[willamette-fcst] Forecast - Monday, March 29th, 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.

NOON UPDATE

Issued: 
     Monday, March 29th, 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:
     Strong southerly winds, gusting to over 80 mph, hit the
     Oregon coast overnight, with gusts close to 50 mph in the
     Willamette Valley.  The National Weather Service wind tower,
     at Garibaldi, recorded a wind gust early this morning of 85
     mph.  77 mph winds were clocked at the Yaquina Bay Bridge,
     in Newport.  Mt. Hebo, in the northern coastal range,
     recorded a peak gust of 96 mph.  In the Willamette Valley,
     southerly winds gusted to 46 mph in Salem and to 38 mph in
     Portland.  Heavy rain accompanied the strong winds, with
     rainfall totals of one-half to one inch common both along
     the coast and in the Willamette Valley over the past 24
     hours.  Troutdale picked an additional .52 inches of rain,
     since 5am, bringing their 36-hour total to 1.58 inches. 
     Salem picked up .55 inches of rain in the 6-hour period
     ending at 11 a.m., with a 36-hour total of 1.56 inches.

     The late-morning ODA surface analysis showed southerly
     pressure gradients continuing across the entire state. 
     South-southwesterly winds have backed off some since early
     this morning but were still gusting to over 30 mph across
     western Oregon...especially south.  Winds were increasing
     east of the Cascades, with gusts over 50 mph at Burns and
     over 40 mph from Hermiston to Rome.

     The strong cold front, responsible for the stormy weather,
     has stalled near the Oregon coast, with an upper-level front
     progressing eastward over eastern Oregon.  Satellite imagery
     showed mostly solid cloud-cover across the entire state,
     with a few breaks in the clouds over northwestern Oregon. 
     Doppler radar and surface reports showed locally heavy rain
     continuing to fall across sections of western Oregon, with
     some spots seeing a break from the rain.  Only a few areas
     of light rain were making it east of the Cascades.

     The freezing level jumped to 6-7000 feet Sunday afternoon but
     was falling late this morning, in the wake of the
     upper-level cold front.  ODOT road cameras showed the rain
     changing to snow over the Cascade passes, where temperatures
     had dropped to near the freezing mark.

     The surface cold front is forecast to slowly progress
     eastward, across western Oregon, and push into eastern
     Oregno later this afternoon.  In its wake, the steady rain
     will turn showery, with colder air aloft continuing to drop
     the snow levels in the Cascades.  Satellite imagery shows
     impressive cumulus cloud development approaching the
     coastline, so scattered thunderstorms are likely to move
     onshore later this afternoon.  Some thunderstorms have
     already developed in the northern Willamette Valley that
     could produce hail up to one-half inch in diameter.

     With lowering snow levels and increasing shower activity
     expected, the National Weather Service has issued a Winter
     Storm Warning, for elevations above 4000 feet, where more
     than foot of new possible is possible later this afternoon
     and tonight.  That is much-needed snowfall but could cause
     serious travel delays over the Cascade passes. 
     Thunderstorms will likely produce bursts of mostly small
     hail along the coast and across the western valleys later
     this afternoon and this evening.  However, some hail could
     be as large as one-half inch in diameter.

     Stormy conditions held overnight temperatures mostly in the
     mid to upper 40s across western Oregon.  Late-morning
     readings ranged from the mid 40s to the low 50s.  Highs this
     afternoon should only warm into the 50-55 degrees range. 
     Pressure gradients are forecast to turn more southwesterly,
     in the wake of the cold front, this afternoon.  Continued
     blustery southwesterly winds and cooling air aloft will
     provide excellent ventilation conditions today for
     agricultural and stack burning.

Surface Winds:
     SW 10-20 G30 this afternoon.
Transport Winds:
     SW 30 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 105.
High Temperature:
     Salem\'s high temperature today will be near 54.
Humidities:
     Minimum relative humidity will be near 61%.
Sunrise/Sunset:
     Salem sunset tonight: 7:36pm; sunrise tomorrow: 6:56am.

Extended Outlook:
     A cold and unstable air mass will move over Oregon Tuesday
     and Wednesday, with frequent showers and likely some
     afternoon thunderstorms.  Coastal and valley locations will
     likely see more bursts of small hail.  Snow levels will
     remain well below the Cascade passes and could drop as low
     as the coastal range passes by Tuesday night.  The main jet
     stream energy will sag southward, to over California, by
     Wednesday.  However, plenty of 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 cool Pacific storm is forecast to bring more valley
     rain and mountain snow on Friday, with snow levels staying
     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 that is getting too far out to call.

Tue (30 Mar):  Showers and T-storms with Small Hail.  Snow Level Dropping to 2500 Feet. 40/51

Wed (31 Mar):  Showers and T-storms with Small Hail.  Snow Level Dropping to 1500 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 3-4000 Feet.  40/53

Sat (03 Apr):  Showers.  Snow Level 3000 Feet.  40/55

Sun (04 Apr):  Chance of Rain...Mainly South.  Snow Level 4000 Feet.  40/55

Mon (05 Apr):  Chance of Rain.  Snow Level 3-4000 Feet.  39/55

ODA Meteorologist
weather at oda.state.or.us