[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Thu Jul 24 11:30:10 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:30 AM PDT THU JUL 24, 2014

BURN ADVISORY:

Recommended times for agricultural burning are from now until 7 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

The strong upper-level trough that brought considerable rain to the northern Willamette Valley the past two days is rapidly moving eastward, with a drier westerly flow aloft developing over Oregon.  A few lingering light showers over the region late this morning should give way to slow clearing this afternoon.  Brisk southerly surface winds will slowly veer to the west during the afternoon; aiding the drying of fields.  Even with some sunbreaks, temperatures will remain well below average.

TODAY'S FORECAST:

Light showers ending with partial clearing.  Continued unseasonably cool.

Salem's high temperature today will be near 73°F (average is 84°F).

Relative humidity:  Dropping to near 50% by 5 p.m.

Surface winds: S 5-15 mph; Becoming W 5-15 mph late this afternoon.

Transport winds: SW 15 mph; Becoming WNW 15 mph late this afternoon.

Mixing height: Above 5000 feet this afternoon.

Salem's sunset tonight: 8:47 p.m.

(Salem Airport data so far today: High 64°F; Rainfall: .03")

(Maximum Ventilation Index expected today: 90)

EXTENDED DISCUSSION:

A drying and warming trend will continue through this weekend, as an upper-level ridge of high pressure builds over the western US.  After areas of morning clouds, afternoon sunshine will lift temperatures in the low 80s on Friday.  Highs will warm into the upper 80s on Saturday and low 90s on Sunday, under sunny skies.  Mostly northerly surface winds will aid in the drying of fields.  However, increasing southerly flow aloft may circulate enough monsoonal moisture northward over Oregon for thundershower development as early as Sunday evening...including west of the Cascades.

Very little change in the overall weather pattern is predicted though next week.  A strong upper-level ridge of high pressure will stay anchored over the Rockies with a south to SW flow aloft over Oregon.  That will keep skies mostly sunny with well above normal temperatures.  It will also maintain a threat of afternoon and evening thunderstorms.  Onshore flow will be restricted mainly to the immediate coastline; reducing burning opportunities.

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
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