[willamette-fcst] Field Burning Forecast - July 31, 2017

[Willamette Valley Field Burning Forecast]

JEFFERSON COUNTY FIELD-BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:30 AM PDT MON JUL 31, 2017


TODAY'S DISCUSSION:

An upper-level ridge is building over SE Oregon, suppressing mixing heights today to barely 3,000 feet during the late afternoon. N winds persist at both the surface and transport levels today, with temperatures several degrees warmer than yesterday.

TODAY'S FORECAST:

Hazy under Clear Skies.

Madras' Forecast High Today: 97°F (Sunday's High: 91°F; Rainfall: .00")
Transport Winds: N at 5-10 mph this morning; N-NW 10-15 mph this afternoon.
Mixing Heights: Reaching 3,000 feet by 4 p.m.
Relative Humidity: Dropping to near 12% by 3 p.m.

EXTENDED DISCUSSION:

The upper-level ridge locks into place and build strength, so there will be little change over the next several days. The hottest day of the week is expected to fall on Thursday afternoon, but the heat wave is likely to persist into the coming weekend.

The National Weather Service's digital forecast is available at:
http://forecast.weather.gov/MapClick.php?lat=44.68&lon=-121.14861&site=pdt&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.  Surface wind direction is the general expected wind direction.
         at a specific point surface winds are highly dependent on local
         terrain conditions.

     4.  Ventilation Index (if you want to calculate it) is the height of the
        mixing layer times the transport wind speed divided by 1000.

This forecast is provided under an agreement between the Oregon Department of
Agriculture (ODA) and the Oregon Department of Forestry (ODF).  For more information, contact ODA at 503-986-4701.

Tom Jenkins, AEM
ODF Meteorologist
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