[willamette-fcst] Forecast - Friday, August 15th, 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.

NOON UPDATE

Issued: 
     Friday, August 15th, 2008 at 12:00pm.

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 strong upper-level ridge of high pressure brought record
     high temperatures to the interior of Western Oregon
     Thursday.  State Fire Marshal conditions were met by 3pm
     Thursday over most of the valley due to high temperatures
     and low humidities.  Much of the Willamette Valley reached
     100 degrees or better with Portland, Hillsboro, and Eugene
     hitting daily records.  Medford also tied their daily record
     high of 108 degrees, set in 1933.  Salem hit 100 degrees
     Thursday, but that was not a record for the date.  Corvallis
     was the valley cool spot with a maximum of 99 degrees. 

     The following records were tied or broken Thursday in the
     Willamette Valley:

     Location                High       Pervious Record

     Portland (Downtown)     101         97 set in 1942

     Portland (Airport)      102         97 set in 1967

     Hillsboro (Airport)     101        100 set in 1933

     Eugene (Airport)        100 (tied) 100 set in 2002

     The upper-level ridge had shifted over Eastern Washington
     and Eastern Oregon this morning with increasing southerly
     flow aloft feeding middle and high clouds over the western
     half of both states, along with the return of some California
     wildfire smoke to much of Western Oregon.  A weak upper-level
     disturbance was rotaing northward offshore and Doppler radar
     indicated some shower and thundershower activity off the Northern
     Oregon and Washington Coastlines moving north-northeastward.  It
     it remain off the Oregon Coast but may clip the Washington Coast today. 

     The late-morning ODA surface analysis showed a strong thermal trough over
     the interior valleys of Western Oregon with low pressure centers near
     Portland and Medford.  High pressure centers were near North Bend, on the
     southern coast, and in NE Oregon near Baker City.  A weak influx of
     marine air made it though the southern coastal gaps into the Southern
     Willamette Valley this morning.  Late-morning temperatures in Corvallis
     and Eugene were 3-5 degrees cooler than at the same time Thursday.  The
     north valley did not see the marine cooling, and late-morning 
     temperatures are running a few degrees warmer than on Thursday.

     Satellite imagery showed mostly clear skies from the creast of the coast
     range eastward across Oregon.  Low clouds continued to blanket the coastline
     late this morning with some sunbreaks along the north coast.  Coastal
     temperatures ranged from the mid 50s sout to the mid 60s north.  Western
     valley temperatures ranged from the mid 70s south to the low 80s north.

     The Salem sounding this morning showed warming aloft since Thursday, so
     high temperatures should easily break 100 degrees where the marine air
     did not penetrate this morning (from Salem north to Portland).  A strong
     subsidence inversion had been created by the upper-level ridge and will
     cap mixing heights near 2000 feet today.  State Fire Marshal Conditions
     will likely be met again by mid-afternoon, especially across the north valley,
     due to high temperatures and low humidities.

     Light southerly flow aloft tonight will continue to feed middle and high
     clouds over the region and hold minimums above 60 degrees.

Surface Winds:
     Variable 5-15.
Transport Winds:
     N to NW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2300 feet.  Ventilation index 23.
High Temperature:
     Salem\'s high temperature today will be near 103 (will be a record).
Humidities:
     Minimum relative humidity will be near 21%.
Sunrise/Sunset:
     Salem sunset tonight: 8:17pm; sunrise tomorrow: 6:16am.

Extended Outlook:
     An upper-level disturbance is forecast to move close enough
     to the coastline Saturday to bring a threat of showers or
     thundershowers to the western half of Oregon...especially
     the Southern Cascades.  It will be another scorcher with
     most valley highs over the century mark for the third
     straight day.  The increase in middle and high clouds may knock
     a couple of degrees off of the high temperatures.

     There is a pretty good chance that showers or thundershowers will
     roll off the Cascades and over the Willamette Valley Saturday evening
     and/or night.  The upper-level ridge is forecast to shift to over Western
     Montana Sunday.  Increasing southerly flow aloft will spread the chance
     of showers or thundershowers eastward across the state.  The thermal
     trough is forecast to finally shift east of the Cascades Sunday afternoon,
     which will begin a cooling trend for Western Oregon.

     The flow aloft will turn southwesterly by Monday afternoon, which will
     stabilize the air mass and push the thundershower threat east of the
     Cascades.  It will also increase the onshore flow and bring a significant
     cool-down to Western Oregon.  A weak cold front may be strong enough to
     produce some light showers along the coast and the Willamette Valley.

     A stronger system is still forecast to move onshore Tuesday afternoon
     or night for another chance of light rain across Western Oregon.  Depending
     on the strength and timing of this system, it may create a burning
     upportunity ahead of it Tuesday afternoon.  The valley will have a good
     chance of showers Tuesday night and Wednesday.  The flow aloft is forecast
     to turn northwesterly and begin drying out Thursday.

Tomorrow (16 Aug):  Sunny and Hot.  Chance of T-Storms Late.  64/102

Sun (17 Aug):  Mostly Cloudy.  Chance of T-Storms.  62/92

Mon (18 Aug):  Chance of AM T-Storms...Cooler with a Chance of Showers.  58/74

Tue (19 Aug):  Partly Cloudy.  Increasing Clouds Late with a Chance of Light Rain.  53/80

Wed (20 Aug):  Chance of Showers and Cooler.  55/74

Thu (21 Aug):  Mostly Cloudy.  Slight Chance of Showers.  52/74

Fri (22 Aug):  Morning Clouds...Afternoon Clearing.  50/78

ODA Meteorologist
weather at oda.state.or.us