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

[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, March 5th, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from 11:00am until 4:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A weather system dropping southeastward into the region,
     from the Gulf of Alaska, spread considerable cloudiness over
     the western half or Oregon overnight.  Increasing clouds
     held overnight temperatures mostly in the upper 30s and low
     40s and inhibited valley fog formation.  Meanwhile, just
     some high clouds advanced as far east as central Oregon. 
     Mid-morning visible satellite imagery showed areas of valley
     low clouds and fog, east of the Cascades, where temperatures
     were allowed to drop into the 20s.

     The ODA surface analysis showed a weakening frontal
     boundary, stretching out just off the Washington and Oregon
     coast, as it encounters the split-flow pattern in the jet
     stream.  With a weak low-pressure trough extending from the
     central Oregon coastal waters southward to over the northern
     California coastal waters, light offshore flow was
     developing across western Oregon.  Doppler radar showed only
     a few areas of sprinkles moving northward up the Willamette
     Valley.  McMinnville was the only location reporting some
     light rain this morning, with .02 inches.

     Infrared satellite imagery showed the main upper-level
     trough energy diving southeastward well off the northern
     California coastline.  That was developing a low-pressure
     wave, along the frontal boundary, off the California coast. 
     The front was stalling and weakening along the Oregon
     coastline.  Rain will push inland, into California, later
     today, with only a chance of light rain or sprinkles across
     mainly the coastal and extreme southern sections of western Oregon.

     Mid-morning temperatures ranged from the upper 30s to the
     mid 40s across western Oregon and from the upper 20s to near
     40 east of the Cascades.  Skies will remain mostly cloudy
     today across western Oregon, with mainly just high clouds
     and areas of valley fog across central and eastern Oregon. 
     Southeasterly flow aloft will lift the freezing level from
     near 5000 feet this morning to over 6000 feet this
     afternoon.

     Warming aloft will combine with an increasing northeasterly
     low-level flow to inhibit rainfall across the Willamette Valley
     today.  The air mass aloft will be warm enough this afternoon
     to support surface temperatures climbing into the 60s.  However,
     Willamette Valley highs should top out in the mid to upper 50s,
     due to the cloud-cover.

Surface Winds:
     NE 0-5 this morning, N 5-12 this afternoon.
Transport Winds:
     E 3 this morning, 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:
     A split-flow jet stream pattern will direct the offshore
     upper-level low-pressure system southeastward, into central
     and southern California, by Saturday evening.   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.  There is a quite cool air
     mass behind this system, so snow levels will drop sharply on Monday.

     Showers will taper off Monday night, with the lowest snow
     levels we\'ve seen in many weeks.  The coast range passes may see
     sticking snow and even some of the higher hills, around the valley,
     may half snow flakes mix in with heavier showers. After a brief break,
     early Tuesday, another cold weather system will bring more
     valley rain and much-needed mountain snow Tuesday night and
     Wednesday.  Yet another system is forecast to bring rain and
     possibly blustery conditions onshore by late Thursday, followed by
     another quite cold upper-level trough 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):  Decreasing Showers.  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 3000 Feet.  40/51

ODA Meteorologist
weather at oda.state.or.us