370
FXUS66 KPDT 142212
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
312 PM PDT Wed Aug 14 2024

.SHORT TERM...Today through Tomorrow Night...A transient ridge
is crossing the region today. Mostly clear skies and near normal
high temperatures today. However, few cumulus clouds are
developing within Wallowa county, the crest of WA Cascades
including south central OR, observed from satellite imagery.
Confined smoke aloft still remains in central OR and Ochoco-John
Day Highlands from local wildfires. Winds will be around at 20 mph
or less across the forecast area this afternoon.

Tonight through tomorrow afternoon, an upper level trough makes its
way through the PacNW which is now offshore the OR/CA border.
There are chances (40-60%) of thunderstorms starting late tonight
over central OR that then ramp up tomorrow afternoon and evening
in terms of both coverage and lightning potential. A bit more
spread/uncertainty in terms of elevated instability overnight
that spreads across south central OR northward. Best signal is
focused across northern Klamath-Lake. Thereafter, environment
becomes more conducive for storms tomorrow. Model soundings
indicated MUCAPEs between 500-1000 J/kg, Lifted indices (LI) of
-3, and lapse rates 6.5-8 C/km across central OR to eastern OR.
Thus a moderately unstable environment. Of note, HREF probability
of thunder is forecast around 30-60% overnight that then ramp to
greater than 80% across portions of eastern OR.

Of note, a mix of wet and dry storms are expected in this event
with storms likely to be more wet than not across the Southern
Blue and Strawberry Mountains north and east. Of which, HREF LPMM
highlights this nature. A reasonable high-end is expected to be
approaching one inch or more. HREF shows raw probs of exceeding
0.5" at around 40-50% in spots. Wetting rains are further
supported by NBM probs. Of which, a tenth or more exceed 60%
across a large area, roughly Crook county southward and northeast
into Wallowa through 06Z Friday. While storms are wet there, the
threat for new fires is sufficient between fuels and lightning
activity. Thus Red Flag Warnings were issued for ORZ644-645.
Elsewhere, the Fire Weather Watches were replaced with a warning
with these zones having two windows of lightning potential, albeit
storms more isolated-widely scattered in character compared to
the storms in the east.

Overall, models are in good agreement with trough returning over
the PacNW with a cyclonic low for tomorrow. Breezy winds will also
develop up to 20-30 mph tomorrow around the Cascade Gaps
extending to Columbia Basin (>50% confidence). This is due to
increasing surface pressure gradients up to 5-8 mb.

Tomorrow night, the worst will come to an end as thunderstorms begin
moving out of the area. Gusty winds will then return at 15-25 mph
with the surface pressure gradient decreasing to 3-5 mb. Clear skies
will return as well as clouds decrease. Temperatures will then
steadily increase by a few degrees with relative humidity above
critical levels. Confidence enhances with the Extreme Forecast Index
(EFI) showing temperatures to be near-normal through the forecast
period. Feaster/97/80

.LONG TERM...Friday through Wednesday...The previous area of low
pressure continues to lift northeast out of the forecast area on
Friday morning. Lingering moisture will provide a slight chance
(15- 20%) for continued shower activity, mainly over Wallowa
County in Oregon and Columbia County in Washington. This system
should generally lift out of the forecast area by the late morning
hours, with another area of low pressure moving over the Pacific
Coast. Models continue to indicate instability, especially over
the Eastern Mountains of Oregon. With atmospheric moisture over
the area, showers and isolated thunderstorms (15-25% chance) will
be possible through Friday afternoon. The best opportunity for
thunderstorm development will be over eastern Union County, with
showers otherwise.

The previously mentioned area of low pressure off the Pacific
Coast will advance east with moisture moving over Washington and
Oregon between Saturday and Sunday. Ahead of the arrival on
Saturday, temperatures will warm around 5 degrees across the area,
with cooler conditions anticipated on Sunday. The best moisture
will be found west of, and including, the Cascades, though
moisture will spill over into the central portions as well (30-50%
for favored locations). Guidance indicates the afternoon and
evening hours to be the favored timeframe for shower activity .
Instability is generally faced in the western reaches of the
moisture with slight chance (10-20%) of development.

The area of low pressure will drift far enough northward to lose
influence over area weather by Sunday afternoon/evening. Drier
conditions expected to persist through the remainder of the
forecast period, though pockets of moisture will produce isolated
showers and thunderstorms over the Washington Cascades through
Wednesday. Temperatures through this period will remain near to
slightly above normal.

Overall, clusters are demonstrating fair agreement with the
progression of these systems. Intensity differences to exist, as
well as how far east the weekend system moves, but significant
differences are not currently present. Branham/76

&&

.AVIATION...18z TAFs...VFR included through TAF period with low
pressure moving across the area. Guidance indicates the
development of showers across central Oregon (KBDN, KRDM) after
05z this evening with the potential for showers lasting through
much of Thursday. There is a low chance (less than 5%) for
nocturnal thunderstorms over those terminals. Cloud cover
increases after 06z with a approach of the incoming system. Any
shower development over terminals could produce periods of MVFR
conditions. Branham/76

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  54  80  54  81 /   0  30  20  10
ALW  57  84  59  85 /   0  20  30  10
PSC  59  87  62  86 /   0  10  20   0
YKM  55  85  54  84 /   0  20  20   0
HRI  59  85  59  86 /   0  10  20   0
ELN  57  85  56  83 /   0  10  20  10
RDM  52  75  47  80 /  40  40  20  10
LGD  52  80  50  83 /   0  50  60  20
GCD  54  80  50  83 /  40  70  40  20
DLS  61  80  59  83 /  10  20  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 11 AM to 11 PM PDT Thursday for ORZ644-645.

     Red Flag Warning from 11 PM this evening to 11 PM PDT Thursday
     for ORZ611-640-642.

WA...None.
&&

$$

SHORT TERM...97/80
LONG TERM....76
AVIATION...76