[willamette-fcst] Forecast - Thursday, July 2nd, 2009

Thu Jul 2 09:14:14 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 May Be Reached This Afternoon...

Issued: 
     Thursday, July 2nd, 2009 at 9:00am.

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

Weather Discussion:
     The upper-level ridge over the region built slightly further
     north Wednesday with the associated surface thermal trough
     pushing orthward, as well, into western Oregon.  That helped
     temperatures climb into the mid 70s along the northern
     Oregon Coast and upper 80s to low 90s in the Willamette
     Valley.  Southwestern Oregon temperatures reached the upper
     90s.  Very dry and fairly brisk northerly winds, gusting to
     25 mph, lowered relative humidity levels well below 30%
     Wednesday afternoon, resulting in Fire Marshal conditions
     across most of the Willaemette Valley.

     With a very dry air mass in place, clear skies overnight
     allowed for strong radiational cooling, and temperatures
     dropped back into the 40s and 50s across western Oregon.
     Newport dipped to 43 degrees, with Tillamook and Astoria
     dropping to 45 and 46 degrees respectively.  McMinnille was
     the cold spot in the Willamette Valley this morning with a
     minimum of 46 degrees.  Portland was the warm spot, due to
     the urban heat-island effect, with a minumum of 63 degrees. 
     Most of the Willamette Valley dropped into the low to mid 50s.

     Sunny skies east of the Cascades Wednesday lifted
     temperatures into the 80s and low 90s.  There was a wide
     range of temperatures across central and eastern Oregon this
     morning...ranging from a minimum of 35 degrees in Meacham to
     a balmy low of 58 degrees in Ontario. 

     The upper-level ridge is contining to build over the region.
     The morning sounding over Salem showed a couple of more
     degrees of warming aloft, between 3000 and 7000 feet,
     compared with Wednesday, so surface temperatures should also
     be a few degrees warmer this afternoon.  The ODA surface
     analysis showed a broad thermal trough extending northward,
     from California, clear into southwestern Washington.  That
     has relaxed the northerly pressure gradients across western
     Oregon.  The winds had turned onshore along the southern
     Oregon Coast, with visible satellite imagery showing coastal
     low clouds and fog advancing northward to about Cape Blanco.
     Sunny skies covered the remainder of the state.  Light
     Southwesterly flow aloft was circulating some mid and
     high-level clouds across south-central and eastern Oregon.

     Daytime heating will intensify the thermal trough over
     western Oregon, especially over the southwest interior. 
     That will produce some increase in northerly winds from the
     north coast to the southwestern valleys, again, this
     afternoon. However, winds should 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 temperatures warming into the low to mid 90s may
     push sections of the Willamette Valley into Fire Marshal
     conditions again this afternoon.  Warm air aloft will also
     keep mixing heights from climbing much above 3000 feet.  The
     northern and central coast will also see sunny skies with
     not as much northerly wind today.  Highs will peak in the
     upper 60s along the central coast and mid 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.  Temperatures east of the Cascades will range
     from the upper 70s to the mid 90s, with the warmest readings
     near the Idaho border.

Surface Winds:
     N 5-12 this morning, N 7-15 this afternoon.
Transport Winds:
     NNE 7 this morning, 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 westerly flow aloft will likely shift the broad
     surface thermal trough just far enough eastward to prevent
     western Oregon temperatures from warming much more, if at
     all, Friday and Saturday, but it will remain very warm.  The
     warmest temperatures will likely shift east of the cascades
     with the threat of afternoon thunderstorms increasing across
     mainly southern and eastern Oregon Friday...shifting to near
     the Idaho border Saturday.

     A stronger trough is forecast to approach the coastline
     Sunday, turning the flow aloft southerly and initiating a
     significant marine push late in the day.  There may be
     enough moisture introduced into the region for showers or
     thundershowers during this transition to a cooler air mass. 
     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.

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.  53/77

ODA Meteorologist
weather at oda.state.or.us