Area forecast discussion
National Weather Service Portland or
234 PM PDT Sat may 18 2013
Synopsis...plenty of clouds and occasional rain today as a weak low
pressure system slowly moves into Oregon and Washington. Showers will
slowly decrease tonight and Sunday as the system moves into the
Great Basin and falls apart. More sunbreaks Sunday should lead to
more seasonable temperatures. Monday is shaping up to be a pleasant
sunny and warm day under high pressure with temperatures in the lower to middle
70s. High clouds will begin to increase from the northwest later in
the day in advance of our next system...which will bring a dramatic
change back to chilly and unsettled weather Tuesday through Friday.
&&
Short term...today through Tuesday night...visible satellite imagery
shows solid cloud cover across the district this afternoon. Krtx
radar shows an area of light rain spreading across Washington County
and entering the greater Portland and eventually Vancouver metropolitan
area. Additionally areas of light rain persist along the coast and
much of the rest of our forecast area. Snow levels remain rather
high...odot pass cams show occasional rain and it appears to be
raining at timberline as well.
Weak and poorly defined low pressure circulation just offshore from
Astoria will drag a weak cold front onshore over the next few hours
with decreasing showers thereafter. What is left of the front will
finally lumber east across the Cascades tonight with decreasing
showers behind the front. By Sunday morning showers will be mainly
confined to the higher terrain...though a stray shower is still
possible elsewhere due to weak shallow instability.
Made very few changes for Monday and Tuesday. The move the midnight
shift made to bump up Monday temperatures into the 70s appears to be a good
one. The air mass looks rather dry throughout Monday on NAM bufr
soundings...from Eugene all the way up to Portland. With 850 mb temperatures
pushing +10 degree c in the Willamette Valley...highs could get well
into the 70s some areas with plenty of sunshine. Onshore gradients
will keep the coast from warming up too much.
Models showing good agreement on rain from our next system holding
off until Tuesday morning. As Tuesday progresses it appears an
unseasonably deep and cold upper low will sink southeast into Washington/or
spreading rain across the region. Rain appears likely a good portion
of the day Tuesday...with snow levels lowering to the Cascade passes
Tuesday night. There is an outside chance we may need to eventually
consider snow advisories for the Cascades as early as Tuesday night.
Weagle
Long term...Tuesday evening through Saturday...few changes. Closed
low pressure system will linger over the Pacific northwest through the week.
With the cold nature of the low...record low maximum temperatures
are possible on Wednesday...with snow down to pass level likely in
the Cascades. Thursday and beyond models begin to disagree on where
the low will propagate...however the overall trend will
remain...with showery and cool conditions persisting through at
least Saturday. Burgess
&&
Aviation...mix of VFR and MVFR ceilings across the region. A
weakening front is pushing across the region...but back edge of
the front is still offshore and not likely to clear the Cascades
until this evening. Not much change...with scattered showers and
mostly low VFR and pockets of MVFR through tonight. Cascades and
passes will frequently be obscured in clouds. Showers should
diminish overnight behind the front...with MVFR ceilings at the coast
and mostly VFR inland. Some patchy fog possible tomorrow morning
in the southern Willamette Valley if any clearing
occurs...possibly affecting keug.
Kpdx and approaches...expect a mix of VFR and MVFR in scattered
showers through this afternoon as a cold works its way through.
Shower activity should decrease later this evening behind the
frontal passage. Mostly VFR conditions overnight. Pyle
Expect light rain or showers off and on through the day.
Predominantly VFR conditions may drop to MVFR at times during heavier
showers. Shower activity should taper off somewhat this evening...
with mainly VFR conditions during the evening and overnight hours.
Pyle
&&
Marine...a cold front is pushing through the coastal waters this
afternoon. The front has been slower than expected...so decided
to extend the Small Craft Advisory for winds into the early
evening hours. Expect winds to decrease and turn northwest later this
evening behind the front. High pressure will build over the NE Pacific
sun into early next week. It appears that there will be a few
chances for small craft advisories for winds over the next few
days. Sunday and Monday may see wind gusts into the 20 to 25 knots
range during the late afternoon and early evening hours.
Seas remain at 5 to 6 feet through the weekend. Seas may bump up a
bit during the periods of gusty winds on sun and Monday. A large
low pressure system may bring another small craft for winds on
Wednesday...along with seas above 10 feet. Pyle
&&
Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...Small Craft Advisory for winds until 7 PM PDT this evening for
coastal waters from Cape Shoalwater Washington to Florence or out 60 nm.
&&
$$
More weather information online at...
http://weather.Gov/Portland
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.
