[willamette-fcst] Field Burning Forecast - July 24, 2017 (Noon Update)

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT MON JUL 24, 2017

BURN ADVISORY:

Recommend times for agricultural burning are now through 7:00 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level disturbance south of the Willamette Valley produces strong north winds today, but gradients have improved and are now positively stacked. Wind speeds and direction remain the limiting factor, and do not appear likely to improve enough for field burning opportunities today. The low humidity this afternoon combined with breezy winds are likely to trigger State Fire Marshal Burn-Ban conditions.

TODAY'S FORECAST:

Mostly Sunny becoming Partly Cloudy this afternoon.

Salem's high temperature today will be near 91°F (average is 84°F).
Relative humidity:  Dropping near 25% by 5 p.m.
Surface winds: Building to N 13-17 mph with occasional gusts up to 25 mph this afternoon.
Transport winds: N 15-25 mph this afternoon.
Mixing height: 3000 feet currently and rising near 4000 feet by 5 p.m.
Salem's sunset tonight: 8:47 p.m.

(Salem Airport data for Sunday, July 23rd: High 89°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 100)

EXTENDED DISCUSSION:

Little change expected for Tuesday, as the disturbance over southern Oregon remains locked in place until Wednesday. Gusty winds from the north and weakened onshore flow may limit the possibilities for field burning again Tuesday, but models are more optimistic that W-NW onshore flow returns Wednesday afternoon ahead of a marine push; this favorable scenario for field burning operations will be further investigated as additional data is collected now through Tuesday afternoon. W flow aloft veers to SW ahead of an approaching upper-level disturbance, and onshore surface flow recovers to produce positive gradients; morning clouds provide shade and keep temperatures closer to seasonal averages with increased humidity.

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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