[willamette-fcst] Field Burn Forecast - August 2, 2017

Wed Aug 2 11:45:07 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT WED AUG 2, 2017

BURN ADVISORY:

***State Fire Marshal Burn-Ban conditions are expected this afternoon***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A compromised airshed and a challenging weather pattern make field burning operations appear unlikely for today. An upper-level ridge has shifted west of the Willamette River, creating N flow aloft with offshore gradients pulling wildfire smoke through the Columbia River Gorge and across the Cascades from a wildfire near Mt. Jefferson. Degraded air quality will impact western Oregon until 7 p.m. Above-average temperatures, very low humidity, and strong N-NE surface winds this afternoon will meet State Fire Marshal Burn-Ban conditions. The gusty winds and intense heating will help mixing heights rise in the afternoon hours, improving air quality briefly until after sunset.

TODAY'S FORECAST:

Hazy with layers of smoke aloft.

Salem's high temperature today will be near 105°F (average is 84°F).
Relative humidity:  Below 30% by 12:30 and nearing 14% by 5 p.m.
Surface winds: N-NE 5-10 mph currently and NE 10-15 mph this afternoon.
Transport winds: NE 10-15 mph currently and through the afternoon.
Mixing height: Rising to 3000 feet around 1 p.m. and reaching 4,000 feet by 5 p.m.
Salem's sunset tonight: 8:37 p.m.

(Salem Airport data for Tuesday, August 1st: High 101°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 60)

EXTENDED DISCUSSION:

A blocking pattern is setting up ahead the weekend, with the upper-level ridge positioning itself over the Oregon coast. N-NW flow aloft will persist, as the ridge suppresses mixing and maintains poor air quality due to regional wildfire emissions. Temperatures will begin to lower as the heat wave breaks on Thursday evening, but remain above seasonal averages. Offshore flow will ease, but surface and transport winds will remain northerly, making conditions appear unfavorable for field burning for the remainder of the week. Weekend relief from afternoon temperatures above 100°F may not last, as the upper-level ridge begins to migrate back toward the Cascades early next week.

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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