[willamette-fcst] Forecast - Monday, July 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: 
     Monday, July 21st, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is allowed from 2:00pm until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     Increasing onshore flow brought cooler conditions to the
     Willamette Valley Friday and Saturday with below normal
     temperatures for the first time this month.  The onshore
     flow weakened Sunday with valley highs rebounding into the
     mid to upper 80s.

     An upper-level low pressure area, centered just off the
     Northern California Coastline, was responsible for
     south-southwesterly flow aloft over Oregon this morning. 
     That was transporting smoke north-northeastward, from
     California wildfires, making for hazy conditions over most
     of Oregon, Idaho, and SE Washington.

     Morning satellite imagery showed low clouds along the
     Washington and Oregon Coastlines with a few low clouds
     making it into the extreme northern and southern Willamette
     Valley.  The remainder of Western Oregon had mostly clear but
     hazy skies.  Moisture from the California system was circulating
     into Central and Eastern Oregon, where skies were partly to mostly
     cloudy this morning.  Afternoon heating should result in scattered
     thunderstorm development over Southern Oregon and areas east
     of the Cascades, as the California system moves onshore. 
     Some storm may form in Lane County, near an over the Cascades.

     The Salem sounding this morning showed minor cooling below
     8000 feet, so high temperatures today should be a few
     degrees cooler than on Monday.  Most of the valley will
     climb into the low 80s this afternoon.  A stable layer from
     the surface to about 3000 feet will not allow mixing heights
     to climb above 3000 feet until surface temperatures reach
     the upper 70s...about 2 pm.  Transport winds were
     north-northeasterly and are forecast to turn northerly at
     midday and north-northwesterly later this afternoon.

     The ODA surface analysis showed high pressure over Western
     Washington and along the Oregon Coast with a weak thermal
     trough extending from Eastern Washington to SW Oregon. 
     Pressure-gradient-stacking and Medford-Draw conditions were
     in effect but are weak enought that daytime heating may act
     to alleviate them.  That may allow for limited open burning
     opportunities this afternoon.  However, thnunderstorm
     development may raise surface pressures over Central Oregon
     this afternoon and reinforce the gradient-stacking problem. 
     That will need to be monitored closely.

Surface Winds:
     N 5-10 this morning, NNW 8-15 this afternoon.
Transport Winds:
     NNE 8 this morning, NNW 11 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 44.
High Temperature:
     Salem\'s high temperature today will be near 82.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 35%.
Sunrise/Sunset:
     Salem sunset tonight: 8:50pm; sunrise tomorrow: 5:47am.

Extended Outlook:
     The California system is forecast to move into Northern
     Nevada Tuesday morning and to over Idaho Tuesday afternoon. 
     That will increase the onshore flow into Western Oregon with
     marine low clouds likely penetrating into the Willamette
     Valley Tuesday morning.  Thundershower activity will be
     shifted mostly into Idaho Tuesday with a more stable
     westerly flow aloft moving over Oregon.  The westerly flow
     aloft should also help to clear the air of haze from the
     California wildfire smoke.

     A weak upper-level system, dropping down from the Gulf of
     Alaska, will maintain the westerly flow aloft over Oregon
     Tuesday and Wednesday.  Tranport winds are forecast to
     become more westerly Tuesday, over the Willamette Valley,
     which may create open buring opportunities, in the
     afternoon, depending on gradient-stacking issues.  The
     trough is forecast to move east of the region Wednesday
     afternoon with the flow aloft turning northwesterly and the
     transport winds becoming more northerly.

     The upper-level winds are forcast to become southwesterly
     Thursday through Monday with weak onshore flow at the
     surface across Western Oregon.  That should produce
     near-normal weather conditions with coastal low clouds and
     mostly sunny conditions over the interior of Western Oregon.
     The southwesterly flow aloft is forecast to strengthen
     Friday, as a weak trough approaches the coast.  That may
     increase the onshore flow enough to create another limited
     burning opportunity.

Tomorrow (22 Jul):  Morning Clouds...Mostly Sunny in the Afternoon.  54/76

Wed (23 Jul):  Brief Morning Clouds.  Sunny in the Afternoon.  50/81

Thu (24 Jul):  Sunny.  50/85

Fri (25 Jul):  Sunny.  51/85

Sat (26 Jul):  Mostly Sunny.  52/83

Sun (27 Jul):  Mostly Sunny.  53/82

Mon (28 Jul):  Mostly Sunny.  53/82

ODA Meteorologist
weather at oda.state.or.us