[willamette-fcst] fbs

Wed Jul 8 11:53:53 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED JUL 08, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

The upper-level ridge continues to weaken, with temperatures cooling closer to seasonal norms. The surface gradient is showing light onshore flow from Newport to Salem, but neutral from Redmond to Salem. Water vapor satellite imagery shows dry air aloft over northern Oregon, with isolated showers and thunderstorms confined to southern Oregon. Wind direction will be northerly today, but gradients will remain light, limiting potential for open burning. Isolated thunderstorm development is expected over the Cascades this afternoon. Mixing conditions will slowly improve today ahead of an evening sea breeze.

TODAY'S FORECAST:

Mostly sunny today, with temperatures a little cooler than yesterday.

Salem's high temperature today will be near 88°F (average is 81°F).

Relative humidity:  Dropping to near 34% this afternoon.

Surface winds: N-NW 5-10 mph this afternoon.

Transport winds: NW 5-10 mph this afternoon.

Mixing height: Rising to 3000 feet by 1:30 p.m. and to 4500 feet by 5 p.m.

Salem's sunset tonight: 9:00 p.m.

(Salem Airport data for Tuesday, July 7th: High 89°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 45)

EXTENDED DISCUSSION:

On Thursday, an upper-level trough will move offshore, turning flow aloft southeasterly in the afternoon hours. Onshore flow at the surface will be light. Temperatures continue to moderate as a result of marine air intruding into Willamette Valley. Upper-level winds turn southerly on Friday morning, with a shift to southwesterly by the afternoon hours as a trough forms over the Pacific Ocean. This aligns with building onshore flow at the surface, possibly providing favorable burning conditions. Saturday will see a strong upper-level trough move onshore Oregon from the Pacific, enhancing westerly flow. Scattered showers are possible Saturday afternoon, with isolated thunderstorm development over the Cascades.

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

ODF Meteorologist

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