[willamette-fcst] Forecast - Wednesday, July 16th, 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: 
     Wednesday, July 16th, 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:
     A weak upper-level disturbance was moving onshore this
     morning and increasing the westerly flow aloft over
     Washington and Oregon.  The Salem sounding this morning
     showed 5-10 degrees of cooling, from the surface up to
     13,000 feet, since Tuesday morning.  There was still a layer
     of northeasterly winds from 2-4000 feet, but that should
     switch to northwesterly by midday.  The ODA surface analysis
     showed high pressure building into the central coast with a
     weak thermal trough extending from Eastern Washington
     through Central and SW Oregon.

     Onshore flow was increasing across Western Oregon this
     morning with gradiant stacking and the Medford Draw
     dominating this morning.  Visible satellite imagery showed a
     solid deck of low clouds and fog along the Washington and
     Oregon Coastlines.  The low clouds were banked up against
     the coastal mountains and making their way up the coastal
     river valleys at mid morning.  Patchy low clouds had made it
     up the Columbia River into the Portland area, with clear
     skies over the remainder of the valley.  Mostly sunny skies
     covered the remainder of the state with only some mid and
     high clouds over North-Central and NE Oregon.

     Temperatures this morning were running about 10 degrees
     cooler than Tuesday morning across he Willamette Valley. 
     Minimums dipped into the upper 40s and low 50s in response
     to the increased onshore flow overnight.  Onshore flow will
     likely cap afternoon temperatures in the low 80s across the
     valley, under sunny skies.  Northwesterly surface winds may
     approach or locally exceed 15 mph later this afternoon,
     which could limit burning opportunities.  Fire Marshal
     conditions are not expected due to lower temperatures and
     higher humidities.

     Cooling aloft will allow mixing heights to climb above 3000
     feet in the early afternoon.  Daytime heating may alleviate
     the pressure-gradient-stacking and Medford-Draw issues later
     this afternoon.  We will begin taking pibal readings at
     12:15pm for possibility of limited open burning.  Transport
     winds are forecast to become northwesterly, during the mid
     to late afternoon, before turning back to northerly this
     evening.  Therefore, any burning opportunities will likely
     be brief.

Surface Winds:
     WSW 5-10 this morning, NW 8-15 this afternoon.
Transport Winds:
     NE 7 this morning, NNW 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 82.
Humidities:
     Relative humidity drops to 50% by 11am.
     Minimum relative humidity will be near 32%.
Sunrise/Sunset:
     Salem sunset tonight: 8:55pm; sunrise tomorrow: 5:42am.

Extended Outlook:
     Another weak upper-level trough is forecast to reinforce the
     onshore flow Thursday and Friday with increasing amounts of
     marine clouds penetrating into the Willamette Valley.  Even
     with northwesterly transport winds,
     pressure-gradiant-stacking issues may limit burning
     opportunities Thursday, as the Willamette Valley become full
     of cooler marine air. Areas of drizzle are likely by Friday
     morning along the coast and western slopes of the coast
     range.  Transport winds may become northerly, again, as
     early as Friday afternoon.

     The upper-level ridge is forecast to rebuild over the region
     Saturday with northerly transport winds and temperatures
     warming back above normal.  The long-range computer models
     are not consistent in the timing of the ridge shifting
     eastward and allowing a southerly flow aloft to move over
     Oregon.  That will likely happen either Sunday or Monday
     with onshore flow and cooler temperatures returning to
     Western Oregon.  That transition may also bring showers or
     thundershowers to much of the state.

     Westerly flow aloft is forecast to stabilize the air mass
     over the region by Tuesday with a more typical onshore flow
     pattern at the surface.

Thu (17 Jul):  Morning Clouds...Partly Cloudy in the Afternoon.  Wind: NW 10-15 mph.  51/79

Fri (18 Jul):  Morning Clouds...Mostly Sunny.  Wind: NNW 10-15 mph.  50/80

Sat (19 Jul):  Sunny and Warmer.  50/85

Sun (20 Jul):  Mostly Sunny and Warm.  55/88

Mon (21 Jul):  Mostly Cloudy and Cooler.  Slight Chance of showers or Thunderstorms.  56/78

Tue (22 Jul):  Morning Clouds...Mostly Sunny.  53/83

Wed (23 Jul):  Patchy Morning Clouds...Sunny & Warm.  53/87

ODA Meteorologist
weather at oda.state.or.us