FXUS66 KPQR 052304
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
304 PM PST Tue Mar 5 2024

.SYNOPSIS...Mostly dry weather today through Friday except for
scattered showers over the Cascades today and the coast and
Coast Range Wednesday. There's a potential for fog and frost in
the evening through early morning hours each day through Friday
morning. Wet and warmer weather is expected to return later
Friday into the weekend with widespread rain and mountain snow.

&&

.DISCUSSION...TUESDAY THROUGH MONDAY...Visible satellite imagery
this afternoon shows partly cloudy skies with many locations
seeing sunlight for the first time in over a week. Dry weather
has returned for most locations except for scattered light
showers over the Cascades which will dissipate this evening. Dry
weather will continue for most locations through Friday as
upper level ridging builds over the eastern Pacific. Ensemble
guidance indicates a weak shortwave will move over the PacNW
tonight into Wednesday. This will bring increased high cloud
cover again overnight as well as a 10-20% chance of isolated
showers along the coast and Coast Range north of Lincoln City
through Wednesday afternoon. With skies more clear tonight and
Wednesday night than previous days along with cold air still
intruding from the north, low temperatures will be cooler
Wednesday and Thursday mornings. All areas except the coast have
a near 100% probability of falling below 32 deg F. Tonight into
Wednesday morning is expected to be the coldest with a 50-80%
probability of most locations except the coast falling to at
least 28 deg F, though temperatures Wednesday night into
Thursday morning could be nearly as cold with a 30-60%
probability of the same areas falling to at least 28 deg F.
Daytime temperatures will be similar, generally in the mid to
upper 40s across the lowlands. Expect frost as well as patchy
fog or low stratus both nights, though fog potential may be
limited to fog prone areas due to high clouds lingering.

By Thursday, the upper level ridge over the eastern Pacific
begins shifting east, with ensembles in high agreement that the
ridge axis will move through the PacNW Thursday night into
Friday. This will produce a brief warming trend to NW Oregon and
SW Washington. Daytime temperatures are forecast to warm a few
degrees Thursday into the upper 40s to low 50s across the
lowlands, then warm quite a bit more into the mid to upper 50s
by Friday. Low temperatures Friday morning will still be on the
cold side with a 40-70% probability of lowland valleys reaching
32 deg F, but they will warm into the upper 30s by Saturday
morning as cloud cover increases again. Frost potential will be
decreasing with warming temperatures, but fog potential will be
increasing with clearer skies expected.

Dry weather will be short lived as WPC's 500 mb cluster analysis
is in good agreement of the next weather system moving into the
West Coast sometime late Friday into Saturday. Confidence is
high in this being a warmer system with snow levels remaining
generally above 3000-3500 feet, which means a rainy weekend for
the lowlands. Ensembles indicate a wet pattern will continue
into early next, though details are a bit more uncertain at this
time. -HEC

&&

.AVIATION...Surface ridging continues to build into NW Oregon and
SW Washington under a departing upper level trough. NW flow in the
upper levels continues to bring drier air into the region which
brought an end to precipitation across the area. Clouds will
continue to thin into the overnight hours which will allow temps
to drop into the upper 20s. The dry air aloft and minimal cloud
cover will lead to the development of a low level inversion and
visibilities in the Willamette Valley dropping below MVFR along
with a 30-50% chance of MVFR CIGs. The coastal sites should remain
VFR through the night. North winds around 5 kts will become light
and variable overnight.

*Note: The observations out of KONP are generally limited to wind
 and pressure at this time. Periodically cloud cover, vis, and
 present wx are reported but are unreliable.

PDX AND APPROACHES...Thick cloud cover dissolved through the day
as surface ridging builds into the area and allowed for some
scattered cumulus to develop around 2-4 kft. Dry air aloft along
with dwindling cloud cover will allow for temps to drop into the
upper 20s tonight along with a developing low level inversion.
Model guidance suggests a 30-50% chance of MVFR or lower CIGs and
a 20-40% chance of IFR or lower visibilities. MVFR CIGs are more
likely at 40-60%. North winds around 5 kts will become light and
variable overnight.

&&

.MARINE...High pressure will continue to build into the area
through Wednesday while an area of low pressure persists along the
northern CA coast. This will maintain northerly winds around
10-15 kt across the coastal waters. A weak front approaching the
area late Wednesday into Thursday pushes the higher pressure south
while winds shift southerly. Seas are expected to hover around 4
to 7 ft through Thursday.

A stronger system will approach the coastal waters toward the end
of the work week. A surface low progressing northward in the Gulf
of Alaska will swing a strong cold front toward the PNW which will
increase S/SW winds. The probability of gale force gusts
developing has increased over the last 12 hours and is now around
40-50%. Seas will gradually build after Thursday as winds
increase ahead of this strong system. /Batz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&

$$

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