[willamette-fcst] Forecast - Thursday, May 8th, 2008

Thu May 8 16:03:06 PDT 2008

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, May 8, 2008 at 4:45pm.

Burn Advisory For Friday, May 9, 2008:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 6:30pm.
     Straw stack burning is allowed from 11:00am until 6:30pm.

Weather Discussion:
     The Pacific Northwest is under the influence of a very cool
     but generally dry northwesterly flow aloft.  The air mass is
     cold for this time of the year.  The freezing level was measured
     over Salem this morning at just 3100 feet.

     The late-afternoon ODA surface analysis continued to show high
     pressure centered just off the Central Oregon Coast with onshore
     flow across Washington and Oregon.  Mostly cloudy skies covered
     Western Washington and NW Oregon, but no rain was being reported.
     Clouds were increasing over SW Oregon and east of the Cascades, in
     response to an upper-level disturbance moving onshore.  Willamette
     Valley temperatures were only in the low to mid 50s...more than 10
     degrees below normal.  Readings east of the Cascades were generally
     in the upper 50s to mid 60s.

     Skies will stay mostly cloudy overnight across NW Oregon, but partial
     clearing and cold air aloft could combine to locally drop valley
     temperatures to the mid 30s by Friday morning.  Most likely the minimums
     will stay near 40 degrees.  However, many of the higher valley locations,
     east of the Cascades, will dip below the freezing mark overnight.

     After a chilly and mostly cloudy start Friday, a weak ridge of high
     pressure should clear skies in the afternoon with temperatures
     recovering to near normal across the Willamette Valley.  Transport winds
     will be fairly light and begin to turn more northerly, so stack burning
     is allowed only after 11am. 

Surface Winds:
     WNW 0-4 Friday morning, NNW 4-8 Friday afternoon.
Transport Winds:
     NW 4 Friday morning, NNW 8 Friday afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height Friday will be near 4200 feet.  Ventilation index 34.
High Temperature:
     Salem\'s high temperature Friday will be near 65.
Humidities:
     Minimum relative humidity will be near 35%.
Sunrise/Sunset:
     Salem sunset tonight: 8:27pm; sunrise Friday: 5:50am; sunset Friday: 8:28pm.

Extended Outlook:
     A weak cold front is forecast to approach the coastline Saturday
     with a chance of light rain moving onshore by late afternoon.
     Temperatures will likely be mild Saturday, before dropping back below
     normal Sunday, as a stronger upper-level trough brings in a few showers.  

     The showers will end Monday, as the upper-level trough pushes
     into Montana and Idaho, and high pressure begins building over Oregon.
     A warm front is forecast to bring some clouds to mainly northern
     Oregon Tuesday with rain most likely staying north of the state.

     An unseasonably warm upper-level ridge is forecast to bring sunny
     and much warmer weather to the region during the second half of next
     week.  Strong offshore flow may help Willamette Valley temperatures
     shoot well into the 80s by Thursday.  We could even see one day 
     near or above 90 degrees, on Friday, with a cooling trend beginning Saturday.  

Tomorrow (09 May):  Becoming Partly Cloudy.  36/65

Sat (10 May):  Increasing Clouds.  Chance of Light Rain Late...Mainly North.  40/67

Sun (11 May):  Chance of Showers and Cooler.  Snow Level Dropping to 3-4000 Feet.  43/58

Mon (12 May):  Mostly Cloudy.  Chance of a Shower Early...Afternoon Clearing.  37/63

Tue (13 May):  Partly Cloudy and Warmer.  42/65

Wed (14 May):  Mostly Sunny and Warmer.  46/75

Thu (15 May):  Sunny and Unseasonably Warm.  50/85

Fri (16 May):  Sunny and Unseasonably Warm.  54/91

ODA Meteorologist
weather at oda.state.or.us

The following is the forecast page from the latest montly update of the ODA
Seasonal Climate Forecast.  The complete forecast is available on the ODA
website at http://oregon.gov/ODA/NRD/weather.shtml#Weather_forecasts

Seasonal Climate Forecast
May through August, 2008

Issued:  May 7, 2008

Purpose:  To provide Oregon farmers and growers with a seasonal climate
outlook that is more accurate than assuming average conditions will prevail.

Basis of Forecast:  Changes in Sea-Surface Temperatures (SST) in the
Tropical Pacific Ocean have been closely linked with subsequent changes in
world-wide weather patterns.  Modern technology makes it possible to accurately
track changes in ocean temperatures.  I compare the current tropical SST structure
(including the evolution since the previous winter) with former years to find the
best matches (analogs).  Using historical data from these analogs, I am able to
construct a climate forecast for the upcoming season.

Accuracy:  Over the past decade, using historical records, from analog years,
to create a climate forecast has proven more accurate than simply forecasting average
conditions.  The accuracy of the forecast increases during El Nino and La Nina events,
because the resultant weather pattern changes are more identifiable and affect the
local climate in fairly consistent ways.

Limitations of Forecast:  Long-range climate forecasts are fundamentally
different from short-term weather forecasts derived from dynamic computer models.
Rather than getting specific, the goal of this product is to forecast general trends
in the local climate during the upcoming season.

Forecast:  La Nina conditions, in the Tropical Pacific, have been weakening
since mid-February.  La Nina is expected to continue to weaken with El Nino-Southern
Oscillation (ENSO) neutral conditions possible by July.  It should be noted that the
link between ENSO and the Pacific Northwest Climate is not as pronounced in the
summer as it is during the other seasons.

The following May through August climate predictions are based on historical weather
data from the top three analog years (1971, 1974, and 1989) with extra weight given
to the top analog year of 1971:

Below normal temperatures in May that will trend to near normal in June and July
(above normal eastern zones).  Above normal temperatures in August, especially eastern zones.

Precipitation generally near or slightly below normal.  The best chance for above normal
precipitation is in June.  The coastal zone may stay slightly damp.

Increased chance of late-season frost damage to crops east of the Cascades.

Your feedback is encouraged to help us maximize the utility of this service.

Pete Parsons - Meteorologist - Oregon Department of Agriculture
(503) 986-4701, pparsons at oda.state.or.us