[willamette-fcst] Forecast - Thursday, July 2nd, 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 Reached This Afternoon...

Issued: 
     Thursday, July 2nd, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:     
     An upper-level ridge is contining to build over the region today.  The morning sounding
     over Salem showed several degrees of warming aloft, between 3000 and 7000 feet,
     compared with Wednesday, so surface temperatures should also be warmer this
     afternoon.  The late-morning ODA surface analysis showed a broad thermal trough
     extending northward, from southwestern Oregon, into southwestern Washington.  That
     has relaxed the northerly pressure gradients across western Oregon with winds
     generally 10 mph or less as of late this morning.  Temperatures had already warmed
     into the mid to upper 70s along the north coast and across the Willamette Valley.
     
     The low-level flow had turned onshore, south of Cape Blanco, on the southern
     Oregon Coast, with late-morning temperatures only in the 50s.  That is typical of a
     developing heat-wave pattern across the interior of western Oregon.  Visible satellite
     imagery showing coastal low clouds and fog along the northern California Coast, extending
     northward to the extreme southern Oregon Coast.  Skies were sunny, with northerly winds,
     north of Cape Blanco.  Highs will range from the mid to upper 60s, on the central coast,
     to well into the 70s along the north coast.  Low clouds and fog could be quite persistent
     along the south coast with onshore flow holding temperatures in the 50s.  

     Sunny skies covered the remainder of the state at midday, except for convective cloud
     development pushing northward, from Nevada, into south-central and southeastern Oregon.
     Radar was not showing any showers, yet, with these clouds, but a few should develop this
     afternoon, along with isolated thunderstorms.  Some storms could produce strong gusty
     winds.  Due to dry air in the low-levels of the atmosphere, these storms are not likely
     to produce much rain, with potential lightning increasing the wildfire risk.
     Temperatures east of the Cascades will range from the upper 70s to the mid 90s, with the
     warmest readings near the Idaho border.

     Daytime heating will intensify the thermal trough over western Oregon this afternoon,
     especially over the southwest interior.  That will produce some increase in northerly
     winds along the north and central coast and across the Willamette Valley.  However,
     winds winds not be as strong as they have been the past few days...peaking around
     15 mph in the Willamette Valley later this afternoon. The combination of low humidity
     levels, increasing northerly winds, and hot temperatures (highs in the low to mid 90s)
     may push sections of the Willamette Valley into Fire Marshal conditions this afternoon.

Surface Winds:
     N 7-15 this afternoon.
Transport Winds:
     N 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3200 feet.  Ventilation index 38.
High Temperature:
     Salem\'s high temperature today will be near 95.
Humidities:
     Minimum relative humidity will be near 17%.
Sunrise/Sunset:
     Salem sunset tonight: 9:02pm; sunrise tomorrow: 5:31am.

Extended Outlook:
     Increasing southwesterly flow aloft will likely shift the broad surface thermal trough
     just far enough eastward to allow some very weak onshore flow into western Oregon
     Friday and Saturday.  That should keep high temperatures from climbing above the mid 90s,
     but it is going to remain very warm through the holiday weekend...especially east of the
     Cascades.  There will continue to be a threat of isolated afternoon thunderstorms across
     mainly south-central and southeastern Oregon.

     A farily strong trough is forecast to approach the coastline Sunday, turning the flow aloft
     more southerly and shifting the surface thermal trough into eastern Oregon.  That will
     initiate a significant marine push by late in the day.  There may be enough upper-level
     energy and moisture for showers or thundershowers during this transition, mainly from
     the Cascades eastward.  It is possible, if the flow aloft turns southerly enough, for
     thundershowers to develop over the Willamette Valley, but that is too far out to call.

     Long-range computer models show the strong upper-level trough moving over the Pacific
     Northwest early next week.  Much cooler weather is forecast for Monday and Tuesday, with
     a chance of showers.  The trough is forecast to weaken, as it stalls over the region
     Wednesday and Thursday.  That would maintain onshore flow and below normal temperatures,
     with a continued risk of showers.

Tomorrow (03 Jul):  Sunny and Very Warm.  55/95

Sat (04 Jul):  Sunny and Very Warm.  56/95

Sun (05 Jul):  Increasing Chance of Showers or T-Storms Late.  56/86

Mon (06 Jul):  Mostly Cloudy and Much Cooler.  Chance of Showers.  55/73

Tue (07 Jul):  Mostly Cloudy.  Chance of Showers.  53/72

Wed (08 Jul):  Mostly Cloudy.  Chance of Showers.  53/72

Thu (09 Jul):  Partly Cloudy.  53/76

ODA Meteorologist
weather at oda.state.or.us