Area forecast discussion
National Weather Service Portland or
850 am PDT Friday may 24 2013
Synopsis...the upper low over Washington Friday morning will weaken this
weekend as it lifts NE into Alberta. A few disturbances will
continue to rotate around the low...keeping a threat of showers in
through the weekend with temperatures warming a bit closer to
normal. An active pattern will continue next week as the flow turns
westerly...and a series of weak disturbances come in off the
Pacific.
&&
Short term...water vapor pictures showed the upper low over central
Washington this morning...with the main vorticity lobe lifting north through
Idaho. A weak surface low was seen just off the coast of kast...
locally enhancing the low level onshore flow over northwest Oregon. Showers
on radar and in surface observations appear to be favoring
orographically enhanced mountains...especially in the north. Will keep showers
likely today in the north and over the mountains...but given the main
shortwave lifting the low NE...expect the heavy precipitation threat
is greatly diminished today.
Remainder of short term discussion unchanged...
the upper low will settle over the Canadian rockies for the
weekend...with a broad upper level troughing pattern over the Pacific northwest.
Expect off and on shower activity much of the weekend. The best
chance at any organized precipitation appears to be Sat night into
early sun...as the models all show a shortwave or weak closed low
pushing into the Pacific northwest. Temperatures should continue to rebound...as we get
more sunbreaks and the airmass moderates. Inland sites should get
into the middle 60s on both Sat and sun.
Another more organized system is being advertised on Monday. There is
plenty of model uncertainy with this system...with some model runs
stretching the upper level forcing and keeping the bulk of it to our
south. However...it appears that we will have a decent shot at
widespread...albeit light...precipitation. Decided to go with likely
probability of precipitation later Monday as most models are bringing precipitation into our forecast area.
Pyle
Long term...no changes. Previous discussion follows...
westerly flow aloft likely to be persist through the early part of
the week. This will keep region under a persistent chance for rain as
a series of shortwaves moves through. The westerly flow off the
Pacific will keep temperatures moderated...likely a little below
seasonal averages. Models tend to diverge some late in the week with
GFS and Canadian cutting off an upper low offshore. Bottom line
though is for a continuation chance of rain.
&&
Aviation...weak low pressure lingering offshore will maintain a
moist air mass and weak flow over the area today. This will allow
showers and local IFR/low MVFR ceilings to remain at the coast and
inland through 18z. Increasing S-SW flow is expected to bring ceilings
above 2000 feet by midday. However occasional showers will reduce ceilings
from time to time...especially at the coast where ceilings look to
remain IFR/low MVFR through the day.
Kpdx and approaches...weak flow and moist air mass will maintain
occasional MVFR showers through 18z. Increasing S-SW flow should
raise ceilings above 2000 feet by midday...with VFR in scattered showers
expected this afternoon. Weagle/Burgess
&&
Marine...no updates. Seas hovering around 8 to 9 feet this morning
will begin to relax this afternoon as low pressure off Astoria moves
inland and northwest fetch dies down. Seas will continue to subside to
around 6 feet by tonight...and remain less than 6 feet through Sunday.
Some gusts to 20 knots reported in mainly the southern waters should
ease today/tonight as the low pressure system weakens and weak high
pressure builds over the waters. A weak low pressure system will move
across the Oregon waters late Sat/early sun...but winds should
generally stay below 25 knots. A more organized system is possible
for Monday which could produce a brief coastal jet for gusts 30 to 35
knots...but this depends on the track. There is still some
possibility this system could focus more on southern Oregon and northern
California than our waters.
Morning ebbs remain very strong due to the full moon...so expect
rough Columbia River bar conditions the next couple mornings.
Weagle/Burgess
&&
Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...Small Craft Advisory for rough Columbia River bar from 4 am
to 8 am PDT Saturday.
&&
$$
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.
