[willamette-fcst] Forecast - Thursday, February 18th, 2010

[Willamette Valley Ag/Burning Forecast]

Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

Issued: 
     Thursday, February 18th, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from 11:00am to 4:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A building upper-level ridge of high pressure, just
     offshore, will bring a dry and progressively cooler
     northerly flow into the region.  The air mass aloft is still
     quite mild.  The freezing levels over Salem and Medford were
     measured at 8400 feet and 9100 feet respectively early this
     morning, which is only slightly lower than on Wednesday
     morning.  Clearing skies allowed overnight temperatures to
     locally drop to the freezing mark in the Willamette Valley,
     with areas of fog south of about Albany.

     Visible satellite imagery showed the areas of valley fog, in
     southern Linn and Lane Counties, as well as extensive fog
     and low clouds in the basins east of the Cascades.  Skies
     were clear along the northern and central coast and over the
     Cascades.  The ODA surface analysis showed increasing
     northeasterly pressure gradients across Oregon, with a cool
     Candian high pressure area diving southward into eastern
     Washington and a building thermal trough along the southern
     Oregon coast.  Offshore flow had cleared skies, north of
     about North Bend, along the Oregon Coast, with low clouds
     banking up along the southern Oregon coast.

     Mid-morning temperatures ranged from near 30, in the foggy
     Eugene area, to the upper 40s along the sunny central Oregon
     coast.  The areas of valley morning fog and low clouds
     should give way to sunshine this afternoon, as the air mass
     continues to dry out.  The central valley will likely have
     the warmest temperatures (around 60 degrees).  The extreme
     north valley will get some cooling influence, from the Gorge
     easterly winds, and the south valley will need to burn off
     the morning fog.  Both the extreme north and south valley
     should stay in the 50s this afternoon.  Down-sloping winds
     should warm central coastal temperatures into the mid 60s. 
     Low clouds will keep the south coast in the 50s, and
     easterly outflow, from the Gorge, will likely hold the
     extreme north coast in the 50s.

Surface Winds:
     NE 5-12 except E 10-20 north this morning, NE 7-17 except E 15-25 north this afternoon.
Transport Winds:
     NE 10 this morning, NE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 60.
Humidities:
     Minimum relative humidity will be near 37%.
Sunrise/Sunset:
     Salem sunset tonight: 5:45pm; sunrise tomorrow: 7:06am.

Extended Outlook:
     The upper-level ridge of high pressure will maintain
     northerly flow aloft over the region Friday and Saturday,
     driving cooler Canadian air into the Columbia Basin of
     eastern Washington and northeastern Oregon.  Increasing
     offshore flow, at the surface, will push more of the cool
     Canadian air through the Columbia Gorge and into the
     Willamette Valley...helping to clear skies but lowering
     overall temperatures.  Brisk easterly winds will continue,
     at the western end of the Columbia Gorge.

     Drier air will make for relatively large temperature spreads
     between overnight minimums and daytime maximums, especially
     in wind-sheltered areas.  Pockets of the Willamette Valley,
     away from the Gorge winds, will drop to near or below
     freezing in the early mornings.  Sunny skies will help
     afternoon temperatures warm into the low to mid 50s. 
     Offshore winds, down-sloping off of the coastal range, will
     likely lift central coastal highs to near 60, but north
     coastal highs will remain in the mid 50s, due to the cool
     easterly outflow from the Gorge.

     A fairly potent weather system is forecast to undercut the
     offshore upper-level ridge and slam into northern California
     over the weekend.  That will help to maintain the strong
     offhsore flow across Oregon, with cool and dry air
     continuing to feed into the Willamette Valley, via the
     Columbia Gorge.  Some precipitation is forecast to advance
     northward, across southern Oregon, Sunday and Monday. 
     Clouds should increase, especially south, over the
     Willamette Valley but with only a chance of light
     precipitation this far north.  Snow levels should be below
     the passes, so southern Oregon mountains may get some needed snowfall.

     The under-cutting weather system is forecast to dive
     southeastward, into Arizona, by Tuesday, with the offshore
     ridge of high pressure moving directly over Oregon.  That
     will decrease the offshore flow, with pressure gradients
     becoming rather weak across the regin.  Warming aloft and a
     backing off of the cool Gorge outflow should lead to warmer
     daytime highs across the Willamette Valley.  However, highs
     along the immediate coastal strip may cool a few degrees. 
     An increasing southwesterly flow aloft is forecast to bring
     back some rain and mountain snow back to the region by about
     next Thursday.

Tomorrow (19 Feb):  Mostly Sunny but Cooler.  31/56

Sat (20 Feb):  Mostly Sunny and Cooler Yet.  29/53

Sun (21 Feb):  Increasing Clouds...Mainly South.  29/53

Mon (22 Feb):  Partly Cloudy South with a Slight Chance of Rain. Fair North.  30/53

Tue (23 Feb):  Mostly Sunny.  Slightly Warmer.  33/55

Wed (24 Feb):  Increasing Clouds.  34/57

Thu (25 Feb):  Rain Likely.  Snow Level 4-5000 Feet.  38/54

ODA Meteorologist
weather at oda.state.or.us