[willamette-fcst] Forecast - Friday, November 21st, 2008

[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, November 21st, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 2:30pm.
     Stack burning is not allowed.

Weather Discussion:
     A vigorous cold front moved across Western Oregon Thursday morning...following by numerous
     showers Thursday afternoon.  Rainfall totals were fairly uniform, around one-half inch,
     across most of western Oregon.  Showers tapered off overnight with clearing skies allowing
     temperatures to fall well into the 30s, with widespread fog reforming, across the
     Willamette Valley.

     The morning sounding over Salem revealed a much colder air mass, in the wake of Thursday\'s
     cold front.  The freezing level had dropped to just 4500 feet, from 8300 feet on Thursday.
     Some valley locations dipped to near or slightly below the freezing mark this morning.
     Eugene had freezing fog with a low of just 30 degrees.  Hillsboro dropped to 32 degrees,
     while McMinnville, Salem, and Corvallis bottomed out at 34.  Those cool surface temperatures
     created a low-level temperature inversion extedning up to about 1000 feet.

     Satelite imagery showed middle and high clouds, associated with a warm front, spreading over
     western Washington and extreme northwest Oregon.  The cold front was still about 400 miles
     offshore.  Rain will stay north of Oregon, until the cold front approaches the coastline
     this evening.  Pesistent valley fog will keep high temperatures from climbing much above 50
     degrees, with some areas likely staying in the 40s.

     Warming aloft will likely maintain the low-level inversion today, so stack burning was not
     allowed.  Increasing southeasterly winds will likely begin lifting the fog late this
     afternoon.  Rain should move onshore shortly after sunset and into the valley this evening.
     The cold front is forecast to move across western Oregon in the pre-dawn hours Saturday.

Surface Winds:
     SE 0-5 this morning, SSE 5-10 this afternoon.
Transport Winds:
     SE 6 this morning, S 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1000 feet.  Ventilation index 10.
High Temperature:
     Salem\'s high temperature today will be near 50.
Humidities:
     Minimum relative humidity will be near 68%.
Sunrise/Sunset:
     Salem sunset tonight: 4:38pm; sunrise tomorrow: 7:20am.

Extended Outlook:
     After some early moring rain, a weak upper-level trough will keep a chance of showers across
     western Oregon though Saturday afternoon.  This will quickly dry out Saturday evening.  Total
     rainfall from this system will be mostly less than one-quarter of an inch, with the
     greatest amounts in the northern Cascade foothills.

     A strong upper-level ridge will likely bring a return of dry weather Sunday and Monday with
     a little sunshine...mainly in the north valley.  Low-level temperature inversions will make
     for poor ventilation conditions and lead to valley fog formation.  Outflow, from the
     Columbia Gorge, should help keep widespread fog from forming in the north valley, but fog
     could become persistent in the central and south valley.

     The ridge is forecast to begin breaking down about Tuesday with increasing southwesterly
     flow aloft.  A developing split-flow pattern in the jet stream will likely take most of the
     punch out of a cold front, as it comes onshore Tuesday afternoon.  A transitory ridge is
     forecast to bring back dry conditions Wednesday.

     The computer model solutions diverge starting on Thanksgiving.  Due to the variety of
     stuffing be put into the long-range forecast, it could turn out to be a real turkey.  There
     is a reasonable chance, however, that a strong upper-level ridge will build close enough to
     the coastline to bring northeasterly flow aloft by Friday.  That would bring rare November
     sunshine to most of the state, which I am sure we would gobble up. 

Tomorrow (22 Nov):  Light Rain AM...Decreasing Showers PM.  Snow Level 4-5000 Feet.  40/51

Sun (23 Nov):  Areas of Fog...Mainly Central and South Valley.  Partly Sunny.  33/50

Mon (24 Nov):  Areas of Fog...Mainly Central and South Valley.  Partly Sunny.  35/52

Tue (25 Nov):  Chance of Light Rain.  Snow Level 5000 Feet.  38/53

Wed (26 Nov):  Areas of Am Fog.  Partly Sunny.  35/50

Thu (27 Nov):  Increasing Clouds and Indigestion.  Chance of Light Rain Late.  35/48

Fri (28 Nov):  Becoming Mostly Sunny.  NE Winds.  34/49

ODA Meteorologist
weather at oda.state.or.us