[willamette-fcst] Forecast - Thursday, April 23rd, 2009

Thu Apr 23 08:59:37 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.

Issued: 
     Thursday, April 23rd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:00pm.
     Straw stack burning is allowed from now until 6:00pm.

Weather Discussion:
     What a difference a couple of days make!  The Pacific
     Northwest rapidly made the transition from an early spring
     heat-wave to the deep chill in just 48 hours.  On Tuesday,
     record highs were being tied or broken across most of
     Oregon, with Willamette Valley highs in the upper 70s and
     lower 80s.  Cooler air began pouring across western Oregon
     Wednesday, with high temperatures dropping 15-20 degrees. 
     However, the eastern third of the state was still basking in
     record warmth.  After setting a record high Tuesday, with 83
     degrees, Burns tied the record high Wednedsay with 77. 
     Ontario, near the Idaho border, hit 86 degrees both Tuesday
     and Wednesday.  Rome, in southeastern Oregon, set a record
     Tuesday with 86 degrees and only cooled to 84 degrees Wednesday.

     By mid-morning today, the ODA surface analysis showed the
     cold front had just pushed through Rome, Oregon, with a much
     colder, but fairly dry, air mass spreading across all but
     the extreme southeast corner of the state. The Salem
     sounding showed about the most impressive 24-hour cooling I
     have ever seen.  The 5000-foot temperature dropped 29
     degrees F from Wednesday morning to this morning, and the
     freezing level plunged from 10,300 feet to just 2700 feet.

     As you have probably guessed, significant westerly winds
     accompanied the push of cold air, especially across central
     and eastern Oregon.  Wind gusts in excess of 30 mph were
     common from Redmond, to Pendleton, to Burns, to Baker City
     Wednesday afternoon.  West winds gusted to more than 40 mph
     at the eastern end of the Columbia Gorge, at The Dalles. 
     Northwesterly winds gusted to about 25 mph from the coast
     across the Willamette Valley Wednesday.  It was a dry cold
     front with no rain reported across the state Wednesday.

     The air mass is slowly moistening, with a cold upper-level
     trough dropping over the region from the northwest. 
     Satellite imagery showed a broad band of mainly middle and
     high clouds, associated with the cold front, stretching from
     Montana, across Idaho and most of eastern Oregon.  The was
     considerable clearing, in the wake of the front, across
     central and southwestern Oregon.  Doppler radar showed some
     instability showers rolling onshore into northwestern
     Oregon, but precipitation amounts so far this morning have
     been very light.  Areas along the northern and central coast
     have picked up a few hundredths of an inch, with showers
     extending about as far south as Newport.  Just trace amounts
     of rain have fallen so far in the northern Willamette
     Valley, and the south valley has remained dry.

     The chance of showers will increase across western Oregon
     today, with the approaching upper-level trough and daytime
     heating combining to increase the instability of the
     atmosphere.  That will also help to create excellent
     ventilation conditions across the region, with mixing
     heights lifting to around 5000 feet this afternoon. 
     Precipitation amounts should be less than one-tenth of an
     inch, with the best chance of showers over the northern
     coast range and Cascades.  Very cold air aloft locally
     dropped the snow level to 1500 feet this morning, and it
     will only lift to about 3000 feet this afternoon.

     Temperatures dropped into the 30s across western Oregon with
     some Willamette Valley locations flirting with the freezing
     mark.  McMinnville dropped to 32 degrees this morning. 
     Hillsboro dipped to 33 and Salem fell to 34.  The coast was
     also chilly this morning, with Newport recording a minimum
     of just 36 degrees.  Mid-morning temperatures had only
     recovered into the upper 30s and low 40s across western
     Oregon.  There was a wide range of temperatures east of the
     Cascades this morning.  Light winds and clear skies allowed
     readings in central Oregon to drop into the mid 20s, while
     clouds and gusty winds held temperatures near 50 along the
     eastern border.

     Considerable sunshine is forecast today for central and
     southwest Oregon, with clearing skies over eastern Oregon. 
     Sun with mix with clouds and a few showers over northwestern
     Oregon.  Further cooling west of the Cascades will keep
     highs below normal, with today being the day for massive
     cooling across central and eastern Oregon.  Highs from
     Redmond to Rome will be 20-30 degrees cooler today, than on
     Wednesday, even with some sunshine.

     The upper-level trough will continue to slide east tonight,
     to over southeastern Oregon by early Friday.  Clearing skies
     and a cold air mass will allow temperatures to fall below
     freezing across much of the Willamette Valley overnight, so
     frost-sensitive vegetation may need protection.

Surface Winds:
     NW 5-10 this morning, NW 5-15 this afternoon.
Transport Winds:
     NW 7 this morning, NW 12 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 55.
Humidities:
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 8:08pm; sunrise tomorrow: 6:12am.

Extended Outlook:
     A cold but dry northerly flow aloft is forecast for Friday. 
     After a frosty morning, mostly sunny skies will help
     temperatures recover to near-normal in the afternoon.  It
     will be another locally frosty morning Saturday, with mostly
     clear skies and light winds.  An upper-level disturbance is
     forecast to turn the flow aloft more northwestly by Saturday
     afternoon, which may bring a few more clouds back to the
     region and a slight chance of showers over the northern
     mountains.  The air aloft will cool slightly, with the snow
     level only around 4000 feet.

     A little stronger upper-level impulse is forecast to side
     mainly across eastern Washington and northeastern Oregon on
     Sunday.  That should bring even more clouds to the region
     with a slight chance of showers extending westward to over
     northwestern Oregon.  Snow levels will remain near 4000 feet
     with a chance of snow showers over the northern Cascades and
     mountains of northeastern Oregon.

     The long-range computer models are beginning to show consensus
     and are trending towards the cooler Canadian and European model
     solutions.  Even the American model is showing another cool
     upper-level trough dropping down from Canada, in the northerly
     flow aloft, and setting up camp over the Pacific Northwest for
     the first half of next week. That would keep temperatures near
     normal and maintain a threat of showers...mainly over the northern
     mountains.  I have trended my extended forecast temperatures
     downward and introduced at least a slight chance of showers
     through next Wednesday.

Tomorrow (24 Apr):  Mostly Sunny But Cool.  31/60

Sat (25 Apr):  Partly Cloudy.  Chance of Mountain Showers.  Snow Level 4000 Feet.  32/59

Sun (26 Apr):  Mostly Cloudy.  Slight Chance of Showers.  Snow Level 4000 Feet.  35/58

Mon (27 Apr):  Partly cloudy.  Slight Chance of Showers.  Snow Level 4500 Feet   35/61

Tue (28 Apr):  Partly Cloudy.  Slight Chance of Showers.  Snow Level 4000 Feet.  35/59

Wed (29 Apr):  Partly Cloudy.  Slight Chance of Showers.  Snow Level 4500 Feet.  36/62

Thu (30 Apr):  Partly Cloudy.  A Little Warmer.  38/65

ODA Meteorologist
weather at oda.state.or.us