[willamette-fcst] Forecast - Friday, June 5th, 2009

Willamette Valley Ag/Burning Forecast willamette-fcst at listsmart.osl.state.or.us
Fri Jun 5 12:11:10 PDT 2009




Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

...Next Update Not Scheduled Until Tuesday, June 9th, 2009

Issued: 
     Friday, June 5th, 2009 at 12:00pm.

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...passing over the
     region during 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.  The thudershowers
     swept northward, on both sides of the Cascades, into southern
     Washington, before running into a more stable air.  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.  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.

     Late-morning satellite imagery showed one band of clouds over northwest
     Oregon and another over south-central Oregon.  Both areas of clouds
     were rotating around the parent low-pressure center, curently over
     central California.  Doppler radar showed scattered showers embedded
     in both areas of clouds.  Skies were sunny this morning over northeastern
     Oregon, but daytime heating was already helping showers develop in the
     unstable air mass still over that region.

     The late-morning ODA surface analysis showed high pressure building into
     the central and southern coast.  Onshore flow was spreading across the state,
     into a thermal trough that was near the Idaho border.  The morning sounding
     over Salem showed considerable low-level cooling, which has acted to stabilize
     the air mass somewhat over western Oregon.  The mid-levels of the air mass were
     still unstable, so daytime heating will act to enhance the showers again this
     afternoon.  Thunderstorms will likely stay confined to areas east of the Cascades,
     where they will produce locally heavy rainfall, hail, and strong gusty winds.
     It is still possible that a thunderstorm or two could develop west of the
     Cascades, but severe storms are unlikely for western Oregon today.

     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 late-morning readings were mostly in the upper
     50s and low 60s across western Oregon.  It will be at least 10 degrees
     cooler across western Oregon today, with Willamette Valley highs only in
     the upper 60s and low 70s.  Temperatures were already in the 70s across
     eastern Oregon at midday, where daytime heating will help to fuel possible
     strong thunderstorm development this afternoon.

Surface Winds:
     SW 5-10 this afternoon.
Transport Winds:
     SW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 68.
Humidities:
     Minimum relative humidity will be near 65%.
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.  52/69

Sun (07 Jun):  Morning Clouds...Afternoon Clearing.  50/73

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



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