[willamette-fcst] Forecast - Tuesday, March 23rd, 2010

Tue Mar 23 08:59:52 PDT 2010

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 23rd, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from 11:00am until 5:30pm.
     Stack burning is not allowed.

Weather Discussion:
     Light winds and clearing skies, combined with cool air
     aloft, allowed temperatures to drop well into the 30s across
     western Oregon early this morning.  Some spots dropped to
     near the freezing mark with patchy frost in the Willamette
     Valley.  Hillsboro dipped to 33 degrees on their hourly
     observations and may have been even colder.  Salem dropped
     to at least 34 degrees and Eugene to at least 35 degrees,
     before fog formed and stabilized the temperature there. 
     Even the normally warmer Portland Airport temperature fell
     into the upper 30s. Those temperatures seem warm, compared
     with the 17 degree minimum recorded so far this morning at
     Burns, and 19 degrees at Baker City, in eastern Oregon.  The
     final morning minimums will be available by the noon update.

     An upper-level ridge of high pressure is building over
     Oregon and Washington this morning.  After dropping below
     5000 feet Monday, the freezing levels over Salem and Medford
     were measured at 7700 feet and 9900 feet respectively early
     this morning.  Infrared satellite imagery showed only a few
     high clouds making it through the ridge and steraming over
     Washington and Oregon in a dry northwesterly flow aloft. 
     Visible satellite imagery showed patchy fog in the northern
     Willamette Valley and more wisespread fog and low clouds
     from the Lane County south into Douglas County. 

     The ODA surface analysis showed high pressure over
     Washington and most of Oregon with weak pressure gradients
     across both states.  A surface thermal trough was beginning
     to push northward along the southern Oregon coast,
     increasing the north-northeasterly gradients across the
     extreme southwestern corner of the state. At mid-morning,
     winds were generally less than 10 mph statewide. 
     Temperatures ranged from the mid 30s to the low 40s across
     western Oregon, with 20s to mid 30s east of the Cascades.

     As the upper-level ridge continues to build over western
     Oregon today, the surface thermal trough will push further
     north into southwestern Oregon.  Increasing
     north-northeasterly pressure gradients will help dry the
     low-level air mass over western Oregon, with areas of
     morning fog and low clouds giving way to mostly sunny skies.
     Afternoon highs should rebound into the low 60s across most
     of the Willamette Valley.  The extreme south valley may not
     make it out of the 50s, due to the more widespread morning
     clouds and a cool northerly breeze.  Warming aloft will
     yield lower mixing heights today, with only fair ventilation
     conditions forecast this afternoon.  North-northeasterly
     transport winds are not conducive to good ventilation for
     stack burning, so it is not allowed today.

Surface Winds:
     NNE 3-10 this morning, N 5-15 this afternoon.
Transport Winds:
     NE 10 this morning, NNE 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 62.
Humidities:
     Minimum relative humidity will be near 39%.
Sunrise/Sunset:
     Salem sunset tonight: 7:29pm; sunrise tomorrow: 7:08am.

Extended Outlook:
     The upper-level ridge will weaken and shift eastward, to
     over Idaho, by Wednesday afternoon.  Increasing southwesterly
     flow aloft will initiate a push of cooling marine air into the
     Willamette Valley in the afternoon but likely after temperatures
     climb into the low to mid 60s. Increasing southwesterly transport
     winds and high mixing heights will likely provide excellent
     ventilation for stack burning.

     A cold front is forecast to spread rain across western
     Oregon late Wednesday night and Thursday morning, followed
     by an upper-level trough Thursday afternoon through perhaps
     much of Friday.  Another upper-level ridge is forecast to
     bring drying conditions late Friday and Saturday.  The next
     weather system, on Sunday, does not look very
     strong...bringing a chance of light rain and high elevation
     snow...mainly north.  A stronger system is forecast to come
     onshore Monday, with more significant rain and possibly
     windy conditions...especially along the coast.  That will be
     followed by a cold upper-level trough Tuesday and Wednesday,
     with showers and mountain snow.

Tomorrow (24 Mar):  Increasing Clouds in the Afternoon.  Rain Late.  35/64

Thu (25 Mar):  Rain Turning to Showers.  Cooler.  Snow Level Dropping to 3-4000 Feet.  44/56

Fri (26 Mar):  Showers Decreasing Late with Partial Clearing. Snow Level 3-4000 Feet.  40/56

Sat (27 Mar):  Chilly Start...Becoming Mostly Sunny and Warmer.  35/63

Sun (28 Mar):  Chance of Light Rain...Mainly North.  Snow Level 5-6000 Feet.  44/58

Mon (29 Mar):  Increasing Rain and Wind.  Snow Level 5-6000 Feet.  43/59

Tue (30 Mar):  Showers.  Snow Level Dropping to 3000 Feet.  40/56

ODA Meteorologist
weather at oda.state.or.us