[willamette-fcst] Forecast - Thursday, September 24th, 2009

[Willamette Valley Ag/Burning Forecast]

Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

...Next Update Not Until Monday, September 28th, 2009 at 9:00am...

NOON UPDATE

Issued: 
     Thursday, September 24th, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 2:00pm until 6:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     Southwesterly flow aloft has shifted the smoke plumes, from
     the southern Oregon Cascade wildfires, eastward to over
     north-central Oregon today. Late-morning visible satellite
     imagery showed the smoke plumes being directed northeastward
     across the central Cascades, north-central Oregon, and
     eastern Washington. Marine low clouds were beginning to
     break up across the Willamette Valley with sections of the
     coastline also starting to get some clearing. Skies were
     mostly clear over southwestern, south-central, and eastern Oregon.

     The ODA surface analysis showed the surface thermal trough
     stretching from eastern Washington through central Oregon,
     with a much cooler northerly flow increasing across the
     Willamette Valley.  North winds had already increased to
     around 10 mph from Corvallis to Eugene.  Temperatures were
     mostly in the mid 60s from the coast eastward across the
     Willamette Valley.

     A dissipating cold front brought some sprinkles to the north
     coast this morning, with Astoria recording .01 inches. 
     Northerly winds will increase across western Oregon this
     afternoon, as a very weak upper-level trough moves onshore. 
     Even through the air aloft is still very warm, valley highs
     will only climb into the mid to upper 70s today, due to the
     strong influx of low-level cool marine air.  That will also
     keep mixig heights from climbing much above 3000 feet this afternoon.

Surface Winds:
     N 10-15 G20 this afternoon.
Transport Winds:
     N 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3300 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 78.
Humidities:
     Relative humidity drops to 50% around 2pm.
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 7:05pm; sunrise tomorrow: 7:03am.

Extended Outlook:
     The upper-level ridge is forecast to rebuild over the region
     Friday but not as strongly as earlier this week.  Low-level
     winds should stay northerly with a full day of sunshine
     warming valley temperatures back into the low 80s.  Warm air
     aloft will make for continued fairly low mixing heights. A
     weak weather system will slide across southern British
     Columbia, flattening the upper-level ridge a bit, on
     Saturday.  That will increase the onshore flow and cool
     temperatures back into the mid to upper 70s.

     The ridge is forecast to rebuild over the region Sunday with
     a thermal trough building northward along the Oregon Coast. 
     That will turn low-level winds offshore and warm valley
     temperatures to as high as the mid 80s.  The warm-up will be
     short-lived, however, with a fairly strong upper-level
     trough forecast by all of the long-range computer models to
     approach the coastline Monday. Increasing southwesterly flow
     aloft will force the surface thermal trough east of the
     Cascades with increasing onshore flow cooling temperatures
     back to near-normal.  That could be a burning opportunity,
     if any fields become available for burning.

     An autumn-like cold front is forecast to come onshore Monday
     night with light rain likely by Tuesday morning along with
     much cooler temperatures.  A drier but cool northwesterly
     flow aloft is forecast for next Wednesday and Thursday.

Tomorrow (25 Sep):  Sunny.  North Winds.  46/82

Sat (26 Sep):  Sunny.  A Touch Cooler.  NW Winds.  46/78

Sun (27 Sep):  Sunny and Warmer.  NE Winds.  45/85

Mon (28 Sep):  Increasing Clouds and Onshore Flow.  Chance of Rain Late.  47/74

Tue (29 Sep):  Light Rain Likely Early...Showers in the Afternoon.  Cool.  50/65

Wed (30 Sep):  Mostly Cloudy AM.  Afternoon Clearing.  44/66

Thu (01 Oct):  Partly Cloudy.  44/68

ODA Meteorologist
weather at oda.state.or.us