JEFFERSON COUNTY FIELD-BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:30 AM PDT MON SEP 30, 2024
TODAY’S DISCUSSION:
Broad upper-level ridging builds early this week with warming highs and dry weather. A surface thermal trough to the west of the region will turn winds more offshore, starting from N at the surface and E for transport winds midday, then more NE during the afternoon. The morning aircraft sounding shows much cooler air aloft. Mixing heights will eventually rise high though may be slowed by the chilly surface temperatures this morning.
TODAY’S FORECAST:
Early frost then sunny and dry, surface winds from N-NE at 6-8 mph.
Madras’ Forecast High Today: 67°F (Sunday High: 64°F; Rainfall: 0.00”)
Transport Winds: ESE 4-6 mph late this morning; then NE-ENE 7-10 mph this afternoon
Mixing Heights: Rising to 2500 feet this morning;
then up to 5000 feet this afternoon
Relative Humidity: Near 40% by 11 a.m.; down to 20% this afternoon
EXTENDED DISCUSSION:
Temperatures heat up as the surface thermal trough builds along with upper-level ridging. Light winds will turn from S all morning to more NW by mid-afternoon and the evening. Warmer air aloft will slow the climb of mixing heights. A weakening front arrives early Wednesday and temperatures stay below average. Winds will be from N-NW from late morning through the afternoon. Sunny and seasonable weather continues through the week.
National Weather Service’s digital forecast is
available at:
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. 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.
Sherri Pugh
ODF Meteorologist