[willamette-fcst] Willamette Valley Field Burning Forecast

Tue Aug 12 08:45:16 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT TUES AUG 12, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Upper level low in the eastern Pacific is combining with the low off the northern California coast bringing upper and lower level southerly flow over the state. While no thunderstorms moved through the Willamette Valley last night, the area is under convective cloud cover. Currently, a line of thunderstorms are moving up from the Corvallis area now. Temperatures in the mid-Willamette Valley have only cooled slightly from yesterday morning. Morning surface chart shows low pressure still in the Willamette Valley with higher pressure to both the east and west. Current pressure gradients are +2.9 mb from Newport to Salem and -1.5 mb from Salem to Redmond.

The combining upper low pattern off the coast will bring in clouds and the chance of showers and thundershowers over the region today and this evening. With more clouds over the area and some cooling aloft, temperatures will likely only reach to the mid-80s. Clouds will also limit mixing heights to most likely under 3000 ft. Despite more favorable S to SW winds today, the possibility of showers, low mixing heights and questionable gradient stacking, will likely limit burn opportunities.

TODAY'S FORECAST:

Mostly cloudy with possible showers or thundershowers.

Salem's high temperature today will be near 85 degrees (average is 83).

Relative humidity: Will drop below 60 percent by 10 a.m. and drop to 35 - 40 percent by 4 p.m.

Surface winds: Light and variable favoring S to W flow. Winds SW to NW at 5 - 10 mph later this afternoon and evening.

Transport winds: S to SW at 4 - 7 mph this morning becoming SW to NW at 6 - 12 mph this afternoon.

Mixing height: Remaining below 2000 ft during the morning rising to near 2800 ft by 5 p.m.

Salem's sunset tonight: 8:23 p.m.

(Salem Airport data for Monday, Aug 11th: High 98°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 28)

EXTENDED DISCUSSION:

Upper level low will move into the state on Wednesday bringing more showers and a chance of thundershowers over the area tomorrow. The low will exit to the east on Thursday with drying conditions Thursday afternoon and Friday. Northwesterly onshore flow continuing into the end of the week may provide a burn opportunity Thursday and/or Friday.

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

Nick Yonker

ODF Meteorologist

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