[willamette-fcst] Forecast - Friday, June 26th, 2009

[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: 
     Friday, June 26th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     Strong onshore flow on Thursday maintained a layer of marine
     low clouds across most of western Oregon with well below
     normal temperatures.  High temperatures only climbed into
     the upper 60s across the Willamette Valley, with low to mid
     60s along the coast.  Skies did clear over southwestern
     Oregon Thursday, and temperatures climbed into the mid 70s
     to low 80s.  Central and eastern Oregon basked in sunshine
     Thursday with highs generally in the comfortable 70s and
     80s.  Ontario, near the Idaho border, was the warm spot in
     the state at 92.

     Skies began clearing over northwestern Oregon Thursday
     evening, as the flow aloft, and at the surface turned more
     northerly.  That allowed temperatures to drop into the mid
     40s across sections of the Willamette Valley by early this
     morning.  McMinnville dipped to 44 degrees, and Eugene
     recorded a minimum of 45.  Portland, Aurora, and Salem all
     stayed in the low 50s.

     Visible satellite imagery showed widespread low clouds
     across western Washington this morning with just pockets of
     low clouds in the Willamette Valley.  Low cloudiness was a
     bit more extensive over the valleys of southwestern Oregon. 
     In stark contrast to Thursday, most of the Washington and
     Oregon coastlines were free of low clouds...and indication
     that the onshore flow had weakened considerably.

     The ODA surface analysis showed high pressure had strongly
     built into the Washington and Oregon coastlines with the
     strongest onshore gradients from the Cascades eastward into
     Idaho.  Gradients had turned more northerly across western
     Oregon with the strongest pressure differences along the
     central and southern coast and from the southern Willamette
     Valley to the California border. Northerly winds were
     already 10 mph or greater from Eugene to Roseburg North
     Bend.  Notherly winds were blowing in the 5-10 mph range
     across the remainder of northwestern Oregon.  Winds were
     still northwesterly across north-central and northeastern
     Oregon but turned northerly from south-central to
     southeastern Oregon.

     The Salem sounding this morning showed warming aloft,
     compared with Thursday morning, associated with a building
     ridge of high pressure.  Winds had turned offshore from the
     surface to the top of the marine layer at about 5200 feet. 
     A dry and warming northwesterly flow prevailed above the
     marine layer.  Patchy low clouds will soon give way to sunny
     skies along the coast and over the Willamette Valley today. 
     Northerly winds will increase this afternoon, as a thermal trough
     pushes northweard into southwestern Oregon and tightens the
     pressure gradients across western Oregon.  The strongest
     winds in the valley will be in the Eugene area.

     With increasing northerly winds and fairly high mixing
     heights forecast today, ventialtion conditions are expected
     to be good for agricultural burning.  However, northerly
     transport winds are not conducive to good smoke evacuation
     for stack burning, so it was not allowed.  Warming aloft and
     plenty of sunshine will combine to lift valley temperatures
     into the mid 70s this afternoon (near-normal).  Mostly clear
     skies and a drier air mass tonight will allow temperatures
     to drop into the mid to upper 40s across most of the valley
     by Saturday morning.

Surface Winds:
     N 5-13 this morning, N 10-17 G25 south this afternoon.
Transport Winds:
     NNE 10 this morning, N 14 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5200 feet.  Ventilation index 73.
High Temperature:
     Salem\'s high temperature today will be near 75.
Humidities:
     Relative humidity drops to 50% by 10.
     Minimum relative humidity will be near 31%.
Sunrise/Sunset:
     Salem sunset tonight: 9:03pm; sunrise tomorrow: 5:28am.

Extended Outlook:
     A fairly strong upper-level trough is forecast to drop
     southeastward, from the northern Gulf of Alaska, on
     Saturday.  That will back the flow aloft over Oregon from
     northwesterly to southwesterly by Saturday evening.
     Initially, that will warm the air mass over the state, with
     sunny skies lifting temperatures into the low to mid 80s
     across the Willamette Valley Saturday afternoon.  The
     trailing end of a cold front is forecast to move onto the
     Washington coast Saturday night and across northwestern
     Oregon Sunday morning.  It may not be strong enough to
     produce much shower activity this far south, but it will
     bring a strong surge of cooler and moist marine air into
     western western Washington and northwestern Oregon Sunday. 
     Marine low clouds will, once again, invade the region and
     cool temperatures back to near-normal.

     Southwesterly flow aloft will continue through Monday with
     onshore flow maintaining a pattern conducive to morning
     clouds and seasonal temperatures across northwestern Oregon.
     The jet stream will migrate slightly northward, to over
     southern British Columbia, Tuesday and Wednesday, with the
     flow aloft weakening and turning more westerly.  That will
     decrease the onshore flow and allow temperatures to warm a
     few degrees more.  A weak weather system may turn the flow
     aloft southwesterly by Thursday with increasing onshore flow
     beginning a cooling trend.

Tomorrow (27 Jun):  Sunny and Warmer.  48/82

Sun (28 Jun):  Mostly Cloudy and Cooler.  Slight Chance of Sprinkles North.  53/76

Mon (29 Jun):  AM Clouds.  Partly Sunny in the Afternoon.  52/78

Tue (30 Jun):  AM Clouds.  Mostly Sunny in the Afternoon.  52/81

Wed (01 Jul):  Mostly Sunny.  53/84

Thu (02 Jul):  Mostly Sunny.  54/82

Fri (03 Jul):  Partly Sunny and Cooler.  52/78

ODA Meteorologist
weather at oda.state.or.us