[willamette-fcst] Forecast - Monday, December 1st, 2008

[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.

NOON UPDATE

...Updated to include stack burning today...

Issued: 
     Monday, December 1st, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is not recommended.
     Straw stack burning is allowed from 12:00pm until 3:00pm.

Weather Discussion:
     The protective ridge of high pressure, that has been
     dominatng the weather across the Pacific Northwest for the
     past couple of weeks, will temporarily weaken enough to
     allow a fast-moving weather system to bring a little rain to
     western Oregon this evening through early Tuesday.  The
     approaching cold front was about 150 miles offshore late
     this morning.  Middle and high clouds spread across western
     Oregon early this morning but pushed east of the cascades by
     late this morning.  Much of western Oregn saw a few hours of
     clearing earlier this morning, but satellite imagery showed
     low clouds rapidly advancing onshore, into the western
     Willamette Valley, late this morning.

     The Salem sounding from early this morning continued to show
     a strong low-level temperature inversion, with surface
     temperatures in the 40s and 3000-foot temperatures in the
     upper 50s.  However, the late-morning ODA surface analysis
     showed increasing southeasterly gradients across most of
     Oregon, in response to the approaching weather system. 
     Southerly winds were gusting between 30 and 40 mph, along
     the coast, from Astoria to Newport.  Willamette Valley winds
     were south-southeasterly between 5 and 15 mph.

     The increasing southerly winds were helping mix warmer air
     aloft down to the surface, with late-morning temperatures in
     the low to mid 50s along the coast and in the Willamette
     Valley.  That had lifted the fog from the valley.  As the
     front approaches, ventilation conditions will continue to
     improve, so stack burning is allowed today until 3 p.m.  The
     cold front is forecast to move onshore late this afternoon
     and should be strong enough to bring about one-quarter of an
     inch of rain to the coast and Willamette Valley by Tuesday morning.

Surface Winds:
     SSE 10-15 G20 Late this afternoon.
Transport Winds:
     S 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 70.
High Temperature:
     Salem\'s high temperature today will be near 57.
Humidities:
     Minimum relative humidity will be near 75%.
Sunrise/Sunset:
     Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:32am.

Extended Outlook:
     The upper-level ridge is expected to rebuild over the region
     beginning Tuesday afternoon and may hold fast into the
     weekend.  That will result in deteriorating ventilation
     conditions by Wednesday with areas of valley fog reforming. 
     The fog and low clouds will be slow to clear, Wednesday and
     Thursday afternoon, especially in the central and southern
     valley.  Increasing offshore flow will help generate enough
     easterly outflow, from the Colubia Gorge, to keep widespread
     fog out of the extreme north valley by Thursday.

     The ridge of high pressure is forecast to remain over the
     region into Saturday.  Some flattening of the ridge may
     begin late Saturday with a chance of light rain as early as
     Sunday.  However, there is considerable disagreement in the
     long-range models regarding how and when the ridge will
     break-down.  A major change in the weather pattern is likely
     after next weekend, but exactly what form that will take
     remains to be seen.

Tomorrow (02 Dec):  Decreasing Showers.  46/54

Wed (03 Dec):  Morning Low Clouds and Fog.  Partial Afternoon Clearing.  37/50

Thu (04 Dec):  Morning Low Clouds and Fog.  Partial Afternoon Clearing.  36/50

Fri (05 Dec):  Morning Low Clouds and Fog.  Partial Afternoon Clearing.  36/50

Sat (06 Dec):  Mostly Cloudy.  Continued Mild.  37/52

Sun (07 Dec):  Chance of Showers.  39/50

Mon (08 Dec):  Areas of Fog.  Partial Afternoon Clearing.  36/50

ODA Meteorologist
weather at oda.state.or.us