[willamette-fcst] Forecast - Friday, July 17th, 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, July 17th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 1:00pm until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     A broad upper-level ridge of high pressure remains over the
     regin today, and the air mass is starting off a few degrees
     warmer than on Thursday.  Minimums in the Willamette Valley
     this morning were mostly in the upper 50s and low 60s. 
     Hillsboro and Eugene were the cool spots with 56, while
     Portland, Aurora, and Corvallis stayed in the 60s
     overnight.

     The mid-morning ODA surface analysis showed a thermal trough
     over southwestern Oregon extending northward, through the
     Willamette Valley, into east-central Washington.  Weak high
     pressure centers were over northeast and south-central
     Oregon, as well as the central Oregon Coast.  Winds across
     the entire state were less than 10 mph with calm winds over
     most of the Willamette Valley.  Satellite imagery
     illusstrated the southwesterly flow aloft via high clouds
     streaming northeastward across Oregon.  Once again this
     morning, there were areas of low clouds and fog along the
     immediate coastline, with some eastward penetration of low
     clouds into the coastal mountain gaps south of about
     Florence.   

     The upper-level ridge will continue to slowly drift eastward
     today and will be centered over Idaho and western Montana
     this afternoon. The surface thermal trough is forecast to
     remain over western Oregon most of today, before shifting
     into central Oregon late this afternoon.  High temperatures
     today will range from the 60s on the central and south
     coast, where low clouds will be the most persistent, to the
     mid 70s on the north coast. Willamette Valley highs today
     should climb into the mid 90s, after peaking in the low 90s
     Wednesday afternoon.  Temperatures will likely climb over
     100 degrees this afternoon over sections of southwestern
     Oregon and from the eastern Columbia Gorge through the
     Columbia Basin of northeastern Oregon.  The remainder of
     central and eastern Oregon will soar well into the 90s.

     Surface and transport winds across the Willamette Valley are
     forecast to remain northerly today, with a slight chance of
     turning northwesterly late this afternoon. Weather
     conditions will be closely monitored this afternoon, but it
     is unlikely that the transport winds will take on enough of
     a westerly component to allow for open burning.  Much of the
     valley will also be bordering on State Fire Marshal
     Conditions this afternoon.

Surface Winds:
     N 3-8 this morning, N 7-15 this afternoon.
Transport Winds:
     NNE 7 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 94.
Humidities:
     Relative humidity drops to 50% by 10am.
     Minimum relative humidity will be near 25%.
Sunrise/Sunset:
     Salem sunset tonight: 8:54pm; sunrise tomorrow: 5:43am.

Extended Outlook:
     The upper-level ridge is forecast to be slightly flattened
     by a weak weather system moving into southwestern British
     Columbia on Satruday.  Increasing southwesterly flow aloft
     over Oregon will drive some mid and high-level moisture into
     central and eastern Oregon for an increasing threat of
     afternoon and evening thunderstorms.  The surface thermal
     trough, and warmest temperatures, are forecast to shift into
     eastern Oregon, with increasing onshore flow across the
     interior of western Oregon.  That should cool temperatures
     back into the 80s across the Willamette Valley.

     The weak upper-level trough is forecast to slide eastward,
     into Alberta, Canada, Sunday with the surface thermal trough
     pushing into Idaho Sunday afternoon.  That will usher a weak
     surge of cooler ocean air across most of Oregon.  The
     extreme southeastern portion of the state will not see much
     cooling.  Willamette Valley highs should cool into the low
     80s (near to slightly below normal) with some marine low
     clouds possibly penetrating into the western valleys Sunday
     morning.  Precipitation west of the Cascades appears as if
     it will be limited to a chance of drizzle along the coast. 
     The thundershower threat, east of the Cascades, will extend
     from south-central to extreme northeastern Oregon, as cooler
     and more stable air surges into north-central Oregon.

     The upper-level ridge is forecast to begin building back
     over the region Monday, for a return to mostly sunny and
     warmer conditions.  The afternoon and evening thundershowers
     will also increase east of the Cascades, with weakening
     south-southesterly flow aloft.  A weak upper-level system
     may approach the Oregon Coast by late Tuesday or Wednesday
     of next week and increase the onshore flow slightly.  That
     would keep temperatures near normal and could create a
     burning opportunity.  Much warmer weather apprears likely
     late next week.

Tomorrow (18 Jul):  Mostly Sunny but Not As Warm.  Increasing Onshore Flow.  59/88

Sun (19 Jul):  Areas of Morning Clouds.  Mostly Sunny but Cooler.  54/81

Mon (20 Jul):  Brief Patchy Morning Clouds.  Sunny and Warmer.  54/85

Tue (21 Jul):  Mostly Sunny.  55/84

Wed (22 Jul):  Mostly Sunny.  55/83

Thu (23 Jul):  Mostly Sunny.  55/87

Fri (24 Jul):  Mostly Sunny.  56/93

ODA Meteorologist
weather at oda.state.or.us