[willamette-fcst] Willamette Valley Ag Weather Forecast

Willamette Valley Ag/Burning Forecast willamette-fcst at listsmart.osl.state.or.us
Thu Oct 8 10:07:41 PDT 2009


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

Issued: Thursday, October 8th, 2009 at 9:00am.

Burn Advisory:

Agricultural burning is allowed.  Suggested burn times are 
from 12:00pm until 4:30pm.
Propane flaming is allowed from 12:00pm until 5:00pm.
Stack burning is not allowed.

Weather Discussion:
      A strong upper-level ridge of high pressure remains 
over the eastern Pacific Ocean with a cool 
north-northwesterly flow aloft over Washington and Oregon. 
 Satellite imagery showed considerable high clouds 
streaming southward over both states.  Light winds and 
fair skies allowed temperatures to drop into the 30s 
across much of the Willamette Valley. McMinnville dipped 
to 35 degrees.  Hillsboro and Eugene both dropped to 38. 
 The overnight cooling led to areas of fog this morning 
along the coast and in the Willamette Valley. Visibilities 
dropped to as low as one-eighth of a mile in the 
west-Eugene area.

Daytime heating should evaporate the areas of fog by 
midday with filtered afternoon sunshine.  The Salem 
sounding   continued to show rather warm air aloft, with 
the freezing level at 12,000 feet.  Afternoon temperatures 
should be able to recover into the mid to upper 60s, 
depending on how quickly the fog burns off.  The ODA 
surface analysis showed a very weak thermal trough along 
the coastline with little to not pressure gradient across 
the Willamette Valley.

Another cold weather system is forecast to slide down the 
 eastern flank of the ridge and into Montana late today. 
   That is forecast to drop surface pressures enough 
across eastern Washington and northeastern Oregon to turn 
the low-level flow onshore across western Oregon late this 
afternoon and this evening.  The weak marnine push should 
bring low clouds back onto the coastline overnight with 
possible areas of light drizzle.  Low clouds should also 
make their way into the Willamette Valley by Friday 
morning...helping to keep overnight temperatures in the 
40s. There is a slight chance of light drizzle in the 
Portland area Friday morning.

As the cold weather system continues southward into the 
northern Rockies Friday, colderlow-level Canadian air will
begin pouring into eastern Washington.  That will raise 
surface pressures east of teh Cascades and cut off the 
onshore flow into western Oregon.  Drying northerly winds 
will help to break up the marine low clouds Friday 
afternoon, with temperatures recovering into the mid 60s.

Surface Winds:
      N 0-7 this morning, NW 5-10 this afternoon.
Transport Winds:
      N 7 this morning, NW 7 this afternoon.
Atmospheric Ventilation Conditions:
      Maximum mixing height today will be near 3000 feet. 
 Ventilation index 21.
High Temperature:
      Salem's high temperature today will be near 68.
Humidities:
      Relative humidity drops to 50% by 2pm.
      Minimum relative humidity will be near 44%.
Sunrise/Sunset:
      Salem sunset tonight: 6:39pm; sunrise tomorrow: 
7:21am.

Extended Outlook:
      Cold air is forecast to continue to pour into 
Montana and eastern Washington Saturday, which will 
generate a cold easterly outflow from the Columbia Gorge, 
into the Willamette Valley.  That will help clear skies 
but keep  temperatures below normal.  Overnight 
temperatures will be  especially chilly by Sunday morning, 
with frost likely in many locations.

The upper-level ridge is forecast to build more directly 
over the west coast by Sunday, with warmer air aloft but
continued cool low-level offshore flow.  The ridge is
forecast to break down and shift east early next week, 
with
increasing westerly flow aloft opening the door for a 
series
of Pacific storms to bring widespread rains onshore.

Fri (09 Oct):  Morning Clouds.  Becoming Partly Sunny. 
 42/65

Sat (10 Oct):  Mostly Sunny.  Offshore Flow Developing. 
 36/65

Sun (11 Oct):  Mostly Sunny.  Offshore Flow.  30/65

Mon (12 Oct):  Increasing Clouds.  Chance of Rain Late. 
 Strong Offshore Flow.  40/63

Tue (13 Oct):  Rain Likely.  Southeast Winds.  46/61

Wed (14 Oct):  Showers Likely.  48/62

Thu (15 Oct):  Mostly Cloudy.  Chance of Showers.  47/64

ODA Meteorologist
weather at oda.state.or.us



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