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000
FXUS66 KPDT 090534 AAA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1033 PM PDT Mon Apr 8 2024

Updated Aviation Discussion

.AVIATION...06Z TAFS...VFR continues for the remaining TAF period
with currently more clouds (FEW to OVC, 050-250 kft) Tuesday except
KRDM/KBDN ending Tuesday night with clear skies. Rain showers are
currently in KPDT/KALW in part to a shortwave trough passing through
until 15Z. Breezy conditions (20-30 kts) are expected for most sites
Tuesday morning as well but will decrease by Tuesday night (70%
confidence). Other than that, winds will vary 10-20 kts (light to
moderate) throughout Tuesday morning until nighttime, except for
KBDN where winds will remain light. Feaster/97

&&

.UPDATE...Latest water vapor imagery shows a low amplitude
shortwave trough moving ESEWD toward the British Columbia and
northwest Washington coasts. Rain will spread across mainly the
Washington Cascade crest (70-90% POPS) and the northeast
Mountains(40-60% POPS) tonight and Tuesday morning. Snow will be
above pass elevations with snow levels 5200-6000 feet MSL. A cold
front will cross the region on Tuesday bringing gusty west winds
to the lower elevations. Winds will be sustained 15 to 25 kt with
gusts to 30-35 kt from late morning to early evening. Winds are
expected to be a little stronger in the Kittitas Valley with a 50%
chance of gusts exceeding 40 kt. A wind advisory is in effect for
the Kittitas Valley Tuesday from 10 AM to 8 PM PDT. Current forecast
is on track and only minor adjustments to the POPS for tonight were
made for the evening update. 78

&&

.PREV DISCUSSION... /issued 444 PM PDT Mon Apr 8 2024/

SHORT TERM...Tonight through Wednesday...Current satellite
imagery shows a warm front pushing across eastern WA/OR with mid
to upper level cloud cover developing with it. At the surface,
breezy west to southwest winds have developed in the Columbia
Basin and Gorge, with light winds elsewhere.

Later this evening, snow/rain chances will increase across the
Cascade east slopes, northern Blues, and Wallowa county as a
shortwave and attendant cold front move across the area. Snow
levels will start off above 5kft to 5.5kft and drop to 4kft to
5kft along the Cascade east slopes behind the cold front passage.
However, the bulk of the precipitation will occur when snow levels
are still elevated, resulting in snow accumulations under an inch
below any of the higher peaks in the Cascades and Wallowas.
Otherwise, much of the lower elevations will remain dry through
this system passage, except across the eastern Columbia Basin and
Blue mountain foothills where light rain will develop tonight with
the shortwave approach. Tomorrow, the cold front and shortwave
passage will also result in a cross Cascade pressure gradient
developing early, with breezy to gusty winds developing through
the WA Cascade gaps and into portions of the Basin. Confidence is
high (80-90%) that the I-90 corridor through the Kittitas valley
will see wind gusts between 45-55 mph tomorrow, with lower
confidence (40-50%) that these wind gusts will materialize in the
Columbia Basin and below 3.5kft in the Simcoe Highlands.

Late tomorrow through Wednesday, an upper ridge in the northeastern
Pacific will build into the PacNW. This will result in a return to
drier conditions with afternoon temperatures warming into the mid
to upper 60s across the lower elevations, and upper 40s to 50s in
the mountains. The breezy west to northwest winds across the
region are expected to decrease Tuesday night as the ridge begins
to influence the region, with light winds continuing into
Wednesday. Lawhorn/82

LONG TERM...Thursday through Monday...There will be a building
ridge of high pressure centered over the Rockies Thursday and Friday
while a closed low pressure system drops south from the Gulf of
Alaska to off the coast of California by Friday. This will change
the flow over the forecast area from southwest to S-SE leading to a
good Spring convective pattern setting up for the latter part of the
week. Ensemble models are in agreement with this pattern further
supporting convective possibilities.

The initial chances for convection will come late Thursday afternoon
and evening mainly over the far eastern mountains. Instability and
forcing are minor but the backing flow (SW to S) should be enough to
trigger some showers Thursday night with a small potential for
thunderstorms through the evening. By Friday the closed low is off
the California coast with a southerly flow in place over eastern
Oregon. Model CAPE values increase as does available moisture
leading a good chance of showers with some thunderstorms. Saturday
looks very similar to Friday but some model differences start to
appear. The ECMWF takes the closed low a littler further south than
the GFS which could impact how for north the showers and
Thunderstorms occur on Saturday. For now the GFS maintains the better
pattern for convection so will maintain forecast aligned with that.
On Sunday the closed low moves into to southern California with the
GFS maintaining some convective possibilities over the eastern
Mountains. The ECMWF reduces this threat by having a more westerly
flow across the Pacific Northwest as the next shortwave trough moves
into western Canada. By Monday, both models kick the low east into
the central Plains and drop the western Canada trough into the
Pacific Northwest with the ECMWF being the more aggressive. This
will transition the forecast area back to cooler conditions Sunday
and Monday following above normal temperatures associated with the
ridging pattern.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  45  62  35  63 /  30  10   0   0
ALW  48  65  38  65 /  50  20   0   0
PSC  50  69  39  67 /  20  10   0   0
YKM  40  65  33  65 /  10   0   0   0
HRI  47  66  37  67 /  20  10   0   0
ELN  38  57  32  62 /  40   0   0   0
RDM  33  59  30  66 /  10   0   0   0
LGD  40  57  32  63 /  40  30   0   0
GCD  36  60  32  66 /  10  10   0   0
DLS  46  64  39  68 /  20  10   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory from 10 AM to 8 PM PDT Tuesday for WAZ026.

&&

$$

SHORT TERM...78
LONG TERM....91
AVIATION...97