[willamette-fcst] Forecast - Wednesday, June 3rd, 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.

...Next Update Schedule For Thursday, June 4th, 2009 at 9:00am...

Issued: 
     Wednesday, June 3rd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 10:00am until 6:30pm.
     Stack burning is not allowed.

Weather Discussion:
     Daytime heating combined with a moist and unstable air mass
     over the region to fuel impressive thunderstorms over the
     southern half of Oregon Tuesday afternoon and evening. 
     Thunderstorms produced locally heavy rainfall in Lane,
     Douglas, Josephine, and Jackson Counties, with some CoCoRaHS
     stations recording over an inch of rainfall from near Eugene
     to the California border.  Strong storms also developed over
     southeastern Oregon Tuesday evening, with Rome picking up
     more than two-thirds of an inch of rain.  Rainfall was much
     lighter over the northern half of Oregon.  The northern and
     central Willamette Valley picked up only from a trace to
     just a couple hundredths of an inch on Tuesday.

     A broad upper-level low pressure trough, centered about 350
     miles off the central California Coastline, was continuing
     to circulate warm, moist, and unstable air over Oregon at
     mid-morning.  Satellite imagery showed a broad,
     counterclockwise circulating, band of clouds covering most
     of Oregon.  There were some sunbreaks, on either side of the
     cloud band, over extreme northeastern and extreme
     southwestern Oregon.  Showers had pretty much dissipated
     overnight with no weather reporting stations picking up
     showers at mid-morning.  Marine low clouds and fog blanketed
     the coastline, with some low clouds in the southern
     Willamette Valley.

     Cloudy skies kept temperatures extremely mild overnight,
     with most of the state staying above 50 degrees.  Some areas
     west of the Cascades did not drop below 60.  Salem recorded a
     balmy minimum of 62 degrees.  Mid-morning temperatures had
     already warmed well into the 60s across most of the state. 
     The ODA surface analysis showed a thermal low-pressure
     trough extending northward across western Oregon with light
     offshore gradients across all areas except along the
     immediate coastal strip.  Winds in the Willamette Valley
     were light variable.

     The Salem sounding this morning showed light winds near the
     surface with easterly winds from about 2000 to 12,000 feet,
     and southeasterly winds above 12,000 feet.  Northeasterly
     transport winds are forecast today, which are not conducive
     to good valley ventilation for stack burning.  Some subreaks
     will help temperatures warm into the upper 70s and low 80s
     again this afternoon, fueling the development of more
     showers and thunderstorms.  Storms that form over the
     Cascades will likely drift over the western valleys.

     The temperature profile of the atmosphere is even more
     unstable than yesterday, so any convection that manages to
     rise above the weak cap near 3000 feet will likely develop
     into impressive thunderstorms this afternoon...likely
     producing locally heavy rain and hail as far north and west
     as the Willamette Valley.  Scattered strong thundershowers
     are likely this afternoon and evening over the Cascades and
     much of central and eastern Oregon.

Surface Winds:
     Var 3-7 this morning, NNE 7-12 this afternoon.
Transport Winds:
     Var 5 this morning, NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3600 feet.  Ventilation index 36.
High Temperature:
     Salem\'s high temperature today will be near 82.
Humidities:
     Minimum relative humidity will be near 43%.
Sunrise/Sunset:
     Salem sunset tonight: 8:53pm; sunrise tomorrow: 5:27am.

Extended Outlook:
     The moist and unstable southeasterly flow aloft will turn
     easterly Thursday, as the parent upper-level low-pressure
     area begins to come onshore into central and southern
     California.  Showers and afternoon thundershowers will
     likely be widespread across Oregon, with increased
     cloud-cover leading to cooler temperatures.  The upper-level
     low-pressure center will move eastward, into nevada, Friday.
     The flow aloft over Oregon will turn northeasterly Friday,
     with the main area of mid and upper-level moisture shifting
     east of the Cascades by Friday afternoon.

     The flow aloft will turn from northeasterly to northwesterly
     over the weekend with increasing low-level onshore flow
     advancing marine low clouds into western Oregon.  A series
     of weak upper-level troughs are forecast, by some of the
     long-range computer models, to possibly bring some morning
     drizzle or light showers to northwest Oregon Sunday through
     Tuesday.  That would drop temperatures to slightly below
     normal.  A little stronger trough is forecast to bring a
     better chance of showers by next Thursday.  Continued
     onshore flow will maintain slightly below normal temperatures.

Tomorrow (04 Jun):  Mostly Cloudy.  Showers and PM T-Storms Likely.  59/76

Fri (05 Jun):  Decreasing Showers...From NW to SE...Late.  57/74

Sat (06 Jun):  Partly to Mostly Cloudy and Cooler with Onshore Flow.  52/74

Sun (07 Jun):  Mostly Cloudy.  Slight Chance of Showers.  52/70

Mon (08 Jun):  Mostly Cloudy.  Slight Chance of Drizzle or Light Showers.  51/67

Tue (09 Jun):  Mostly Cloudy.  Slight Chance of Drizzle or Light Showers.  50/69

Wed (10 Jun):  Morning Clouds.  Partly Sunny in the Afternoon.  50/71

ODA Meteorologist
weather at oda.state.or.us