[willamette-fcst] Forecast - Tuesday, July 28th, 2009

Tue Jul 28 08:37:31 PDT 2009

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 will likely be met by early this afternoon...

Issued: 
     Tuesday, July 28th, 2009 at 8:35am.

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

Weather Discussion:
     Temperatures soared over 100 degrees across the Willamette
     Valley Monday afternoon, with the hot and dry air sending
     the valley into State Fire Marshall conditions.  Many
     locations approached their daily record high temperatures
     Monday, but most of the established records were quite warm
     due to a hot spell in 1998.  Eugene reached 102 degrees. 
     Salem and Corvallis hit 103...none of which was a record. 
     However, 103 degrees at Portland and Troutdale did set new
     daily record highs.  Most daily records in the valley are
     much lower today, so many should be broken.

     One all-time record that was tied yesterday was the warmest
     minimum temperature in Salem, at 70 degrees.  That may be
     broken today, because the recorded minimum, so far this
     morning, at the Salem Airport was 71 degrees.  The final
     minimum will be reported by the automated weather station at
     11am, but this could be the warmest morning on record in
     Salem.  Of course, the growth of the city over the past
     century makes that record less meaningful, because of the
     urban heat-island effect, but it is still a long-standing
     record (over a century) that may be broken today.

     A strong upper-level ridge of high pressure remains parked
     along the west coast of North America this morning.  On the
     surface, a well-developed thermal heat-low extends northward
     across the Willamette Valley and into southwestern
     Washington.  Dry northerly or northeasterly flow and clear
     skies prevail across all of western Oregon this morning,
     except for along the southern coast.  Temperatures range
     from near 50 on the south coast, with low clouds and fog, to
     the 60s on the north coast, under sunny skies.  Inland,
     mid-morning temperatures were running several degrees warmer
     than 24 hours ago, with some Willamette Valley locations
     already in the low 80s.

     It promises to be a scorcher today across the interior of
     western Oregon.  Willamette Valley highs should climb even
     warmer than on Monday with many locations maxing out around
     105 degrees.  Dry north-northeasterly flow and hot
     temperatures will likely push most of the Willamette Valley
     into State Fire Marshal Conditions by 2-3pm this afternoon. 
     With the thermal trough expanding to the coast, temperatures
     there should climb into the 70s and 80s today.  The warmest
     coastal temperatures will be in the north, with onshore flow
     more reluctant to give way on the south coast.

Surface Winds:
     N 3-8 this morning, N 5-15 this afternoon.
Transport Winds:
     NNE 8 this morning, N 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 105.
Humidities:
     Relative humidity drops to 50% by 10am.
     Minimum relative humidity will be near 21%.
Sunrise/Sunset:
     Salem sunset tonight: 8:43pm; sunrise tomorrow: 5:55am.

Extended Outlook:
     Computer models show little change in the weather pattern
     Wednesday and Thursday, with more record-breaking heat
     across western Oregon. Willamette Valley highs will likely
     cool a couple of degrees by Thursday but may still top 100
     degrees.  Overnight minimums will continue to struggle to
     get much below 70 degrees in urban areas.  The impressively
     strong upper-level ridge may shift eastward enough by
     Thursday to return onshore flow to the immediate coastline
     for more pronounced cooling there...especially from about
     Newport south.

     The upper-level ridge is forecast to shift far enough east
     by Friday to send the surface thermal trough east of the
     Cascades.  That should bring enough onshore flow into
     western Oregon to cool Willamette Valley highs back into the
     90s.  By the weekend, increasing southerly flow aloft may
     introduce a chance of thunderstorms to most of the state,
     along with moderating temperatures.  That would be a typical
     scenario following an intense heat-wave, but the computer
     models are still not clear on the details of how this hot
     pattern will break down.

Tomorrow (29 Jul):  Sunny and Hot.  70/105

Thu (30 Jul):  Sunny and Hot.  67/100

Fri (31 Jul):  Sunny.  A Little Cooler with Weak Onshore Flow.  62/95

Sat (01 Aug):  Partly Cloudy.  Muggy.  Chance of T-Storms.  62/93

Sun (02 Aug):  Mostly Cloudy.  Muggy.  Chance of T-Storms.  60/90

Mon (03 Aug):  Mostly Cloudy.  Chance of Showers or T-Storms.  Cooler.  58/86

Tue (04 Aug):  Mostly Cloudy.  Chance of Showers and T-Storms.  57/83

ODA Meteorologist
weather at oda.state.or.us