983
FXUS66 KPDT 242330
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
430 PM PDT Tue Sep 24 2024

Updated Aviation Discussion

.AVIATION...00Z TAFs...VFR conditions expected over the next 24
hours. Cloud decks will drop to around 10k feet starting tomorrow
afternoon with the cold front. A chance of showers should be
creeping up on most sites by late in the period, but for now have
left rain out and will look for more exact timing on the 06Z
update. Winds 10 knots or less expected overnight, becoming gusty
tomorrow all sites as the cold front moves across the region.
Goatley/87


&&

.PREV DISCUSSION... /issued 336 PM PDT Tue Sep 24 2024/

SHORT TERM...Tonight through Thursday night...The strong ridge
of high pressure overhead will persist through tonight, shifting
east through the day Wednesday as a shortwave trough and attendant
strong cold front sweep across the Pacific Northwest. Southerly
winds across the Blue Mountains and adjacent foothills overnight
coupled with the lingering warm air mass (850-mb temperatures of
20-25 C) should facilitate some warm overnight low temperatures
relative to climatology (ECMWF EFI of 0.6-0.95).

Wednesday afternoon and evening, a strong Pacific cold front will
sweep across the Pacific Northwest. NWP guidance suggests the
closed low offshore of central California will eject north-
northeastward and merge with the approaching shortwave trough as
it tracks into the region. Southwesterly flow aloft will advect
steep (7-8.5 C/km) mid-level (700-500 mb) lapse rates across
eastern Oregon Wednesday, aiding in some modest instability of a
couple hundred J/kg of MUCAPE. Synoptic forcing and orographic
lift may facilitate isolated thunderstorms across portions of the
Blue Mountains and WA Cascade crest (10-20% chance) Wednesday
afternoon and evening, though confidence is higher in showers
(15-60% chance).

Winds will be the primary concern for Wednesday; 700-mb and
850-mb jets of 40-60 kts and 30-40 kts, respectively, signal
enough momentum aloft for widespread breezy to windy westerly
winds with frontal passage. Have issued wind advisories, in effect
11 am to 11 pm, for much of the Columbia Plateau. Recently plowed
fields may also pose a concern for patchy to areas of blowing
dust across the lower Columbia Basin, and blowing dust advisories
have been issued.

Drier conditions return Thursday in the wake of the cold frontal
passage. Plunkett/86

LONG TERM...Friday through Tuesday...

Bottom Line Up Front

1. High mountains showers Friday

2. Quite weather through the period

Models are in decent agreement with an upper level shortwave
bringing very light showers to the WA Cascades while the remainder
of the region stays under dry zonal flow. 80% of the raw ensembles
show Snoqualmie Pass will see upwards of 0.02 inches of rain and
probabilities steadily decrease as you move southeast into the
eastern slopes. Raw ensembles decrease to 20% as you reach
Ellensburg then dissipate completely east of Vantage. Models show
the majority of the rainfall to cease near 11 AM and mostly zonal
flow will take over Friday afternoon and continue through Friday
night.

Models show a disturbance off the coast of the PacNW which will
shift the flow aloft to a more southwestern component. However,
models keep the region dry through Monday. Clusters show the
majority of the ensembles to be favoring the slight southwest flow
through day 6 before clusters show variances between the ensembles
with whether an upper level ridge or an upper level trough will
move overhead. Regardless, models show the forecast area to be
under dry conditions Friday through Tuesday with slight chances
(>15%) of rain returning to the high crests of the WA Cascades.
With that said, fall like temperatures will prevail through the
period with the EFI favoring at or near normal seasonal
conditions. 80-100% of the raw ensembles show Friday and Saturday
to be the warmest days with temperatures across the majority of
the lower elevations and central OR to be in the mid to high 70s
with isolated spots in the Ochoco-John Day Highlands and John Day
Basin seeing mid 80s. The remainder of the period, 70-80% of the
raw ensembles have the lower elevations and central OR in the low
to mid-70s with higher elevations in the mid 60s. Bennese/90


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  58  83  47  73 /   0  20  40   0
ALW  64  87  50  76 /   0  20  50   0
PSC  62  87  51  76 /   0  20  30   0
YKM  55  81  40  73 /   0  30  20   0
HRI  60  84  49  76 /   0  20  30   0
ELN  57  79  43  72 /   0  50  20   0
RDM  54  81  40  78 /   0  10  20   0
LGD  57  87  47  77 /   0  20  50   0
GCD  54  86  47  80 /   0  20  20   0
DLS  60  79  50  77 /   0  40  20   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 11 AM to 11 PM PDT Wednesday for ORZ041-507-
     508-510.

     Blowing Dust Advisory from 11 AM to 11 PM PDT Wednesday for
     ORZ044.

WA...Wind Advisory from 11 AM to 11 PM PDT Wednesday for WAZ024-026-
     027-029-521.

     Blowing Dust Advisory from 11 AM to 11 PM PDT Wednesday for
     WAZ028.

&&

$$

SHORT TERM...86
LONG TERM....90
AVIATION...87