664
FXUS66 KPDT 120942
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
242 AM PDT Mon Aug 12 2024

.SHORT TERM...Today through Wednesday night...Complex forecast
for the next 36 hours with the main concern focused on
thunderstorm potential over the eastern mountains. Latest water
vapor imagery shows a vorticity maximum off the northern
California coast. Models are in good agreement on moving it east
and inland initially then turning it northeast across eastern
Oregon tonight through midday Tuesday. An area of showers and
embedded thunderstorms will accompany this feature. The NAM and
NAM Nest have been the most consistent from run to run with this
scenario. The CAMS are showing this evolution now too with some
variability in the west edge of the precipitation shield. The big
question is how much lightning will accompany this activity. The
HREF TSTM probabilities are lack luster but peak at 40% over Baker
County around 14Z Tuesday....then decrease thereafter.
Instability will be weak overnight as well with cool surface
temperatures in the 40s and 50s and marginal elevated instability.
Thus the current thinking is that the potential for abundant
lightning is low (30-40% chance mainly eastern Grant and Wallowa
counties) and fire weather highlights will not be issued. Plus
precipitable water is forecast to increase to around 1.0 inch
tonight and thunderstorms are expected to be accompanied by
decent rainfall of .10-.25 inches.

There is a small chance (20%) that a stray storm could pop over
the northeastern mountains late this afternoon or evening before
the main activity arrives overnight. CAMS are hinting at this
possibility mainly over Wallowa County. Otherwise today will be
warm with high temperatures near 90 in the lower elevations and
in the 80s mountains.

It will be noticeably cooler on Tuesday with highs in the mid 70s
to lower 80s lower elevations and mid 60s to mid 70s mountains.
It will be rather cool Wednesday morning with the mountain valleys
in central Oregon falling into the mid to upper 30s for lows.
Wednesday will be a pleasant day with highs in the 80s except 70s
in the mountains. Models are in good agreement on bringing an
upper low into the region late Wednesday night. For now kept the
forecast dry with pops less than 15% but would not be surprised if
slightly higher POPS are introduced in later forecasts. 78

.LONG TERM...Thursday through Monday...Much of the period looks cool
and wet as ensemble guidance is in good agreement on a closed low
enveloping the region next weekend through early next week. The NW
origin of this low will allow cooler air to spill in, making for
high temps in the 70s and 80s across much of the forecast area,
which is about average or just below. Ideally, these conditions will
temper fire behavior enough to help put a cap on what`s been a
particularly active wildfire season.

Thursday looks to be the warmest day of the period as a more SW
trough rolls through and provides for a chance of showers and
isolated thunderstorms across an area stretching from central Oregon
to Wallowa County. Opted to leave storm chances in the forecast even
though instability isn`t particularly great as the flow is SW
enough to at least produce a marginal chance of orographic storms
over the eastern mountains. Once the aforementioned closed low
arrives on Friday, however, instability drops off quite a bit, and
while shower chances will be persistent across much of the CWA,
current thinking is that the pattern just isn`t supportive for
storm activity through the weekend. Would say right now that
chances for storms from central Oregon through the eastern
mountains on Thursday stands at around 15-20%, down to around 10%
Friday onward. Moisture will certainly be there, but with a closed
low overhead, cloud cover will likely remain persistent across
the forecast area.

With temps dropping to more seasonal averages, minimum RHs increase
toward the 20s and even 30s across even the lowest elevation zones
of the forecast area, at least according to the NBM. Winds are
expected to pick up with this synoptic pattern, but that shouldn`t
be too much of a concern with how wetter the forecast is trending.
That, and winds at this time don`t look to be strong enough to cause
widespread issues as far as fire spread is concerned. Overall
forecast confidence is on the higher end (60-70%) on a cool and wet
pattern that many will likely welcome given what`s been a hot, dry,
and fiery summer. Evans/74

&&

.AVIATION...12z TAFs...VFR conditions expected. Winds will pick up
at many sites during the day as a front moves through the region,
gusting up to 25 kts out of the W and NW at times. Otherwise, expect
sct high clouds through the period with any precipitation threats
associated with this front limited to the eastern mountains of
Oregon and SE Washington. Evans/74

.PRELIMINARY POINT TEMPS/POPS...
PDT  87  54  79  50 /   0  10   0   0
ALW  91  60  83  56 /   0  10  10   0
PSC  92  60  84  59 /   0   0   0   0
YKM  90  55  83  52 /   0   0   0   0
HRI  91  60  83  57 /   0   0   0   0
ELN  86  57  80  54 /   0   0   0   0
RDM  86  45  78  44 /   0   0   0   0
LGD  90  54  80  49 /  10  40  30  10
GCD  90  53  84  49 /  10  40  10   0
DLS  82  59  77  58 /   0   0   0   0

&&

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

$$

SHORT TERM...78
LONG TERM....74
AVIATION...74