[willamette-fcst] Silverton Hills AM Forecast_Gary.doc
Willamette Valley Field Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Thu Aug 4 08:53:17 PDT 2016
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:55 AM PDT THU AUG 4, 2016
BURN ADVISORY:
***STATE FIRE MARSHAL CONDITIONS POSSIBLE THIS AFTERNOON***
Agricultural burning is not recommended.
Prep burning is not allowed.
WEATHER DISCUSSION:
A thermal trough over Willamette Valley will cause very poor burning conditions today, with northerly transport winds and low mixing heights. Conditions will approach fire marshal, mainly on the relative humidity and wind. Pressure gradients also suggest that air flow would converge over the valley.
Sunny and very warm.
Salem's high temperature today will be near 92°F (average is 84°F).
Relative humidity: Falling below 60% before 10:00 a.m. and below 30% around 4:00 p.m.
Surface winds: N 9-12 mph increasing to 12-15 mph around 3:00 p.m.
Transport winds: N 14-18 mph, increasing to 17-21 mph about 3:00 p.m.
Mixing height: Rising to 2000 feet about 1:00 p.m. and 3500 feet at 5:00 p.m.
Salem's sunset tonight: 8:34 p.m.
(Salem Airport data for Wednesday, August 3rd: High 83°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 73)
EXTENDED DISCUSSION:
An upper level low will be over Vancouver Island on Friday, not moving onshore until Sunday night. This will provide a marine push on Friday and possibly a good burning opportunity. Pressure gradient stacking appears to be the factor to watch. Current models indicate that transport winds will begin turning northwest just before noon and increasingly become northwest into early afternoon while mixing heights would be good. But they also show gradient stacking to be the one possible negative factor and will have to be monitored.
There is a chance of showers due to the upper low on Sunday through Tuesday which could hamper burning. Once the low moves out by mid-week we will have a warming trend. Each day next week has potential burning.
The National Weather Service's digital forecast is available at:
http://forecast.weather.gov/MapClick.php?lat=44.90549606158295&lon=-122.8106689453125&site=pqr&unit=0&lg=en&FcstType=text
Notes:
1. Mixing height, as used here, is the lowest height at which the
potential temperature exceeds the potential temperature at the
surface. As a practical matter it is the approximate height to
which a smoke plume will rise assuming good ignition, dry fuels,
and winds less than about 15 mph.
2. Transport winds are a layer average through the mixing height,
weighted slightly toward the winds at the top of the layer.
3. Ventilation Index is the height of the mixing layer (ft) times
the transport wind speed (mph) divided by 1000.
4. Surface wind direction is the general expected wind direction.
At a specific point surface winds are highly dependent on local
terrain conditions.
This forecast is provided under an agreement between the Oregon Department
of Agriculture (ODA) and the Oregon Department of Forestry (ODF). For
information contact ODA at 503-986-4701.
To add/remove your email address from this list, please go to:
http://listsmart.osl.state.or.us/mailman/listinfo/willamette-fcst
Gary Votaw
ODF Meteorologist
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