[willamette-fcst] Forecast - Friday, March 5th, 2010

Fri Mar 5 12:09:41 PST 2010

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, March 5th, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 4:00pm.
     Stack burning is not allowed.

Weather Discussion:
     The ODA surface analysis showed a Pacific frontal boundary stretching out along the
     coastline late this morning.  It was weakening under the El Nino driven split-flow jet
     stream pattern that has been sending the bulk of the storm activity south of Oregon
     all winter.  The air mass is drying out across Oregon with many locations on both sides
     of the Cascades left with only middle and high clouds.  There were still pockets of
     low clouds in the river basins...mainly over the southern half of the state.

     Light offshore flow was turning more northerly across western Oregon, with north winds
     incresing to 5-10 mph across the Willamette Valley.  Late-morning temperatures ranged
     from near 40 degrees, at Medford and Klamath Falls, to the mid 50s along the coast.
     Most of the Willamette Valley had warmed into the low 50s, with some 50-degree readings
     also showing up in the Columbia Basin of northeastern Oregon.

     Infrared satellite imagery showed a developing low-pressure wave, along the frontal
     boundary, off the north-central California coast. That was stalling the eastward
     progression of the front and taking energy away from it north of the California border.
     Doppler radar was showing a band of rain along the northern California coast but no rain
     north of about the Oregon/California border.  Rain is forecast to push inland, across
     northern and central California, later today.  Some sprinkles could migrate as far north
     as extreme southern Oregon.  Conditions should remain dry in the Willamette Valley.

     Considerable middle and high clouds will continue to filter the sunshine, over western
     Oregon, through the afternoon. Southeasterly flow aloft will lift the freezing level to
     above 6000 feet.  The air mass aloft will be warm enough this afternoon to support surface
     temperatures climbing into 60s.  However, Willamette Valley highs will have a tough time
     hitting the 60 degree mark, due to the sun-filtering middle and high clouds.

Surface Winds:
     N 5-12 this afternoon.
Transport Winds:
     NNE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 38.
High Temperature:
     Salem\'s high temperature today will be near 59.
Humidities:
     Minimum relative humidity will be near 47%.
Sunrise/Sunset:
     Salem sunset tonight: 6:05pm; sunrise tomorrow: 6:41am.

Extended Outlook:
     The persistent split-flow jet stream pattern will direct the offshore
     upper-level low-pressure system southeastward, into central
     and southern California, on Saturday.   Oregon will be in a \"calm zone\"
     between the polar jet stream, over northern Canada, and the active
     subtropical jet stream, over southern California and Mexico.  Afternoon
     sunshine should warm valley highs into the low 60s Saturday.  By late
     Sunday, the polar jet stream will sag far enough south to direct a cold
     front onshore and across western Oregon.

     A cold upper-level trough will drop snow levels sharply on Monday, as the
     preciitation turns to showers.  Western Oregon will likely see
     the lowest snow levels since December, with significant snow possible over
     the Cascade passes.  The coast range passes may also get sticking snow, with
     a chance of wet snow even mixing with rain, in heavier showers, in the higher
     hills around the Willamette Valley.  After a brief break early Tuesday, another
     cold weather system will bring more valley rain and much-needed mountain snow
     Tuesday night and Wednesday.  Another system is forecast to bring rain and
     possibly blustery conditions onshore by late Thursday, followed by another
     cold upper-level trough, with very low snow levels, on Friday.

Tomorrow (06 Mar):  Becoming Partly Sunny and Mild.  37/61

Sun (07 Mar):  Rain Developing in the Afternoon.  Snow Level Dropping to 3-4000 Feet.  36/53

Mon (08 Mar):  Showers and Cool.  Chance T-Storms.  Snow Level Below 2500 Feet.  35/49

Tue (09 Mar):  Increasing Clouds.  Chance of Rain Late.  Snow level 3-4000 Feet.  31/51

Wed (10 Mar):  Rain Turning to Showers.  Snow Level Near 3000 Feet.  38/51

Thu (11 Mar):  Rain Late and Turning Blustery.  Snow Level Rising To 5000 Feet.  36/55

Fri (12 Mar):  Rain Turning to Showers. Snow Level Dropping Below 2500 Feet.  40/51

ODA Meteorologist
weather at oda.state.or.us