[willamette-fcst] Forecast - Thursday, January 10th, 2008

Thu Jan 10 09:00:44 PST 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.

Issued: 
     Thursday, January 10th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 3:00pm.
     Straw stack burning is allowed from now until 3:00pm.

Weather Discussion:
     A strong warm front brought rainy and windy conditions to
     Western Oregon overnight.  Strong south winds hit the
     northern and central Oregon Coast again around midnight last
     night.  Some peak gusts along the north coast were:

     Cape Mears (1421 Feet near Tillamook):  71 mph

     CLatsop Spit:  53 mph

     Roacaway Beach:  46 mph

     Winds were generally strongest along the central coast. 
     Here are a few of the peak gusts recorded from that
     region:

     Sea Lion Caves:  65 mph

     Newport (US 101 Bridge):  60 mph

     Florence (Siuslaw Jetty):  58 mph

     Lincoln City:  54 mph

     South winds gusting to near 30 mph brought warmer air into
     the Willamette Valley overnight, with temperatures climbing
     from the low 40s around midnight into the upper 40s by
     mid-morning.  Surface observations and satellite imagery
     indicated that the cold front was moving onshore at
     mid-morning and should sweep eastward to near the Cascades
     by midday.  The air behind the cold front is not that cold,
     so continued breezy south winds should lift valley
     temperatures into the low 50s today with the steady rain
     becoming showery in nature.

     The freezing level over Northwestern Oregon took a huge jump
     overnight from near 3000 feet to nearly 6000 feet.  Snow
     turned to rain over the Northern Cascade passes with pass
     temperatures in the low to mid 30s this morning.  The snow
     level ranges from about 5000 over Northern Oregon to nearly
     7000 feet over Southern Oregon this morning.  It will
     retreat back to about 3500 feet north and 4500 feet south,
     in the wake of the cold front this afternoon.  The cooler
     air aloft and strong onshore flow will combine to bring
     locally heavy snow back to the mountain passes this
     afternoon through tonight.

     The National Weather Service has issued a heavy snow warning
     for the Northern Oregon Cascades from now until until 4 am
     Friday.  The passes could pick up 1-2 feet of of snow by
     Friday morning.  The valley will see very mild temperatures
     along with breezy conditions and rain showers.  Ventilation
     conditions are excellent for burning.

Surface Winds:
     S 15-25 G30 this morning, SSW 10-20 G25 this afternoon.
Transport Winds:
     SW 30 this morning, SW 30 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 90.
High Temperature:
     Salem\'s high temperature today will be near 52.
Humidities:
     Minimum relative humidity will be near 74%.
Sunrise/Sunset:
     Salem sunset tonight: 4:51pm; sunrise tomorrow: 7:49am.

Extended Outlook:
     Showers will taper off Friday as a transitory ridge of high
     pressure moves over the region.  The next weather system is
     expected to be much weaker, as it moves across Oregon
     Saturday with only a little rain and mountain snow likely. 
     Temperatures will remain above normal with snow levels
     staying in the 4-5000 foot range.  Ventilation conditions
     are likely to stay good through Saturday and then
     deteriorate Sunday, as a stronger ridge builds over the
     region.

     The long-range computer models are coming in-line with their
     forecast of the next system moving down the British Columbia
     Coastline and into the region Monday afternoon.  The real
     punch of this system is forecast to stay just north of
     Oregon, but it does appear to be strong enough to bring some
     rain and mountain snow back to the region.  More
     significantly, it signals what now looks to be a significant
     change in the jet stream pattern...

     The long-range models have indication the likelihood of an
     amplification of the jet stream pattern over North America,
     but have been flip-flopping around on the forecast positions
     of the large upper-level ridges and troughs expected to
     develop.  They are now moving towards a consensus solution
     of an amplified ridge offshore, in the eastern Pacific
     Ocean, which will open the door for arctic air to pour into
     the Northern US.

     Some modified cold and dry air is forecast to begin seeping
     into the Pacific Northwest Tuesday and Wednesday, as the
     upper-level flow switches from westerly to northerly.  That
     will bring an abrupt end to the wet and mild conditions west
     of the Cascades.  Temperatures should progressively cool to
     below normal by Wednesday, as more cold and dry air pours
     into the Columbia Basin, from Canada.  Offshore flow is
     likely to develop with the cold and dry air eventually
     getting funneled through the Columbia Gorge and into the
     Willamette Valley.

     This is a weather pattern not typically seen this late in
     the winter season, except during a La Nina episode like we
     are currently experiencing in the tropical Pacific Ocean. 
     That could be why the computer models have been havning a
     tough time forecasting this major change in the weather. My
     confidence in the forecast beyond Monday is still below
     average, but a transition to colder and drier weather
     appears likely.  It is likely that much of the region will
     experience their coldest temperatures so far this winter by
     late next week...especially east of the Cascades.  There is
     also some indication that this may be a prolonged period of
     cold weather, but my confidence in the computer models that
     far out is very low.

Tomorrow (11 Jan):  Decreasing Showers.  Snow Level 4000 feet.  42/49

Sat (12 Jan):  Light Rain Likely.  Snow Level 4500 feet.  37/48

Sun (13 Jan):  Partly Cloudy.  Areas of Fog.  35/47

Mon (14 Jan):  Increasing Clouds.  Light Rain Likely...Mainly North.  33/47

Tue (15 Jan):  Partly Cloudy.  32/42

Wed (16 Jan):  Partly Cloudy.  28/37

Thu (17 Jan):  Mostly Sunny.  25/35

ODA Meteorologist
weather at oda.state.or.us