[willamette-fcst] Forecast - Tuesday, March 30th, 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: 
     Tuesday, March 30th, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 5:30pm.
     Straw stack burning is allowed from now until 5:00pm.

Weather Discussion:
     Cold air aloft began moving over western Oregon Monday afternoon and continues to surge
     inland over the region today, in the wake of a powerful cold front that has stalled over
     southeastern Oregon.  The late-morning ODA surface analysis showed a weak low-pressure
     center moving slowly northeastward, out of central Oregon, with an occluded front
     extending from it across southeastern Oregon.

     What\'s left of the warm air associated with this system has been forced aloft, so surface
     temperatures are cold enough to support snow across much of central and eastern Oregon.
     In addition, winds are still fairly brisk near the front.  Southwesterly wind-gusts between
     20 and 30 mph are making for a bone-chilling late March day across central and southeastern
     Oregon, where temperatures are barely above freezing.  The front appears to have just passed
     through Rome, Oregon, where winds were gusting to nearly 40 mph with a temperature of 35.

     The freezing level over Salem was measured early this morning at just 2500 feet, which puts
     the snow level near 1500 feet.  Strong onshore flow was producing heavy upslope snow over
     the Cascades, with more than 6 inches of new snow over the passes creating winter driving
     conditions.  The higher ski areas have received up to a foot and a half of new snow. 1-2
     inches of snow fell down to as low as 1100 feet, just east of Lyons, in the western Cascade
     foothills, this morning.

     Strong onshore flow is continuing to rotate significant shower activity onshore and across
     Oregon.  Doppler Radar shows widespread, mostly light, showers across all of western Oregon.
     Upslope conditions are still producing significant snow over the Cascades, with the passes
     picking up 2-4 inches of new snow since the morning report.  Due to the rainshadowing
     effect of the Cascades, showers are more widely scattered over central and eastern Oregon.

     Satellite imagery continues to show impressive cumulus cloud development moving onshore, so
     numerous showers are in store for all of western Oregon today.  What little daytime heating
     we are able to get could help some thunderstorms develop this afternoon.  Some storms could
     produce small hail.  Snow levels may drop low enough for wet snow over the coastal
     range passes by this evening. The strong onshore flow will begin to shift south of the
     region tonight, but cold air aloft and nighttime cooling will drop the snow level down to
     between 500 and 1000 feet.  

     Midday temperatures had only warmed to near 40 degrees and highs today will be lucky to
     climb into the upper 40s across western Oregon.  High mixing heights and continued
     blustery south-southwesterly winds will make for good ventilation conditions today.

Surface Winds:
     S 5-15 G20 this morning, SSW 7-17 G25 this afternoon.
Transport Winds:
     S 18 this morning, SW 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 100.
High Temperature:
     Salem\'s high temperature today will be near 47.
Humidities:
     Minimum relative humidity will be near 69%.
Sunrise/Sunset:
     Salem sunset tonight: 7:37pm; sunrise tomorrow: 6:55am.

Extended Outlook:
     A cold and unstable air mass will remain over Oregon
     Wednesday, with frequent showers and likely some afternoon
     thunderstorms.  Coastal and valley locations may get bursts
     of small hail.  Snow levels will be near the coastal range
     passes, with wet snow mixing with heavier showers in the
     higher hills around the Willamette Valley.  The main jet
     stream energy will sag southward, to over
     California...taking the main thrust of shower activity will
     it.  However, cold air aloft will combine with daytime
     heating to trigger plenty of showers across Oregon, with the
     mountains continuing to pick up much-needed snowfall.

     A transitory ridge of high pressure is forecast to move
     onshore Thursday and warm the air aloft enough to stabilize
     the atmosphere and decrease the showers across the state. 
     Clearing skies could allow temperatures to approach the
     freezing mark across the Willamette Valley Thursday morning.
     Partly sunny skies and warmer air aloft will help daytime
     highs climb closer to normal Thursday afternoon, with only a
     slight chance of a shower.

     Another cold Pacific storm is forecast to bring more valley
     rain and mountain snow on Friday, with snow levels well
     below the Cascade passes.  Showers will follow the cold
     front on Saturday, with more snow expected in the mountains.
     The next system may take aim more at California, on Easter
     Sunday, but it appears as if it will be close enough for
     more rain and mountain snow to spread northward over Oregon.
     Temperatures will remain well below normal.

Wed (31 Mar):  Showers and T-storms with Small Hail.  Snow Level as Low as 1000 Feet. 36/50

Thu (01 Apr):  Decreasing Showers.  Becoming Partly Sunny.  Snow Level 2500 Feet.  34/54

Fri (02 Apr):  Rain and Mountain Snow.  Snow Level 2-3000 Feet.  40/51

Sat (03 Apr):  Showers.  Snow Level 3000 Feet.  38/52

Easter Sunday (04 Apr):  Rain and Mountain Snow Likely.  Snow Level 3000 Feet.  38/52

Mon (05 Apr):  Showers Likely.  Snow Level Near 3000 Feet.  39/54

Tue (06 Apr):  Partly Sunny.  41/57

ODA Meteorologist
weather at oda.state.or.us