Hermiston, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

046
FXUS66 KPDT 220630 CCA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1030 PM PST Fri Feb 21 2025

.UPDATED AVIATION DISCUSSION...

.AVIATION...06Z TAFs...KPSC is currently in VFR before briefly
deteriorating to IFR due to low clouds and mist until tomorrow
morning. And with the system arriving, fog may develop tonight
around KDLS as well (<20% chance). KPDT/KALW/KPSC may receive
lingering rain later tonight, but chances are low (20-40% chance).
Otherwise, most sites (KDLS/KPDT/KRDM/KBDN/KYKM/KALW) will be in
VFR throughout the TAF period. Widespread showers is forecasted
for KDLS/KPDT/KRDM/KBDN/KYKM tomorrow night. Gusty winds will
develop late morning to afternoon as high as 20-30 kts for sites
KRDM/KBDN/KALW. Feaster/97

&&


.PREV DISCUSSION... /issued 350 PM PST Fri Feb 21 2025/

SHORT TERM...Today through Sunday night...

Key Messages:

1. Light mountain snow and Basin showers tonight.

2. Widespread rain returns Saturday afternoon through Sunday.

3. Windy conditions Saturday evening through Sunday.

4. Warming temperatures through the weekend.

Current radar and visible satellite imagery showing light returns
extending across the Basin under partly to mostly cloudy skies.
This is in response to an upper level shortwave that is
suppressing the upper level ridge that brought us mostly clear
skies Thursday and through the early part of today. The light
returns are indicative of elevated moisture that is currently not
reaching the ground surface due to the lingering dry air at lower
levels of the atmosphere. This air will slowly moisten through the
evening, but is only expected to result in light accumulations of
a trace to 0.01" across the Lower Columbia Basin of Washington.
Confidence in these rain amounts is high (80%) as the NBM
suggests only a 10-30% chance of measurable rainfall (0.01" or
more) this evening. Higher elevations above 4000 feet across the
Cascade and northern Blue Mountains will receive 0.5-1.5 inches of
snow, with elevations between 3000 and 4000 feet receiving
primarily rain with 0.05-0.15" likely.

Tonight`s shortwave will allow for southwest flow aloft to set up
ahead of the next shortwave that will pass through the area
Saturday afternoon, accompanied with a weak Atmospheric River
supplying the moisture. This will increase snow levels into the
7500-8500 foot range by Saturday afternoon, extending through
Sunday. Showers will begin along the Washington Cascades by 4 PM
before extending into the Basin by 8 PM and the northern Blue
Mountains by 10 PM. Precipitation will then enhance overnight and
through Sunday evening as the Atmospheric River dissipates shortly
after 4 PM Sunday. Highest rain amounts are expected to occur
across the Cascades with 1 to 2 inches of rainfall Saturday with
an additional 1.5 to 2.5 inches Sunday for elevations above 4000
feet. Confidence in these rain amounts is high (80-90%) as the NBM
suggests an 85-95% chance of 1 inch of rain or more for both
Saturday and Sunday. Rain amounts along the northern Blue
Mountains will be between 0.50 to 1.0 inch Saturday with an
additional 1 to 2 inches Sunday primarily above 3500 feet.
Confidence in these rain amounts is moderate to high (60-80%) as
the NBM advertises a 50-60% chance of 0.75" of rain or more on
Saturday and a 70-80% chance of 1 inch or more on Sunday. The Blue
Mountain foothills should receive 0.05 to 0.15" Saturday and 0.25
to 0.60" Sunday, with the NBM showing a 40-60% chance of 0.10" or
greater Saturday and a 50-80% chance of 0.40" or greater Sunday.
Lower elevations of the Basin is expected to receive 0.01-0.10"
Saturday and 0.10-0.20" on Sunday, with the NBM showing a 35-55%
chance of 0.05" or more Saturday and a 50-75% chance of 0.15" or
more on Sunday.

The shortwave Saturday will also develop a pressure gradient along
the Blue Mountains to allow windy conditions across the Grande
Ronde Valley Saturday evening, extending along the Blue Mountains
and foothills Saturday night into Sunday morning. Gusts of 40-50
mph out of the south look possible (60-70% confidence) as the GFS,
NAM, and SREF highlight a pressure gradient of 6-8 mph between
Baker City (KBKE) and Meacham (KMEH) and a 10-12 mb gradient
between Ontario (KONO) and Meacham (KMEH). Further confidence is
gleaned from the NBM, which suggests a 55-75% chance of advisory
level wind gusts (45 mph or greater) over the Grande Ronde Valley
Saturday evening through Sunday morning. The pressure gradient
along the Blue Mountains will also lead to downsloping winds along
the Blue Mountain foothills, as the GFS, NAM, and SREF suggest a
pressure gradient of 4-7 mb between Pendleton (KPDT) and Meacham
(KMEH). The GFS is the only guidance hinting at a gradient of
above 5 mb, with the NBM indicating a 25-55% chance of advisory
level wind gusts (45 mph or greater). Thus, further analysis is
necessary as confidence in advisory-level winds is currently
lacking (below 60%) for both regions. Winds will slacken through
Sunday morning, but will briefly increase late Sunday evening.

Southwest flow aloft will also lead to warming temperatures over
the weekend, with high temperatures breaking into the mid-to
upper 50s Saturday and low to mid-60s on Sunday across lower
elevations of the Columbia Basin and Blue Mountain foothills.
These temperatures are 10 to 15 degrees above normal. Confidence
in these high temperatures is high (80-90%) as the NBM suggests a
50-65% chance of highs reaching 60 degrees or above on Saturday
over lower elevations of the Basin, and a 60-80% chance on Sunday.
75

LONG TERM...Monday through Friday...

Bottom Line Up Front

1) Moderate mountain rain/snow, light lowland rain to start

2) Warmer and drier conditions return by midweek

3) Hydrological concerns from Mondays system

Monday into Tuesday night, models show yet another wet shortwave
system making its way briefly across the region exiting by Tuesday
night. The 48-hr raw ensemble probabilities ending Tuesday for
precipitation accumulations for 2 inches or greater, show
probabilities are between 80-90% along the Cascade crests, with less
than 15-25% along the crests of the Northern Blues. Lower elevations
show there is generally a 40-70% chance of 0.25 inches of rain
across central & north central OR, the Yakima/Kittitas/Grande Ronde
valleys, and along the northern Blue Mountain Foothills. Snow levels
will be relatively high to begin with then steadily decrease to near
5500 feet. There is snow expected to fall above 5500 feet both
Monday night through Tuesday night. By Tuesday night models show the
leading edge of an upper level ridge making its way back over the
region. Clusters show the models are struggling with the amplitude
and timing of the ridge. Even with the variances, models show the
region to be under dry conditions with precipitation returning to
the Cascades while the remainder of the region stays dry through
Friday with precipitation backing off the Cascades again.

The southwesterly flow associated with these upper level shortwaves
as well as the surface warm fronts associated with them will bring
warmer temperatures across the region. Comparing the currently
forecasted temperatures against the climate data temperatures for
this time of year, these temperatures are anywhere from 5 to 10
degrees above normal for the lower and mid elevations and 2 to 5
degrees above normal for the higher terrains. By the end of the
period, the entire region will be 5 to 10 degrees above
climatological normal with a few isolated areas in central OR being
nearly 15 degrees above. EFI is continuing to show temperatures are
decently above normal for this time in the season with temperatures
averaging in the upper 50s to low 60s in lower elevations, low to
mid 50s along the mid elevations and in the upper 30 to mid 40s
through the higher terrains on Monday. After Monday temperatures are
still averaging above normal with temperatures in the 50s along the
lower terrains, high 40s to low 50s along the mid elevations and mid
30s to low 40s for the higher terrains. Confidence is high (<85%)
with temperatures that are forecasted for the long term.

Lastly and most importantly, there are some hydrological concerns
that are popping up from all the warm temperatures and
precipitation. Rivers through the Yakima, Naches, Klickitat, Walla
Walla and the lower Yakima River Basins will see rises in the rivers
within the Naches at Cliffdell forecasted to break above bankfull by
Monday with probabilities of 10-25%, Walla Walla River near Touchet
with probabilities of 25-75% breaching action stage and Klickitat
River near Pitt 10-25% reaching action stage as well. A hydrologic
outlook has been issued and we will continue to closely monitor the
river forecasts and work with the river centers as the day draws
closer. In the meantime, be prepared and continue to remain vigilant
and check the website for updated information regarding the rivers.
Bennese/90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  34  59  45  61 /  20  30  80  90
ALW  36  54  45  57 /  30  40  90  90
PSC  35  58  46  63 /  30  40  70  80
YKM  32  49  40  58 /  30  20  50  80
HRI  33  59  46  64 /  20  30  60  80
ELN  32  46  37  53 /  40  30  60  80
RDM  35  59  45  60 /  20  10  40  80
LGD  33  45  37  47 /  20  30  80 100
GCD  33  52  40  52 /  20  30  70  90
DLS  38  54  46  60 /  20  30  80  90

&&

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

$$

SHORT TERM...75
LONG TERM....90
AVIATION...97