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

Burn Advisory:

  ...State Fire Marshal conditions may locally be reached late
     this afternoon, mainly from Salem south, due to low relative
     humidities and increasing northwesterly winds...

     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 2:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A weak upper-level trough is moved across NW Oregon early
     this morning.  Infrared satellite imagery showed a band of
     middle and high clouds, associated with this system,
     stretching from Northern Idaho across NE and North-Central
     Oregon.  The system will weaken as it pushes southeast
     across this remainder of Oregon this afternoon.

     A dry north-northwesterly flow aloft was moving in behind
     that system over NW Oregon, so skies will continue to be
     sunny today east of the coastal range.  The upper-level
     trough was strong enough to kick the surface thermal trough
     east of the Cascades with onshore flow increasing across
     Western Oregon at mid-morning.  The ODA surface analysis
     showed high pressure centered near the Central Oregon Coast
     with a weak thermal trough extending from Central Washington
     through South-Central Oregon.

     The onshore flow brought marine low clouds into the
     coastline overnight, but there was not much penetration east
     of the coastal range at mid-morning.  Skies were mostly
     sunny in the western valleys.  The air mass was still quite
     dry over Western Oregon early this morning with dew-point
     temperatures remaining in the 40s.  However, over the past
     couple of hours, dew-point temperatures are beginning to
     rise, as the onshore flow increases.  That may help the
     valley avoid Fire Marshal conditions this afternoon, as
     temperatures rise into the low 80s and northwesterly winds
     increase.

     The Salem sounding this morning showed considerable cooling
     aloft since Monday, so mixing heights should approach 3000
     feet by noon and top out near 5000 feet this afternoon.  The
     increasing onshore flow will likely create a burning
     opportunity, for north valley, this afternoon, as trasport
     winds become northwesterly.

     Another upper-level trough, currently over SE British
     Columbia, will slide to near NE Washington this evening. 
     That should keep the upper-level ridge from rapidly building
     back over Western Oregon and maintain northwesterly
     transport winds across the Northern Willamette Valley
     through the afternoon.  It is also possible that transport
     winds will turn enough northwesterly to allow for limited
     open burning in the south valley this afternoon.

Surface Winds:
     NW 5-10 this morning, NW 8-16 this afternoon.
Transport Winds:
     NNW 7 this morning, NW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4800 feet.  Ventilation index 48.
High Temperature:
     Salem\'s high temperature today will be near 82.
Humidities:
     Minimum relative humidity will be near 30%.
Sunrise/Sunset:
     Salem sunset tonight: 7:33pm; sunrise tomorrow: 6:46am.

Extended Outlook:
     High pressure is forecast to begin building back over
     Western Oregon by Wednesday morning with the flow aloft
     becoming northerly and the air mass warming back up. 
     Conditions may allow for the burning of the remaining west
     valley fields either Wednesday or Thursday morning, as the
     transport winds become increasingly offshore.  Very dry
     conditions and northerly surface winds may put much of the
     valley back into Fire Marshal conditions in the
     afternoons.

     A weak upper-level disturbance is forecast to flatten the
     ridge and turn the flow weakly onshore Friday.  That will
     bring another cool-down to the region and a potential
     burning opportunity, especially for the north valley.

     The strong upper-level ridge is forecast to build over the
     Pacific Northwest this weekend for sunny and warmer weather.
     The ridge will slowly push east of the region early next
     week with increasing southwesterly flow aloft beginning a
     cooling trend.  The weather pattern for next week still
     appears dry for Western Oregon, so there could be some
     burning opportunities...especially for the north valley.

Tomorrow (10 Sep):  Sunny and Warm.  46/84

Thu (11 Sep):  Sunny and Warmer.  48/88

Fri (12 Sep):  Mostly Sunny but Cooler with Onshore Flow.  52/80

Sat (13 Sep):  Sunny and Warmer.  49/84

Sun (14 Sep):  Sunny and Very Warmer.  53/90

Mon (15 Sep):  Mostly Sunny and Very Warm.  53/88

Tue (16 Sep):  Mostly Sunny and Cooler.  51/83

ODA Meteorologist
weather at oda.state.or.us