292
FXUS66 KPDT 090416
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
916 PM PDT Sun Sep 8 2024

.UPDATE...Weather concerns have diminished in the near term.
Latest radar display shows a few weak returns over Wallowa with
the last CG lightning strikes having occurred prior to 02 UTC. The
Red Flag Warning was cancelled early given the latest trends and
limited support in the near storm environment based on
mesoanalysis. Latest CAMs show no additional development with HREF
showing a strong signal that the threat for storms. Otherwise,
little changes were made to the forecast beside capturing this
and the latest trends rest of tonight. Tomorrow, dry and light
breezes, however, a red flag event is not anticipated (high
confidence).

&&

.PREV DISCUSSION... /issued 409 PM PDT Sun Sep 8 2024/

UPDATED AVIATION...

PREV DISCUSSION... /issued 226 PM PDT Sun Sep 8 2024/

SHORT TERM...Tonight through Tuesday...In the immediate term
through this evening, scattered showers and storms are beginning
to become enhanced from Grant County up into Umatilla and across
through Wallowa. The environment continues to remain conducive of
this activity, as mesoanalysis indicates a widespread 500 J/kg of
MUCAPE and pockets on the border of ours and Boise`s CWA of near
1000. This with low level lapse rates of 8-9 C/km should continue
to fuel this activity through the evening hours. But the surface
remains very dry. For example, RH values of 20-25% are seen in the
Wallowa Valley, with dewpoints of 40-45 degrees. Likely these
storms should continue to be dry as showers are going to struggle
to make it to the surface. These conditions are favorable of some
stronger storms though, and noting some stronger reflectivity
values in Baker & Grant County, so it wouldn`t be surprising if we
saw a special weather statement on stronger storms with enhanced
outflow winds, maybe some small hail.

The negatively tilted shortwave that produced this activity will
move out of the region as we head into the beginning of the
workweek. Quasi-zonal flow will establish but should then become
southwesterly on Tuesday as a deepening low approaches from the
Gulf of Alaska. Main concerns during this time should be related
to winds as the pressure gradients tighten with the approach of
this system. The NBM shows a 70-90% probability of gusts 25+ mph
in the Columbia Gorge, lower Columbia Basin of Oregon, and
Kittitas Valley on Monday, increasing to 80-100% probability on
Tuesday. Even with stronger winds, our RH values will be low, but
not low enough to produce enhanced fire concerns as of this time.

Late Tuesday night into Wednesday morning with the approaching
system, showers begin to increase in coverage, with isolated to
scattered activity possible across the higher terrain and into the
foothills/slopes of. NBM shows a 5-10% chance of thunder in the
eastern mountains of Oregon during this time, not enough to add
into the forecast though. Finally, temperatures were complicated
as we continue to see highs relegated by haze/cloud cover. Did
some increases to the base NBM overnight tonight to account for
the trapped warmth, and also tempered down highs tomorrow to match
closer to what we`re seeing today, with highs then dropping
around 3-6 degrees on Tuesday as we enter a cooler pattern.
Goatley/87

LONG TERM...Wednesday through Sunday...Models and ensemble clusters
are in excellent agreement on moving an upper low across the region
Wednesday into Thursday. The trend is for slightly wetter conditions
Wednesday afternoon and Wednesday night with NBM POPS in the
mountains now in the likely/categorical range (60-85%) and chance
category (25-50%) across the lower elevations. There is some limited
CAPE forecast (100-250 J/kg) across central Oregon and Wallowa
County Wednesday afternoon and evening which may be sufficient for
an isolated thunderstorm or two (15-20% chance). The NBM 24 hour
probabilities of at least .10 inches of rain ending at 5 AM Thursday
across the mountains are 50-80%. Probabilities of .25 inches of rain
for the same time period over the mountains are 30-55% with the best
chance in Wallowa County. The lower elevations are expected to see
05-.10 inches of rain. On Thursday the rain shield will shift to
the eastern mountains and then out of the area Thursday night.
Temperatures will be quite cool Wednesday and Thursday with highs in
the mid 60s to mid 70s...except 50s mountains. Thursday and Friday
morning will be chilly with a 50-80% chance that the typically cold
spots in the mountains of central Oregon will fall below freezing.

Dry westerly flow aloft will be over the area Friday. The flow turns
southwesterly on Saturday as a trough develops off the PACNW coast.
Temperatures these two days will be closer to normal. There are
differences in the clusters on the timing and depth of this next
trough but it appears that by Sunday afternoon a few showers may
move into the area.  Models show little instability so have kept
thunderstorms out of the forecast for now. Depending on the
trajectory of the trough, there could be enough instability for a
storm or two over the central and eastern mountains. However there
is plenty of time to monitor trends in the models for this
possibility. 78

AVIATION...00Z TAFS...VFR conditions will prevail through the
period. VSBYS 5-6SM in HZ from area wildfires are expected at
KBDN/KRDM/KYKM with HZ aloft elsewhere. Winds will be 5-15kt but
gusts to 25 kt at KDLS this afternoon and early evening. Winds
elsewhere will remain mostly from the west and below 06KT. Cigs
will be mostly SKC with a few high clouds slipping through.
Bennese/90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  87  56  81 /  10   0   0   0
ALW  66  90  61  85 /  20   0   0   0
PSC  65  91  62  86 /   0   0   0   0
YKM  58  88  53  83 /   0   0   0   0
HRI  63  91  60  86 /   0   0   0   0
ELN  62  85  54  81 /   0   0   0   0
RDM  53  87  51  81 /   0   0   0   0
LGD  55  89  54  84 /  20   0   0   0
GCD  56  89  54  85 /  20   0   0   0
DLS  63  87  59  81 /   0   0   0   0

&&

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

$$

SHORT TERM...87
LONG TERM....78
AVIATION...90
UPDATE...80