[willamette-fcst] Forecast - Thursday, August 14th, 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: 
     Thursday, August 14th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     A strong ridge will continue building over the Pacific
     Northwest today with offshore surface flow.  The Salem
     sounding this morning showed considerable warming aloft
     since Wednesday with north-northeasterly winds below 3000
     feet.  Temperatures are forecast to continue to warm aloft
     enough to support 100 degree heat in the Willamette Valley
     this afternoon. 

     NNE transport winds are expected to continue today and are
     conducive to good ventilation of smoke from western valley
     fields.     The morning ODA surface analysis showed a broad
     thermal trough of low pressure over Western Oregon with weak
     northerly gradients across the Willamette Valley.  Surface
     winds were generally from the north at less than 10 mph
     across Western Oregon.

     Satellite imgery showed a narrow band of low clouds along
     the coast with clear skies over the remainder of Oregon. 
     Temperatures were already quite warm with most of the
     western valleys near 70 degrees.  It was cooler on the coast
     with readings near 60.  The air mass aloft will continue to
     warm today in response to the building ridge over the
     region.  Valley temperatures will approach daily record
     highs with increasing north to northeasterly winds.

     The combination of hot temperatures and low humidities
     should push the Willamette Valley into State Fire Marshal
     conditions around 2-3pm.  The winds may also pick up enough
     to meet Fire Marshal criteria.

Surface Winds:
     N 5-12 this morning, NNE 10-20 this afternoon.
Transport Winds:
     NNE 15 this morning, NE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 53.
High Temperature:
     Salem\'s high temperature today will be near 100.
Humidities:
     Minimum relative humidity will be near 23%.
Sunrise/Sunset:
     Salem sunset tonight: 8:19pm; sunrise tomorrow: 6:15am.

Extended Outlook:
     The upper-level ridge axis is forecast to shift far enough
     east Friday for southerly flow aloft to develop over Western
     Oregon.  That will likely begin transporting smoke, from
     California wildfires, back over Western Oregon and begin to
     turn skies hazy.  The air aloft will continue to warm.  A
     broad thermal surface trough will remain over Western Oregon
     with offshore flow sending valley temperatures over the
     century mark...likely setting some new daily record highs.

     An upper-level disturbance is forecast to move close enough
     to the coastline Saturday to bring a threat of
     thundershowers to the state...mainly from the Cascades
     westward starting Saturday afternoon.  The best chance of
     thunderstorms in the Willamette Valley appears to be
     Saturday night.  The increasing southerly flow aloft may
     shift the thermal trough east of the Cascades late Saturday,
     which would cool temperatures a few degrees in the
     Willamette Valley.

     The upper-level ridge is forecast to shift over Western
     Montana Sunday with increasing southerly flow aloft
     spreading the chance of thunderstorms eastward across
     Oregon.  The thermal trough is expected to shift to Eastern
     Oregon Sunday with onshore flow bringing some cooling to
     Western Oregon.

     There is considerable uncertainty in the long-range models
     regarding the transition out of the hot weather early next
     week.  There could be burning opportunities early next week,
     depending on the strenghth and timing of the systems
     forecast to move onshore.  The flow aloft is forecast to
     become southwesterly Monday, which would stabilize the air
     mass over Western Oregon and bring additional cooling with
     onshore flow.  A stronger trough forecast to move onshore
     Tuesday.  Either system may end up being strong enough to
     produce light showers across Western Oregon.

     Most of the computer models (not all) bring a significant
     trough onshore by Wednesday of next week.  That would bring
     much cooler temperatures to the region and at least a chance
     of showers statewide.  

Tomorrow (15 Aug):  Record Heat and Turning Hazy.  65/103

Sat (16 Aug):  Mostly Sunny, Hot, and Hazy.  Slight Chance of T-Storms Late.  65/99

Sun (17 Aug):  Partly Cloudy.  Slight Chance of T-storms.  60/90

Mon (18 Aug):  Mostly Cloudy and Cooler.  Chance of Showers.  55/75

Tue (19 Aug):  Mostly Cloudy.  Chance of Showers Late.  55/77

Wed (20 Aug):  Mostly Cloudy and Cooler.  Chance of Showers or Light Rain.  55/72

Thu (21 Aug):  Mostly Cloudy.  Chance of Showers.  55/70

ODA Meteorologist
weather at oda.state.or.us