[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Wed Aug 6 11:49:27 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED AUG 6, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from now until 1 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Increasing westerly flow aloft has cleared wildfire smoke from the skies over NW Oregon, with onshore flow cooling temperatures back to near average.  Marine low clouds were able to penetrate into the extreme northern and southern ends of the Willamette Valley this morning, but skies stayed clear over the mid-valley region.

Mixing heights should rise to near 5000 feet later this afternoon, and ample sunshine has already balanced the onshore flow from Newport to Redmond.  However, an 11 a.m. PIBAL showed north to NE winds in the transport layer, which are not favorable for burning.  Winds are predicted to back to northerly, and perhaps northwesterly, this afternoon and will be monitored closely.  The next PIBAL is scheduled for 1 p.m.

TODAY'S FORECAST:

Sunny and seasonably warm.

Salem's high temperature today will be near 84°F (average is 84°F).

Relative humidity:  Dropping to near 40% by 5 p.m.

Surface winds: NNE to NNW 5-10 mph.

Transport winds: N-NE 10-15 mph; becoming NW-N 10-15 mph this afternoon.

Mixing height: Rising to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:31 p.m.

(Salem Airport data for Tuesday, August 5th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

The flow aloft is predicted to become more southwesterly by Friday, with continued onshore flow.  Expect some morning marine clouds both Thursday and Friday with sunny afternoons.  Transport winds should be mostly northerly but may turn northwesterly in the afternoons.  Daytime mixing should continue to be good, but gradient-stacking may be an issue.

Very little change is forecast through Monday.  A weak upper-level trough may trigger a few thundershowers over the Cascades this weekend, but it is looking less likely that any precipitation will make its way to the Willamette Valley.  A little stronger trough may increase the onshore flow enough to create a burning opportunity next Tuesday, with an upper-level ridge predicted to rebuild over Oregon during the second half of 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

Pete Parsons

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140806/25052081/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills Midday Forecast_Pete.doc
Type: application/msword
Size: 33792 bytes
Desc: Silverton Hills Midday Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140806/25052081/attachment.doc>