[willamette-fcst] Willamette Valley Ag/Burning Forecast

[Willamette Valley Ag/Burning Forecast]

Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette 
Valley Growers and Fire Districts.

Issued:
      Thursday, December 24th, 2009 at 9:00am.

Burn Advisory:
      Agricultural burning is not recommended.
      Stack burning is not allowed.

Weather Discussion:
      A strong upper-level ridge of high pressure is 
continuing
      the dry northwesterly flow aloft over the Pacific 
Northwest.
      The freezing level over western Oregon is around 
9000 feet,
      with the warm air aloft trapping cold air near the 
interior
      valley surfaces.  Fog is widespread again this 
morning
      across the Willamette Valley.  Visibilities are 
around
      one-quarter of a mile, or less, in most areas.  The 
moist
      low-level air held valley temperatures near the 
freezing
      mark overnight, with some spots dropping into the 
upper 20s.

      The mid-morning ODA surface analysis showed 
increasing
      offshore flow, with high pressure strengthening over 
eastern
      Washington and a thermal trough building northward 
along the
      southern Oregon coast.  Easterly winds were keeping 
the
      coastline clear this morning, where sushine had 
already
      warmed temperatures into the mid to upper 30s. 
 Meanwhile,
      only a light northerly drift was being felt in the 
foggy
      Willamette Valley, at mid-morning, with temperatures 
ranging
      from the upper 20s to just above freezing.  Easterly 
outflow
      was beginning to increase at the western end of the 
Columbia
      Gorge but had not penetrated as far west as 
Troutdale, where
      it was still foggy.

      Very still air overnight allowed temperatures to 
drop into
      the single digits across sections of central and 
eastern
      Oregon by early this morning.  Meacham, in 
northeastern
      Oregon, was just 1 degree above zero at mid-morning. 
 Burns
      recorded a minimum of 4 degrees and Lakeview dipped 
down to
      7 degrees.  Redmond, in north-central Oregon, had a 
minimum
      of 11.

      Easterly outflow is forecast to increase, from the 
Columbia
      Gorge, and will help to clear fog from the extreme 
north
      valley later today.  However, fog and low clouds 
should be
      more persistent from about Salem southward to 
Eugene.
      Valley highs will struggle into the mid to upper 30s 
in the
      foggy south valley but should climb into the low 
40s, where
      the sun is able to pierce the fog, in the north 
valley.  Low
      level temperatures inversions will continue to make 
for poor
      ventilation conditions.

      It will be a foggy Chistmas Eve for most of the 
central and
      southern Willamette Valley, where Santa will need 
Rudolph to
      deliver his toys.  It will also be chilly, again, 
with
      temperatures near the freezing mark.  Increasing 
easterly
      winds will likely keep fog from forming in the 
western
      Columbia Gorge and much of the immediate Portland 
area.

Surface Winds:
      NNE 3-8 this morning, NNE 5-10 this afternoon.
Transport Winds:
      NNE 8 this morning, NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
      Maximum mixing height today will be near 1500 feet. 
 Ventilation index 15.
High Temperature:
      Salem's high temperature today will be near 42.
Humidities:
      Minimum relative humidity will be near 59%.
Sunrise/Sunset:
      Salem sunset tonight: 4:35pm; sunrise tomorrow: 
7:49am.

Extended Outlook:
      The upper-level ridge of high pressure will move 
directoy
      over Oregon Christmas Day, with continued dry 
conditions.
      At the surface, increasing offshore flow should dry 
the air
      mass enough in the north valley for mostly sunny 
skies.
      However, the central and south valley will have 
considerable
      fog and low clouds.  High temperatures will vary 
from the
      upper 30s to the mid 40s, depending on the extent of 
fog.
      The coolest readings should be in the south valley.

      The upper-level ridge is forecast to shift east of 
the
      region on Saturday, with a weak weather system 
moving
      onshore late in the day.  A split-flow pattern in 
the
      westerly jet stream will take most of the punch out 
of that
      system, with only a slight chance of sprinkles 
making it
      onshore Saturday night...mainly near the California 
border.
      However, increasing offshore winds may break up the 
fog
      across more of the Willamette Valley.

      The next weather system is forecast to move mainly 
south of
      the region, into California, Sunday and Monday. 
 Some middle
      and high clouds could spread across western Oregon, 
but it
      is unlikely that this system will be strong enough 
to lift
      the fog from the Willamette Valley.  The next system 
is
      forecast to come onshore late Tuesday or Wednesday 
of next
      week, but it may not be strong enough to produce 
much in the
      way of rain.  A stronger system is forecast to 
finally break
      through the ridge and bring some rain, to close out 
the
      year, on Thursday.

Tomorrow (25 Dec):  Sunny North.  Fog Central and South 
with PM Clearing.  27/43

Sat (26 Dec):  Foggy Morning Central and 
South...Increasing Clouds PM.  27/43

Sun (27 Dec):  Mostly Cloudy/Foggy.  30/44

Mon (28 Dec):  Mostly Cloudy/Foggy.  32/45

Tue (29 Dec):  Mostly Cloudy.  Slight Chance of Rain Late. 
 Snow Level 4000 Feet.  33/45

Wed (30 Dec):  Mostly Cloudy.  Slight Chance of Rain. 
 Snow Level 4-5000 Feet.  34/45

Thu (31 Dec):  Rain Likely and Warmer.  Snow Level Rising 
to 6000 Feet.  35/50

ODA Meteorologist
weather at oda.state.or.us