National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KPDT 220523
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1020 PM PDT Sun Apr 21 2024

Updated Aviation Discussion

.SHORT TERM...
Tonight through Tuesday night...Any lingering precipitation over
the Cascades should come to an end this evening as a dry westerly
flow takes over followed by upper level ridging. As the ridge
builds in, and gusty winds will also subside during the evening
and overnight hours. Winds should generally become light.

The combination of light winds and a clearing sky will create
another cool night and freeze warnings will be issued for the
Yakima and Kittitas Valleys. Expect temperatures from 30 to 32
degrees in these areas with moderate confidence (40-70%), due to
discrepancies in the guidance. The MET guidance which has been
colder (and verified) is not necessarily colder this time around.
The NBM seems too warm and the MAV is colder in some cases,
leading to lower confidence. However, even the NBM probabilities
for lows of 32 degrees or lower are 50% or greater at these
locations and the NBM seems a bit high. Elsewhere, confidence is
even lower, so no warnings will be issued at this time and will
see if how later guidance comes in and temperatures respond to
diminishing winds and a clearing sky.

With the ridge overhead on Monday, expect a dry day with light
winds and warmer temperatures. The dry conditions will remain over
the region through much of Tuesday, but the ridge will move
eastward as a trough approaches the coast.

By later afternoon Tuesday into Tuesday evening, there is a low
(<20%) chance of showers and possibly thunderstorms. The best
CAPE and LI is not coinciding with the best moisture at this time,
but we will see if later model runs bring these into better
alignment. The NAM has a swath of CAPE over central Oregon and
then over the higher terrain of eastern and south central Oregon
in the afternoon, but POPS (20% or less) later in the afternoon
and evening. Most of the models agree at this point that the CAPE
is pretty much gone around 00Z Wednesday.

Anything that falls overnight Tuesday night into Wednesday would
mainly be rain showers or possibly snow showers at the higher
terrain of the Washington Cascades.

Temperatures will be anywhere from 2 to about 5 degrees warmer on
Monday than today and by Tuesday, we will end up in the low to mid
70s in most locations which is about 5 to 8 degrees above normal,
depending on location.

.LONG TERM...
Wednesday through Sunday...Models continue to show considerable
differences over time in the long term, but at least through
Friday, the differences end up with generally similar outcomes for
area weather, so confidence is improved but still just average
before becoming low next weekend.

Models start out in good agreement on Wednesday in having a shallow
trough over the area with an upper low in northern British Columbia
while off to the east, a ridge is over the Rockies. A generally west
flow into the Cascades will bring a chance of light rain showers to
the Cascade crest while the rest of the area is dry. Pressure
gradients will be tightening up and the afternoon will see west to
northwest winds at 15 to 25 mph. The trough will bring cooler air
and drop high temperatures 2 to 4 degrees from Tuesday to the mid
60s to lower 70s with mid 50s to mid 60s in the mountains.

Models continue to be in reasonable agreement on Thursday in having
a shortwave enter the trough and move into our area. The mountains
will have a 20-40 percent chance of rain developing in the afternoon
increasing to 40-60 percent Thursday night while the lower
elevations will have a 15-30 percent chance of rain Thursday night.
The Washington Columbia Basin will remain dry. Snow levels will be
around 5000-6000 feet (where they remain through the long term) so
mainly rain is expected with amounts of up to a half inch in the
Cascades, up to a quarter inch in the eastern mountains and less
than a tenth of an inch in the lower elevations. Temperatures on
Thursday will drop about 5 degrees due to the rain and cloudiness to
the upper 50s to mid 60s with mainly 50s in the mountains.

Model differences increase on Friday as 77 percent of GFS model
ensemble members and about 25 percent of the ECMWF and Canadian
models favor a deeper trough centered along the coast while the rest
of the model ensemble members have a shallower trough centered over
our area. Have gone with a 50-70 percent chance of rain over the
mountains and a 15-30 percent chance of rain in the lower elevations
with rain tapering off Friday night. Mountain rain amounts of one to
two tenths of an inch are expected with just a few hundredths in the
lower elevations. Temperatures Friday will cool a couple more
degrees to the lower to mid 60s in the Columbia Basin and in the 50s
elsewhere.

By Saturday, 70 percent model ensemble members favor the trough axis
being over Arizona and Utah, while the other 30 percent have it over
southern California. In addition, 60 percent favor a strong ridge
building offshore in the eastern Pacific with the rest having a
shallow ridge further away from the coast. The varying solutions do
indicate some form of weak wave moving through the area, so have a
20-40 percent chance of rain in the mountains and a 10-20 percent
chance elsewhere. Rain amounts will be just a few hundredths of an
inch. Temperatures will be a couple of degrees warmer than Friday.

By Sunday, model clusters fall equally into 4 differing camps. One
has a weak ridge offshore and a weak trough over the Rockies,
another has a strong ridge offshore and a deep trough over the
Rockies, a third is between the two and the fourth has a wide
shallow trough over much of the CONUS. Since these solutions would
all favor precipitation, have a 30-60 percent chance of rain in the
mountains with a 10-30 percent chance off rain in the lower
elevations. Rain amounts should be very light. Temperatures are up a
degree or two to the 60s and lower 70s with mainly 50s in the
mountains. Winds are expected to increase to 15 to 20 mph in the
afternoon. Perry/83

&&

.AVIATION...06Z TAFs...Skies will clear and winds will diminish
tonight.  Winds on Monday will be 10kt or less and skies will be SCT-
BKN AOA 20kft.  Wister/85


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  33  62  36  68 /   0   0   0   0
ALW  35  65  38  71 /   0   0   0   0
PSC  39  67  40  73 /   0   0   0   0
YKM  32  65  38  71 /   0   0   0   0
HRI  35  66  38  72 /   0   0   0   0
ELN  32  63  36  69 /   0   0   0   0
RDM  29  65  35  69 /   0   0   0   0
LGD  30  62  35  71 /   0   0   0   0
GCD  31  66  37  74 /   0   0   0  10
DLS  38  68  43  72 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Freeze Warning from 2 AM to 9 AM PDT Monday for WAZ026-027.

&&

$$

SHORT TERM...77
LONG TERM....83
AVIATION...85