216
FXUS66 KPDT 251753 CCA
AFDPDT

Area Forecast Discussion...CORRECTED
National Weather Service Pendleton OR
1053 AM PDT Wed Sep 25 2024

.Updated for Aviation...

.AVIATION...
18Z TAFS...A strong cold front will move across the area
from west to east this afternoon into early evening.  Winds will
increase and become quite gusty along and ahead of the front with
gusts generally in the 25 to 30 kt range. By early early evening
winds should begin to subside to around 10 kts and become less
than 10 kts by Thursday morning. With the gusty winds, it is
possibly for some BLDU, especially in the Columbia Basin, which
would most likely impact DLS and PSC, but could affect anywhere.
If BLDU does occur, it would bring reduced VSBYS to MVFR, and
possibly lower. The timing and extent is difficult to pinpoint.
For now, have added some reduced VSBYS at PSC and excluded it
elsewhere.

&&

.PREV DISCUSSION... /issued 432 AM PDT Wed Sep 25 2024/

Aviation...12Z TAFS...VFR conditions are expected for this period.
KPSC will have some blowing dusts during afternoon hours, which
could bring MVFR or less with sub-5sm vsby (50% confidence). Chances
(30-40%) of afternoon showers might occur for KDLS, KYKM, and KPSC
due to the arrival of the cold front. Winds will be moderate at
around 12-20kts with gusts at 20-30kts for all sites during the
day. Feaster/97

PREV DISCUSSION... /issued 259 AM PDT Wed Sep 25 2024/

SHORT TERM...Today through Friday night...Wind advisories and
blowing dust advisories are in effect this afternoon and evening
across portions of south central WA and north central OR. A mostly
dry cold front accompanied by a strong low level jet will sweep
across the region this afternoon and evening. The front has
stalled along the eastern Pacific this morning due to a shortwave
circulation riding north along the leading edge of the front off
the northern CA coast, as evident by water vapor loops. Due to its
slower timing, the gusty winds will not materialize until mid
afternoon. Therefore, the start time of the advisories will be
postponed to 2 PM rather than 11 AM. ECMWF EFI continues to place
a large portion of the forecast area in the 0.7-0.9 for wind gusts
meaning winds will be stronger than seasonal climatology. There
are signs of isentropic descent bringing 35-40 kts of 850mb
towards the surface. Blowing dust is common in late September
across the Columbia Basin, so confidence that patchy blowing dust
will be observed is high (80%) and confidence in areas of blowing
dust is moderate to high (50-60%). The hot dry windy product has
consistently indicated unusually dry and windy conditions today
for eastern WA/OR. Although the RHs will not be critically low
where the strongest winds occur, the expected dry and breezy
weather is something to highlight in the fire weather forecast and
social media.

Models have trended drier with the front, so the QPF amounts today
will be light. PoPs will show 40-60% over the mountains, primarily
due to orographic lift and just a few hours of scattered showers.
The Columbia Basin down to central OR may see little to no
measurable rainfall with the passing front. Will keep the
isolated thunderstorms over the eastern mountains with the best
chance over the Blue Mountains north of Meacham. There are modest
CAPEs approaching 500 J/kg and 60-70 kts of 0-6km shear, so storms
will be organized and capable of brief heavy downpours, hail and
strong outflows. NBM continued to shows 20% chance of
thunderstorms along the WA Cascades and will keep, although CAMS
have little indications of storms in that area.

Near seasonal temperatures, partly to mostly cloudy skies, and
locally breezy winds can be expected Thursday through Friday
night. There is a 30-60% chance of showers along the east slopes
of the WA Cascades Thursday night, associated with a Pacific
front over western WA that falls apart Friday morning with
the advection of mid level dry air. Wister/85

LONG TERM...Saturday through Wednesday...A shortwave trough
moves inland of the PacNW through the weekend, bringing southwest
flow but no significant weather. Winds will remain fairly light
with occasional breezes up to 20 mph due to increased westerly
flow (>70% probability).

An upper ridge will then build over to the PacNW Monday with
remained fairly light winds and lingering breezes (>70%
probability). Models deviate for Monday where the ECMWF and Canadian
model both favor the ridge building over, but with GFS appearing
more zonal.

Tuesday through Wednesday, the ridge will break down as another
shortwave trough occurs with a cold front inland of the forecast
area. With orographic lifting and southwest flow, slight chances (15-
20%) of showers could increase at the west of Kittitas Valley.
Overall, models are in good agreement with the southwest flow over
the forecast area. High temperatures will remain mainly in the 70s
through the long term period. Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  83  47  73  49 /  20  50   0   0
ALW  87  51  75  53 /  30  60   0   0
PSC  87  52  76  56 /  20  30   0   0
YKM  82  40  73  46 /  30  10   0  10
HRI  85  50  76  53 /  20  30   0   0
ELN  79  43  73  49 /  40  20   0  20
RDM  82  45  78  44 /  10  20   0   0
LGD  87  48  76  48 /  10  60   0   0
GCD  87  48  80  48 /  10  30   0   0
DLS  79  48  77  54 /  40  30   0  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 2 PM this afternoon to 11 PM PDT this evening
     for ORZ041-507-508-510.

     Blowing Dust Advisory from 2 PM this afternoon to 11 PM PDT this
     evening for ORZ044.

WA...Wind Advisory from 2 PM this afternoon to 11 PM PDT this evening
     for WAZ024-026-027-029-521.

     Blowing Dust Advisory from 2 PM this afternoon to 11 PM PDT this
     evening for WAZ028.

&&

$$

SHORT TERM...85
LONG TERM....97
AVIATION...77