[willamette-fcst] Forecast - Tuesday, February 23rd, 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: 
     Tuesday, February 23rd, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from 1:00pm to 4:00pm.
     Straw stack burning is allowed from 1:00pm until 4:00pm.

Weather Discussion:
     The upper-level ridge that brought unseasonably warm and dry weather over the weekend
     shifted east or Oregon by early this morning.  An increasing southwesterly flow aloft
     pushed clouds over western Oregon during the night with rain movning onshore early
     this morning.  Some sections of the Willamette Valley bottomed out near the freezing
     mark, shortly after midnight, before warming in response to the increasing cloud-cover.
     
     The incoming westerly jet stream is aimed at northern California, and that is where the
     bulk of the moisture from this weather system is being directed. A weakening occluded front
     was about 150 miles offshore, late this morning, and slowly advancing towards the coastline.
     Satellite imagery showed the associated cloud-shield had pushed eastward to the Idaho border,
     although it was composed mainly of just middle and high clouds east of the Cascades.

     Doppler radar and surface reports indicated that light rain had spread over most of
     western Oregon by midday.  Most of the Willamette Valley had picked up a few hundredths of
     an inch, with about one-tenth of an inch falling so far today in the Salem area.  Up to
     one-quarter of an inch of rain has fallen along the coast so far today. ODOT road cameras
     showed dry pavement still over the Cascade passes with pass temperatures in the upper 30s
     and lower 40s.

     The ODA surface analysis continued to show weak offshore pressure gradients across Oregon,
     in response to the approaching frontal system.  Winds around to the state were mostly less
     than 10 mph, with easterly gusts to around 25 mph at the western end of the Columbia Gorge.
     Light rain at times is likely across the Willamette Valley today.  Winds will remain
     light southeasterly.  Rainfall totals should range from about one-tenth to one-quarter of
     an inch.  Willamette Valley highs should be held in the 40s today (the normal high for
     Salem today is 53 degrees).

     The air aloft is still mild, with the freezing levels over Salem and Medford measured at
     more than 7000 feet early this morning.  The snow level should remain above 5000 feet today
     and then lower to around 4000 feet by Wednesday morning.  The Cascades passes will likely
     get a mix of rain and snow today with accumulating snow likely overnight.

Surface Winds:
     SE 5-10 this afternoon.
Transport Winds:
     SE 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2000 feet.  Ventilation index 20.
High Temperature:
     Salem\'s high temperature today will be near 47 (high on Monday was 55 degrees).
Humidities:
     Minimum relative humidity will be near 74%.
Sunrise/Sunset:
     Salem sunset tonight: 5:52pm; sunrise tomorrow: 6:58am.

Extended Outlook:
     The main frontal band is forecast to come onshore early
     Wednesday and could bring another one-tenth to one-quarter of
     an inch of rain to the Willamette Valley, followed by
     showers Wednesday afternoon.  The snow level should drop to
     about 3500 feet by Wednesday afternoon, with a few inches of
     snow likely over the Cascade passes.  Light southerly
     surface winds will help coastal and western valley
     temperatures climb close to normal Wednesday afternoon.

     A transitory ridge of high pressure will bring some drying
     on Thursday, with another system coming onshore Friday. That
     system will also encounter the split-flow jet stream
     pattern, just off the west coast, with the main surge of
     moisture headed south into California.  Enough energy will
     swing over Oregon, however, to bring back some rain and
     mountain snow.

     A ridge of high pressure is forecast to rebuild back over
     the west coast this weekend, with unseasonably mild
     conditions returning to western Oregon by Sunday. 
     Increasing southwesterly flow aloft will likely bring a
     weakening weather system onshore by late Monday. 
     Progressively stronger systems are forecast to come onshore
     later next week, as the jet stream takes aim a little more
     at Oregon, instead of California.

Tomorrow (24 Feb):  AM Rain...PM Showers.  Snow Level near 3500 Feet.  41/53

Thu (25 Feb):  Mostly Cloudy.  Showers Ending.  Snow Level 4000 Feet.  40/56

Fri (26 Feb):  Rain Likely.  Snow Level near 5000 Feet.  42/54

Sat (27 Feb):  Mostly Cloudy.  Showers Ending.  38/55

Sun (28 Feb):  Partly Cloudy and Unseasonably Mild.  37/62

Mon (01 Mar):  Increasing Clouds.  Chance of Rain.  Snow Level 6000 feet.  38/59

Tue (02 Mar):  Rain Likely.  Snow Level 5-6000 Feet.  41/57

ODA Meteorologist
weather at oda.state.or.us