[willamette-fcst] Willamette Valley Field Burning Forecast - Noon Update

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT MON AUG 4, 2014



BURN ADVISORY:



State Fire Marshal Burn-ban conditions may be reached this afternoon.



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Upper level ridge extends over the state with the axis over the intermountain states and the Rockies. Weak marine layer is along the coast with just minor inland penetration. Otherwise skies are clear with smoke from wildfires in southern Oregon and northern California providing hazy conditions. Current pressure gradients are +3.5 mb from Newport to Salem and +.4 mb from Salem to Redmond.



Little change today with the high pressure ridge remaining anchored in place to the east. With weak southerly flow aloft, some thunderstorms will likely develop along the Cascade crest and prevent much gradient stacking from Salem to Redmond during the afternoon hours. In general, expect mostly northerly low-level flow through the day with minor marine onshore flow late this afternoon and evening. Skies will remain clear but hazy and temperatures fairly hot, getting into the low 90s.



TODAY'S FORECAST:



Clear, hazy and very warm.



Salem's high temperature today will be near 93 degrees (average is 84).

Relative humidity: Dropping to 28 - 30 percent around 4 p.m.

Surface winds: Light and variable, increasing to northerly at 6 - 12 mph by early afternoon. NW to NNW late this afternoon and evening.

Transport winds: Northerly at 5 - 8 mph during the morning increasing to northerly at 8 - 15 mph this afternoon, and NW to N late afternoon and evening at 8 - 15 mph.

Mixing height: Rising to near 3000 ft by 1 p.m. and to 4500 ft by 5 p.m.

Salem's sunset tonight: 8:34 p.m.



(Salem Airport data for Sunday, Aug 3rd: High 94°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 54)



EXTENDED DISCUSSION:



Upper level ridge gradually flattens over the next few days opening the door to a little earlier and stronger onshore flow during the afternoon and evening. Expect slightly cooler temperatures. In addition, thunderstorms on the east side of the Cascades will be less prevalent. However, still expect mostly northerly to northwesterly flow so marginal burning conditions will be about the best we get this 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



Nick Yonker

ODF Meteorologist

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