[willamette-fcst] SILVERTON HILLS FIELD BURNING FORECAST - Noon Update

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT MON JUL 15, 2013



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



A weak summertime pattern prevails over the Pacific NW.  To the north an upper level trough is passing by to the east in British Columbia and to the south a weak trough is developing off the northern California coast. Marine low clouds are dissipating along the Oregon coastline.  Pressure gradients are onshore with a 2.4 mb onshore gradient from Newport to Salem and a 1.4 mb onshore gradient from Salem to Redmond.  Valley observations show a consistent 7-10 mph north wind however.



Expect little change from yesterday with the trough to the north ejecting eastward and the trough to the southwest slowly bringing more southerly flow aloft later today and tomorrow.  Transport and surface winds are northerly and will remain northerly through the day.  Expect continued sunshine and very warm temperatures.



(Salem Airport data for Sunday, July 14th: High 91°F; Rainfall .00")

(Maximum Ventilation Index expected today:  60)

TODAY'S FORECAST:



Clear skies with above normal temperatures.



Salem's high temperature today will be near 91.

Minimum relative humidity 27%.

Surface winds: N at 5-10 mph.

Transport winds: N at 10-15 mph.

Maximum mixing height:  4500 ft.

Sunset tonight: 8:55 pm



EXTENDED DISCUSSION:



For Tuesday the upper level trough to the southwest will make its presence more known bringing a minor marine push to the region during the later afternoon and evening.  The marine push appears it will start from the south and work its way northward during the day.  Will have to monitor for a possible burn opportunity late.



Expect onshore flow and cooler temperatures for Wednesday as the trough lifts to the north and through the region.  Expect a minor influx of marine low clouds into the Willamette Valley Wednesday morning.  The trough will weaken allowing for sunny skies during the day.  This may present another burn opportunity depending on gradient stacking.



A ridge builds into the state Thursday and Friday with wind flow turning northerly and temperatures heating up again.



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 15mph.



     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 times

         the transport wind speed 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 and the Oregon Department of Forestry.  For information contact ODA at 503-986-4701.



Nick Yonker

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