Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
246 am PDT Friday Oct 31 2014
Synopsis..steady rain associated with a moist frontal boundary will
slowly push eastward today. Hit or miss showers will likely develop
this afternoon...with most containing brief heavy rain...small hail
and possibly some thunder. Showers should taper off during the
evening hours for those trick or treating. Some additional showers
may linger into Saturday...before more clouds and light rain spread
back across our northern zones Sunday. Another wet and breezy storm
system is expected to arrive late Monday and Tuesday.
Short term...today through Monday...satellite and radar composites
show an elongated front bringing widespread rain to western Oregon
and Washington. Coastal locations and western portions of the
Willamette Valley have received between a third and a half inch of
rain so far. Valley locations closer to the Cascades are pushing one
inch...while one to two inches of rain have fallen across the
Cascades in the past 24 hours. Cloud tops continue to cool upstream
along the northern California and southern Oregon coast this
morning. This should result in an additional area of steady rain
spreading northward into western Oregon and Washington early this
morning. Most locations should see another quarter to half inch of
rain this morning.
Infrared satellite imagery also shows plenty of showers and isolated
thunderstorms near 130w...which are associated with 500mb
temperatures of -26c to -30c. This cold air aloft will modify a bit
as it spreads eastward over the area today. Nonetheless...as the
atmosphere destabilizes today...expect breaks in cloud cover to
develop. Shortly thereafter...showers and isolated thunderstorms
should bubble up across northwest Oregon and southwest Washington.
Small hail...brief heavy rain and a stray lightning strike or two
will be the main threats with these storms.
Showers over the interior should taper quickly as sunset approaches
this evening...which should result in most trick or treaters staying
dry. Coastal locations will stand the best chance of seeing showers
linger through the evening hours where the relatively warm ocean
surface temperatures nearby will allow showers to continue overnight.
Additional showers may bubble up Saturday afternoon...especially
across the interior...but in general...the day as a whole appears
A warm front still looks on track to spread light rain into our
northern zones late Saturday night...or more likely...Sunday. Light
rain may linger well into Monday...especially across our northern
zones...before the next wet storm system approaches the region late
Long term...Monday night through Thursday...models continue to agree
a stronger frontal system will bring a good bout of rain to the area
late Monday night into Tuesday. Models suggest southwest Washington
will receive the brunt of the heaviest precipitation...while quantitative precipitation forecast
amounts will remain much more modest towards Lane County. Flashier
river systems like the Grays River may need to be monitored based on
the latest model output. Probability of precipitation were pushed into the likely and
categorical mentions due to increased confidence in rain chances.
While this system will bring windy conditions to the coast...high
winds do not appear to be a large threat at this point. Brief
shortwave ridging may develop for a day or so before the next storm
system arrives late in the week. Nonetheless...high end chance to low
end likely probability of precipitation were maintained the in extended given uncertainty in
the pattern and climatology. /Neuman
Aviation...stalled front will slowly push east of the Cascades
later this morning...with showers filling in behind it. A mix of
VFR/MVFR/IFR conditions will continue early today...with lower
ceilings in showers. Could see another morning with IFR or even LIFR
ceilings around sle and eug. Showers will continue today with a small
chance of thunder mainly during the afternoon hours...expect
overall conditions to improve with a mix of low end VFR/high end
Kpdx and approaches...MVFR ceilings linger through this morning...then
expect mostly VFR ceilings after 18-20z today. Slight chance of
thunder this afternoon...with lower conditions in heavier showers.
Marine...winds have dropped to 10 knots or less behind the front.
With swell continuing to decrease...conditions will remain benign
outside of the Columbia bar this morning before west-northwest swell
increases seas to at least near Small Craft Advisory criteria this evening and
overnight. Raised seas to around 10 feet based on latest model
guidance...but seas forecast is somewhat uncertain and borderline
for Small Craft Advisory so will let midnight shift reassess and issue if
necessary. Could see a couple of thunderstorms this afternoon
with associated localized gusty winds. Winds overall will shift
southerly later today and increase a bit with gusts less than 20
knots. Next round of gusty winds arrive early next week. Bowen/27
Pz...Small Craft Advisory for hazardous seas from 2 PM this
afternoon to 2 am PDT Saturday for waters from Cape Shoalwater
Washington to Florence or from 10 to 60 nm.
Small Craft Advisory for rough Columbia River bar from 10 am
this morning to 2 PM PDT this afternoon...then again from
10 PM this evening to 3 am PDT Saturday.
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This discussion is for northwest Oregon and southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.