[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Aug 25 08:58:36 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT TUE AUG 25, 2015

BURN ADVISORY:

*** State Fire Marshal Burn-Ban Conditions Possible This Afternoon. ***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

SW flow aloft and weak onshore flow at the surface have finally cleared the bulk of the wildfire smoke from NW Oregon.  Lyons and Springfield still have slightly elevated smoke levels this morning, but all NW Oregon air monitoring stations are indicating "good" air quality. The SW flow aloft may destabilize the air mass enough for isolated thunderstorm development over the Cascades this afternoon.  Otherwise, expect fair skies and slightly warmer temperatures today, due to less wildfire smoke.

Surface and transport winds are expected to stay mostly northerly this afternoon, which would be a limiting factor for burning.  In addition, the air mass remains very dry, with afternoon humidity levels expected to drop well below 30%.  Wind speeds will need to be closely monitored for State Fire Marshal Burn-Ban conditions (RH of 30% or less and wind speeds of 15 mph or greater).

TODAY'S FORECAST:

Partly cloudy and warm.

Salem's high temperature today will be near 85°F (average is 81°F).

Relative humidity:  Dropping below 50% by 11 a.m. and below 30% by 2 p.m.

Surface winds: N 3-8 mph this morning; N 5-15 mph this afternoon.

Transport winds: NNE 5-10 mph this morning; N 7-15 mph this afternoon.

Mixing height: Rising to 3000 feet about 1 p.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:02 p.m.

(Salem Airport data for Monday, August 24th: High 84°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

An upper-level trough, centered about 800 miles off the northern Oregon coast, will move very little through Thursday.  Continued dry SW flow aloft will maintain partly cloudy and warm weather with just a chance for isolated afternoon thundershowers over the Cascades.  Wildfire smoke should generally remain east of the region.  Increasing onshore flow may create favorable burning conditions, especially on Thursday.

The upper-level trough is expected to advance towards the coast on Friday.  Increasing onshore flow will bring clouds, cooler temperatures, and the threat of showers.  Computer models have slowed down their timing for the onset of showers, to late Friday afternoon, so another burning opportunity is possible.  Wetting rains are still expected Friday night and Saturday, with  over one-half inch of rain possible in the Silverton Hills.

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/20150825/5f4750b4/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Pete.doc
Type: application/msword
Size: 36352 bytes
Desc: Silverton Hills AM Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150825/5f4750b4/attachment.doc>