[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:30 AM PDT THU AUG 25, 2016


BURN ADVISORY:



***STATE FIRE MARSHAL CONDITIONS TO BEGIN SHORTLY AFTER NOON***



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



A thermal trough remains over Willamette Valley and to the coast. It will cause NE transport winds throughout the region and prevent any burning again today. State Fire Marshal conditions will persist through at least the afternoon, mainly due to temperature and relative humidity but possibly also wind as it did on Wednesday.



Sunny and very hot.



Salem's high temperature today will be near 98°F (average is 81°F).

Relative humidity:  Falling below 20% about 2:00 p.m. and near 15% at 5:00 p.m.

Surface winds: N 10-12 mph increasing this afternoon to 12-16 mph.

Transport winds: NNE 10-15 mph becoming NE 14-18 mph by mid-afternoon.

Mixing height: Rising to 6000 feet near 2:00 p.m. then 8000 feet by 5:00 p.m.

Salem's sunset tonight: 8:00 p.m.



(Salem Airport data for Wednesday, August 24th: High 94°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 144)



EXTENDED DISCUSSION:



The thermal trough will begin to shift eastward late on Friday and but transport winds will still be NNE and Fire Marshal conditions will occur again. A marine push is still expected late on Saturday just ahead of an upper level trough arriving from the northwest. The outlook for next Monday through Wednesday is for the upper level trough to be just offshore, nearly stationary, and intensifying into the middle part of the week. Transport winds on those days would likely be NW or W. Potential for burning still looks encouraging with the most uncertainty lying in pressure gradient stacking. The chance of showers will also increase through the 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



Gary Votaw

ODF Meteorologist

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