[willamette-fcst] Willamette Valley Field Burning Forecast - Noon Update

Tue Aug 5 11:50:45 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT TUES AUG 5, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from noon to 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Upper level ridge remains over the state and to the east. With little upper level air movement, smoky and hazy skies from wildfire smoke remains. Current pressure gradients are +1.7 mb from Newport to Salem and +4.0 mb from Salem to Redmond.

Ridge will slowly weaken and move to the east today. This minor shift will eventually aid in the dispersing wildfire smoke. With the marine air that came in last evening, expect several degrees of cooling from yesterday. However, wind flow is turning back to NNW to N and will remain no better than NNW until early evening.

TODAY'S FORECAST:

Mostly hazy. Some clearing through the day. Cooler.

Salem's high temperature today will be near 86 degrees (average is 84).

Relative humidity: Dropping to near 35 percent around 4 p.m.

Surface winds: NNW to N at 6 - 12 mph by early afternoon, turning to NW during the early evening.

Transport winds: NNW to N at 6 - 12 mph this afternoon, turning NW'erly at 8 - 15 mph this evening.

Mixing height: Rising to 4500 - 5000 ft by 5 p.m.

Salem's sunset tonight: 8:33 p.m.

(Salem Airport data for Monday, Aug 4th: High 94°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 54)

EXTENDED DISCUSSION:

Upper level ridge gradually flattens over the next few days bringing high temperatures down to near average. However, models show wind flow remaining quite northerly with just minor onshore NNW to NW flow during the later afternoon to evening hours. Mixing levels should be fair to good during the day but with winds showing considerable northerly flow, burning opportunities will be limited.

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140805/6a6d7bcb/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills Midday Forecast_Nick.doc
Type: application/msword
Size: 33792 bytes
Desc: Silverton Hills Midday Forecast_Nick.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140805/6a6d7bcb/attachment.doc>