[willamette-fcst] Forecast - Monday, October 5th, 2009

[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: 
     Monday, October 5th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 9:00am until 5:00pm.
     Propane flaming is allowed from 1:00pm until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     The strong upper-level trough that brought showery and cool
     weather the Oregon over the weekend had shifted east, to
     over Idaho, this morning. Satellite imagery showed mostly
     cloudy skies over southeastern Oregon, where a few showers
     were still indicated by Doppler radar.  Clearing skies over
     the remainder of the state allowed temperatures to drop well
     into to the 30s with some areas of the Willamette Valley
     flirting with the freezing mark.  McMinnville dropped to 32
     degrees this morning, and Hillsboro dipped down to 34. Corvallis
     and Eugene both dropped to 36 degrees, and Salem hit 38.

     As is typical for October, low-level cooling and light winds
     overnight led to formation of fairly extensive fog and low
     clouds across the Willamette Valley this morning. Visibilities
     were locally reduced to around one-quarter of a mile.  The
     mid-morning ODA surface analysis showed high pressure extending
     from western Washington southward across western Oregon with
     very weak pressure gradients and light soth-southeasterly winds
     across the Willamette Valley.  Low pressure over Idaho was
     maintaining brisk north-northwesterly winds across much of
     central and eastern Oregon...keeping fog from forming.

     A strong upper-level ridge of high pressure, over the
     eastern Pacific Ocean, will slowly build inland today, with
     a drying northeasterly flow aloft over Oregon.  The morning
     fog and low clouds, blanketing most of the Willamette
     Valley, should give way to plenty of sunshine this
     afternoon, as the low-level flow backs from southeasterly to
     north-northeasterly.  The air mass is still chilly, with the
     freezing level over Salem measured at just 6800 feet this
     morning, so highs today will likely only manage to climb
     into the mid 60s (about 5 degrees below average).

Surface Winds:
     SSE 3-8 this morning, N 5-12 this afternoon.
Transport Winds:
     SE 5 this morning, NE 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 24.
High Temperature:
     Salem\'s high temperature today will be near 66.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 6:45pm; sunrise tomorrow: 7:17am.

Extended Outlook:
     A dry and cool northeasterly flow aloft will allow
     Willamette Valley temperatures to cool into the 30s again
     Tuesday morning with local pockets of frost possible.  The
     upper-level ridge is forecast to build slightly more into
     the coastline Tuesday.  After areas of morning fog, mostly
     sunny skies should warm temperatuers close to normal.

     A weather system moving over the top of the ridge will drop
     southward, into Montana, on Wednesday...keeping the
     upper-level ridge from building over Oregon.  That will
     maintain a dry and cool north-northeasterly flow aloft. 
     Overnight minimums will likely moderate a few degrees, but
     afternoon highs will still struggle to hit 70 degrees...even
     with plenty of sunshine.

     The flow aloft is forecast to turn north-northwesterly, over
     Oregon, Thursday and Friday, as a reinforcing surge of cool
     Canadian air brings some early autumn snow to the northern
     Rockies.  The air aloft will stay cool enough to keep
     Willamette Valley temperatures slightly below normal, even
     with plenty of afternoon sunshine.  By Saturday, the
     upper-level ridge is forecast to build more directly over
     the west coast, with warmer air aloft and increasingly
     offshore surface winds combining to warm valley temperatures
     into the 70s (slightly above normal).

     The ridge is forecast to shift east, to over Idaho, Sunday,
     with increasing westerly flow aloft introducing some Pacific
     moisture back into Oregon.  A weak cold front could bring
     some light rain to the north coast by Sunday afternoon, with
     increasing clouds and onshore flow cooling Willamette Valley
     temperatures back into the 60s.  A more potent system is
     forecast to bring widespread rain onshore next Monday.

Tue (06 Oct):  Areas of AM Fog.  Chilly in the Morning.  Sunny and a Touch Warmer.  36/68

Wed (07 Oct):  Areas of AM Fog.  Sunny.  40/68

Thu (08 Oct):  Areas of AM Fog.  A Few High Clouds in the Afternoon.  41/68

Fri (09 Oct):  Mostly Sunny.  39/68

Sat (10 Oct):  Sunny.  41/71

Sun (11 Oct):  Increasing Clouds.  43/68

Mon (12 Oct):  Rain Likely.  44/64

ODA Meteorologist
weather at oda.state.or.us