Hermiston, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

938
FXUS66 KPDT 220603
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1003 PM PST Sat Dec 21 2024

.AVIATION...06Z TAFs...Aside from some lingering isolated showers
in the vicinity of PDT/ALW this evening, a break in precipitation
is expected (>80% chance) at all terminals overnight into Sunday
morning as a shortwave trough exits to the east and a transient
upper-level ridge moves overhead. Low chances (30%) of -RA are
forecast at BDN/RDM early Sunday morning in response to a weak
shortwave embedded within the ridge. Otherwise, the next round of
-SHRA or -RA will arrive Sunday afternoon through evening as
another upper-level shortwave trough swings across the PacNW.

With regard to CIGs/VSBYs, confidence is low (<30%) in sub-VFR
conditions at BDN/RDM/PDT/ALW through the period, with the
exception of temporary reductions in showers. Cannot rule out some
BR or FG overnight at PDT/ALW, but confidence is low. At PSC,
already seeing some BR forming, and patchy dense fog has developed
to the west in the Hanford area. Best fog chances will be to the
west of PSC, but still have high confidence (80%) in at least MVFR
VSBYs (BR), while confidence in dense FG is low (<40%). DLS/YKM
have the best chance (50-80%) of CIGs reaching low-end MVFR/IFR
overnight. Plunkett/86

&&

.PREV DISCUSSION... /issued 322 PM PST Sat Dec 21 2024/

.SHORT TERM...Today through Monday...A negatively-tilted trough
lifting through the PacNW is currently spreading light
precipitation through the forecast area. The SW approach of this
system has kept snow levels elevated, so snow is currently falling
above our major mountain passes, namely at 4500 feet and higher.
Only ptype concern this afternoon has been in the Kittitas Valley,
where dense fog earlier this morning kept a layer of cold air
trapped at the surface, leading to periods of freezing rain at
times. Fortunately, precip has been on the lighter end, and temps
are gradually warming up with the SW flow aloft and subsequent
warm air advection. Expect precip to generally end here in the
next few hours as transitory ridging moves into its place.

Only other concern for the day today has been downsloping winds at
the base of the Blues and through the Grande Ronde Valley, however
winds have generally trended downward throughout the day. Opted
to cancel the Wind Advisory for the GRV early as advisory-level
winds have failed to materialize. With quieter weather expected
this evening, confidence is on the higher end (70-80%) on fog
redeveloping overnight. Only question is where and to what extent,
but current thinking is that the lower Basin, Yakima/Kittitas
Valleys, and the foothills of the Blues will be particularly
vulnerable, what with high pressure moving in and recent moisture
aiding in fog development. Opted to mention a wide swath of the
Basin and adjacent valleys for patchy fog in the forecast tonight
through tomorrow morning.

The next round of precip is expected to arrive Sunday afternoon
and last into early Monday morning as a warm front lifts through
the region. This system looks to be more moisture-laden than
today`s, however the story remains much of the same: snow levels
will be much too elevated for any major concerns to materialize
across our major mountain passes. Yet another round of moisture is
expected overnight Monday into Tuesday as another surge of SW
flow moves in, continuing a series of SW systems moving through
much of the holiday week. May need to keep an eye on the Kittitas
Valley as to how much the warm air aloft settles in, but as of now
still expecting a primarily rain forecast for our populated, non-
mountain zones. Evans/74

&&

.LONG TERM...Tuesday through Saturday...An upper level trough
will move onshore on Tuesday, bringing precipitation to the
region. This trough will depart later Tuesday/Tuesday
night...Christmas eve and ridging will then build in. This ridge
should bring dry weather everywhere, with the possible exception
of the Washington Cascades for much of Christmas Day.

By later afternoon Wednesday/Wednesday night, the next system
will be moving onshore and will bring more precipitation to the
Pacific Northwest. This trough will move out of the area on
Thursday, but right on its heels is yet another system for Friday
and more precipitation. Another system is then expected Saturday.
There could be some breaks, but the end of the week certainly
looks to be more wet than dry.

Snow levels will initially be quite high on Tuesday, especially
for late December...in the 4000-6000 foot range, so most locations
will se rain except at the highest elevations. By Thursday morning
will range from 2700 feet in the Washington Cascades to above
4500 feet in the Oregon Cascades. Snow levels are expected to rise
again into Friday and Saturday, with snow mainly confined to the
above 4500 feet. QPF values look to be quite high over the period
with amounts over an inch liquid equivalent each day Wednesday
through Friday along the crest of the Cascades and Blue Mountains.
Even in the Columbia Basin, amounts over 0.10 inches to upwards
of 0.25 inches are expected each day. The ECMWF EFI keys in on the
QPF on Tuesday across a good portion of eastern Oregon, with
values of 0.7 to 0.8. It also highlights Thursday across much of
Washington, with the same 0.7 to 0.8 values. It also keys in on
snow across the Washington Cascades Thursday with 0.7 to 0.8
anomalies.

Snow on Tuesday looks to be confined to the highest elevations,
but Wednesday into Thursday and Thursday into Friday, there looks
to be significant snow certainly at the higher elevations and
along the crest. Will definitely need to keep an eye on how this
develops over the course of the next week.

Additionally, there will be some breezy winds, especially
Thursday and Friday in the normally breezy locations...the
Columbia Basin, Kittitas Valley, Cascade Gaps, Blue Mountain
Foothills and Simcoe Highlands. At this time it looks like winds
could gust in the 25 to 35 mph range. NBM probabilities of wind
gusts >=39 mph are 50 to 80 percent, while NBM probabilities of
greater wind gusts decrease to generally 30 to 50 percent.

Through the extended period, high temperatures look to be about 5
to 10 degrees above normal, especially in the Columbia Basin.
Highs will mainly be in the 40s and lower 50s through the period.
By Friday and Saturday, the ECMWF EFI has anomalies of 0.6 to 0.7
for high temperatures across Washington and Oregon centered along
the Basin.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  33  47  38  49 /  30  20  90   0
ALW  36  46  40  50 /  50  10  90  10
PSC  34  43  38  47 /  10  20  80   0
YKM  30  39  32  42 /  10  60  80   0
HRI  34  44  37  50 /  20  30  80   0
ELN  30  39  31  40 /  10  70  80   0
RDM  31  46  31  46 /  20  50  70   0
LGD  31  43  37  45 /  70  20 100  20
GCD  31  45  34  44 /  20  40 100   0
DLS  38  44  39  49 /  20  80 100   0

&&

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

$$

SHORT TERM...74
LONG TERM....77
AVIATION...86