[willamette-fcst] Forecast - Tuesday, August 12th, 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: 
     Tuesday, August 12th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is allowed from 12:00pm until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     The upper-level ridge has flattened over Washington and
     Oregon today in response to a weakening cold front about 250
     miles off the coast this morning.  Satellite imagery showed
     high clouds from this system spreading across Western
     Washington and NW Oregon with low clouds blanketing the
     coastline and up the Columbia River into the Portland area. 
     The remainder of Oregon was under sunny skies this morning
     with a more westerly flow aloft purging the California
     wildfire smoke from most of the state.

     A weak upper-level trough is forecast to move across
     Washington and Northern Oregon later today with increasing
     middle and high clouds across the Willamette Valley.  The
     cold front may bring some sprinkles or light drizzle to the
     north coast tonight, but it should remain dry east of the
     coast range.  Transport winds may back from northerly to
     northwesterly this afternoon, which may allow for limited
     open burning.  Mixing heights will climb to 3000 feet around
     noon today with cooling aloft raising mixing heights to
     about 5000 feet by late this afternoon.

     An increase in the onshore flow will cap valley temperatures
     near or slightly below where they were Monday with highs in
     the mid 80s.  However, the onshore flow will be weak and
     brief with northerly flow forecast to return to the valley
     by tonight, as high pressure rebuilds over the region.

Surface Winds:
     NW 5-10 this morning, NW 7-15 this afternoon.
Transport Winds:
     N 7 this morning, NW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 84.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 8:22pm; sunrise tomorrow: 6:12am.

Extended Outlook:
     A strong ridge is forecast to rebuild over the Pacific
     Northwest Wednesday with the surface flow turning northerly
     and valley highs climbing into the mid to upper 80s.  The
     ridge will amplify Thursday with warmer air aloft helping
     surface temperatures climb into the mid 90s across the
     Willamette Valley.  An upper-level disturbance is forecast
     to approach the Oregon Coast Thursday, turning the flow
     aloft southerly and bringing a chance of thundershowers to
     the region Thursday evening throgh Friday morning. 

     The upper-level disturbance is forecast to move northward
     along the Oregon and Washington Coastlines with flow aloft
     staying southerly through Friday.  Southerly flow is not a
     good transport direction for valley smoke, so this system
     will not likely create a burning opportunity.   It may force
     some marine air to filter into the valley Friday afternoon,
     but not enough to keep temperaturs from climbing into the
     90s for the second straight day.

     Southerly flow aloft is forecast to continue the very warm
     weather Saturday with a slight increase in the onshore flow
     possibly cooling valley temperatures a few degrees. 
     Saturday may be the third straight day with 90+ degree heat
     in the valley.  The upper-level ridge is forecast to shift
     over Montana by Sunday with increasing southwesterly flow
     aloft over Oregon.  That will bring more stable air into the
     region and increase the onshore flow for cooler temperatures
     across the interior of Western Oregon.

     The ridge is forecast to rebuild over the Pacific Northwest
     Monday with a weak trough flattening it and increasing the
     onshore flow again Tuesday.  That transition may create a
     burning opportunity Tuesday or Wednesday of next week.

Tomorrow (13 Aug):  Mostly Sunny and Warmer.  Wind: N 5-15 mph G25 south valley.  55/87

Thu (14 Aug):  Mostly Sunny and Hot. Chance T-Storm Late.  Wind: NNE 5-15 mph.  57/95

Fri (15 Aug):  Partly Cloudy.  Chance T-Storm.  Wind: N 5-15.  59/95

Sat (16 Aug):  Mostly Sunny and Very Warm.  Slight Chance T-Storm.  60/92

Sun (17 Aug):  Mostly Sunny and Cooler.  Increasing Onshore Flow.  56/85

Mon (18 Aug):  Sunny and Warmer.  54/88

Tue (19 Aug):  Mostly Sunny.  56/86

ODA Meteorologist
weather at oda.state.or.us