000
FXUS66 KPDT 230603
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1103 PM PDT Mon Apr 22 2024

.UPDATED AVIATION...06Z TAFs...VFR conditions will continue to
dominate across all TAF sites through the period. High clouds will
move in over the period with CIGs of BKN200. Winds will remain
variable and below 6kts. Bennese/90


&&


PREV DISCUSSION... /issued 222 PM PDT Mon Apr 22 2024/

SHORT TERM...Tonight through Wednesday...A transitory upper level
ridge will be passing over the region tonight and Tuesday before
moving off to the east. This will allow an upper level trough off
the Canadian coast to begin moving into Canada Tuesday night and
Wednesday. The southern portion of the trough will clip the Pacific
Northwest on Wednesday bringing a few showers to the Washington
Cascades but also increasing the west to east pressure gradients.
This will lead to some breezy to windy conditions on Wednesday that
linger into the overnight hours before decreasing. NBM probabilities
are showing 60-90% chance of sustained 20-25 mph winds across the
western portion of the Lower Columbia Basin with the 25-30 mph wind
probability dropping to less than 30% across most of the Basin. A
couple of exceptions will be the Kittitas Valley and eastern
Columbia River Gorge where 25-30 mph probabilities remains 60-80%.
Overall this event appears to be less than advisory level at this
time but will be monitored for any changes. Temperatures will peak
on Tuesday with highs around 70 in the lower elevations and 60s in
the mountains then cool slightly on Wednesday. Low temperatures
overnight will be slightly moderated by some passing high clouds.
However, can not rule out the possibility of some isolated cold
prone areas around the Lower Columbia Basin dropping to or
approaching 32 degrees. Advise continued protection of sensitive
plants for those living in cold prone areas as temperatures could
still flirt with near freezing temperatures overnight.

LONG TERM...Thursday through Monday...Models in fair agreement
through the period. However, they do begin to diverge Saturday as an
upper level low strengthens over the Aleutians. The ensembles paint
an unsettled weather pattern over the Pacific Northwest through much
of the period, especially over the mountains. An upper level trough
pushes onshore Thursday spreading showers from west to east and
continuing into Friday. The deterministic ECMWF shows a shortwave
upper level ridge moving through the area Saturday for a brief
drying trend, especially over the Columbia Basin. However, the GFS
does not show this upper ridge and shows more zonal flow which would
indicate a continued threat for showers over the Cascades and Blue
mountains. By Sunday, the models begin to diverge even more as their
solutions differ on the evolution of the upper low dropping down
from the Gulf of Alaska. GFS shows the upper low remaining closed
offshore while the ECMWF shows it developing into a open trough off
the coast. Either way, the weather will remain unsettled with
scattered showers developing over the mountains each afternoon and
continuing into the evening hours. At this time, the best chance to
see a 0.10 of an inch or more of precipitation will be Friday with
the mountains having the best chance (70-85%) while the Columbia
Basin the lowest chance (15-30%). In addition, we could see some
isolated afternoon/evening thunderstorms over our eastern mountains
Friday if the cloud cover isn`t too thick. Timing systems will
become difficult Sunday and Monday as spaghetti plots show a wide
range of possible solutions (uncertainty). Daytime highs will be
near normal through the period. Earle/81

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  34  68  41  67 /   0   0   0   0
ALW  35  70  45  70 /   0   0   0   0
PSC  38  72  44  74 /   0   0   0   0
YKM  36  70  42  70 /   0   0   0   0
HRI  35  71  43  72 /   0   0   0   0
ELN  34  67  43  64 /   0   0   0   0
RDM  31  68  36  66 /   0   0   0   0
LGD  31  69  42  67 /   0   0   0   0
GCD  33  72  42  69 /   0   0   0   0
DLS  41  73  46  69 /   0   0   0   0

&&

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

$$

SHORT TERM...91
LONG TERM....81
AVIATION...90