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

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT MON JUL 31, 2017

BURN ADVISORY:

Recommended times for agricultural burning are from 2 p.m. to 6:30 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level ridge over eastern Oregon will create unfavorable conditions for field burning, as mixing will be suppressed and temperatures in the Willamette Valley will soar above seasonal averages. Flat gradients over the Silverton Hills allow positive gradients along the Columbia River to dominate, keeping surface & transport winds northerly and increasing with afternoon heating. High temperatures and low humidity, as well as gusty afternoon winds, all increase the possibility of meeting State Fire Marshal Burn-Ban criteria later this afternoon and into the early evening hours. A Red Flag Warning for fire danger goes into effect just after sunset tonight, at 9:00 p.m. for the entire Willamette Valley, and will be in effect until 4 a.m tomorrow morning.

TODAY'S FORECAST:

Hazy under Clear Skies.

Salem's high temperature today will be near 96°F (average is 84°F).
Relative humidity:  Currently below 60% and dropping near 22% by 5 p.m.
Surface winds: N 8-12 mph this morning; shifting N-NE 10-15 mph this afternoon.
Transport winds: N-NE 15-20 mph this morning and through the afternoon.
Mixing height: Rising to 3000 feet around 2 p.m. and reaching 3200 feet by 5 p.m.
Salem's sunset tonight: 8:39 p.m.

(Salem Airport data for Sunday, July 30th: High 92°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 64)

EXTENDED DISCUSSION:

The upper-level ridge in SE Oregon remains locked in place for the next several days, as a heat wave develops across Oregon. Easterly winds develop as offshore flow sets up over the Cascades, with temperatures elevated and humidity very low in the afternoon hours Tuesday, Wednesday, and even into Thursday. A Fire Weather Watch has been issued by the National Weather Service in Portland for the Willamette Valley until 6 a.m. Friday. These conditions will be unsuitable for fair smoke ventilation until the time of day when fire control & safety become an even greater concern. Field burning operations appear unlikely and this situation may well persist into the coming 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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