[willamette-fcst] Field Burning Forecast - August 7, 2017

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT MON AUG 7, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Mediocre mixing this afternoon with questionable gradients create a challenging environment for field burning today. An upper-level ridge moves over the Oregon coast today, and will begin to warm the atmosphere as mixing becomes restricted. Mixing heights will struggle to reach 3,000ft briefly this afternoon, while transport winds become N-NW by early afternoon. Temperatures, wind speeds, and humidity do not appear to reach State Fire Marshal conditions today. Cloud cover across the Cascades and central Oregon may prevent onshore gradients from positively stacking this afternoon.

TODAY'S FORECAST:

Mostly Cloudy with Smoke & Haze.

Salem's high temperature today will be near 92°F (average is 84°F).
Relative humidity:  Below 60% by 11 a.m. and nearing 35% by 5 p.m.
Surface winds: Variable 5 mph or less this morning, becoming N 5-10 mph this afternoon.
Transport winds: N 5-10 mph this morning, becoming N-NW 5-10 mph this afternoon.
Mixing height: Rising to 3000 feet by 5 p.m.
Salem's sunset tonight: 8:30 p.m.

(Salem Airport data for Sunday, August 6th: High 91°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 30)

EXTENDED DISCUSSION:

Conditions for the week ahead do not favor safe, effective field burning opportunities. The upper-level ridge will slowly strengthen over NW Oregon through mid-week, further limiting mixing conditions as the flow aloft turns more N-NE by Tuesday afternoon. This shift to offshore flow will cause temperatures to climb higher as another heat wave develops, and the offshore flow will also draw more regional wildfire smoke into the Willamette Valley from across the Cascades. There will be little change for Wednesday and Thursday, as the heat wave reaches its apex and the reduced humidity appear likely to meet State Fire Marshal conditions each day. The suppressed mixing during daytime heating will also make air quality progressively worse as the week continues, with regional wildfire smoke being funneled through the Columbia River Gorge and Santiam Pass.

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

Tom Jenkins, AEM
ODF Meteorologist
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