[willamette-fcst] Forecast - Wednesday, April 15th, 2009

Wed Apr 15 09:01:16 PDT 2009

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: 
     Wednesday, April 15th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 6:30pm.
     Straw stack burning is allowed from 11:00am until 6:30pm.

Weather Discussion:
     The center of the upper-level trough that brought cool and
     showery weather to the region the past two days dropped
     south, to over Nevada, overnight.  That turned the flow
     aloft over western Oregon more northerly and began drying
     out the air mass.  However, moisture was continuing to
     circulate into eastern Oregon, where some snow flurries were
     falling this morning.  Significant snow fell in the Cascades
     Tuesday.  Timberline Lodge reported 10 inches of new snow,
     Mt. hood Meadows and Skibowl both reported 8 inches, Mt.
     Bachelor 4 inches, and Willamette Pass had 6 inches.  The
     air aloft is still quite cold this morning, with the freezing
     level over Salem measured at 2700 feet.  The Cascades passes
     were snow-packed with temperatures in the mid 20s. 

     The combination of a cold air mass over the region and some
     partial clearing overnight allowed Willamette Valley
     temperatures to drop near or slightly below the freezing
     mark early this morning.  Hillsboro and McMinnville dropped
     down to at least 30 degrees, and Corvallis hit the freezing
     mark.  The ODA surface analysis showed onshore flow across
     Oregon with weak strong pressure gradients across western
     Oregon and very strong gradients east of the Cascades. 
     Westerly winds were gusting to more than 30 mph across
     eastern Oregon with gusts of 52 mph at Baker City.  In
     contrast, westerly winds were blowing less than 10 mph
     across western Oregon.

     The strong onshore flow was very evident on the mid-morning
     visible satellite imagery. It was forming a cloud-deck along
     the western slopes of the Cascades...extending westward over
     much of the central and eastern Willamette Valley.  There
     were also low clouds along the coast and western slopes of
     the coast range.  A pronounced area of clearing extended
     along the eastern slopes of the coast range and the
     Cascades, due to downsloping westerly winds.  That was
     helping to bring some sunshine to the western side of the
     Willamette Valley and much of central Oregon this morning. 
     Meanwhile, considerable cloud-cover, from the low-pressure
     system over Nevada, had circulated northweard over the east
     half of Oregon.

     Dopper radar showed most of the shower activity was just
     south and east of Oregon, but some light precipitation was
     making it into eastern Oregon.  Low clouds along the coast
     were also producing areas of light rain or drizzle.  No rain
     was being reported in the Willamette Valley, but radar was
     showing some possible light rain, drizzle, or flurries
     (depending on elevation) along the western slopes of the
     Cascades...extending westward into the eastern Willamette
     Valley.  Willamette Valley temperatures were in the 30s to
     low 40s with low to mid 40s along the coast.  It was much
     colder east of the Cascades, where temperatures were
     struggling to get much above freezing in most areas.

     As the Nevada weather system continues to slowly drift to
     the east, the air aloft over Oregon with will slowly warm
     today.  However, it should still be cold enough for daytime
     heating to spawn convective clouds, which will fill in the
     clear areas over the western Willamette Valley.  Although
     showers over the western valleys are unlikely today, a few
     snow showers will likely persist over the Cascades into this
     evening.  The snow level will only lift to around 3000 feet
     this afternoon.  Slightly warmer air aloft will help
     Willamette Valley temperatures climb in the mid 50s this
     afternoon, after only reaching the upper 40s and low 50s Tuesday.

Surface Winds:
     WSW 5-10 this morning, NW 5-15 this afternoon.
Transport Winds:
     NW 10 this morning, NW 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5500 feet.  Ventilation index 83.
High Temperature:
     Salem\'s high temperature today will be near 56.
Humidities:
     Minimum relative humidity will be near 45%.
Sunrise/Sunset:
     Salem sunset tonight: 7:58pm; sunrise tomorrow: 6:25am.

Extended Outlook:
     Clearing skies tonight will, once again, allow western
     valley temperatures to drop to near or locally below the
     freezing mark with light winds.  The next weather system
     will increase clouds across western Oregon by Thursday
     afternoon.  Warming aloft, ahead of a weak cold front, will
     help temperatures climb to near-normal Thursday afternoon.

     The cold front is forecast to bring some light rain to
     mainly the northern sections of the western Oregon,
     beginning Thursday evening.  Moslty cloudy skies should
     spread across the State Friday, but precipitation will be
     light and limited mainly to areas from the Cascade crest
     westward.  An upper-level ridge is forecast to build over
     the Pacific Northwest this weekend for dry and warmer
     conditions.  The ridge will likely extend the warm and dry
     weather through the first half of next week.

Tomorrow (16 Apr):  Chilly Start...Increasing Clouds and Warmer in the Afternoon.  34/62

Fri (17 Apr):  Mostly Cloudy.  Light Rain at Times...Mainly North.  44/62

Sat (18 Apr):  Becoming Mostly Sunny and Warmer.  42/70

Sun (19 Apr):  Mostly Sunny and Warmer.  44/75

Mon (20 Apr):  Sunny and Warm.  46/76

Tue (21 Apr):  Mostly Sunny and Warm.  47/75

Wed (22 Apr):  Mostly Sunny and Mild.  43/69

ODA Meteorologist
weather at oda.state.or.us