354
FXUS66 KPDT 082350
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
450 PM PDT Wed May 8 2024

Updated Aviation Discussion

.SHORT TERM...Tonight through Friday night...Quiet weather
accompanied by a notable warming trend is forecast through the
period as an amplified ridge of high pressure influences the
region.

Synoptically, the region is currently under northeast flow aloft,
located between an amplified offshore ridge that is nosing into
the PacNW and a broad closed low centered over the Great Plains.
Tonight, cloud cover and precipitation chances will diminish
across the region as wraparound moisture decreases.

Ensemble guidance is in excellent agreement that a closed low
will develop northwest of the Four Corners region tomorrow and
retrograde over the Desert Southwest through Friday. This will set
up a textbook Rex block over the West with the aforementioned
amplified upper-level ridge building across the PacNW. The result
will be warming accompanied by dry conditions and offshore-
oriented pressure gradients. Locally breezy northeast winds are
forecast tomorrow, especially along wind-prone ridges.

The main tangible consequence of the ridge will be warming
temperatures with a 5-10 degree warming each afternoon Thursday
and Friday. Confidence is very high (70-99% chance per NBM
probabilities) that Friday afternoon highs will exceed 80 degrees
in the lower elevations (especially the Columbia Basin, Yakima
and Kittitas valleys, and along the lower elevations of the Blue
Mountain foothills). Raising the threshold, confidence is medium-
high (50-80% chance) that Friday afternoon highs will exceed 85
degrees in the lower Columbia Basin and Yakima Valley. In the
populated areas of central Oregon, chances of 80 degrees are lower
(15-50%) and are highest for the Redmond area. Plunkett/86

.LONG TERM...Saturday through Wednesday...Models in pretty good
agreement through the period. However, they do differ on the
timing  of a weak shortwave Sunday night into Monday and in the
strength of a developing upper level ridge off the coast. The EOFs
show the greatest variance (50+%) Tuesday and Wednesday. In fact,
by Wednesday, the WPC cluster analysis shows 57% of the members
believe in an upper level ridge off the coast while 43% depict a
more zonal flow pattern. Depending on the pattern, we could be
near normal or 10-15 degrees above normal by the middle of next
week. In addition, the ensemble means are leaning towards more
zonal flow by Wednesday. NBM is trending more to normal
temperatures (slightly above normal at this time) as well which is
not surprising given aforementioned discrepancies. The
deterministic models are surprisingly in relative alignment with a
weak shortwave moving through Sunday evening. The ECMWF shows
another shortwave moving through the northwesterly flow Monday
afternoon. The disturbances are so weak their only impact on our
CWA should be an increase in cloud cover and slightly cooler
temperatures. However, the Washington Cascade Crest may see some
isolated showers on Wednesday if more westerly flow develops.

In summary, the extended period will start off with an upper level
ridge weakening but daytime highs still 10-15 degrees above normal
Saturday and Sunday. Several shortwaves should continue to
flatten the ridge with more zonal flow developing, dropping highs
back down to 5 degrees or so above normal. Another amplifying
ridge could develop (low to moderate confidence) over the eastern
Pacific, but resulting in a "cooler" northwest flow pattern aloft
for our CWA.

There will be some hydrological concerns over the weekend as an
upper level ridge continues to produce above normal temperatures
over the area. This will provide ideal conditions for melting some
of our winter snowpack. All rivers will see rises, but portions of
the Naches River are expected to recede bankfull by Saturday or
Sunday. Earle/81

.AVIATION...00Z TAFs...VFR conditions to prevail through the
period. Periodic CIGS of few-bkn AOA 20kft AGL will impact sites
through the period. Breezy winds between 12-15kts and gusts up to
20kts will continue at site RDM/BDN through 4Z, becoming less than
12kts the remainder of the period. Everywhere else winds will be
12kts or less, with winds mostly from the north tomorrow...except
site DLS where winds will be from the east. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  40  73  46  79 /   0   0   0   0
ALW  42  78  49  83 /   0   0   0   0
PSC  46  81  52  86 /   0   0   0   0
YKM  42  80  48  85 /   0   0   0   0
HRI  42  79  49  85 /   0   0   0   0
ELN  43  78  49  84 /   0   0   0   0
RDM  34  71  40  79 /   0   0   0   0
LGD  37  71  43  77 /   0   0   0   0
GCD  33  72  42  77 /   0   0   0   0
DLS  47  80  52  86 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...86
LONG TERM....81
AVIATION...82