[willamette-fcst] Forecast - Thursday, December 10th, 2009
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Thu Dec 10 09:15:34 PST 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.
Issued:
Thursday, December 10th, 2009 at 9:00am.
Burn Advisory:
Agricultural burning is not recommended.
Stack burning is not allowed.
Weather Discussion:
A very cold and dry air mass will remain in place over
Washington and Oregon today. With the exception of a few
mid and high-level clouds, satellite imagery and surface
reports show mostly clear skies over both states. The ODA
surface analysis showed high pressure centered near the
eastern end of the Columbia Gorge, with continued weak
offshore flow across western Oregon. Light winds and clear
skies allowed temperatures to locally drop into the single
digits across the Willamette Valley early this morning.
Even the southwestern valleys dropped well down into the
teens, with coastal minimums mostly in the low 20s.
The very cold northerly jet stream, that brought the Arctic
air into the region, is slowly shifting east...allowing
temperatures aloft to begin warming. The Salem sounding
from early this morning showed several degrees of warming,
between 2000 feet and 16,000 feet. A strengthening
low-level temperature inversion is is making for poor
ventilation conditions. Even though the air mass aloft is
warming, temperatures were still below freezing.
Another full day of sunshine is expected today, but the
shortened day and low sun-angle will not allow for enough
surface warming to break the strong low-level temperature
inversion. Valley highs, once again, will struggle to get
to the freezing mark. Winds will remain light from the
north-northeast, except for near the western end of the
Columbia Gorge, where easterly winds will gust to around 30
mph...making for very cold windchill temperatures.
Surface Winds:
NNE 0-6 this morning, NNE 3-8 this afternoon.
Transport Winds:
NNE 6 this morning, NNE 6 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 1700 feet. Ventilation index 10.
High Temperature:
Salem\'s high temperature today will be near 31.
Humidities:
Minimum relative humidity will be near 40%.
Sunrise/Sunset:
Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:40am.
Extended Outlook:
Skies should remain mostly clear overnight across the
Willamette Valley, making for very cold temperatures, again,
Friday morning. However, some changes will begin to show up
by Friday afternoon. The flow aloft over Oregon will turn
westerly, with clouds increasing across southern Oregon, as
a Pacific weather system moves into California. Clouds will
begin to increase, from the south, across the Willamette
Valley, Friday afternoon and evening. Continued
north-northeastery surface winds will maintain the cold
layer of air, below about 2000 feet, while the upper-levels
of the atmosphere warm above freezing. That will set the
stage for a wintry mix of precipitation Friday night and Saturday...
By early Saturday morning, enough moisture is forecast to
spread northward into the Willamette Valley for
precipitation to begin. The air mass aloft will be
continuing to warm, but low-level cold air will reamin
entrenched across the Willamette Valley. The cold air mass
will be deepest in the north valley, where precipitation
will likely begin as all snow. However,the air aloft over
the central and south valley will be warmer, so some sleet
and/or freezing rain is likely to at least mix with snow.
Precipitation amounts are not forecast to be heavy, with
most of the moisture staying south of the region. However,
even small amounts of freezing rain can make for very
hazardous travel conditions.
Precipitation is expected to taper off Sunday, with the
low-level flow turning weakly onshore. That should help most
of the Willamette Valley transition to just plain rain.
However, there could still be enough cold air coming out of
the Columbia Gorge to keep wintry precipitation in the
immediate Portland area. Another weather system is forecast
to come onshore late Monday. There could still be enough
cold air remaining in the Columbia Gorge, and the immediate
Portland area, for a wintry mix of precipitation, but the
rest of the Willamette Valley should get just rain. Even
the Gorge should get scoured out by Tuesday, with warmer
Pacific air moving back into the region.
Tomorrow (11 Dec): Mostly Sunny and Cold Early. Increasing Clouds. 15/34
Sat (12 Dec): Snow, Sleet, or Freezing Rain...Likely Changing to Rain South. 28/35
Sun (13 Dec): Showers...Possible Wintry Mix Near the Gorge. 32/42
Mon (14 Dec): Mostly Cloudy. Chance of Rain...Possible Freezing Rain North. 32/40
Tue (15 Dec): Rain. Possibly Starting as Freezing Rain North. 32/47
Wed (16 Dec): Mostly Cloudy and Warmer. Rain Likely Late. 37/49
Thu (17 Dec): Rain Turning to Showers. 42/49
ODA Meteorologist
weather at oda.state.or.us
More information about the willamette-fcst
mailing list