[willamette-fcst] Forecast - Tuesday, September 23rd, 2008
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Tue Sep 23 07:55:12 PDT 2008
Daily Smoke Management Forecast
Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.
Tuesday, September 23rd, 2008 at 9:00am.
Agricultural burning is allowed. Suggested burn times are from 2:00pm until 6:00pm.
Preparatory burning is not allowed.
Propane flaming is not allowed.
Stack burning is not allowed.
A transitory ridge of high pressure is forecast to bring
some sunshine and warmer temperatures to Oregon today.
Willamette valley highs should climb int the low 70s, which
is still slightly below aferage but much warmer than the mid
60s we saw Monday afternoon. The sounding over Salem this
morning showed considerable warming above 3500 feet compared
with Monday morning and more warming aloft is forecast
today. That will cap afternoon mixing heights near 3500.
Forecast northerly transport winds this afternoon makes open
The ODA surface analysis showed a weak thermal trough trying
to build northward, across Western Oregon, in reponse to
transitory upper-level ridge moving over the state.
Pressure gradients were weak northerly across the Western
Oregon this morning with a slight offshore component.
Clearing skies overnight allowed temperatures to drop to
their lowest values since last spring for many Western
Oregon locations. Hillsboro dipped to at least 36 degrees
this morning, and Eugene dropped to 37. McMinnville was not
much warmer at 38. Recent rains and cool surface
temperatures helped create areas of shallow valley fog this
morning, but it should be short-lived this morning.
Infrared satellite imagery showed an impressive-looking
cloud-shield from an approaching weather system about 300
miles offshore at mid-morning. Some middle and high clouds,
from this system, had already advanced onshore and over the
Willamette Valley this morning. The latest computer models
speed up the timing of this system, which does not bode well
for creating a burning opportunity. It will likely stay too
far offshore today, with transport winds remaining northerly
and the air aloft staying too warm. By Midday Wednesday, it
may be too close, with stong southwesterly winds near the
surface and rain moving into the Willamette Valley.
The best chance for a burning opportunity will be in the
early afternoon Wednesday, if the winds stay weak enough and
the rain has not moved onshore by that time. Fluffing of
damp fields would be required to take advantage of this
potential burning opportunity. It is looking more likely,
however, that the timing of this system will not allow for a
burning opportunity. We will monitor transport winds this
afternoon for the unlikely event that they react early to
the approaching storm and turn more westerly. That is not
forecast to happen until around sundown or shortly
NNE 5-10 this morning, NNE 5-10 this afternoon.
NE 10 this morning, N 7 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 3500 feet. Ventilation index 35.
Salem\'s high temperature today will be near 71.
Relative humidity drops to 50% by 1pm.
Minimum relative humidity will be near 38%.
Salem sunset tonight: 7:07pm; sunrise tomorrow: 7:02am.
Computer models had been holding off rain until late
Wednesday, which may have allowed for a burning opportunity
Wednesday afternoon. However, the latest guidance is
suggesting that light rain will move into the Northern
Willamette Valley as early as tomorrow morning with rain
slowly spreading south during the afternoon. The associated
upper-level trough should maintani a little shower activity
through Thursday...mainly in the north valley.
Interestingly, the bulk of the rain from this storm is
forecast to stay north of Oregon with only about one-tenth
of an inch projected to fall in the Willamette Valley. This
system has entrained some tropical moisture, and will
produce impressive low-level southwesterly winds, so I
suspect total rainfall amounts will be closer to one-quarter
of an inch in the upslope regions of the north valley, near
the Cascade Foothills.
The weak upper-level trough that was forecast to approach
the coastline Friday now appears as if it will stay north of
the region, with weak westerly flow aloft. However, it may
come close enough to turn transport winds onshore and create
a burning opportunity, for dry fields, Friday afternoon.
The long-range models are still forecasting a stronger ridge
of high pressure to build over the Pacific Northwest
beginning Saturday with a return to above normal
temperatures. Weak west-northwesterly flow aloft is
forecast Saturday. The upper-level ridge to forecast to
amplify just east of the region Sunday, putting Western
Oregon under weak southwesterly flow aloft with possible
offshore flow at the surface.
The upper-level ridge is forecast to slowly slide eastward,
early next week, with a series of weather systems coming
onshore beginning as early as late Monday. This transition may
bring another burning opportunity early next week, and then
there is every indication that the 2008 burn season will
come to a wet conclusion.
Tomorrow (24 Sep): Cloudy and Blustery with Rain Spreading South During the Day. 48/69
Thu (25 Sep): Mostly Cloudy North with a Chance of Showers. Partly Cloudy South. 50/67
Fri (26 Sep): Partly Sunny. 46/73
Sat (27 Sep): Partly Sunny. 47/76
Sun (28 Sep): Sunny and Warm. 47/80
Mon (29 Sep): Increasing Clouds. 48/77
Tue (30 Sep): Increasing Chance of Rain. 49/69
weather at oda.state.or.us
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