446
FXUS66 KPDT 221202
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
502 AM PDT Sat Jun 22 2024

.AVIATION...12z TAFs...VFR conditions through the forecast period
with any shower activity expected to remain over the Washington
Cascades. The main forecast challenge remains the development of
gusty wind this afternoon. While most Washington-based terminals
will see wind at generally less than 12 kts, most Oregon-based
terminals will see the potential for a wind speeds of 12 to 15 kts
with stronger gusts. These stronger winds will develop after 21z
this afternoon, with the strongest wind expected at KDLS where
gusts to 25 kts are favored. KBDN and KRDM will also see gusts
above 20 kts this afternoon and evening. Wind is expected to
lessen after 06z. Branham/76

&&

.PREV DISCUSSION... /issued 205 AM PDT Sat Jun 22 2024/

SHORT TERM...Today through Monday night...A Fire Weather Watch
in effect for Sunday afternoon and evening for the Lower Columbia
Basin zones (fire zones WA691 and OR641) was issued yesterday. A
Wind Advisory for the Kittitas Valley in effect from 4 AM to
midnight on Sunday will be issued for the morning package.

A strong inverted thermal trough at the surface currently extends
across CA/NV and into eastern OR/WA, and this has resulted in
above average temperatures. There has been little relief from
yesterday`s hot summer weather, as overnight temperatures have
only dipped into the 50s and 60s for most of the forecast area.
Today`s highs in the mid 80s to upper 90s are about 15 degrees
above seasonal average. It would have been much warmer if not for
the westerly flow aloft keeping the pressure thickness from
climbing and the high level clouds over the area. Based on the
NBM, there is a chance (around 30-50%) that a few locations in
the Lower Columbia Basin and the John Day Basin near Monument and
Spray will reach 100 degrees.

Cool marine air due to the onshore flow and the thermal trough
over eastern WA/OR will cause winds to increase in the eastern CR
Gorge and the Cascade gaps tonight. The marine air will deepen on
Sunday when a shortwave trough traverses across northern WA.
Forecast soundings near Seattle indicate the marine layer
deepening to a depth of 6k feet which increases the confidence to
around 80% that the marine push will be strong and deep enough to
cause sustained winds around 30 mph and gusts 45-50 mph in the
Kittitas Valley and locally in the CR Gorge--mainly near Maryhill
and Rufus. Will issue the wind advisory for the Kittitas Valley,
and one may be needed for the Gorge if the very windy conditions
are expected to cover a larger area.

Dry air will accompany the shortwave and surface cold front.
Water vapor shows significant darkening along the bottom of the
trough, and models have consistently shown H7 RHs in the single
digits. The marine push will cause RHs to increase into the upper
20s to lower 30s along the Cascade gaps. However, the Columbia
Basin and the Blue Mtn Foothills will observe RHs in the teens as
the dry air mixes down with the front (confidence 80%). The low
RHs combined with WSW winds 20-30 mph gusting to 40 mph warrants a
fire weather watch. Any precipitation associated with the
shortwave will be light showers in the far northwest corner of the
CWA north of Cle Elum.

Gradients will relax Sunday night and the flow will become
slightly more anticyclonic with weak ridging on Monday.
Temperatures will be closer to seasonal average and winds will be
15 mph or less. Skies will be mostly clear Monday and Monday
night. Wister/85

LONG TERM...Tuesday through Saturday...The ridge axis begins to
sweep across the forecast area at the onset of the forecast period.
Temperatures will remain warm on Tuesday, with values around 5-10
degrees above normal. Aside from keeping warm and dry conditions
across the area, this ridge axis will also briefly produce an
opportunity for gusty winds. Areas of the Columbia River Gorge
and south into Central Oregon will be favored for these stronger
winds on Tuesday afternoon and evening with a 30-40% chance for
gusts to 25 mph.

Winds will see a brief reprieve Wednesday morning. Building
southwest flow and an associated approaching low pressure system
will produce additional gusty wind, with more coverage expected.
While much of the area will see at least a slight chance (10-25%)
for gusts to 25 mph, areas along the Washington/Oregon border, into
the Columbia Basin, and south into Central Oregon remain the areas
anticipated to see the strongest wind. At these locations, there
will be a moderate to high chance (70-90%) for gusts to 25 mph, with
the Columbia River Gorge area seeing a 40-60% chance for gusts of 30-
35 mph. On a more limited note, this approaching system will produce
some shower activity, mainly over the Cascade Mountains.
Temperatures will see a few degrees of cooling but will still see
around 5 degrees above normal values on Wednesday.

While some model variation regarding the path and intensity of the
low pressure is present on Wednesday, the differences become more
noticeable on Thursday with some solutions keeping the area of low
pressure off the Pacific Coast, and others pushing it into the
PacNW. As anticipated, the cluster analysis also shows variation on
the departure of the ridge and the arrival of the low pressure
system. Utilizing the NBM, further cooling of temperatures is
favored on Thursday when values drop to around 5 degrees below
normal. The area of low pressure will work its way through the
region Thursday and Friday with mountain showers. Northwest flow
builds over the region on Friday with a few degrees of warming and
weakened shower presence. High pressure will arrive into Saturday,
allowing temperatures to rise to a few degrees above normal, and
help to further reduce shower activity. Branham/76

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  93  59  81  49 /   0   0   0   0
ALW  96  63  86  52 /   0   0   0   0
PSC  98  64  88  53 /   0   0   0   0
YKM  96  56  83  48 /   0   0   0   0
HRI  98  63  85  53 /   0   0   0   0
ELN  92  56  75  48 /   0   0   0   0
RDM  91  51  83  43 /   0   0   0   0
LGD  91  56  83  48 /   0   0   0   0
GCD  95  55  89  48 /   0   0   0   0
DLS  92  60  78  53 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Sunday afternoon through Sunday evening
     for ORZ641.

WA...Fire Weather Watch from Sunday afternoon through Sunday evening
     for WAZ691.

     Wind Advisory from 5 AM Sunday to midnight PDT Sunday night for
     WAZ026.

&&

$$

SHORT TERM...85
LONG TERM....76
AVIATION...76