Hermiston, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

454
FXUS66 KPDT 182347 CCA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
437 PM PDT Sun May 18 2025

.Updated for Aviation...


SHORT TERM...Tonight through Tuesday Night...An upper trough is
moving east out of the region this afternoon though a closed is
still over northern Washington as it also tracks eastward with the
trough. Satellite imagery shows partly to mostly cloudy skies
over the eastern mountains and some cloud streets over the
Cascades indicating mechanical turbulence and strong winds aloft.
Breezy to windy conditions continue this afternoon with most sites
at 20 to 30 mph with gusts to 40 mph. Ellensburg had a gust to 56
mph in the last observation but overall, has generally has
remained in the lower to mid 40 mph range. Model forecasts show
the pressure gradients peaking in the next couple of hours and
observations support that. Pressure gradients relaxing this
evening will allow and winds to steadily decrease this evening and
overnight.

Radar shows circulation around the low developing some showers
over the eastern mountains this afternoon and would not be
surprised by a stray thunderstorms before sundown down instability
and moisture is lacking. Showers will taper off this evening with
just another tenth of an inch in the eastern mountains and little
if any precipitation in the rest of the area. NBM model ensemble
members have a 50 percent chance of a tenth of an inch of rain in
the Oregon Blue and Wallowa Mountains while the rest of the area
has less than a 10 percent chance of even 5 hundredths of an inch.

Tonight will see a transitory ridge moving in from the west ahead
of a cold front approaching the coast. Temperatures will be a few
degrees cooler than last night due to the colder air left in the
wake of the departing low. Temperatures will be in the mid 30s to
lower 40s in most lower elevation locations. In the mountains
temperatures will be in the upper 20s to lower 30s. A tricky
question is the Grande Ronde Valley which is forecast to reach 32.
That zone is eligible for freeze warnings, but most guidance is a
degree or two warmer than freezing and expect that freezing
temperatures, if they happen there, will only be for a short
period, so will hold off on issuing a Freeze Warning for the
Grande Ronde Valley. NBM probabilities show a 30 percent chance of
less than 32 degrees at La Grande at 4 AM, a 50 percent chance at
5 AM and a 13 percent chance at 6 AM.

Monday will see a quick moving shortwave move across the Cascades in
the late morning bring a chance of light rain to the area in the
afternoon then moving off to east in the evening with just a slight
chance of light showers in the eastern mountains Monday night. The
Cascade crest and eastern mountains will take the brunt of the
precipitation with up to a quarter inch of rain. The Blue Mountain
Foothills are expected to get up to a tenth of an inch in the
afternoon with the rest of the area getting just a few hundredths of
an inch. The effects of the departing ridge and a slightly southwest
flow ahead of the shortwave will warm temperatures 4 to 7 degrees to
the mid 60s to lower 70s with mainly 50s in the mountains. Winds
will be much lighter tomorrow but still reaching 10 to 20 mph from
the west to southwest in the afternoon. Tuesday night will be
several degrees warmer due to rising heights and lingering cloud
cover from the shortwave. Lows will be in the mid 30s to mid 40s
and even the mountains will be mostly above freezing.

With a zonal west to northwest flow aloft with no disturbances,
Tuesday and Tuesday night will have quieter weather. Do not
foresee any showers during the day. Temperatures remain similar
to Monday and winds will be the typical west to northwest winds at
10 to 20 mph in the afternoon. Perry/83

LONG TERM...Wednesday through Sunday...Ensembles are in fairly
good agreement early on about having a generally flat westerly
flow aloft over our area Wednesday which gives us a quiet day with
few concerns. Temperatures warm a few degrees to the upper 60s to
lower 70s with 60s in the mountains. Some light upslope showers
will be possible in the mountains in the afternoon with minor
amounts of rain.

Thursday will see a weak wave move through the area with a chance
of showers in the mountains mainly in the morning. Amounts will be
up to a tenth of an inch. Due to the wave being mostly off to the
east in the afternoon, winds remain in a typical afternoon range
of 10 to 20 mph. Temperatures will be up a couple of degrees in
the Columbia Basin, down a couple of degrees in central Oregon and
similar to Wednesday elsewhere.

Friday through Sunday, models struggle with an upper low and
trough and differences increase over time. On Friday, 51 percent
of model ensemble members have a trough just offshore with a wave
moving through the area which would give us showers while the
other 49 percent favor a drier west to southwest flow which would
be drier for us. Given the uncertainty, have a chance of rain in
the mountains with amounts up to a tenth of an inch while the rest
of the area has a slight chance of rain with barely measurable
amounts. Saturday sees 67 percent of the model ensemble members
see a large upper low off of northern British Columbia build a
ridge over our area while the other 33 percent have a lingering
wave which would give us showers. Have kept a slight chance of
light mountain showers for Saturday afternoon. By Sunday, 87
percent of the members favor a ridge and dry weather while the
other 13 percent develop a trough offshore but too far away to
generate much in the way of showers. Temperatures Friday through
Sunday look to be in the mid 70s to lower 80s with upper 60s to
mid 70s though Saturday may be a degree or two cooler than the
other two days. Perry/83

AVIATION... 00Z TAFS...VFR conditions are expected for through the
evening and overnight hours. However, guidance suggests MVFR
conditions at DLS, BDN and RDM Monday morning as the next wave of
SHRA moves in, followed by a return to VFR in the afternoon. All
other sites should remain VFR through the period.

Gusty winds, generally in the 20 to 30 kt range will decrease this
evening. Winds are generally expected to be 10 kts or less
overnight. Gusty winds will redevelop on Monday afternoon for DLS,
BDN and RDM in the 20 to 25 kt range.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  40  67  43  65 /   0  80  30  10
ALW  43  65  46  64 /  10  80  50  20
PSC  41  72  44  70 /   0  70  20   0
YKM  38  70  40  68 /  10  50  10   0
HRI  42  71  44  69 /   0  70  10   0
ELN  38  64  40  63 /  10  60  20  10
RDM  35  65  34  63 /  10  30   0   0
LGD  33  60  41  59 /  10  70  70  20
GCD  32  64  38  61 /  10  70  50  10
DLS  45  68  46  66 /  10  60  10  10

&&

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

&&

$$

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