[willamette-fcst] Forecast - Monday, June 29th, 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.

State Fire Marshal Conditions May Be Met This Afternoon Due to Low Humidity and Wind...

Issued: 
     Monday, June 29th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     A flat upper-level ridge of high pressure over the Pacific
     Northwest is allowing weak weather systems to skirt across
     southern British Columbia.  The southern end of a dry cold
     front swept across Washington and Oregon Saturday night and
     Sunday.  It did not produce much in the way of cloudiness,
     and only trace amounts of rain as far south as the extreme
     northwest corner of Oregon.  However, increasing onshore
     flow cooled temperatures in the Willamette Valley from the
     mid 80s on Saturday to the upper 70s on Sunday.

     A dry and weak westerly flow aloft prevailed over Washington
     and Oregon this morning.  Satellite imagery showed a pretty
     solid coverage of marine low clouds banked up against the
     Washington and extreme northern Oregon coastlines...about as
     far south as Lincoln City.  In the wake of the dry cold
     front, the Salem sounding this morning showed some minor
     cooling, compared with Sunday morning, below 4200 feet, with
     not much change aloft.  North-northeasterly winds just above
     the surface turned northerly above about 3000 feet and
     westerly above 10,000 feet.  That windflow pattern is not
     westerly enough to force marine low clouds east of the
     coastal range, so skies were generally sunny over the
     interior of Washington and Oregon.

     With clear skies overnight and a fairly dry air mass in
     place, temperatures were able to drop well into the 40s
     across the Willamette Valley this morning.  McMinnville was
     one of the colder spots with a minimum of 43 degrees.  The
     Portland area was about the only spot to stay above 50
     degrees overnight, likely due to the urban heat-island
     effect. Meacham, in northeastern Oregon, was the cold spot
     in the state this morning with a low of 35 degrees.

     The mid-morning ODA-surface analysis showed high pressure
     nosing into the Washington Coast with weak troughs of low
     pressure over eastern Washington and southeastern Oregon. 
     Surface gradients were mostly northerly across Oregon,
     except for westerly channeling through the Columbia Gorge. 
     Northerly winds were already increasing to about 15 mph
     along the coast and in the southern Willamette Valley. 
     Temperatures were mostly in the mid to upper 50s across
     western Oregon and ranged from the upper 50s to the mid 70s
     east of the Cascades.  The warmest temperatures were along
     the Idaho Border.

     A very weak upper-level trough will maintain westerly flow
     aloft today.  Morning clouds along north coast should clear
     this afternoon with sunny skies continuing elsewhere across
     Oregon.  Northerly winds will increase through this
     afternoon along the coast and in the Willamette Valley, as a
     surface thermal trough attempts to build into southern
     Oregon and tightens the pressure gradients.  State Fire
     Marshal conditions may locally be reached later this
     afternoon, in the Willamette Valley, as humidity levels drop
     to or below 30 percent with northerly winds at or above 15 mph.

Surface Winds:
     N 5-15 this morning, N 10-17 G25 this afternoon.
Transport Winds:
     NNE 15 this morning, N 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4200 feet.  Ventilation index 84.
High Temperature:
     Salem\'s high temperature today will be near 79.
Humidities:
     Relative humidity drops to 50% by 10am.
     Minimum relative humidity will be near 29%.
Sunrise/Sunset:
     Salem sunset tonight: 9:02pm; sunrise tomorrow: 5:29am.

Extended Outlook:
     The weak upper-level trough over the region will shift east
     Tuesday, with the flow aloft turning northwesterly and
     warming Tuesday and Wednesday.  That should continue to
     bring sunshine to the interior of Washington and Oregon with
     some morning low clouds restricted to the immediate
     coastline.  After morning minimums in the 40s to low 50s,
     afternoon highs should warm into the lower 80s Tuesday and
     mid to upper 80s Wednesday.  State Fire Marshal Conditions
     may be reached again, in the afternoons, due to low
     humidites and brisk northerly winds.

     The jet stream will migrate even farther north on Thursday,
     with the flow aloft turning southwesterly.  The surface
     thermal trough will build northward into Oregon.  That may
     warm valley temperatures to near 90 and will introduce a
     chance of afternoon thunderstorms to southern Oregon.
     Increasing southwesterly flow aloft will likely shift the
     surface thermal trough eastward, into central and eastern
     Oregon, Friday and Satruday, along with the warmest temperatures.

     By Saturday night or Sunday, a strong enough upper-level
     trough may approach the coastline to introduce a chance of
     showers or thundershowers to the state, along with continued
     cooling.  There appears to be a good chance of a significant
     marine push and chance of showers by the end of the weekend
     and early next week.

Tomorrow (30 Jun):  Sunny.  Brisk Afternoon Northerly Winds.  47/81

Wed (01 Jul):  Sunny and Warmer.  Brisk Afternoon Northerly Winds.  49/88

Thu (02 Jul):  Mostly Sunny and Very Warm.  52/90

Fri (03 Jul):  Sunny.  53/86

Sat (04 Jul):  Patchy AM Clouds...Mostly Sunny and Cooler.  53/83

Sun (05 Jul):  Becoming Mostly Cloudy and Cooler.  Increasing Chance of Showers.  53/77

Mon (06 Jul):  Mostly Cloudy and Much Cooler.  Chance of Showers.  53/70

ODA Meteorologist
weather at oda.state.or.us