[willamette-fcst] Forecast - Tuesday, April 22nd, 2008

Tue Apr 22 08:10:52 PDT 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: 
     Tuesday, April 22nd, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:00pm.
     Straw stack burning is allowed from now until 6:00pm.

Weather Discussion:
     The very cold upper-level low pressure system that brought
     rain, hail, and snow showers to the region over the weekend
     backed off the Washington Coastline Monday and combined
     forces with another system off the Oregon coast.  Strong
     westerly flow aloft continued to circulate cold showers into
     the region with snow levels slowly rising to about 1500 feet
     by Monday evening.

     The Showers changed to a steady rain across Western Oregon
     overnight in response to a potent warm front from the
     offshore system.  As a surface low pressure area approached
     the Central Oregon Coast overnight, the resultant offshore
     flow kept cool air in place across Oregon with snow levels
     remaining near 1500 feet across Northern Oregon.  Warmer air
     aloft had lifted snow levels to near 4000 feet over Southern
     Oregon by early this morning.

     The clouds and rain kept valley temperatures from dropping
     below about 40 degrees overnight, even though the air aloft
     remains unseasonably cold.  Total rainfall amounts in the 24
     hours ending at 5 am today ranged from around one-tenth to
     one-third of an inch in the Willamette Valley with just
     under one-half inch falling along the Oregon Coast.  Spotty
     light rain and snow fell east of the Cascades, under cloudy
     skies, with precipitation amounts less than one-tenth of an inch.

     There was some concern that the air mass would be cold
     enough overnight and early this morning for a rare April
     snowfall in the Upper Hood River Valley and perhaps the
     eastern end of the Columbia Gorge.  However, The Dalles had
     light rain and 40 degrees at mid-morning, so it appears
     slightly too warm for snow in the lowest elevations there. 
     Some wet snow is still possible in that region, above about
     1000 feet this morning.

     This is a very cold storm that would have produced
     widespread snow over Western Oregon, had this pattern set up
     during the winter season.  It did produce snow overnight in
     the northern coastal range and in the Cascades above about
     1500 feet.  The northern coastal passes were covered in snow
     and slush early this morning with near-freezing
     temperatures.  Packed snow covered the Cascade Passes this
     morning, where temperatures were in the mid 20s.

     Not much in the way of rain or snow made it into Central and
     Eastern Oregon overnight, but skies had turned cloudy.  As
     the storm progresses eastward, precipitation should push
     into Central Oregon later this morning mainly as snow.  The
     National Weather Service has issued a snow advisory for The
     Bend and Redmond areas for up to a couple of inches of snow
     later this morning.  Areas of light rain and snow will
     spread eastward across the state today and tonight, but
     significant snow accumulations are not expected.

     The ODA surface analysis showed a low pressure center about
     150 miles west of Newport with a warm front extending
     eastward to near Newport.  Ahead of the warm front, winds in
     the Northern Willamette Valley and along the north coast
     were northeasterly at 5-15 mph.  On the south side of the
     warm front, southeasterly winds of 5-15 were blowing along
     and south of a Newport to Eugene line.  Temperatures ranged
     from from near 40 in the north valley, and the north coast,
     to the upper 40s along the southern coast.

     The warm front is forecast to weaken and slowly progress
     northward today with rain at times continuing and
     southeasterly winds moving northward across Western Oregon. 
     The warmer air aloft over Southern Oregon will filter
     northward this afternoon with the snow level over Northern
     Oregon creeping up to around 3000 feet.  The snow level over
     Southern Oregon will stay near 4000 feet.  Clouds and rain
     will help hold valley temperatures in the low 50s (about 10
     degrees below average).

Surface Winds:
     SE 5-15 this morning, SE 5-15 this afternoon.
Transport Winds:
     S 25-30 this morning, S 20-25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 100.
High Temperature:
     Salem\'s high temperature today will be near 52.
Humidities:
     Minimum relative humidity will be near 69%.
Sunrise/Sunset:
     Salem sunset tonight: 8:07pm; sunrise tomorrow: 6:13am.

Extended Outlook:
     The cold front from the slow-moving offshore storm system
     will finally move inland tonight.  The associated cold
     upper-level trough will move over the region Wednesday and
     Thursday for showers and a return of quite low snow levels.

     High pressure will build into the coastline Friday and begin
     to dry out the air mass.  That may lead to cool temperatures
     over sections of the valley Friday and/or Saturday mornings
     with daytime temperatures shooting above normal Saturday. 
     The next weather system is forecast to move onshore Sunday
     night and Monday.

Tomorrow (23 Apr):  Showers.  Chance T-Storm.  Snow Level Dropping to 1500 Feet.  42/52

Thu (24 Apr):  Mostly Cloudy.  Chance of Showers.   Snow Level Rising to 3000 Feet.  37/56

Fri (25 Apr):  Mostly Cloudy.  Decreasing Chance of Showers.  Snow Level 4000 Feet.  36/58

Sat (26 Apr):  Becoming Mostly Sunny and Warmer.  34/67

Sun (27 Apr):  Increasing Clouds.  Rain Likely Late.  40/63

Mon (28 Apr):  Rain Likely and Cooler. 44/58

Tue (29 Apr):  Showers.  Snow Level 2500 Feet.  40/55

ODA Meteorologist
weather at oda.state.or.us