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SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON AUG 06 2012
BURN ADVISORY:
Agricultural burning burning is not recommended.
Prep burning is allowed from 12:00pm to 2:00pm with a 50 acre limit.
Propane flaming is allowed from 12:00pm to 5:00pm.
WEATHER DISCUSSION:
Temperatures will continue a slow cool-off today following 100 degree readings on
Saturday and 90 degree temperatures yesterday. Highs today in the central Willamette
Valley should peak in the mid to upper 80's.
The morning Salem sounding shows an average of about 5 degrees fahrenheit of cooling
since yesterday from the surface to above 14,000 feet. There were shallow inversions from
about 1200 to 1500 feet and from about 2700 to 3100 feet. Both of these inversions
should mix out today and mixing heights should top out at around 3500 feet this
afternoon. Low level winds on the sounding were southeasterly but very light while above
about 2000 feet a light southwesterly wind prevailed.
The thermal trough has broadened and pressure gradients are fairly flat across the
Willamette Valley this morning. As of 8am this morning the pressure at Salem was lower
than the pressures at either Newport of Redmond. Newport to Salem was 1.7mb onshore
while Redmond to Salem was 0.3mb offshore.
Satellite pictures show low marine clouds pushing to about the crest of the coast range
and even pushing into parts of the Willamette Valley in Lane County.
The key today will be the Salem to Redmond pressure gradient. It must become onshore and
increase yet not increase so much as to produce gradient stacking to the east. We need
about 1.5 millibars or better to evacuate smoke across the Cascades. In addition
transport wind direction needs to be monitored. We will close to too much northerly this
afternoon and pibals will be needed to confirm a favorable wind direction. Bottom line,
however, - prospects are decent for limited open field burning this afternoon.
TODAY'S FORECAST:
Mostly sunny.
Salem's high temperature today will be near 88.
Relative humidity drops to 50% by 2pm. Minimum relative humidity 35%.
Surface winds: Light southwest to west-southwest.
Transport winds: Light southwesterly to northwesterly.
Maximum mixing height: 3500 feet.
Sunset tonight: 8:31 pm
THREE-HOURLY DATA:
11am 2pm 5pm 8pm
Temperature: 78 86 88 74
Relative Humidity: 52% 37% 37% 55%
Surface Wind Direction: 220 220 290 250
Surface Wind Speed: 4 6 7 5
Transport Wind Direction: 220 300 300 280
Transport Wind Speed: 4 5 10 13
Estimated Mixing Height: 1700 3000 3500 2200
Ventilation Index: 7 15 35 29
EXTENDED DISCUSSION:
The week ahead looks dry and warm with temperatures remaining above average for early
August. Forecast charts indicate somewhat of a marine push tomorrow night and the
coolest day of the week looks to be Wednesday with highs around 80. Temperatures warm
again later in the week - approaching 90 by Saturday.
Tomorrow may present a burn opportunity ahead of a marine push.
Generally the first day after a marine push does not give good burning conditions so
Wednesday does not look favorable.
Thursday and Friday may present small windows of opportunity.
The National Weather Service’s digital forecast is available at:
<a
href="http://forecast.weather.gov/MapClick.php?lat=44.905&lon=-122.810">http://forecast.weather.gov/MapClick.php?lat=44.905&lon=-122.810</a>.
Notes:
1. Mixing height, as used here, is the lowest height at which the
potential temperature exceeds the equivalent 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 times
the transport wind speed 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.
Jim Little
ODF Meteorologist
jlwx:060812:0827
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