[willamette-fcst] Forecast - Wednesday, October 22nd, 2008

[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: 
     Wednesday, October 22nd, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     An upper-level ridge is amplifying over the region this
     morning.  The Salem sounding showed massive warming above
     2000 feet, since Teuesday afternoon.  There was a strong
     temperature inversion this morning from about 1000 feet up
     to 1800 feet.  The temperature at the top of the inversion
     was 57 degrees, while temperatures at the surface were in
     the low to mid 30s.  Normally that would be a classic set up
     for fog. However, increasing offshore flow is drying the
     low-level air mass enough to limit fog formation in the
     Willamette Valey this morning.

     The ODA surface analysis showed high pressure centered over
     Eastern Washington with a thermal trough building along the
     southern Oregon Coast.  Strong offshore gradients were
     producing brisk easterly winds, just above the inversion
     layer.  The easterly winds were dropping off the coast range
     and busting through the inversion along sections of the
     coastal strip.  Newport was recording gusts over 25 mph this
     morning with tempertures in the low 50s.  Strong east winds
     had also developed at the western end of the Columbia Gorge.
     Troutdale was getting gusts to 35 mph this morning and also
     had temperatures near 50 degrees.

     Below the inversion, winds were light across most of the the
     Willamette Valley at mid-morning.  Sections of the valley
     had frost this morning.  Skies were generally clear in the
     north valley, but there were areas of fog in the more
     sheltered south valley, from Corvallis to Eugene. 
     Visibilities were locally less than one-quarter of a mile. 
     Corvallis was also one of the coldest spots in the valley
     this morning, recording a minimum of just 28 degrees. 
     Aurora and Hillsboro both dropped to the freezing mark and
     Salem dipped to 33 degrees.  Meanwhile, north winds kept the
     low-level air mixed, in McMinnville, where the temperature
     stayed in the upper 30s.  Portland also stayed warmer with a
     low of 38. 

     Visible satellite imagery showed the fog and low clouds in
     the western valleys from about Corvallis south to Roseburg. 
     The remainder of the state had sunny skies this morning. 
     Valley temperatures were still mostly in the 30s.  It was
     quite cold east of the Cascades with temperatures mostly in
     the 20s and a few spots in the teens.  Burns and Rome both
     recorded minimums of just 18 degrees.

     Continued offshore flow today will clear the areas of fog
     from the southern valleys later this morning and bring
     sunshine to the entire state.  The air aloft will continue
     to warm and may support surface temperatures locally
     climbing into the low 70s, if there is enough down-mixing of
     warm air through the inversion layer.  In any case, mixing
     heights will remain below 2000 feet.

     A weak cold front will begin to spread some high clouds
     across northwest Oregon tonight and weaken the offshore flow
     enough to allow for areas of fog to form in the Willamette
     Valley.  Low temperatures will likely be a few degrees
     warmer than they were this morning...staying mostly above
     the freezing mark.

Surface Winds:
     NNE 5-10 this morning, NNE 5-10 this afternoon.
Transport Winds:
     NE 10 this morning, ENE 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1800 feet.  Ventilation index 18.
High Temperature:
     Salem\'s high temperature today will be near 72.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 26%.
Sunrise/Sunset:
     Salem sunset tonight: 6:15pm; sunrise tomorrow: 7:39am.

Extended Outlook:
     A weak cold front will flatten the ridge of high pressure,
     as it slides north of Oregon Thursday.  The trailing end of
     the front will bring onshore flow and some clouds into
     northwest Oregon.  That will knock 5-10 degrees off high
     temperatures, but no rainfall is expected.  Another cold
     front is forecast to do approximately the same thing Friday,
     with some clouds but no rain expected.

     The long-range models all show a strong ridge of high
     pressure building over the region this weekend and lasting
     through the first half of next week.  Offshore flow may
     develop as soon as Saturday, which would send temperatures
     well above normal with sunny skies statewide.  It is
     possible that western Oregon highs could approach record
     warm levels Sunday through Tuesday.

     The ridge will likely begin to break down about Wednesday of
     next week with increasing southwesterly flow aloft.  A cold
     front may bring a chance of rain on Thursday with
     temperatures dropping closer to normal.

Tomorrow (23 Oct):  Partly Sunny.  37/64

Fri (24 Oct):  Partly Sunny.  38/63

Sat (25 Oct):  Areas of AM Fog...Mainly South.  Mostly Sunny and Mild.  39/68

Sun (26 Oct):  Patchy AM Fog...Mainly South.  Sunny and Near Record Warmth.  42/74

Mon (27 Oct):  Patchy AM Fog...Mainly South.  Sunny and Near Record Warmth.  43/74

Tue (28 Oct):  Patchy AM Fog...Mainly South.  Sunny and Near Record Warmth.  43/71

Wed (29 Oct):  Mostly Sunny.  Increasing Clouds Late.  42/65

ODA Meteorologist
weather at oda.state.or.us