[willamette-fcst] Forecast - Thursday, May 15th, 2008

Thu May 15 16:19:45 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: 
     Thursday, May 15th, 2008 at 4:45 pm.

Burn Advisory For Friday, May 16th, 2008:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 6:30pm.
     Stack burning is not allowed.

Weather Discussion:
     High pressure aloft built strongly northward, just offshore,
     Wednesday and dried out the air mass over the Pacific
     Northwest.  It was a mild this morning with minimums in the
     low to mid 50s across Western Oregon.  It was also mild
     from the Cascades eastward.  Timberline Lodge recording a
     low temperature this morning of 49 degrees with early
     morning readings across Central and Eastern Oregon in the
     40s and 50s.  Extensive low clouds covered most of Western
     Washington and the Willamette Valley early this morning but
     gave way to sunny skies by midday.  The rest of the region
     enjoyed a full day of sunshine...including the coastline.

     A building surface thermal trough, just off the Southern
     Oregon Coastline, combined with high pressure over Eastern
     Washington and NE Oregon to turn the surface winds
     northeasterly across Western Oregon.  The offshore flow,
     ample sunshine, and very warm air aloft sent Western Oregon
     temperatures to their highest values so far this year.  Late
     afternoon readings climed into the 70s and low 80s along the
     Northern and Central Oregon Coast and into the low to mid
     80s across the Willamette Valley.  The southwestern valleys
     soared into the upper 80s to mid 90s.  Temperatures were
     generally in the 70s to mid 80s east of the Cascades.

     The warm spot in the state today was in an unusual
     place...The town of Brookings, on the extreme South Oregon
     Coast was 100 degrees this afternoon due to the local
     downsloping winds off the mountains just to their north. 
     This is known as the \"Brookings Effect\" and sometimes
     occurs during the onset of a heat-wave, in the summer
     season, when the winds in that regino turn
     north-northeasterly.  That is the one part of the state
     (along the Southern Oregon Coast) that will see cooler
     temperatures Friday.  the rest of Oregon will see even
     warmer temperatures Friday.

     The upper-level ridge is forecast to continue to build over
     the Pacific Northwest Friday with the surface thermal trough
     remaining along the coastline for offshore flow across
     Western Oregon.  That will push Willamette Valley high
     temperatures to daily record values...in the low to mid 90s.
     Temperatures will also warm into the 90s across Central and
     Eastern Oregon.   Onshore flow will likely kick in along the
     southern and central coast Friday afternoon, as the center
     of the thermal low-pressure area moves up the coast.  The
     north coast will have another sunny day with highs likely
     well into the 80s and perhaps hitting 90. 

     Very warm air aloft will cap mixing heights at or below
     about 3000 feet again Friday, but ventilation will be good
     enough for agricultural burning in the afternoon.  However,
     northeasterly transport winds are not favorable for
     evacuation of smoke from the valley from stack burns, so
     they are not allowed Friday.  Friday night will be very warm
     with valley minimums near 60 degrees.

Surface Winds:
     NE 5-10 Friday morning, NE 5-10 Friday afternoon.
Transport Winds:
     NE 8 Friday morning, NNE 7 Friday afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height Friday will be near 3000 feet.  Ventilation index 24.
High Temperature:
     Salem\'s high temperature Friday will be near 95.
Humidities:
     Minimum relative humidity will be near 24%.
Sunrise/Sunset:
     Salem sunset tonight: 8:35pm; sunrise tomorrow: 5:42am.

Extended Outlook:
     It appears that Friday will be the warmest day west of the
     Cascades.  the upper-level ridge is forecast to shift east
     of the Cascades Saturday, along with the associated surface
     thermal trough.  That should bring cooler onshore winds into
     the Willamette Valley Saturday afternooon, in time to cap
     tempertures in the mid 80s.  That will shift the record hot
     weather into Central and Eastern Oregon Saturday afternoon. 
     Cooler ocean air begin filtering into Central and much of
     Eastern Oregon Sunday, with increasing onshore flow west of
     the Cascades cooling temperatures back into the upper 70s
     and perhaps low 80s.

     A increasing southwesterly flow aloft will bring
     progressively cooler temperatures early next week.  A
     weather system is forecast to bring a good chance of rain to
     all of Western Oregon Monday night and early Tuesday with
     some drying on Wednesday.  The long-range models diverge
     beginning next Thursday with some calling for dry and
     seasonal conditions and others calling for a chance of more
     rain.  I am splitting the difference and calling for cool
     but mostly dry weather.  That is subject to major change
     when I return on Monday.  Have a great weekend.

Tomorrow (16 May):  Sunny with Record High Temperatures.  58/95

Sat (17 May):  Sunny and Very Warm.  59/87

Sun (18 May):  Partly Cloudy and Cooler.  52/77

Mon (19 May):  Mostly Cloudy.  Chance of Rain Late.  50/70

Tue (20 May):  Chance of Rain and Cooler.  46/65

Wed (21 May):  Partly Sunny.  42/69

Thu (22 May):  Partly Sunny.  43/72

Fri (23 May):  Partly Sunny.  43/74

ODA Meteorologist
weather at oda.state.or.us