Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland
245 PM PDT Thursday Mar 26 2015
Synopsis...high pressure will lead to another day with above
average temperatures and some morning fog in The Lowlands Friday.
However...a front will spread rain showers into the area Friday
night with a drying trend on Saturday. Dry and mild weather look to
return late Saturday through early Monday before another front
brings more rain and cooler weather to the area beginning late
Monday and continuing into the middle part of next week. Snow levels
will likely drop below Cascade Pass levels during this period.
Short term...tonight through Sunday...visible satellite imagery
indicates sunny skies across the area with temperatures climbing well
into the 60s. With a couple more hours of solid sunshine...expect
most interior locations to warm to near 70f. With mostly clear skies
expected overnight...expect more lowland fog to develop tonight...but
coverage should be a bit less than this morning.
A front currently positioned between 130w and 140w will shift toward
the region on Friday. Lift ahead of the upper level trough and
cooling temperatures aloft may initiate a few showers and possibly a
thunderstorm across the Cascades Friday afternoon. Expect the bulk of
the showers associated with the upper level trough to arrive across
northwest Oregon and southwest Washington Friday evening...likely
continuing for much of the night. Rainfall amounts should be
relatively light...likely less than a half inch in the Coast Range
and Cascades...and probably closer to a tenth or two tenths of an
inch in the Willamette Valley.
A lowering subsidence inversion late Friday night should result in
showers becoming increasingly confined to the coast and Cascades
before decreasing further Saturday morning. A relatively Flat Ridge
should then build into the region late Saturday and Sunday and bring
another round of above average temperatures. This should result in
generally dry conditions across the area. However...moisture
streaming northeastward along the edge of the high pressure will take
aim at southwest British Columbia and northwest Washington. As a
result...there is a chance this rain could shift briefly into far
southwest Washington during this period. If nothing else...low to
middle level clouds will likely be a bit more persistent across the
northern portion of our County Warning Area during this period. /Neuman
Long term...Sun night through Thursday...overall pattern remains rather
zonal...with westerly flow aloft over the region. This means fronts
will push across the region from time to time...but no significantly
strong or organized systems expected. After a dry period Sat night
through Sun night...clouds will increase on Monday with another round
of rain for late in the day and Monday night. Likely see showers
continue on Tuesday and Tuesday night as cooler air aloft pushes across
region. Afterwards...confidence in any solution begins to drop as
models diverge on any particular solution. Will trend towards drier
but keep some minor threat of showers with near seasonable
temperatures for second half of next week. Rockey.
Aviation...based on the latest visible satellite imagery...the
widespread fog and low stratus has now burned off for most
everyone. Expect VFR conditions through the remainder of the
afternoon and into this evening. With high pressure and mostly clear
skies in place again tonight...expect a repeat of the overnight
and morning IFR fog and low stratus. Will go with a near
persistence forecast overnight into Friday morning...although fog may be
a bit faster to lift tomorrow. Light rain is expected to move onto
the coast Friday afternoon ahead of an approaching front.
Kpdx and approaches...VFR remains in control through this evening.
Expect IFR fog and low stratus to reform by 09z and continue
through around 18z Friday. Conditions will then improve to VFR
through the remainder of Friday. Pyle
Marine...fairly benign conditions currently being observed over
the coastal waters as weak high pressure sits over the region. Winds
are in the 5 to 10 knots range and seas remain around 7 to 8 feet.
Expect little change through early Friday.
A slow moving cold front will move into the waters later
Friday...bringing increase south/southwesterly winds. There is the
potential for a period of low end Small Craft Advisory
winds...with gusts to 25 knots possible mainly Friday afternoon and
evening. Seas may also increase a bit with the winds...but
expected them to remain below 10 feet.
Weak high pressure returns to the waters over the weekend. Another
front is expected to move through on Monday. This front looks a
little more impressive and should bring a solid round of Small
Craft Advisory winds...with a small chance of gales. A more
progressive weather pattern for the first half of next week.
Expect seas to reach into the low teens late sun or Monday and remain
above 10 feet for the next several days. Pyle
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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.