[willamette-fcst] Field Burning Forecast - July 11th, 2017

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT TUE JUL 11, 2017

BURN ADVISORY:

Recommended times for agricultural burning are from 9 a.m. until 7 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

W flow aloft maintains high pressure and stable weather over the Willamette Valley today, with clear skies allowing temperatures to creep above seasonal averages. Pressure gradients are negatively stacked, but rapid heating in central Oregon this morning may flatten and eventually switch the gradient by mid-afternoon. Onshore flow will remain weak with northerly transport winds until this occurs, though mixing conditions will become favorable by noon.

TODAY'S FORECAST:

Clear skies with afternoon haze.

Salem's high temperature today will be near 85°F (average is 81°F).
Relative humidity:  Dropping below 60% by 9 a.m. and nearing 28% by 5 p.m.
Surface winds: N-NE at 5-10 mph becoming N-NW at 8-12 mph after 4 p.m.
Transport winds: N 5-10 mph becoming N-NW 10-15 mph after 4 p.m.
Mixing height: Above 3000 feet by 9 a.m. and increasing to 5000 feet by 1 p.m.
Salem's sunset tonight: 8:58 p.m.

(Salem Airport data for Monday, July 10th: High 82°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Dry SW flow aloft develops slowly on Wednesday, providing another sunny day with temperatures above seasonal averages. Onshore flow will remain weakened, but transport winds should be more NW and could provide better conditions for field burning if gradients become favorable after noon. Thursday will see SW flow aloft shift to more W-SW and increase by the afternoon, strengthening onshore flow. This trend continues through Friday, with the W-SW flow lowering temperatures to seasonal averages ahead of the weekend.


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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