[willamette-fcst] Forecast - Tuesday, April 14th, 2009

Tue Apr 14 09:00:56 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: 
     Tuesday, April 14th, 2009 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:
     A strong cold front moved across Oregon Sunday, with a very
     cold upper-level trough dropping southward over the region
     Monday.  The Easter Sunday cold front dropped more than an
     inch of rain along the northern Oregon coast and from
     one-quarter to one-half inch of rain along the central coast
     and across the Willamette Valley.  The subsequent
     upper-level trough dramaticaly dropped the freezing level to
     just 3400 feet by Monday morning and down to 2100 feet this morning.

     Cold instability showers developed over the region Monday. 
     Rainfall amounts varied from about one-tenth to one-third of
     an inch, from the coast to the Willamette Valley, with some
     hail and a few claps of thunder thrown in.  Valley high
     temperatures were only near 50 degrees Monday afternoon,
     more than 10 degrees below normal.  Strong westerly flow
     aloft created upslope conditions over the Cascades, with
     significant accumulations of new snow.  Timberline Lodge has
     received 10 inches of snow in the past 24 hours and 18
     inches of new snow since the weekend.  They reported a base
     total this morning of a whopping 619 inches.  Mt. Bachelor
     picked up 5 inches of new snow in the past 24 hours, and 6
     inches fell on Willamette Pass.

     ODOT road cameras showed a December-like scene this morning
     over the Cascade passes, with snow-packed highways and
     temperatures near 20 degrees.  Snow was visible on road
     surfaces in the Cascade foothills down to about 1000 feet
     this morning.  It was also cold in the lower elevations of
     western Oregon this morning.  Most of the Willamette Valley
     dropped at least into the mid 30s, and some spots, like
     Hillsboro and McMinnville, dipped to the freezing mark or below.

     Satellite imagery and doppler radar showed an organized
     cluster of showers rotating southward down the Oregon Coast
     and into southwestern Oregon.  Another area of lighter
     showers was rotating southward along the southern Washington
     and northern Oregon Cascades.  The air aloft is very cold
     with these showers and is supporting snowfall to very low
     elevations.  Roseburg, at an elevation of only 525 feet, was
     reporting snow showers this morning with a temperature of 34
     degrees.  Some snow could mix with showers all the way to
     sea level this morning, but sticking snow will be confined
     to areas above 1000 feet.

     The cold upper-level trough will slowly slide southward
     today, with the center of circulation, currently over
     southern Oregon, moving into Nevada.  That will turn the
     flow aloft more northerly and begin to dry out the air mass.
      However, the air aloft will remain very cold today, so
     daytime heating will generate instability showers with small
     hail and thunder possible.  Mixing of cold air aloft down to
     the surface will hold Willamette Valley high temperatures
     near 50 degrees again this afternoon.  Surface winds were
     quite variable this morning but should turn northwesterly
     this afternoon.

     The flow aloft is forecast to turn almost due northerly over
     western Oregon by tonight.  Normally that is a dry pattern. 
     However, the counterclockwise circulation around the Nevada
     upper-level low-pressure center will continue to feed
     moisture into Oregon for a chance of showers.  Snow levels
     will reamin quite low.  Partial clearing will, once again,
     allow western valley temperatures to drop to near the
     freezing mark.

Surface Winds:
     SW 3-8 this morning, NW 5-15 this afternoon.
Transport Winds:
     SW 8 this morning, NW 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4400 feet.  Ventilation index 66.
High Temperature:
     Salem\'s high temperature today will be near 51.
Humidities:
     Minimum relative humidity will be near 52%.
Sunrise/Sunset:
     Salem sunset tonight: 7:57pm; sunrise tomorrow: 6:27am.

Extended Outlook:
     Showers should end across northwestern Oregon Wednesday with
     slowly clearing skies.  The snow level will be slow to climb
     and should only lift to around 3000 feet by Wednesday
     afternoon.  Some showers could linger in the Cascades, and
     across eastern Oregon, through Wednesday evening. 
     Willamette Valley high temperatures will stay well below
     normal but should recover into the mid 50s.

     a transitory ridge of high pressure will clear skies
     Wednesday evening, making for another chilly night across
     the western valleys.  The next weather system will move
     mainly north of the regin but will increase clouds by
     Thursday afternoon.  Temperatures should climb to
     near-normal Thursday afternoon.  A weak cold front is
     forecast to bring a chance of rain back to northwestern
     Oregon Thursday night and Friday.

     A flat upper-level ridge is forecast to build over the
     Pacific Northwest this weekend, but it is still not certain
     how strong the ridge will be.  At this time, I will indicate
     a general warming and drying trend.

Tomorrow (15 Apr):  Slight Chance of an AM Shower.  Afternoon Clearing.  33/56

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

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

Sat (18 Apr):  Partly Cloudy and Warmer.  45/68

Sun (19 Apr):  Partly Cloudy and Warm.  45/68

Mon (20 Apr):  Mostly Sunny and Warm.  45/72

Tue (21 Apr):  Mostly Sunny and Warm.  45/72

ODA Meteorologist
weather at oda.state.or.us