[willamette-fcst] Forecast - Tuesday, September 2nd, 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 2nd, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 7:00pm.
     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 cool but fairly dry upper-level trough moved over the
     Pacific Northwest during the Labor Day Weekend and brought
     well below normal temperatures to Western Oregon.  Valley
     highs Saturday cooled to near 70 degrees and stayed in the
     60s Sunday.  The trough did produce afternoon thundershowers
     Sunday with locally brief heavy rain.  Most of the valley
     picked up one-tenth of an inch or less, but some local areas
     got hit with over one-third of an inch.

     The trough moved east Monday with a transitory ridge
     bringing dry and continued cool northwesterly flow aloft to
     the state.  High temperatures warmed a few degrees from
     Sunday but stayed mostly in the upper 60s.  Dry conditions,
     with fairly low afternoon humidities, allowed for the drying
     of any damp fields from the shower activity Sunday.

     A weak upper-level disturbance, in the northwesterly flow
     aloft, was moving onshore this morning and spreading some
     middle and high clouds across mainly the northern half of
     Oregon.  Radar and surface reports were not indicating any
     precipitation associated wtih this system.  Willamette
     Valley minimums were mostly in the mid 40s early this
     morning with mid-morning temperatures near 50 degrees.

     The Salem sounding this morning showed several degrees of
     warming aloft since Monday morning with a subsidence
     inversion at 3000 feet.  Below the inversion, winds were
     from the NNE at about 10 mph.  A little cooling aloft,
     associated the the passing of the upper-level disturbance,
     should combine with daytime heating to break the inversion
     and lift mixing heights to near 5000 feet later this
     afternoon.  However, forecast northerly transport winds will
     significantly limit any burning opportunities...especially
     in the south valley.

     The ODA surface analysis showed very weak northerly
     gradients across Western Oregon this morning with a weak
     thermal trough trying to build northward along the extreme
     south coast.  Winds should stay northerly and increase this
     afternoon in the south valley.  It is possible that the
     upper-level disturbance will be strong enough to turn the
     transport winds north-northwesterly in the north valley this
     afternoon.  Valley temperatures will remain below normal
     today but recover a few degrees from Monday with high
     reaching into the mid 70s.

     A ridge is forecast to begin building into the west coast
     this evening with the northwesterly flow aloft drying out. 
     That should help to clear skies and allow overnight
     temperatures to drop back into the mid 40s across the valley.

Surface Winds:
     N 5-10 this morning, NW 5-10 north valley...N 5-15 south valley this afternoon.
Transport Winds:
     NNE 12 this morning, NNW 10 north valley...N 15 south valley this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 60.
High Temperature:
     Salem\'s high temperature today will be near 75.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 35%.
Sunrise/Sunset:
     Salem sunset tonight: 7:46pm; sunrise tomorrow: 6:37am.

Extended Outlook:
     The dry northwesterly flow aloft will bring sunny skies and
     warmer temperatures to Western Oregon Wednesday with
     northerly transport winds across the Willamette Valley.  The
     upper-level ridge axis is forecast to stay offshore, but it
     may build close enough to the coastline for transport winds
     to turn north-northeasterly Thursday and/or Friday.  That
     may allow for the burning of the remaining fields on the
     west side of the valley.

     A weak upper-level disturbance is forecast to move over the
     top of the offshore ridge and drop southward to near the
     Washington/Canadian border Saturday.  That should continue
     the dry northwesterly flow aloft with little change in
     temperatures.  The ridge is forecast to build a little
     closer the the coastline Sunday for a few degrees of warming.

     Another weak system is forecast to flatten the upper-level
     ridge a little Monday and Tuesday with the flow aloft
     becoming more westerly.  A few clouds may make it though the
     ridge, but no precipitation is forecast.  Temperatures will
     likely cool a few degrees.  This system may create a limited
     burning opportunity for the north valley, but a significant
     burning opportunity is not apparent at this time.

Tomorrow (03 Sep):  Sunny.  North Winds.  45/78

Thu (04 Sep):  Sunny and a Little Warmer.  NNE Winds.  47/80

Fri (05 Sep):  Sunny. NNE Winds.  50/83

Sat (06 Sep):  Sunny.  50/83

Sun (07 Sep):  Sunny.  51/86

Mon (08 Sep):  Mostly Sunny.  51/83

Tue (09 Sep):  Mostly Sunny.  51/79

ODA Meteorologist
weather at oda.state.or.us