[willamette-fcst] Forecast - Thursday, November 13th, 2008

[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.

Issued: 
     Thursday, November 13th, 2008 at 9:00am.

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

Weather Discussion:
     A cold front, laden with tropical moisture, moved southward
     across Washington Wednesday afternoon, dumping more than
     three inches of rain in sections of southwestern Washington.
     Heavy rain also fell along the Oregon Coast and in the
     Cascades, where one and one-half to three inches of rain were
     common.  Astoria recorded three and one-third inches of rain
     in the past 24 hours, and Timberline Lodge picked up three
     and one-half inches.  Meacham, in the northeast mountains,
     picked up over an inch of rain.

     The front lost strength, as it moved across Oregon overnight
     but was still was able to drop between one-half and one inch
     of rain over the Willamette Valley.  The ODA surface analysis
     showed the cold front extending from southwestern Idaho across
     southern Oregon at mid-morning.  Light rain was falling near
     the front, but skies were beginning to clear over the northern
     half or Oregon.  The brisk southerly winds of the past couple
     of days decreased and turned northwesterly, in the wake of the
     cold front this morning.

     Cooler air was moving over northern Oregon this morning. 
     The freezing level over Salem early this morning had only
     dropped to 8200 feet, but that has likely continued to come
     down.  The 6000-foot temperature at Timberline Lodge cooled
     from near 40 degrees Wednesday afternoon to 30 degrees by
     this morning.  Valley temperatures also staring to cool off
     this morning with some spots dipping into the upper 40s.

     A major change, to a drier weather pattern, will begin
     today.  A bulding upper-level ridge of high pressure, just
     off the west coast, is turning the flow aloft northwesterly
     and shutting off the tropical moisture tap.  Some sunshine
     was brightening things up this morning across the valley, even
     through temperatures were running close to 10 degrees cooler
     than yesterday at this time.

     A little sunshine should help temperatures climb into the upper
     50s this afternoon, even with cooler air aloft.  Northwesterly
     surface and transport winds will become more northerly later this
     afternoon, as high pressure continues to build over the region.

Surface Winds:
     NW 5-10 this morning, NNW 5-10 this afternoon.
Transport Winds:
     NW 10 this morning, N 7 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 25.
High Temperature:
     Salem\'s high temperature today will be near 59.
Humidities:
     Minimum relative humidity will be near 57%.
Sunrise/Sunset:
     Salem sunset tonight: 4:45pm; sunrise tomorrow: 7:09am.

Extended Outlook:
     The strengthening upper-level ridge is forecast to move
     directly over Oregon Friday through Sunday, with weak
     weather systems riding over the top of it across Washington
     and southern British Columbia.  Northerly surface flow may
     turn slightly offshore for further drying of the air mass.
     The freezing level will likely jump back over 10,000 feet,
     with low-level temperature inversions developing.  Light
     easterly winds, near the Columbia Gorge, will help to clear
     morning fog from the north valley, but fog could be fairly
     persistent in the south valley.

     Weekend temperatures will vary considerably, depending on
     the extent and duration of valley fog. The Cascade
     foothills, coast range, and sections of the coast could be
     much warmer than in the Willamette Valley, due to low-level
     temperature inversions.  The air aloft will be warm enough
     to support afternoon surface temperature well above 60
     degrees, for areas that escape the fog.  Fair skies and
     light winds will lead to colder overnight temperatures with
     much of the valley dropping into the 30s the next few nights.

     The ridge if forecast to weaken and shift far enough east to
     allow a weak cold front to approach the coastline late
     Monday.  This system will likely weaken considerably, as it
     comes onshore early Tuesday, but it may be strong enough to
     bring a little rain to western Oregon and break up the fog.
 
     A transitory weak ridge is forecast to dry things out Wednesday,
     with less valley fog formation due to increasing offshore flow.
     A stronger weather system is forecast bring rain, cooler temperatures,
     and perhaps blustery conditions back to western Oregon next Thursday. 
     Snow levels may drop to the Cascade passes by late Thursday, which
     would be welcome news for the ski industry but create winter driving
     conditions over the mountain passes.

Tomorrow (14 Nov):  Morning Fog.  Afternoon Clearing...Mainly North.  36/54

Sat (15 Nov):  Morning Fog.  Afternoon Clearing...Mainly North.  37/57

Sun (16 Nov):  Morning Fog.  Afternoon Clearing...Mainly North.  39/58

Mon (17 Nov):  Increasing Clouds.  Chance of Light Rain Late.  41/59

Tue (18 Nov):  Chance of Light Rain Early.  Becoming Partly Cloudy.  43/53

Wed (19 Nov):  Areas of AM Fog...Becoming Mostly Sunny.   35/56

Thu (20 Nov):  Increasing Rain and Wind.  Snow Level Dropping to 4000 Feet.  40/51

ODA Meteorologist
weather at oda.state.or.us