[willamette-fcst] Forecast - Thursday, May 14th, 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: 
     Thursday, May 14th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:30pm.
     Straw stack burning is allowed, for dry stacks, from now until 6:30pm.

Weather Discussion:
     A strong Pacific frontal system brought a soaking rain to
     northwestern Oregon Wednesday afternoon and night.  Rainfall
     amounts tapered off over southwestern Oregon, but all areas
     west of the Cascades picked up measurable rainfall.  Over an
     inch of rain fell along the northern Oregon Coast, one-half
     inch on the central coast, and about one-quarter of an inch
     on the south coast.  Rainfall totals in the Willamette
     Valley generally ranged from one-third to two-thirds of an inch.

     The mid-morning ODA surface analysis showed the cold front
     had weakended and pushed east of the Cascades.  It extended
     from central Washington to south-central Oregon.  Areas of
     light rain were focused along and east of a line from
     northeastern Oregon to southwest Oregon.  In the wake of the
     cold front, visible satellite imagery showed some clearing
     across northwestern Oregon and only minimal shower activity
     west of the Cascades.  However, the air aloft is still
     fairly cool (The freezing level over Salem was measured at
     6700 feet this morning), so daytime heating should produce
     some convective clouds and possibly a few showers across
     western Oregon today.

     Surface winds are generally southwesterly in the Willamette
     Valley this morning and should turn northwesterly this
     afternoon, as drier air begin filtering into the region. 
     Overnight temperatures were mild with minimums near 50
     across western Oregon.  Mid-morning readings were in the low
     to mid 50s.  Highs today will only climb into the lower 60s.
     High mixing heights and onshore flow will make for good
     ventilation conditions across the Willamette Valley today.

Surface Winds:
     SW 5-15 G20 this morning, NW 5-15 this afternoon.
Transport Winds:
     SW 20 this morning, WNW 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5500 feet.  Ventilation index 110.
High Temperature:
     Salem\'s high temperature today will be near 63.
Humidities:
     Minimum relative humidity will be near 54%.
Sunrise/Sunset:
     Salem sunset tonight: 8:34pm; sunrise tomorrow: 5:43am.

Extended Outlook:
     A drier northwesterly flow aloft will bring clearing skies
     tonight.  That will allow radiational cooling to locally
     drop valley temperatures into the upper 30s.  Residual
     moisture, from the recent rainfall, may be high enough to
     promote patchy valley fog formation early Friday.  Skies
     will become mostly sunny Friday, as the upper-level ridge
     begins building into the coastline.  Surface winds will turn
     northerly across western Oregon.  Warming aloft and a full
     day of sunshine will help valley temperatures climb into the
     lower 70s.

     A flat upper-level ridge is forecast to build over Oregon
     Saturday with continued warming aloft helping valley high
     temperatuers climb to near 80 degrees.  The jet stream is
     forecast to migrate northward to over central British
     Columbia.  Some high clouds may extend as far south as
     northern Oregon.  The flat upper-level ridge will shift
     eastward, to over eastern Oregon and Idaho, on Sunday, with
     increasing westerly flow aloft over Oregon.  That will
     induce onshore flow into western Oregon by Sunday
     evening...bringing cooler weather to the coastline and
     capping high temperatures near 80 degrees across the
     Willamette Valley.  Temperatures will continue to warm Sunday,
     over central and eastern Oregon, as the surface thermal trough
     shifts east of the Cascades.

     A developing southwesterly flow aloft will extend the marine
     push eastward Monday, with cooler air penetrating to the
     Idaho border by Monday night.  Strong onshore flow will
     bring marine low clouds and much cooler conditions into
     western Oregon Monday with an increasing chance of showers. 
     A farily vigorous upper-level trough is now forecast by most
     of the long-range computer models to bring showers to the
     region Tuesday and possibly drop snow levels to near 4000
     feet in the northern Cascades.

     A transitory and weak upper-level ridge is forecast to bring
     some drying and warming Wednesday and Thursday.  Another
     cool weather system is forecast to drop down from the Gulf
     of Alaska, and possibly into the Pacific Northwest, as we
     move into Memorial Weekend.  However, that is still very
     much in question.

Tomorrow (15 May):  Patchy Early Morning Fog.  Sunny and Warmer.  North Winds.  39/72

Sat (16 May):  Mostly Sunny and Warm.  North Winds.  41/79

Sun (17 May):  Mostly Sunny and Warm.  Increasing Onshore Flow in the Afternoon.  47/79

Mon (18 May):  Partly to Mostly Cloudy and Cooler.  Increasing Chance of Showers.  51/65

Tue (19 May):  Showers Likely and Cool.  Snow Level Dropping to Near 4000 feet.  46/59

Wed (20 May):  Slight Chance of Showers Early.  Becoming Partly Cloudy and Warmer.  43/66

Thu (21 May):  Partly Cloudy.  45/69

ODA Meteorologist
weather at oda.state.or.us