Area Forecast Discussion Issued by NWS Pendleton, OR
000
FXUS66 KPDT 160952
AFDPDT
Area Forecast Discussion
National Weather Service Pendleton OR
252 AM PDT Tue Apr 16 2024
.SHORT TERM...Today through Thursday night...Although winds have
decreased overnight, breezy to windy conditions remain for areas
in and around the Lower Columbia Basin. A strong westerly flow
aloft and a tight westerly pressure gradient will be present
throughout the day. An upper level trough along the WA/BC border
will sag southward today which will continue the cold air
advection. The Kittitas Valley observed high winds yesterday.
Winds will not be as strong as yesterday, but there is high enough
confidence to issue another Wind Advisory for this afternoon
through early evening covering I-90 from Ellensburg to Vantage.
Moisture ahead of the trough mostly high level and shallow, but
there is a Puget Sound Convergence Zone that has set up in the WNW
flow, and KATX Doppler Radar shows light precipitation north of
Snoqualmie Pass. Current temperatures east of Snoqualmie Summit
are in the mid 30s and road temps are in the mid 40s, so it is
highly unlikely for snow accumulations to be observed east of the
summit this morning.
Cold and drier air has spread across the forecast area with
dewpoints currently in the 20s to lower 30s. One forecast
challenge tonight will be whether the Kittitas Valley, Yakima
Valley, and the Oregon portion of the northern Blue Mtn Foothills
will have freezing temps--locations where the growing season
usually begins in mid April. Forecast has been consistently
showing overnight lows between 31-33F for these zones. I`ve
decided to not issue Freeze Warnings for two reasons--winds and
cloud cover. The Kittitas Valley will have winds to provide mixing
until late in the evening, and the Yakima Valley will have
overnight lows around 32F with low probabilities for subfreezing
temps (30% for min temps less than 32F and 5% for 28F or less
per the NBM). Cloud cover will be the inhibiting factor for the
Pendleton, Athena, and Milton-Freewater areas to observe
subfreezing temperatures, but there is some uncertainty. Clouds
will be broken-overcast through midnight with clearing early
Wednesday morning. For now, will cover the cold overnight lows
with weather stories and social media posts.
There will be slight warming Wed-Thur with chilly overnight lows.
Surface winds will shift to the north and will be locally breezy.
The PacNW will be on the bottom of the broad trough and under a
cyclonic flow aloft. Any showers will be widely scattered over
the northeast mountains. Once again, moisture is very limited,
thus any snow amounts will be very light. Wister/85
.LONG TERM...Friday through Tuesday...Overall benign weather is
currently forecast for the period with no good ensemble agreement in
any highlight-worthy or climatologically unusual events.
Ensemble guidance is in good agreement that the forecast area will
be on the back side of a departing upper-level trough Friday, and a
shortwave ridge axis will be placed just offshore. Differences among
ensemble members are small and dry weather is anticipated area-wide
(<5% PoPs). A surface thermal trough on the west side of the
Cascades will support easterly to northeasterly winds for the
Columbia Plateau. Forecast soundings show a low-level jet of 25-35
kts from north-central OR to central WA. While wind highlights
appear unlikely at this time, NBM probabilities of exceeding 24-hr
maximum gusts of 45 mph are 30-50% for ridges and highlands prone to
northeast winds.
Over the weekend, uncertainty in the pattern grows, though the upper-
level ridge axis is favored (>50% chance) to slide overhead.
Uncertainty in the pattern peaks late Saturday as guidance is
advertising a range of solutions. Broadly speaking, a trough is
forecast (87% of members) to approach BC or the PacNW while the
remaining members (13%) retain an amplified ridge. While 59% of
members suggest the trough will impact BC, 28% track it across the
PacNW.
Sunday afternoon through Monday, ensemble clusters show some
differences in the depth of the trough as it tracks inland across
the Northern Rockies and Northern Plains - 56% of members favor an
upper-level ridge building into the PacNW while 22% suggest a deeper
trough downstream with northwest flow lingering across the PacNW.
Tuesday, ensemble solutions range from a deep trough approaching the
PacNW (9% of members) to an amplified ridge overhead (29% of
members). The remaining members are indicating a solution somewhere
between the two. Plunkett/86
&&
.AVIATION...06z TAFs...VFR conditions expected. Winds will
lighten through the overnight hours, but are expected to pick
back up by Tuesday afternoon, albeit a bit decreased compared to
today with W/NW winds gusting up to 25 kts. Expect primarily sct-
bkn mid to high level clouds. Evans/74
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 53 31 56 31 / 0 0 0 0
ALW 57 35 58 34 / 0 10 10 0
PSC 61 37 63 37 / 0 0 0 0
YKM 58 31 61 33 / 0 0 0 0
HRI 59 33 62 33 / 0 0 0 0
ELN 53 32 59 33 / 0 0 0 0
RDM 54 25 53 25 / 0 0 0 0
LGD 52 28 51 28 / 0 0 10 0
GCD 55 27 53 27 / 0 0 0 0
DLS 56 35 62 38 / 0 0 0 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory from 1 PM this afternoon to 8 PM PDT this evening
for WAZ026.
&&
$$
SHORT TERM...85
LONG TERM....86
AVIATION...74