[willamette-fcst] Forecast - Wednesday, June 17th, 2009

[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: 
     Wednesday, June 17th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 7:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Straw stack burning is allowed from 12:00pm until 7:00pm.

Weather Discussion:
     A strong upper-level ridge of high pressure remains anchored
     over the eastern Pacific Ocean this morning.  The main jet
     stream is being forced over the ridge, into the northern
     Gulf of Alaska, and then southeastward towards the Pacific
     Northwest.  A split in the jet stream, just off the
     Washington and Oregon coastlines, weakened a cold front, as
     it moved onshore Tuesday evening and across Oregon Tuesday
     night.  The weather front brought lots of clouds but little
     in the way of precipitation to the state.  Some sprinkles
     fell along the central coast and in the southern Willamette
     Valley.  Parts of Lane county picked up a couple of
     hundredths of an inch of rain, as did sections of Jackson
     County in southwestern Oregon.

     As the cold front advanced across central and eastern Oregon
     overnight, it produced scattered showers and a few
     thunderstorms.  Light rain was reported in Lakeview, Baker
     City, and Rome, but amounts were less than one-tenth of an
     inch.  What was left of the cold front was pusing into Idaho
     at mid-morning.  Doppler radar showed some scattered light
     showers near the Idaho border but otherwise dry conditions
     prevailed across Oregon.  Visible satellite imagery showed
     cloudy skies along the Idaho border and much of Idaho, in
     association with the weakening cold front.  In the wake of
     the front, skies were only partly cloudy over most of
     central and eastern Oregon.  Low-level onshore flow was
     resulting in extensive marine low clouds along the northern
     and central coast and across the Willamette Valley.  Skies
     were mostly sunny over much of the south coast and
     southwestern interior.

     The mid-morning ODA surface analysis showed high pressure
     building into the central and southern Oregon Coast, with
     onshore flow extending across all of Oregon and into extreme
     western Idaho.  The strongest gradients were east of the
     Willamette valley...a condition commonly referred to as
     gradient-stacking.  That is typical after a marine intrusion
     and results in sinking air over the western slopes of the
     Cascades and is not conducive to good evacuation of smoke
     through the Cascade Passes.

     Temperatures dropped into the mid to upper 50s across the
     Willamette valley overnight and were mostly in the low 60s
     at mid morning.  Onshore flow will likely keep considerable
     marine low clouds over the coast and the Willamette Valley
     this morning, with slow clearing this afternoon.  The air
     aloft has cooled slightly since Tuesday, so valley
     temperatures will struggle into the mid 70s this afternoon,
     even with some sunbreaks.  A building ridge of high
     pressure, both at the surface and aloft, will turn surface
     and transport winds northwesterly this afternoon, making for
     favorable ventililation conditions for both agricultural and
     stack burning.

Surface Winds:
     W 3-8 this morning, NW 5-15 this afternoon.
Transport Winds:
     W 10 this morning, NW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4200 feet.  Ventilation index 42.
High Temperature:
     Salem\'s high temperature today will be near 75.
Humidities:
     Minimum relative humidity will be near 51%.
Sunrise/Sunset:
     Salem sunset tonight: 9:01pm; sunrise tomorrow: 5:25am.

Extended Outlook:
     A weak ridge will build over the region Thursday, with more
     afternoon sunshine and warmer temperatures.  Weak onshore
     flow will maintain some morning cloudiness across western
     Oregon and keep temperatures from getting too much above normal.

     A little stronger weather system is forecast to move onshore
     Friday, with more clouds, cooler temperatures, and a chance
     of light showers.  Another system will bring a reinforcing
     shot of marine air and a continued chance of showers over
     the weekend.  An upper-level trough is forecast to remain
     over the region during at least the first half of next week,
     with continued onshore flow, below normal temperatures, and
     a chance of showers at times.

Tomorrow (18 Jun):  Morning Clouds.  Mostly Sunny in the Afternoon.  55/78

Fri (19 Jun):  Mostly Cloudy and Cooler.  Chance of Light Showers.  54/70

Sat (20 Jun):  Mostly Cloudy.  Chance of Showers. 51/69

Sun (21 Jun):  Mostly Cloudy.  Chance of Showers.  50/68

Mon (22 Jun):  Mostly Cloudy.  Slight Chance of Showers.  50/73

Tue (23 Jun):  Mostly Cloudy.  Slight Chance of Showers.  52/74

Wed (24 Jun):  Mostly Cloudy.  Chance of Showers.  51/70

ODA Meteorologist
weather at oda.state.or.us