Hermiston, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

126
FXUS66 KPDT 181750
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1050 AM PDT Sun May 18 2025

Updated aviation discussion


.AVIATION...18Z TAFs...VFR conditions will be prevalent for the
next 24 hours. Radar shows some showers near KDLS and from the
Blue Mountains eastward. There is a low chance for a thunderstorm
or two this afternoon over the eastern mountains but any storms
that develop should not approach KALW and KPDT. Showers at KDLS
are expected to end by 20Z. Skies will see scattered mid level
clouds this afternoon before clearing this evening. Another
disturbance will bring a few light showers across the Cascades
after 12Z with -SHRA possible at KRDM, KBDN, KDLS and KYKM 12-18Z.
West to southwest winds today will reach 15 to 25 kts with gusts
of 25 to 35 kts this afternoon before decreasing after 00Z and
dropping below 12 kts after 04Z-08Z. Perry/83

&&

.PREV DISCUSSION... /issued 242 AM PDT Sun May 18 2025/

SHORT TERM...Today through Tuesday...Overnight satellite imagery
shows clearing taking place as an upper-level trough exits our CWA
and digs toward the Four Corners region. This will leave us under a
dry NW flow pattern aloft, leading to a cool day today with high
temps as low as 15 degrees below average, as well as some light PoPs
across our high mountain zones. Expectation is that the bulk of the
rainfall associated with yesterday`s system is over with, but the
flow pattern aloft is amplified enough to trigger at least some
light orographic precip through the day. NBM guidance wants to put
in some slight thunder chances across the eastern mountains of
Oregon, but given the cooler airmass moving in, reducing snow levels
to the 4000-4500 ft range and inhibiting instability, am thinking
that we`ll only realistically see light showers across the mountains
today.

With this transition from yesetday`s trough to an amplified NW to
zonal flow pattern, winds will pick up, especially through the
Cascade Gaps and along exposed ridgetops through the forecast area.
Already seeing gusts eclipse 40 mph early this morning along these
ridgetops, with the Gaps expected to see their strongest winds after
daybreak. Guidance did seem to trend down, however, just from
looking at latest NBM gusts as well as UW WRF values for the
Kittitas Valley and the Columbia River Gorge, with both expected to
see gusts in the 30-40 mph range today. Will opt to leave the
Kittitas`s Wind Advisory in place, but should note that it looks to
be an edge case with sustained winds more likely to verify than
gusts. Elsewhere, expect gusts in the 20-30 mph range, stronger
downslope of the southern Blues and east slopes of the Cascades,
mainly out of the west and northwest.

A shortwave embedded within the amplified flow aloft will deliver
another round of light precip to the forecast area during the day
Monday, but this looks to be a quick-hitting system with rainfall
amounts generally less than a tenth of an inch outside of our high
mountain zones and the Grande Ronde Valley. There, probabilistic
guidance generally suggests about a 60-70% chance for liquid precip
over a tenth of an inch. Heading into Tuesday, the pattern aloft
starts to become zonal, which will provide the high mountains with
persistent light PoPs (20-30%) through much of the week, with
temperatures warming back up to more seasonable values. Under such a
pattern, the lowlands will remain dry, with winds remaining elevated
through the Cascade Gaps and east slopes as well. Evans/74

LONG TERM...Wednesday through Sunday...Ensembles continue to keep
us under a relatively benign zonal flow pattern until around Friday,
when both the consensus across ensemble members and deterministic
guidance is to bring in a negatively tilted trough that could spawn
showers and isolated thunderstorms to the forecast area. Guidance is
split on just how strong this system could be, and just how much
moisture advection the CWA could see, but the pattern is favorable
for at least the mountains to receive showers and possibly storms,
especially across the eastern mountains of Oregon.

Starting around late Saturday onward, ensembles and both the
deterministic GFS and ECMWF hint at ridging building over the PacNW,
lasting through at least the start of next work week. Uncertainty
remains on the strength and position of the ridge, but the NBM does
seem to pick up on this trend, as it suggests high temps climbing
back into the 80s by the tail end of the period. That leaves Friday
into Saturday being the main period of concern for sensible weather,
depending on how that potential trough shapes up across subsequent
model runs. Evans/74



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  39  67  44 /  10  10  70  20
ALW  60  42  65  46 /  20  10  70  30
PSC  68  40  71  43 /   0   0  50  10
YKM  65  39  69  40 /   0   0  30   0
HRI  66  42  71  45 /   0   0  50  10
ELN  60  38  64  41 /  10   0  40  10
RDM  58  34  65  35 /   0   0  20   0
LGD  53  33  62  42 /  20  20  60  60
GCD  55  32  65  39 /  30  10  60  50
DLS  63  44  66  47 /  10   0  20   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 8 PM PDT this evening for WAZ026.

&&

$$

SHORT TERM...74
LONG TERM....74
AVIATION...83