[willamette-fcst] Silverton Hills AM Forecast_doug.doc
Willamette Valley Field Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Fri Jul 19 08:48:02 PDT 2013
SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT FRI. JUL 19, 2013
BURN ADVISORY:
Agricultural burning is not recommended today.
Prep burning is allowed from 1:00 p.m. to 3:00 p.m. with a 50 acre limit.
WEATHER DISCUSSION:
Low clouds have again developed this morning over much of the valley and coastal areas. Dissipation of this low cloud cover is expected by late-morning and mixing depth should increase through the afternoon. Northerly flow will continue to dominate the low levels. More favorable local gradient patterns are likely by mid-afternoon, but no significant westerly component is expected prior to this evening.
TODAY'S FORECAST:
Mostly cloudy this morning, becoming mostly sunny by early afternoon. Very light surface winds are expected.
Salem's high temperature today will be in the upper 80s.
Relative humidity will drop below 60% by noon and to 30-35% by 5 p.m.
Surface winds: Winds light and variable this morning becoming N 5-10 mph this afternoon.
Transport winds: Generally N 5-10 mph.
Mixing height: Rising to near 3500 feet late this afternoon.
Salem's sunset tonight: 8:52 p.m.
(Salem Airport data for Thurs., July 18th: High 87°F; Rainfall .00")
(Maximum Ventilation index expected today: 35)
EXTENDED DISCUSSION:
Upper ridging will strengthen through Saturday, and then slowly weaken in the Sunday-Monday timeframe. Expect mostly sunny conditions and continued very warm temperatures with maximums in the middle 80s to around 90 and mostly northerly transport winds. Model guidance continues to portray a more favorable onshore flow pattern later next week.
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 15mph.
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 and the Oregon Department of Forestry. For information contact ODA at 503-986-4701.
Doug Wesley
ODF Meteorologist
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