[willamette-fcst] Forecast - Thursday, July 26th, 2007
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Thu Jul 26 12:02:14 PDT 2007
Daily Smoke Management Forecast
Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.
Thursday, July 26th, 2007 at 12:00pm.
Agricultural burning is allowed. Suggested burn times are from 3:00pm until 6:00pm.
Preparatory burning is not allowed.
Propane flaming is allowed from 3:00pm until 6:00pm.
Stack burning is not allowed.
An upper-level ridge of high pressure is centered over the
Rocky Mountains, with a large trough of low pressure in the
Northern Gulf of Alaska. That is giving the Pacific Northwest
a southwesterly flow aloft and onshore flow at the surface.
The low-level onshore flow increased this morning, as a a very weak
weather disturbance approached the Washington and Oregon Coast. Visible
satellite imagery still showed a solid deck of marine low clouds from the
coast to the Cascades late this morning. The base of the cloud deck has
been measured over Salem at 1600 feet with pilot reports showing cloud-tops
at 3000 feet. That is a thick enough layer so that break-up will not likely
begin before 2pm. I have lowered my high temperature and mixing height
forecasts accordingly. The start times for agricultural and propane burning
have also been changed from 1pm to 3pm.
The chances for a burn opportunity are low this afternoon. The low clouds
need to break up, before we can launch pibals, then the surface tempertures
need to reach the middle 70s, before mixing heights rise above 3000 feet.
I don\'t expect that to happen until at least 3-4pm, so that doesn\'t leave much
of a burning window.
It is possible that the weak cold front will help to break up the low-cloud
deck, as it moves across Wetern Oregon this afternoon. If it does, that will
give us a chance to see if the transport winds have become more westerly, which
will also need to happen for burning to occur today.
The chances for a burn opportunity increase some, Friday afternoon. The morning
low clouds should break up sooner and the transport winds will back a little more
to the west. However, there may still be too much fresh marine air in the valley
for optimal burning conditions.
NNW 8 this afternoon.
NNW 10 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 4200 feet. Ventilation index 42.
Salem\'s high temperature today will be near 78.
Relative humidity drops to 50% by 3pm.
Minimum relative humidity will be near 43%.
Salem sunset tonight: 8:46pm; sunrise tomorrow: 5:52am.
After a brief warm-up Friday and Saturday, the upper-level trough,
in the Northern Gulf of Alaska, will move close enough to Pacific
Coastline to spin another weak cold front across Washington and Northern
Oregon Saturday night and early Sunday. That will increase the onshore
flow and cool tempertures to near or slightly below seasonal normals.
High pressure is forecast to rebuild over the region early
next week. Northerly transport winds are forecast for
Monday and Tuesday, with the flow aloft, and at the surface, becoming
more westerly as the week progresses.
The long-range computer models are consistent in swinging
another, somewhat stronger, weather system onto the coastline around next
Thursday. That is the next significant burn opportunity for the valley.
Tomorrow (27 Jul): Morning Clouds...Afternoon Sun. 53/85
Sat (28 Jul): Morning Clouds...Afternoon Sun. 54/84
Sun (29 Jul): MOrning Clouds...Slight Chance Shower. Partly Sunny. 56/78
Mon (30 Jul): Areas Morning Clouds....Sunny with North Winds. 51/84
Tue (31 Jul): Morning Clouds...Afternoon Sun. 53/85
Wed (01 Aug): Sunny. 55/88
Thu (02 Aug): Increasing Clouds. 55/82
weather at oda.state.or.us
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