[willamette-fcst] Forecast - Friday, June 5th, 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, June 5th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 7:00pm.
     Straw stack burning is allowed, for dry stacks, from now until 7:00pm.

Weather Discussion:
     The broad upper-level low-pressure area that has been
     centered off the California coastline for the past several
     days moved close enough to spin a spoke of upper-level
     energy northward across Oregon Thursday afternoon.  That
     acted on the already moist and unstable air mass to produce
     a line of locally severe thunderstorms.  The timing of that
     system added to the severity of the storms, since it came
     through at the warmest, and most unstable, time of the day.

     The storms first developed just after midday along an arc
     from north of Roseburg to Bend, to southeastern Oregon and
     gained strength as they moved north and west, across Oregon,
     Thursday afternoon and evening.  The thudershowers swept
     northward as far as southern Washington, before running into
     a more stable northeasterly flow aloft.  There were numerous
     reports of heavy rainfall, hail, strong winds (60-80 mph)
     and even possible weak tornadic development with these storms.

     The storms generally dumped between one-half and
     three-quarters of an inch of rain over much of the
     Willamette Valley in just a couple of hours Thursday
     afternoon.  Sections of central and eastern Oregon also got
     blasted by the storms.  Pendleton picked up almost an inch
     of rain Thursday evening along with strong and gusty winds. 
     The thundershowers had ended across the state by this
     morning but some showers were continuing...mainly over
     northwestern and southeastern Oregon.

     Mid-morning satellite imagery showed extensive cloud-cover
     over western Oregon and across south-central and
     southeastern Oregon.  Skies were mostly clear across
     north-central and northeastern Oregon.  The ODA surface
     analysis showed high pressure building into the central and
     southern coast with onshore flow into a thermal trough now
     extending from northeastern Nevada into southern Idaho.

     The sounding over Salem this morning showed considerable
     low-level cooling of the air mass, which will make for more
     stable conditions west of the Cascades today.  The middle
     and upper levels of the air mass were still unstable, so the
     threat of afternoon thundershower development remains high
     today east of the Cascades.  Some of those stroms could, once
     again, produce locally heavy rain, strong gusty winds, and hail.

     Onshore low-level flow and a continued moist mid-level northeasterly
     flow will keep skies mostly cloudy over western Oregon today with
     showers slowly tapering off by this evening.  Temperatures are
     cooler this morning with mid-morning readings were mostly in the mid
     to upper 50s across western Oregon.  It will be about 10 degrees
     across western Oregon today, with Willamette Valley highs only in
     the low 70s...that is about average for early June.  Transport winds
     are forecast to be southwesterly and eventually westerly today, which
     will make for good ventilation over the valley.

Surface Winds:
     S 5-10 this morning, SW 5-10 this afternoon.
Transport Winds:
     SW 8 this morning, WSW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3800 feet.  Ventilation index 38.
High Temperature:
     Salem\'s high temperature today will be near 72.
Humidities:
     Minimum relative humidity will be near 59%.
Sunrise/Sunset:
     Salem sunset tonight: 8:55pm; sunrise tomorrow: 5:27am.

Extended Outlook:
     The flow aloft will turn from northeasterly to northwesterly
     Saturday, as the upper-lever low-pressure system over California
     shifts eastward to over Nevada.  Increasing onshore surface flow
     will drive marine low clouds into the western valleys and further
     stabilize the air mass.  The marine layer may become enhanced enough
     for drizzle or light showers across northwestern Oregon...especially
     over the north coast range and along the coastal strip.

     A transitory weak upper-level ridge is forecast to keep things dry
     Sunday and Monday, although continued onshore flow will maintain
     considerable morning cloudiness across western Oregon.  A couple of
     weak upper-level troughs will possibly produce some morning
     drizzle or light showers across northwest Oregon Tuesday and/or
     Wednesday of next week, followed by another weak transitory ridge.
     Temperatures will likely be near-normal through next week.

Tomorrow (06 Jun):  Cloudy AM...Chance of Drizzle or Light Showers.  Partly Sunny PM.  52/70

Sun (07 Jun):  Partly to Mostly Cloudy.  52/73

Mon (08 Jun):  Partly Sunny after Morning Clouds.  52/75

Tue (09 Jun):  Mostly Cloudy.  Chance of Drizzle or Light Showers.  50/69

Wed (10 Jun):  Mostly Cloudy.  Chance of Morning Drizzle or Light Showers.  50/68

Thu (11 Jun):  Morning Clouds.  Partly Sunny in the Afternoon.  50/71

Fri (12 Jun):  Morning Clouds.  Partly Sunny in the Afternoon.  50/74

ODA Meteorologist
weather at oda.state.or.us