[willamette-fcst] Forecast - Wednesday, July 15th, 2009

Wed Jul 15 08:59:33 PDT 2009

Daily Smoke Management Forecast

Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

...State Fire Marshal conditions may be met late this afternoon due to low humidities and wind...

Issued: 
     Wednesday, July 15th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 1:00pm until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     Clear skies overnight allowed temperatures to locally drop
     into the 40s again across the Willamette Valley by early
     this morning.  Eugene dipped to 47 degrees and Hillsboro hit
     48.  Most of the valley and the coast stayed in the 50s. 
     Portland and Medford were the warm spots in the state this
     morning, both recording minimums of 59.  Meacham, in northeastern
     Oregon, was the cool spot, with a low of 36 degrees.

     Visible satellite imagery showed a deck of marine low clouds
     banked up against the length of the Washington and Oregon
     coastlines.  Only a few low clouds had penetrated some of
     the coastal gaps and advanced into the western valleys. 
     Skies were sunny over the reaminder of Washington, Oregon,
     and Idaho this morning.  Fog and low clouds were holding
     mid-morning temperatures along the Oregon coastal strip in
     the 50s, but sunshine had already warmed inland
     temperatures, on both sides of the Cascades, into the 60s.

     A broad and fairly flat upper-level ridge will move directly
     over Oregon today.  The Salem sounding this morning showed
     more warming above 3000 feet with weak westerly flow aloft
     and north-northeasterly flow near the surface.  The
     mid-morning ODA surface analysis showed a weak trough
     extending from south-central Washington to southwestern
     Oregon with weak pressure gradients across Oregon.  Winds
     were generally light and variable across the state.

     Sunshine will prevail over the interior of western Oregon
     today.  Northerly winds will increase across the Willamette
     Valley this afternoon, in response to a building thermal
     trough into southwestern Oregon.  Warmer air aloft and
     continued drying of the air mass will help Willamette Valley
     high temperatures climb into the upper 80s this afternoon,
     after peaking out near 80 on Tuesday.  Coastal morning fog
     and low clouds should clear over the northern and central
     beaches this afternoon, but the southern coast may stay
     cloudy all day.  Sunny skies will help temperatures east of
     the Cascades climb into the 80s and 90s.

Surface Winds:
     N 3-10 this morning, N 5-15 G20 south this afternoon.
Transport Winds:
     NNE 10 this morning, N 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3300 feet.  Ventilation index 33.
High Temperature:
     Salem\'s high temperature today will be near 89.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 24%.
Sunrise/Sunset:
     Salem sunset tonight: 8:55pm; sunrise tomorrow: 5:41am.

Extended Outlook:
     The upper-level ridge is forecast to slowly shift eastward
     to near the Oregon/Idaho border Thursday, with increasing
     southwesterly flow aloft over western Oregon.  That would
     allow temperatures to continue warming over all of Oregon,
     with the exception of the immediate coastline, where
     increasing onshore flow would keep maintain lots of marine
     low clouds and cooler temperaturs.  Sunny skies should
     continue inland with transport winds remaining northerly
     over the Willamette Valley.

     The upper-level ridge is forecast to shift eastward, to over
     Idaho and western Montana, by Friday with the associated
     broad surface thermal trough finally sliding east of the
     Cascades.  That may bring enough onshore flow into western
     Oregon Friday afternoon to turn transport winds from
     northerly to northwesterly.  That could create a burning
     opportunity...especially for the north valley, but the
     region may also be flirting with State Fire Marshal
     conditions due to high temperatures and low humidities.

     The upper-level ridge will shift further east over the
     weekend, with increasing onshore flow at the surface
     eventually spreading across all of Oregon. Increasing
     south-southwesterly flow aloft will likely spread enough mid
     and high-level moisture into central and eastern Oregon to
     trigger some afternoon and evening thunderstorms.  Marine
     low clouds should penetrate into the western valleys by
     Sunday morning for significant cooling.  Precipitation west
     of the Cascades appears as if it will be limited to some
     possible drizzle along the coast...mainly in the late-night
     and early morning periods.

     A weak upper-level trough is forecast to move by to our
     north Monday, with onshore flow beginning to turn more
     northerly in the afternoon.  An upper-level ridge is
     forecast to begin building back over the region on Tuesday
     for a return to sunny and warmer conditions.  There is some
     indication that this ridge may be rather persistent and
     possibly quite strong by the end of next week.  That would
     bring hot weather to western Oregon, but that is still too
     far out to be certain of at this time.

Tomorrow (16 Jul):  Sunny and Warm.  North Winds.  55/91

Fri (17 Jul):  Mostly Sunny and Very Warm.  Increasing Onshore Flow Late.  56/93

Sat (18 Jul):  Mostly Sunny but Not As Warm.  Increasing Onshore Flow.  54/85

Sun (19 Jul):  Morning Clouds.  Partly Sunny in the Afternoon.  Cooler.  55/78

Mon (20 Jul):  Morning Clouds.  Mostly Sunny in the Afternoon.  52/80

Tue (21 Jul):  Mostly Sunny and Warmer.  52/85

Wed (22 Jul):  Sunny and Warm.  55/87

ODA Meteorologist
weather at oda.state.or.us