[willamette-fcst] Forecast - Friday, December 12th, 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.

NOON UPDATE

...Corrected Extended Forecast...

...Next Update Scheduled For 9 am Tuesday, December 16th, 2008...

Issued: 
     Friday, December 12th, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 2:30pm.
     Straw stack burning is allowed from now until 2:30pm.

Weather Discussion:
     A highly advertised change in the weather pattern is
     underway, with an amplifying upper-level ridge of high
     pressure, in the Gulf of Alaska, sending a strong and cold
     weather system down the British Columbia coastline towards
     the Pacific Northwest.  After many days with stagnant
     weather conditions, increasing southerly winds and rapid
     cooling aloft will combine to greatly improve ventilation
     across western Oregon today.

     Satellite imagery and surface observations indicate a
     rapidly strengthening low-pressure system was centered just
     off the northern Washington coast late this morning.  A
     broad cloud-shield extended across all of Washington and
     Oregon.  Doppler radar and surface reports indicate that
     olcally heavy rain was moving into northwest Oregon along
     with strong south winds. The ODA surface analysis showed
     rapidly increasing southerly gradients across western
     Oregon.  Southerly winds were gusting to about 30 mph in the
     northern and central Willamette Valley and to about 40 mph
     along the northern and central Oregon coast.

     The low-pressure center is forecast to continue to
     strengthen and move inland, to near Seattle, by late this
     afternoon and into eastern Washington tonight.  That strom
     track will bring increasingly strong south and southwesterly
     winds to western Oregon and southwestern Washington this
     afternoon through tonight.  The National Weather Service has
     issued a High Winds Warning for the northern and central
     Oregon coast and coastal range, for gusts to 65 mph, through
     tonight.  A Wind Advisory has been issued for the Willamette
     Valley, through tonight, for gusts to 45 mph.  The strongest
     valley winds will likely be from Salem north to Portland. 
     Gusts to 50 mph are possible, in the Portland area, later
     this afternoon through early this evening.

     A strong cold front will bring increasing rain to western
     Oregon this afternoon.  Snow levels have already dropped to
     about 4000 feet, with ODOT road cameras showing accumulating
     snow over the Cascade passes.  Snow levels will drop at
     least down to 1000 feet tonight. Valley highs should only
     climb into the mid 40s.  Heavy snow and strong winds will
     make for blizzard conditions, at times, in the Cascade
     passes through tonight.  A Blizzard Warning has been issued
     for the Cascade passes through Saturday morning.  Winter
     Storm Warnings have been issued, for the Cascade foothills
     and coastal passes, for this afternoon through Saturday.

     The latest National Weather Service forecasts, watches, and
     warnings may be accessed at:

     http://www.wrh.noaa.gov/pqr/

     By tonight, cold instability showers may locally drop snow
     levels to near 500 feet across western Oregon.  Some snow
     accumulations are possible in the higher hills of the
     northern and central Willamette Valley.  Brisk southwesterly
     winds should keep overnight temperatures in the mid 30s on
     the valley floor, where roads should stay mainly wet and
     accumulating snow is not expected...yet...

Surface Winds:
     SSW 15-30 G45 this afternoon.
Transport Winds:
     SSW 45 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3400 feet.  Ventilation index 153.
High Temperature:
     Salem\'s high temperature today will be near 46.
Humidities:
     Minimum relative humidity will be near 68%.
Sunrise/Sunset:
     Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:42am.

Extended Outlook:
     In the wake of the cold front, cold and unstable
     northwestery flow aloft will bring heavy snow showers to
     both the coastal and Cascade passes Saturday and Sunday.
     Total snow accumulations could exceed two feet over the
     Cascade passes with up to a foot of snow over the coast
     range passes.  Be prepared for extreme winter driving
     conditions over any mountain passes this weekend.

     Cold Arctic air will slowly sag southward, into Washington,
     Saturday and through the Columbia Gorge into Portland as
     early as Saturday night. Ahead of the Arctic cold front, The
     surface winds will be coming from off the relatively warmer
     ocean, so snow levels will likely remain above the valley
     floor. Sticking snow will probably get as low as 500 feet
     Saturday in the north valley and 500-1000 feet in the south valley.

     The snow level will drop to the valley floors, from north to
     south, Saturday night through Sunday, as the cold Arctic air
     begins pouring directly into the valley, via the Columbia
     Gorge.  The Arctic cold front has the potential to bring the
     most significant snow accumulations to the Willamette Valley
     floor since January, 2004.  Accumulating snow, on the valley
     floors, is likely Sunday through early Monday with several
     inches possible.

     Drier and cold Canadian air will continue to move into the
     region Sunday night and Monday, with snow showers tapering
     off and temperatures dropping well below freezing.  Brisk
     easterly winds will develop in the Portland area with
     northerly winds in the remainder of the valley.  The next
     weather system is forecast to drop down the British Columbia
     coastline around the middle of next week.  With cold air
     already in place, precipitation from that system will fall
     in the form of snow.  It is still too far out to forecast
     how much snow may fall, but it is looking more likely that
     the valley will get another measurable snowfall late Wednesday
     and Thursday of next week, with more cold weather to follow.

Tomorrow (13 Dec):  Rain or Snow Showers.  Snow Level 500-1000 Feet.  35/41

Sun (14 Dec):  Snow.  Valley Accumulations Likely.  32/34

Mon (15 Dec):  Decreasing Snow Showers.  Clearing and Turning Much Colder.  23/28

Tue (16 Dec):  Mostly Sunny and Cold.  12/25

Wed (17 Dec):  Snow Likely Late.  12/28

Thu (18 Dec):  Snow Likely...Decreasing Late.  24/28

Fri (19 Dec):  Snow Ending...becoming Partly Cloudy. Continued Cold.  17/23

ODA Meteorologist
weather at oda.state.or.us