Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 250010
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
510 PM PDT Sun Mar 24 2024

Updated Aviation Discussion

.AVIATION...00Z TAFS...As rain showers continues dissipating, there
is a chance (40%) of a thunderstorm impacting KALW based on the
radar data. However, the timing is questionable (<30% confidence).
Nonetheless, the remaining sites are currently at VFR with winds
below 10kts. Breezy conditions are expected for KDLS, KRDM, and KBDN
thus bringing in moderate winds. Feaster/97

&&

.SHORT TERM...Today through Tuesday...A broad low pressure system
departing to our east will orient the winds aloft more north to
northwest, leading to orographic precip across the forecast area,
concentrated primarily across the eastern mountains. Radar imagery
through the early afternoon has depicted a blob of showers over the
Blue Mountains, with some light sprinkles observed across the
foothills. Snow levels have been elevated enough to keep more wintry
precip up closer to crest level, but even then, webcams suggest that
snow is having trouble sticking to the roads at Tollgate, so snow
impacts are expected to be very limited today.

Did have a mention of isolated t-storms across the eastern mountains
this afternoon, lining up with meager CAPE values and decent lapse
rates in model soundings, but thus far convection has been observed
well to the east of our forecast area. Latest SPC mesoanalysis
largely agrees with this morning`s model soundings, and SPC`s
convective outlook continues to paint a tiny portion of the far
eastern section of the forecast area under a general thunderstorm
risk, so will keep mention of storms across the eastern mountains,
but would not be surprised if not much of anything materializes
today.

Once the low officially departs the PacNW, broad troughing will
envelop the central CONUS, leaving us under NW flow through the
midweek. Main effect through the rest of the period will be
continued chances for precip across the Cascade crests and eastern
mountains, with temps largely remaining seasonal. This ongoing
pattern will induce breezy winds through the Gorge into the Oregon
Basin as high pressure builds in over the Pacific coast, but
otherwise precip impacts will be limited until another organized low
moves into the region around the midweek timeframe. Evans/74

.LONG TERM...Wednesday through Sunday...An active period of
weather is in store for the long term forecast as an upper low
offshore the PacNW provides consistent chances of precipitation
Wednesday through Friday, with drying conditions into the weekend.

Wednesday will start with an upper level ridge axis pushing east
of the region, allowing an upper low to approach the PacNW coast.
Ensemble guidance is in good agreement that the upper low will sit
off the PacNW coast through early Friday while pushing a moist
southwest flow inland, providing consistent chances of mountain
snow/rain and lower elevation rain. The upper low will initially
push a cold front boundary across the PacNW during the day
Wednesday, resulting in the heaviest precipitation through the
period (confidence 60-70%). By Thursday morning, NBM probabilities
for exceeding 0.5 inches of QPF in 24 hours across the Cascades,
northern Blues, and the Wallowas is around 50-75%; the eastern
mountains will see a 60-70% chance of at least 0.25 inches of
liquid equivalent; and the lower elevations will see a 70-80%
chance of receiving 0.1 inches of rain by Thursday morning.
Precipitation chances will become light Thursday as the cold front
exits to the east, with only 50-70% chance of 0.1 inches of QPF
in the mountains, with sharp drop-off to 10-25% in the lower
elevations. With the heaviest precipitation occurring ahead of
the cold front where snow levels will push above 4.5kft to 5.5kft,
snow amounts in the mountains will be fairly light with only
locally moderate snow accumulations expected along the peaks/crest
of the Cascades and Wallowas. Only thing to note is that ensemble
guidance, mainly between members of the GFS and ECMWF, do show
some disagreement on the proximity of the main low circulation
offshore, though there is little difference in impacts to the
forecast area.

Friday through Saturday, ensemble guidance shows the center of
the upper low diving south along the coast towards southern CA,
while the axis of the low takes on a positive tilt. This will
effectively result in precipitation chances disappearing in the
lower elevations by Friday evening, while light snow chances will
hang on across the mountains through Saturday(confidence 50-60%).
Ensemble members continue to be in good agreement in the arrival
of an upper ridge to the PacNW Sunday as the upper low continues
to sit off the southern CA coast.

While temperatures are expected to remain near to just below
normal Wednesday and Thursday, the departure of the low will
result in a gradual warming trend with above normal temperatures
expected to develop over the weekend. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  35  53  35  55 /  50  20  30  30
ALW  37  55  38  57 /  30  30  40  40
PSC  39  60  40  62 /  20  10  10  10
YKM  34  58  34  60 /   0  10  10   0
HRI  37  58  37  60 /  40  10  10  10
ELN  32  54  31  55 /   0  10  10   0
RDM  31  51  30  52 /   0  10  20  10
LGD  32  49  33  49 /  40  30  40  40
GCD  33  49  32  49 /  50  30  40  30
DLS  40  57  40  58 /   0  10  20  10

&&

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

$$

SHORT TERM...74
LONG TERM....82
AVIATION...97


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