cascades and
     moved through The Dalles around daybreak.  Another batch of
     storms moved northeastward across NE Oregon this morning. 
     The flow aloft over Oregon is starting to stabilize and
     become more southwesterly.  Most of the shower and
     thundershower activity had moved north and east of the state
     by mid-morning.

     The Salem sounding showed a few degrees of cooling from the
     surface through 13,000 feet since Thursday morning, in
     response to an approaching upper-level trough about 300
     miles offshore.  The ODA surface analysis showed the thermal
     trough extending from SE Washington through Central Oregon
     and into SW Oregon.  Onshore flow was a little stronger west
     of the Cascades this morning with marine low clouds
     extending inland to the Cascades.  However, pilot reports
     indicate that the low clouds are only about 1300 feet thick,
     so an early afternoon break-out into sunshine is likely.

     Due to the weak influx of marine aire overnight, there is
     some gradient-stacking this morning, but afternoon heating
     should drop the pressures enough in the Willamette Valley to
     reverse that.     Southwesterly aloft should stabiize the
     air mass over Central Oregon today, so thundershower
     development there is not likely.  Mixing heights will stay
     below 3000 feet until surface temperatures climb into the
     low 70s this afternoon.  The transport winds should have
     more of a westerly component this afternoon and cooler air
     aloft will help mixing heights climb to near 6000 feet, when
     surface temperatures hit about 80 degrees.

     If the marine layer breaks up, and allows the Willamette
     Valley to warm into the 70s this afternoon, there is a
     strong possibility that ventilation conditions will allow
     for open burning.   The low-level winds will be increasing
     this afternoon and may become too strong for good plume    
     rise by late in the day.  A cold front is forecast to move
     onshore tonight and should significantly increase the
     onshore flow across the state.  A thick low cloud-deck is
     likely Saturday morning with areas of drizzle across the
     valley...mainly in the north.

Surface Winds:
     SW 4-8 this morning, W 7-15 this afternoon.
Transport Winds:
     SSW 7 this morning, SW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5800 feet.  Ventilation index 58.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Relative humidity drops to 50% by 1pm.
     Minimum relative humidity will be near 41%.
Sunrise/Sunset:
     Salem sunset tonight: 8:28pm; sunrise tomorrow: 6:08am.

Extended Outlook:
     The upper-level trough is forecast to move onshore over the
     weekend with the flow aloft turning westerly.  Temperatures
     will cool further Saturday with areas of morning drizzle or
     light rain likely...mainly in the north valley.

     A transitory ridge of high pressure is forecast for early next
     week.  A weak trough is forecast to approach the coastline
     Tuesday, which could create another burning opportunity.  A
     ridge is forecast for the end of next week with temperatures
     warming above normal and surface winds becoming mostly northerly.

Tomorrow (09 Aug):  Morning Clouds...Areas of Drizzle.  Afternoon Clearing.  56/75

Sun (10 Aug):  Morning Clouds.  Mostly Sunny in the Afternoon.  53/79

Mon (11 Aug):  Sunny and Warmer.  50/85

Tue (12 Aug):  Mostly Sunny and Warm.  Increasing Onshore Flow Late.  52/87

Wed (13 Aug):  Patchy Morning Clouds.  Mostly Sunny.  53/85

Thu (14 Aug):  Sunny and Warmer.  54/90

Fri (15 Aug):  Sunny and Warm.  55/90

ODA Meteorologist
weather at oda.state.or.us