[willamette-fcst] Forecast - Thursday, October 22nd, 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.

      The October Update of the ODA Seasonal Climate Forecast is Available at:
              http://oregon.gov/ODA/NRD/weather.shtml#Weather_forecasts

Issued: 
     Thursday, October 22nd, 2009 at 9:00am.

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

Weather Discussion:
     An active cold front spread rain across vitually all of
     western Oregon and the northern half of central and eastern
     Oregon on Wednesday.  Rainfall amounts were greatest to the
     north and west, with the extreme north coast picking up over
     an inch.  About one-quarter to one-half inch of rain fell
     along the central coast...decreasing to about one-tenth of
     an inch on the south coast.  The northern Willamette Valley
     received about one-quarter of an inch, with amounts tapering
     off to as low as one-tenth of an inch in the south valley. 
     Around one-tenth of an inch of rain, or less, fell from
     north-central to northeastern Oregon, with conditions
     remaining dry over southeastern Oregon.

     Rain tapered off Wednesday afternoon across western Oregon
     with partly sunny skies and fairly warm air aloft helping
     temperatures climb into the low to mid 60s.  Continued
     clearing overnight, combined with the recent rainfall and
     light winds, lead to the widespread formation of fog across
     western Oregon by this morning.  Visibilities were locally
     below one-quarter of a mile throughout the Willamette Valley.

     The mid-morning ODA surface analysis showed high pressure
     extending from western Washington into north-central Oregon
     with weak northeasterly gradients across western Oregon. 
     Surface reports showed offshore winds at around 5 mph or
     less.  Temperatures were mostly in the upper 40s and low
     50s.  Hillsboro was the exception with a bone-chilling
     reading of just 39 degrees.

     A transitory upper-level ridge will move over Oregon and
     Washington this afternoon, with warm air aloft and light
     winds helping to maintain the low-level temperature
     inversion.  Satellite imagery showed the widespread valley
     fog across western Oregon.  In addition, high clouds from
     the next weather system were already advancing onto the
     Washington and northern Oregon coastlines.

     The air aloft is still very warm, with the freezing level
     over Salem measured this morning at 11,500 feet.  High
     temperatures will vary, depending on the local duration of
     fog.  Most of the Willamette Valley should climb into the
     low 60s, with some areas possibly reaching the mid 60s. High
     and mid-level clouds should be thickening, when the fog
     finally does begin to break up this afternoon.  A few
     sprinkles are even possible along the extreme north coast by
     late this afternoon.

Surface Winds:
     NE 0-5 this morning, Var 0-5 this afternoon.
Transport Winds:
     NE 3 this morning, Var 4 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 6.
High Temperature:
     Salem\'s high temperature today will be near 62.
Humidities:
     Minimum relative humidity will be near 62%.
Sunrise/Sunset:
     Salem sunset tonight: 6:15pm; sunrise tomorrow: 7:39am.

Extended Outlook:
     The next weather system is forecast to spread more rain
     across western Oregon Friday.  Rainfall amounts could exceed
     one-half inch along the north coast and one-third of an inch
     in the northern Willamette Valley.  Rainfall totals will
     taper off to to south, but even the southern Willamette
     Valley should pick up between one-tenth and one-quarter of
     an inch.  Some rain will also spread across central and
     eastern Oregon Friday afternoon...perhaps making it all the
     way to the southeastern corner of the state by Friday night.

     The rain should taper off Friday night, across western
     Oregon, with areas of fog forming by Saturday morning.  A
     transitory ridge of high pressure will likely bring some
     clearing Saturday afternoon through early Sunday, which will
     likely lead to at least patchy fog formation again Sunday morning.

     The next weather system is forecast to swing more rain
     onshore Sunday afternoon.  The storm track is forecast to
     sag southward, over Washington and Oregon, late Sunday
     through Tuesday.  Colder air aloft will drop the snow level
     down to the northern Cascade passes by Monday afternoon.
     Strong northwesterly flow aloft is forecast next Tuesday and
     Wednesday, which will dry things out but keep temperatures
     below normal.  A more vigorous system is forecast to come
     onshore next Thursday.

Tomorrow (23 Oct):  Areas of AM Fog.  Increasing Clouds.  PM Rain Developing.  48/61

Sat (24 Oct):  AM Fog.  Partial Afternoon Clearing.  43/62

Sun (25 Oct):  Areas of AM Fog.  Rain Developing by the Afternoon.  41/60

Mon (26 Oct):  Rain Turning to Showers.  Snow Level Dropping to 4000 Feet.  45/57

Tue (27 Oct):  Showers Ending Early.  Clearing and Cool.  Snow level 4000 Feet.  40/56

Wed (28 Oct):  Areas of AM Fog. Partly Sunny and Cool. Slight Chance Sprinkles North. 39/57

Thu (29 Oct):  Rainy and Possibly Windy.  Snow Level Dropping to 3000 Feet Late.  42/59

ODA Meteorologist
weather at oda.state.or.us