[willamette-fcst] Forecast - Thursday, April 30th, 2009

Thu Apr 30 09:01:57 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 scheduled for Tuesday, May 5th, 2009 at 9:00am...

Issued: 
     Thursday, April 30th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 6:30pm.
     Stack burning is not allowed.

Weather Discussion:
     A cold upper-level trough over the region combined with
     daytime heating Wednesday afternoon to enhanced the shower
     activity across Oregon.  A few claps of thunder were heard
     over portions of the Willamette Valley late in the day,
     before evening cooling stabilized the air mass.  The
     upper-level trough that brought cool and damp weather to the
     entire Pacific Northwest Tuesday and Wednesday moved inland
     late Wednesday and was centered near the Oregon/ Idaho
     border this morning.

     Skies began clearing Wednesday evening across western Oregon
     with light winds allowing temperatures to generally cool
     into the mid 30s.  Corvallis briefly dipped to the freezing
     mark early this morning.  Hillsboro and McMinnville dropped
     to 33 degrees, while Salem and Eugene hit 34.  Risidual low
     clouds covered most of the Willamette Valley this morning
     with areas of fog from the north coast to the south valley
     around Eugene.  However, visible satellite imagery showed
     mostly clear skies from the coastal mountains west to most
     of the the beaches and over the Cascades.  Closer to the
     upper-level trough, cloudy skies continued to cover much of
     central and eastern Oregon with scattered snow showers over
     the eastern third of the state.

     Rainfall totals were quite variable across western Oregon on
     Wednesday, with the greatest totals a little farther south
     than on Tuesday.  Astoria and Hillsboro did not record
     measurable rain, while Corvallis and Eugene picked up around
     one-quarter of an inch.  A few showers also fell over
     southwestern Oregon with Roseburg recording .03 inches. 
     Scattered rain and snow showers fell Wednesday from the
     Cascades eastward into Idaho.  Mt. Hood Skibowl received 6
     inches of new snow, Timberline Lodge had 4 inches, and Mt.
     Bachelor had 3 inches.  Areas east of the Cascades picked up
     between a few hundredths to nearly one-quarter of an inch of
     rain Wednesday, with snow showers dropping as low as about
     3000 feet by this morning.  Both John Day and Baker City
     were getting snow showers this morning with temperatures in
     the low to mid 30s.

     Doppler radar showed only light shower activity over eastern
     Oregon at mid-morning, with drier conditions moving in from
     the west.  Mid-morning temperatures ranged from the upper
     30s to mid 40s across western Oregon, with readings in the
     30s and 40s east of the Cascades.  The morning sounding over
     Salem showed several degrees of warming and much drier air
     above 2000 feet, compared with Wednesday morning, which was
     an indication that the upper-level trough had moved east. 
     Transport winds had turned northeasterly and the freezing
     level had risen to 5000 feet.  Clearing skies overnight
     allowed a thin layer of near-freezing air to develop below
     500 feet, but it was already responding to the warming
     effects of the April sun by mid-morning.

     The air mass will continue to dry out and warm up across
     Oregon today, from west to east, as the cold and moist
     upper-level trough, near the Idaho border, drifts eastward
     and weakens. The mid-morning ODA surface analysis showed
     high pressure building over western Oregon with weak
     northerly gradients beginnning to develop in the Willamette
     Valley.  Onshore flow continued from the Cascades into
     Idaho.  Northerly gradients are forecast to strengthen
     slightly today across western Oregon.  Skies should clear
     over the Willamette Valley by this afternoon with mostly
     sunny and warmer conditions.  Highs will climb to
     near-normal.

Surface Winds:
     N 3-8 this morning, N 5-15 this afternoon.
Transport Winds:
     NE 6 this morning, NE 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 60.
High Temperature:
     Salem\'s high temperature today will be near 64.
Humidities:
     Minimum relative humidity will be near 39%.
Sunrise/Sunset:
     Salem sunset tonight: 8:17pm; sunrise tomorrow: 6:01am.

Extended Outlook:
     A warmer westerly flow aloft will send a weak weather system
     into southern Oregon and northern California Friday with a
     slight chance of light rain moving as far north as the
     southern Willamette Valley Friday aftenoon and night. Valley
     temperatures could climb above normal Friday afternoon.

     A stronger system is forecast to come onshore Saturday night
     with rain becoming likely by late in the day.  Rain will
     turn to showers Sunday.  Monday appears to be a break
     between storms with another system slated to move onshore
     Tuesday, in a strengthening west-southwesterly flow aloft.
     Depending on the track of the low-pressure system, that
     system could make for windy conditions along the coast and
     in the Willamette Valley.  Yet another storm is forecast to
     move onshore later Wednesday.

Tomorrow (01 May):  Increasing Clouds and Warmer.  Slight Chance of Rain South Late.  38/69

Sat (02 May):  Mostly Cloudy.  Chance of Rain.  Rain Likely Late.  47/63

Sun (03 May):  Rain Turning to Showers.  Snow Level Dropping to 4000 Feet.  47/58

Mon (04 May):  Mostly Cloudy.  Chance of Showers...Mainly North.  42/62

Tue (05 May):  Rain Likely and Possibly Windy.  47/63

Wed (06 May):  Increasing Rain Late.  44/62

Thu (07 May):  Showers.  44/62

ODA Meteorologist
weather at oda.state.or.us