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

Mon May 12 11:16:35 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.

NOON UPDATE

Issued: 
     Monday, May 12th, 2008 at 12:00pm.

...Next Update 9 am Tuesday, May 13th, 2008...

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 eastward by late this
     morning and extended from Central Montana through Nevada.  A
     drier northwesterly flow aloft prevailed over Oregon.  Some
     clouds were still circulating into NE Oregon, with mostly
     sunny skies across the remainder of Central and Eastern Oregon.
     Temperatures there ranged from the mid 40s to the mid 50s.  
     West of the Cascades, a fair amount of low cloudiness was 
     persisting along the north coast and in the Northern Willamette
     Valley, north of about Salem, with mostly sunny skies elsewhere.
     Willamette Valley temperatures were in the mid 50s.

     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 38 degrees, early this morning, while
     Hillsboro and Eugene dipped to 37.  Many areas east of the
     Cascades fell below the freezing mark.  Redmond was the cool
     spot in the state this morning at 21 degrees.

     The ODA surface analysis showed high pressure centered over
     the Willamette Valley...making for very weak pressure
     gradients and light winds.  Onshore gradients were stronger
     east of the Cascades with westerly winds in the 15-25 mph
     range common.  Infrared satellite pictures showed mid and
     high clouds already pushing onshore at midday, in response
     to an apporaching warm front, so sunshine will become
     filtered this afternoon across Western Oregon.

     The low clouds in the north valley should continue to break
     up this afternoon.  Temperatures should 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.

     The approaching warm front is forecast to bring some light
     rain to Western Washington Tuesday.  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 for one more day.  It
     still appears as if we will get a taste of summer during the
     second half of the week...

Surface Winds:
     N 5 this afternoon.
Transport Winds:
     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 as early as Thursday afternoon.
     Temperatures will become progressively warmer each day.

     Willamette Valley highs may shoot well into the 80s by
     Thursday.  It appears that the warmest day will be Friday,
     west of the Cascades, and Saturday for Eastern Oregon. 
     Strong offshore flow and very warm air aloft could push
     Friday afternoon temperatures to near record values across
     much of Western Oregon.  Saturday could be a record-breaker
     east of the Cascades.

     The upper-level ridge, and associated surface thermal
     trough, are forecast to push east of the Cascades Saturday. 
     Cooling onshore winds should cap Saturday afternoon 
     temperatures in the low 80s across the Willamette Valley.

     The cooling trend is forecast to progress eastward, across
     Central and Eastern Oregon, Sunday, with increasing onshore
     flow west of the Cascades cooling temperatures back to near
     normal.  A strong westerly jet stream is forcast to bring
     back a chance of rain to Western Oregon by Monday evening.

Tomorrow (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.  Chance of Rain Late.  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