[willamette-fcst] Forecast - Friday, February 26th, 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: 
     Friday, February 26th, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 4:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A moist and very slow-moving Pacific frontal system remained just off the coast lates thhis
     morning, with satellite imagery showing a broad cloud-shield covering all of Washington,
     Oregon and most of California.  Middle and high clouds from this system extend eastward
     across all of Idaho, Nevada, and Utah.  A strong westerly jet stream is cutting across the
     frontal zone off the northern California coast and helping to form a new low-pressure
     circulation center.  That will further slow the eastward progress of the entire frontal
     system today and maintain steady rain across western Oregon.

     The bulk of the rainfall from this system, believe it or not, is following the jet stream
     into California. However, there is enough subtropical moisture entrained into the frontal
     zone to spread plenty of rain northward over western Oregon. Light to moderate rain was
     continuing to fall across all of western Oregon, late this morning, with some very light
     rain also spreading east of the Cascades.

     Through early this moring, rainfall amounts were greatest along the southern
     Oregon coast, and near the California border in southwestern Oregon.  CoCoRaHS and National
     Weather Service reporting stations in Curry and southern Josephine Counties received 1-2
     inches of rain overnight, with coastal sections as far north as Lane County receiving
     over an inch of rain.  About one-half inch of rain fell overnight along the north coast,
     with between one-quarter and three-quarters of an inch of rain in the Willamette Valley.

     In the 6-hour period ending at 10am, another one-quarter to one-half inch of rain has
     fallen across most of western Oregon.  Rainfalll amounts taper drastically east of the
     Cascades, where most areas have received very little rainfall over the past 6 hours.

     The late-morning ODA surface analysis showed the southeasterly pressure gradients
     beginning to turn more easterly, across all of Oregon, due to a strengthening
     low-pressure area, forming along the front, just off the northern California coast.
     The Cascades shelter the Willamette Valley from much wind, with this pressure
     pattern, except for areas near the western end of the Columbia Gorge.  Willamette Valley
     winds have generally been under 10 mph, except for easterly gusts to near 30 mph in the
     Troutdale area.  Southeasterly winds have picked up across sections of central and
     eastern Oregon.  Klamath Falls was recording gusts over 35 mph and La Grande was getting
     gusts over 40 mph.  Remond was getting windy, as well, with gusts over 20 mph.  Winds on
     the central and southern coast have been gusting to between 20 and 25 mph at times.  

     Warming aloft has lifted the freezing level to 7-8000 feet over western Oregon, with
     the snow level at 6000 feet or higher.  ODOT road cameras showed rain and mainly just
     wet pavement over the Cascade passes late this morning with temperatures in the mid
     to upper 30s.  The air aloft is warm enough to support surface temperatures in the
     60s today, if the rain stopped, the sun came out, and the wind turned southerly.  However,
     none of those things is going to happen this afternoon... 

     With a new low-pressure circulation center forming off the California coast, the frontal
     system will stall and maintain a thick cloud-shield smack-dab over western Oregon. Surface
     winds will continue to back from southeasterly to more of an easterly direction this
     afternoon, as the low-pressure wave moves into southwestern Oregon.  The combination of
     continued rain...possibly heavy at times, and easterly low-level flow will hold
     valley highs in the low 50s.  Total rainfall amounts from this storm could exceed one
     inch in sections of the Willamette Valley.

     The occluded front is forecast to finally move inland this evening, with the steady rain
     tapering off to occasional showers.  Surface winds will likely turn southerly overnight,
     which could result in midnight high temperatures across sections of western Oregon.  Snow
     levels will drop to near the Cascade passes overnight, but the precipitation will be
     decreasing at the same time.

Surface Winds:
     ESE 5-12 this afternoon...possibly becoming ENE 5-12.
Transport Winds:
     SE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature this afternoon will be near 52...possibly warmer later tonight.
Humidities:
     Minimum relative humidity this afternoon will be near 85%.
Sunrise/Sunset:
     Salem sunset tonight: 5:56pm; sunrise tomorrow: 6:53am.

Extended Outlook:
     A cool (not cold) upper-level trough will drop snow levels slightly below the Cascade
     passes Saturday, as showers taper off across western Oregon.  Valley highs will climb
     above normal with some afternoon sunbreaks.  A strong ridge of high pressure is forecast
     to build over the west coast late in the weekend, with mostly sunny and very mild
     conditions likely returning to western Oregon Sunday and Monday.

     Increasing south-southwesterly flow aloft will likely bring a weakening weather system
     onshore by late Monday, with rain and much cooler temperatures Tuesday. Showers will
     taper off Wednesday with a break in the weather possible on Thursday. The next weather
     system will head mainly into southern Oregon on Friday, but it will bring at least a
     chance of rain, and mountain snow, to all of western Oregon.

Tomorrow (27 Feb):  Mostly Cloudy.  Showers Ending.  Snow Level 4000 Feet.  45/57

Sun (28 Feb):  Partly to Mostly Sunny and Very Mild.  37/60

Mon (01 Mar):  Increasing Clouds. Continued Mild.  Freezing Level Near 7000 feet.  38/62

Tue (02 Mar):  Rain Likely.  Snow Level 5-6000 Feet.  44/53

Wed (03 Mar):  Mostly Cloudy.  Decreasing Showers.  Snow Level 3500 Feet.  38/54

Thu (04 Mar):  Partly Sunny.  Increasing Clouds Late.  39/57

Fri (05 Mar):  Rain Likely South. Chance of Rain North.  Snow Level 3-4000 Feet.  41/53

ODA Meteorologist
weather at oda.state.or.us