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

Thu May 8 10:59:52 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: 
     Thursday, May 8th, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:30pm.
     Straw stack burning is allowed from now until 6:30pm.

Weather Discussion:
     The Pacific Northwest is under the influence of a very cool
     but generally dry northwesterly flow aloft.  Marine low
     clouds were persistent across the Willamette Valley
     Wednesday and held afternoon temperatures in the mid 50s (10
     degrees below normal).  The low clouds also held valley
     temperatures up in the low 40s overnight.  The air aloft was
     even colder this morning than it was Wednesday morning with
     the freezing level over Salem measured at just 3100 feet.

     The late-morning ODA surface analysis continued to show high
     pressure centered just off the Central Oregon Coast this
     morning with onshore flow across Washington and Oregon. 
     Mostly cloudy skies covered Western Washington and NW
     Oregon, with local areas of drizzle.  Skies were mostly
     sunny over much of SW Oregon and east of the Cascades, much
     like they were Wednesday.  Valley temperatures were near 50
     degrees late this morning with readings ranging from the mid
     40s to the mid 50s over the rest of the state.

     The onshore flow is a little weaker than it was Wednesday. 
     Visible satellite pictures show less expansive marine low
     clouds over Western Oregon compared with Wednesday, so some
     partial clearing is possible this afternoon. However, an
     upper-level disturbance was just offshore late this morning
     and will rotate inland later this afternoon.  That will
     combine with daytime heating to destabilize the atmosphere
     and help cumulus clouds develop across the state.  There is
     a slight chance of a shower, mainly near the mountains,
     later this afternoon and evening, but a stable layer of air
     aloft should keep cloud-tops over the valley from going much
     above the mixing height of 6000 feet.

     Willamette valley temperatures will likely stay in the mid
     50s again today, due to continued onshore flow, mostly
     cloudy skies, and cold air aloft.  Even with more sunshine,
     temperatures east of the Cascades will only climb into the
     upper 50s and 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.  Many of the higher valley locations,
     east of the Cascades, will dip below the freezing mark overnight.

Surface Winds:
     NW 7-12 this afternoon.
Transport Winds:
     NW 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 6000 feet.  Ventilation index 72.
High Temperature:
     Salem\'s high temperature today will be near 56.
Humidities:
     Minimum relative humidity will be near 49%.
Sunrise/Sunset:
     Salem sunset tonight: 8:27pm; sunrise tomorrow: 5:50am.

Extended Outlook:
     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.  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, ahead of the front, Saturday and then drop back below
     normal as a stronger upper-level trough brings a few showers
     to the region Sunday.  

     The showers will end Monday, as the upper-level trough
     pushes into Montana and Idaho, and high pressuer being
     building over Oregon.  A warm front is forecast to bring
     clouds and perhaps light rain as far south as Northwestern
     Oregon Tuesday, but that will be the last threat of rain for
     awhile...

     An unseasonably warm upper-level ridge is forecast to build
     over the Pacific Northwest, beginning late Tuesday, for
     sunny and much warmer weather during the second half of next
     week.  It now appears that we will get a taste of
     summer-like weather with strong offshore surface flow and
     Willamette Valley temperatures shooting well into the 80s as
     early as next Thursday.  If the upper-level ridge ends up
     being as strong as currently forecast, then we could be in
     for a day or two of near record high temperatures next
     Friday and/or 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.  40/63

Tue (13 May):  Chance of Light Rain North.  Partly Cloudy South.  45/65

Wed (14 May):  Becoming 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