[willamette-fcst] Field Burning Forecast - September 18, 2017 (Noon Update)

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT MON SEP 18, 2017

BURN ADVISORY:

Agricultural burning is recommended to be limited to the hours of 8 a.m. to 5:30 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

A strong upper-level disturbance is destabilizing the atmosphere, as a surface frontal system brings scattered showers and isolated thunderstorms across the Willamette Valley today. Strong thundershowers are moving through the Oregon coast towards the Silverton Hills, and will bring heavy showers, gusty winds & the possibility of small hail this afternoon. A waterspout was sighted near Netarts, Oregon and indicates that severe weather may impact western Oregon as this storm passes.

TODAY'S FORECAST:

Windy with Thundershowers. Small Hail is possible.

Salem's high temperature today will be near 61°F (average is 77°F).
Relative humidity:  70% or higher for the next 24 hours.
Surface winds: S 10-15 mph this morning, becoming SW 13-18 mph this afternoon.
Transport winds: W-SW 15-20 mph this morning, becoming SW 20-30 mph this afternoon.
Mixing height: Above 5000 feet for the next 24 hours.
Salem's sunset tonight: 7:16 p.m.

(Salem Airport data for Sunday, September 17th: High 67°F; Rainfall: .22")
(Maximum Ventilation Index expected today: 150)

EXTENDED DISCUSSION:

Fall weather continues with little to no change between Monday night and the arrival of the Autumnal Equinox on Friday morning, when the calendar "officially" marks the end of the 2017 summer. The jet stream will remain over southern Oregon, bringing polar air and stormy weather for the next several days. Cloudy skies with only brief periods of sunbreaks will limit any drying, though parched soil and stiff winds will help in a limited fashion. Occasional thundershowers with lingering rainfall will continue to dampen fields until a ridge develops and forces the jet stream back north of the Silverton Hills, but current weather models indicate unfavorable field burning conditions for the next 7-10 days.


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.

     5.  In accordance with OAR 837-110-0090, all field burning shall be
         banned when any two of the following criteria are present:
         A. Temperature of 95 degrees Fahrenheit or above
         B. Relative humidity of 30 percent or below
         C. Wind speed of 15 miles per hour or higher

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, AEM
ODF Meteorologist
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