[willamette-fcst] Forecast - Friday, April 3rd, 2009

Fri Apr 3 09:04:08 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: 
     Friday, April 3rd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 5:30pm.
     Straw stack burning is allowed from now until 5:30pm.

Weather Discussion:
     Another strong cold front moved across western Oregon early
     Thursday, followed by an unseasonably cold upper-level
     trough Thursday afternoon and night.  Strong mid-level
     westerly winds created a rain-shadow effect, in the lee of
     the coastal range, which limited Willamette Valley rainfall
     over the past 48 hours to around one-quarter of an inch or
     less.  In contrast, strong upslope flow brought much heavier
     precipitation to the western slopes of the coast range and
     the Cascades.

     Much of the precipitation in the mountains fell as snow,
     over the past 24 hours, with the snow level rapidly dropping
     below the Cascades passes Thursday morning and continuing to
     fall to just 1000 feet by this morning.  ODOT road cameras
     confirmed sticking snow all the way down to Brightwood
     (elevation 1070 feet) this morning on Hwy 26 east of
     Portland.  Snow also covered the roadways near Detroit
     (elevation 1670 feet) this morning, on Hwy 22 east of Salem.

     Mountain snow totals were impressive over the past 24 hours,
     with about a foot of new snow from Mt. Hood to Willamette
     Pass.  That adds to what was an amazingly snowy month of
     March in the mountains.  Government Camp received more snow
     this March (108 inches) that they accumulated in November,
     December, and Janurary combined!  The recent snowfall lifted
     the base snow total at Timberline Lodge over 200 inches (207
     inches) this morning.  That is well above normal, after a
     slow start to the snow season.  Cascades passes looked as if
     it were early January this morning, with snow-packed
     conditions and temperatures in the low 20s.

     Satellite imagery and Doppler radar showed showers
     continuing to rotate onshore across northwest Oregon, with
     westerly flow aloft continuing to enhance the showers over
     the mountains and create a rain-shadow over the Willamette
     Valley.  A few showers were making it into the valley, but
     the real focus of the precipitation continued to be over the
     coast range and the Cascades this morning.  Clouds and
     breezy conditions kept valley temperatures above freezing
     overnight, even though the freezing level was measured at
     just 2100 feet over Salem this morning.

     The upper-level trough is forecast to shift east of the
     Cascades this afternoon, with the flow aloft becoming
     northwesterly and drying out.  Showers will taper off today
     with increasing sun-breaks this afternoon.  Very cold air
     aloft will provide excellent mixing of the air mass today
     and prevent high temperatures from climbing above 50 degrees
     in the western valleys (about 10 degrees below normal). 
     Surface winds were southwesterly in the valley this morning
     and will slowly turn more northwesterly this afternoon. 
     Clearing skies this evening will allow temperatures to
     rapidly drop with near-record low temperatures and
     widespread frost likely across the Willamette Valley overnight.

Surface Winds:
     SW 5-15 this morning, WNW 5-15 G20 this afternoon.
Transport Winds:
     W 15 this morning, NW 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4700 feet.  Ventilation index 94.
High Temperature:
     Salem\'s high temperature today will be near 49.
Humidities:
     Minimum relative humidity will be near 50%.
Sunrise/Sunset:
     Salem sunset tonight: 7:43pm; sunrise tomorrow: 6:47am.

Extended Outlook:
     More spring-like conditions will finally arrive over the
     weekend, as an upper-level ridge builds over the region. 
     Surface winds will turn offshore Saturday afternoon through
     Sunday with the frezeing level jumping above 8000 feet by
     Sunday.  After a cold start Saturday, valley temperatures
     will recover to near-normal Saturday afternoon and shoot
     well above normal, for a change, on Sunday.

     The long-range computer models forecast the next weather
     system to be directed more at California, wit a split-flow
     jet stream pattern developing over the Pacific Northwest. 
     That should extend the dry weather at least through Monday
     with continued offshore flow at the surface.  The flow is
     forecast to turn onshore by midweek with cooler temperatures
     and a returning threat of rain and mountain snow.

Tomorrow (04 Apr):  Frosty Start with Patchy Fog...Sunny and Warmer in the Afternoon.  28/59

Sun (05 Apr):  Mostly Sunny and Warmer.  33/69

Mon (06 Apr):  Mostly Sunny.  39/69

Tue (07 Apr):  Partly Cloudy.  Slight Chance of Showers...Mainly South.  42/65

Wed (08 Apr):  Mostly Cloudy.  Slight Chance of Showers.  42/60

Thu (09 Apr):  Rain Likely.  Snow Level Dropping to 3-4000 Feet.  43/53

Fri (10 Apr):  Mostly Cloudy.  Chance of Showers.  40/53

ODA Meteorologist
weather at oda.state.or.us