[willamette-fcst] Forecast - Monday, May 12th, 2008

Mon May 12 08:00:34 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: 
     Monday, May 12th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     A weak cold front moved across Oregon Saturday with onshore
     flow and scattered sprinkles across the state.  Willamette
     Valley temperatures were near normal Saturday with highs in
     the low to mid 60s.  A cool upper-level trough brought
     scattered light showers and cooler temperatures to the state
     Sunday.  Highs Sunday were only in the mid to upper 50s
     along the Oregon Coast and in the Willamette Valley. Southwest,
     Central, and Eastern Oregon temperatures Sunday ranged from
     the mid 50s to the mid 60s.

     The upper-level trough had moved to over Idaho by this morning
     with northwesterly flow aloft over Oregon.  A few showers
     will still circulating around this system into Eastern
     Washington and Eastern Oregon.  West of the Cascades, a fair
     amount of low cloudiness was persisting in the Northern
     Willamette Valley with a few light showers.  The south
     valley had partly sunny skies.  The ODA surface analysis
     showed high pressure over Western Oregon with weak pressure
     gradients across the Willamette Valley.  Gradients were stronger
     from the Cascades to the Idaho Border with westerly winds gusting
     to about 25 mph in the Columbia Basin near Pendleton.

     The air mass over Oregon is quite cool with the freezing
     levels measured over Salem and Medford early this morning at
     just 3800 feet and 4600 feet respectively.  Partial clearing
     allowed Willamette Valley temperatures to locally drop into
     the upper 30s overnight.  McMinnville, Salem, and Corvallis
     all dropped to at least 38 degrees early this morning and
     Hillsboro dipped to at least 37.  Many areas east of the
     Cascades fell below the freezing mark.  Redmond was the cool
     spot in the state this morning at 23 degrees.

     The showers will end today, as the upper-level trough pushes
     into the Northern Rockies and high pressure begins building
     over Oregon.  Partly sunnny skies will help temperatures
     recover into the low 60s across the Willamette Valley this
     afternoon.  Weak surface pressure gradients and light
     transport winds will make for poor ventilation conditions
     over the Willamette Valley today, in spite of relatively
     high mixing heights this afternoon.

     As an upper-level ridge of high pressure continues to push
     onshore Tuesday, a warm front is forecast to bring some
     light rain to Western Washington.  Considerable mid and high
     clouds will cover Oregon with a chance of light rain over the
     northern half of the state.  Even with warming aloft, cloudy
     skies will keep surface temperatues near or below normal across
     Western Oregon Tuesday.  It still appears as if we will get a
     taste of summer during the second half of the week...

Surface Winds:
     Var 0-4 this morning, N 5 this afternoon.
Transport Winds:
     Var 3 this morning, NNW 5 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 25.
High Temperature:
     Salem\'s high temperature today will be near 62.
Humidities:
     Minimum relative humidity will be near 46%.
Sunrise/Sunset:
     Salem sunset tonight: 8:32pm; sunrise tomorrow: 5:45am.

Extended Outlook:
     An unseasonably strong upper-level ridge is forecast to
     bring sunny and much warmer weather to all of Oregon later this week.
     Onshore flow Tuesday will turn northerly Wednesday and offshore by Thursday
     afternoon.  Temperatures will become progressively warmer each day.

     Willamette Valley highs may shoot well into the 80s by Thursday.
     The warmest day, west of the Cascades, appears to be Friday, with
     strong offshore flow helping temperatures climb to near record values
     across much of Western Oregon.

     The upper-level ridge, and associated surface thermal
     trough, are forecast to push east of the Cascades Saturday.
     That would shift the warmest weather to Central and Eastern
     Oregon with cooling onshore winds moving back into Western Oregon.

     The cooling trend should progress eastward, across
     Central and Eastern Oregon, Sunday, with increasing onshore flow
     west of the Cascades.  A strong westerly jet stream is forcast
     to return more typical weather to the region by Monday.

Tue (13 May):  Mostly Cloudy North...Slight Chance of Rain.  Partly Cloudy South.  42/65

Wed (14 May):  Becoming Mostly Sunny and Warmer.  49/74

Thu (15 May):  Sunny and Unseasonably Warm.  50/84

Fri (16 May):  Sunny with Possible Record High Temperatures.  54/91

Sat (17 May):  Sunny and Very Warm.  55/83

Sun (18 May):  Mostly Cloudy and Much Cooler.  48/68

Mon (19 May):  Mostly Cloudy.  46/66

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