[willamette-fcst] Forecast - Thursday, March 5th, 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.

Issued: 
     Thursday, March 5th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 4:00pm.
     Straw stack burning is allowed from now until 4:00pm.

Weather Discussion:
     Daytime heating combined with cold air aloft to trigger
     numerous showers across western Oregon Wednesday afternoon. 
     Rainfall amounts varied from only a trace (Salem Airport),
     to one-third of an inch.  The heavier totals were in the
     Cascade foothills of Lane County.  Most of the Willamette
     Valley received less than one-tenth of an inch.  There were
     also reports of small hail in the vigorous showers Wednesday
     afternoon.

     A quite cold system dropped southward into the region, from
     southern British Columbia, overnight and early this morning.
     Increasing clouds and southerly winds held minimum
     temperatures in the upper 30s and low 40s across the
     Willamette Valley.  The ODA surface analysis showed a cold
     front extending from low-pressure center over northeastern
     Washington westward to near Seattle.  To the south of the
     front, fairly tight pressure-gradients were resulting in
     brisk south-southwesterly winds across the northern
     two-thirds of Oregon.

     The main energy from this system is
     aimed at extreme eastern Washington and northern Idaho, so
     the strongest winds, in Oregon, were blowing across the
     northeastern section of the state.  Southwesterly winds were
     gusting over 30 mph in the Columbia Basin from Hermiston to
     Pendleton, with gusts to 25 mph all the way south and east
     to Rome, Oregon.  Southerly winds in the Willamette
     generally in the 10-20 mph range.

     Satellite imagery showed cloudy skies covering Washington
     and Oregon.  Doppler radar and surface reports indicated
     that rain had spread southward across across Washington and
     the northern half of Oregon.  Rain had spread south to
     Eugene by mid-morning.  Morning rainfall amounts so far have
     been less than one-tenth of an inch across the Willamette
     Valley.  The air mass is still quite cold with the freezing
     levels over Salem and Medford measured at just 3400 and 2600
     feet respectively early this morning.  That puts the snow
     level at 2-3000 feet over Oregon this morning, and it will
     hold steady or drop a little more during the day.

     Winter Weather Advisories are in efefct for the northern
     Cascade passes, through 6pm, where more than 6 inches of new
     snow are likely.  ODOT road cameras showed snow-packed
     Cascade passes this morning, with a couple of inches of new
     snow already.  Pass temperatures were only in the mid 20s,
     with gusty winds making for poor driving conditions.  Around
     one-quarter of an inch of rain is expected across the
     Willamette Valley today, with the steady rain tapering off
     to showers later this afternoon and tonight.  Fairly high
     mixing heights and westerly transport winds will make for
     good ventilation conditions today.

Surface Winds:
     SW 10-20 G25 this morning, W 10-20 G25 this afternoon.
Transport Winds:
     SW 25 this morning, W 25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 75.
High Temperature:
     Salem\'s high temperature today will be near 47.
Humidities:
     Minimum relative humidity will be near 63%.
Sunrise/Sunset:
     Salem sunset tonight: 6:05pm; sunrise tomorrow: 6:40am.

Extended Outlook:
     Showers will taper off early Friday, with snow levels likely
     lifting to 3000 feet Friday afternoon.  The break in the
     weather may last through Saturday morning, before a very
     cold system drops into the region Saturday afternoon through
     Sunday.  This system is forecast drop straight down the
     British Columbia Coastline and into Washington and Oregon. 
     It will pull cold air from the interior of British Columbia
     out over the warmer ocean and then back inland across Oregon.

     The forecast weather pattern is a perfect set-up for very
     low snow levels by the second half of the weekend. Snow
     levels will likely drop to near the Willamette Valley floor
     Sunday through Monday morning, with some accumulations of
     wet snow possible, even at the lowest elevations. Expect
     winter driving conditions over the coast range and Cascade
     passes, beginning Saturday night and continuing thorugh
     Monday morning.

     Showers will taper off Monday with gradually clearing skies
     across western Oregon.  Temperatures will be well below
     normal with snow levels only lifting to around 1500 feet
     Monday afternoon. Partial clearing and a cold
     north-northwesterly flow aloft should allow much of the
     valley to drop well below freezing Monday night.

     An upper-level ridge is forecast to shift over the region
     Tuesday with a weak forecast to push through the ridge
     Tuesday night.  Things should dry out again, starting
     Wednesday Afternoon.  Thursday looks like a another break in
     the weather, with a transitory ridge building over the region.

Tomorrow (06 Mar):  Showers Ending.  Partly Sunny.  Snow Level Rising to 3000 Feet.  33/48

Sat (07 Mar):  Rain Developing by Afternoon. Snow Levels Lowering to 2000 Feet.  32/47

Sun (08 Mar):  Rain and Snow Showers.  Snow Level Near the Valley Floor.  32/43

Mon (09 Mar):  Rain/Snow Showers Ending with Partial Clearing.  Cool.  29/47

Tue (10 Mar):  A Frosty Morning...Increasing Clouds.  Chance of Showers Late.  29/50

Wed (11 Mar):  Chance of Showers Early.  Partial Afternoon Clearing.  37/53

Thu (12 Mar):  Partly Cloudy and Warmer.  36/55

ODA Meteorologist
weather at oda.state.or.us