[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.

...Next Update Not Scheduled Until Monday, May 18th at 9:00am...

Issued: 
     Thursday, May 14th, 2009 at 12:00pm.

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 soaking rains to most of the
     coast and across the northwestern interior of Oregon Wednesday afternoon
     and night.  Rainfall amounts were lighter over southwestern Oregon, but
     measurable rain fell across all of western Oregon.  Rainfall along the
     coast ranged from over an inch, at Astoria, to less than one-quarter of
     an inch at North Bend.

     Rainfall totals in the Willamette Valley were generally from
     one-third to two-thirds of an inch since midday Wednesday. The main
     area of rain had shifted into extreme southwestern Oregon by late
     this morning, where Medford picked up a tenth of an inch in the
     6-hour period ending at 11am this morning.

     Overnight temperatures were mild with minimums near 50 degrees across
     western Oregon.  Late-morning readings had warmed to near 60 degrees.
     Highs today will only climb into the lower 60s, due to cool air aloft
     enhancing convective mixing this afternoon. High mixing heights and
     strong onshore flow will make for good ventilation conditions across
     the Willamette Valley this afternoon.

     The late-morning ODA surface analysis showed the cold front
     stretching from northern Idaho, across northestern Oregon, to
     south-central Oregon.  Areas of rain accompanied the frontal
     zone, with more than one-tenth of an inch of rain falling at Meacham,
     in the Blue Mountains of NE Oregon, in just the past couple of
     hours.  Burns also picked up .05 inches of rain in the past 6 hours.
     Brisk southerly winds ahead of the front were rapidly turning
     westerly in the wake of the front, across eastern Oregon.

     Areas of light rain were continuing to show up on Doppler radar
     late this morning across much of eastern Oregon and extending into
     southwestern Oregon.  Visible satellite imagery continued to show some
     areas of clearing, mainly just east of the coast range and the Cascades,
     due to downsloping westerly winds.  A few showers were forming over
     northwestern Oregon, with daytime heating acting to destabilize the
     air mass.  The freezing level is only near 6000 feet, over northern
     Oregon, so convective clouds should increase this afternoon over
     northwestern Oregon with a few showers likely.

     Surface winds were southwesterly across the Willamette Valley this
     morning...gusting as high as 25 mph.  Winds were beginning to turn more
     westerly late this morning, as high pressure continued to build northward
     along the coast. Winds should become northwesterly later this afternoon,
     with the air mass rapidly stabilizing around sundown.
 
Surface Winds:
     W 5-15 G20...becoming NW 5-15 G20 later this afternoon.
Transport Winds:
     W 20...becoming WNW 15 later 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.
     Radiational cooling will locally drop valley temperatures into the
     upper 30s with patchy fog forming Friday morning.  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 will help valley temperatures climb into the lower 70s.

     A flat upper-level ridge is forecast to build over Oregon
     Saturday with valleys highs climbing to near 80 degrees.  A strong jet
     stream, moving over central British Columbia, could send high clouds 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 valley high temperatures near 80 degrees.  The surface thermal
     trough, and warmest weather, will shift east of the Cascades Monday.

     A developing southwesterly flow aloft will extend the marine push eastward
     Monday, with cooler air penetrating to the Idaho border by Monday night.
     A cold front will bring increasing clouds and a good chance of rain to
     northwestern Oregon by Monday evening with rain likely Monday night. A
     fairly vigorous upper-level trough is forecast to bring showers to the
     region Tuesday, with snow levels dropping to near the Cascade passes.

     A transitory and weak upper-level ridge is forecast to bring some drying
     and warming Wednesday.  Another cool weather system is forecast to drop
     down from the Gulf of Alaska, with increasing onshore flow again by late
     Thursday.  That system may be bring showers to northwest Oregon by Friday,
     with a cooler than normal start to the Memorial Day Weekend likely.

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):  Becoming Mostly Cloudy and Cooler.  Increasing Chance of Rain.  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