167
FXUS66 KPDT 140508
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1008 PM PDT Sat Jul 13 2024

Updated Aviation Discussion

.AVIATION...06Z TAFS...VFR conditions continue with clear
skies. Gusty winds will start picking up at
KDLS/KPDT/KRDM/KBDN/KYKM/KALW around Sunday morning and afternoon
hours. Area haze and smoke may stick around in the horizon but no
surface VSBYs will be reduced below VFR at these terminals.
Feaster/97

&&

.PREV DISCUSSION... /issued 233 PM PDT Sat Jul 13 2024/

.SHORT TERM...Today through Monday...

Bottom Line Up Front

1. Critical fire weather conditions through the weekend

2. Above normal heat still lingers through the weekend

Models are in firm agreement with a strong upper level high still
parked over the Four Corners with and an upper level trough still
off shore. This synoptic pattern will allow for southwesterly
flow and the ability to continue to push in upper level moisture
over the region. This flow will continue to keep the region under
hot and dry conditions. Small shortwave pulses will allow the
region to see periods of breezy winds as well as increased
potential for some dry isolated thunderstorms in southern Oregon
Sunday. This set up will lead to some critical fire weather
concerns through the remainder of the weekend.

Short term models are indicating thunderstorm activity but has
shifted the larger threat originally for today a bit farther south
of the region. Model derived soundings along the southern flank of
the region shows a very dry and unstable atmosphere with lapse rates
cresting 9.5 C/km. Today`s fire weather concerns remain in southern
OR in Deschutes, Crook and Grant Counties. Sunday short term models
begin to ramp up the instability with model derived sounding showing
an increase in lapse rates to over 10 C/km. Chances of isolated dry
thunderstorms in the far southern portions of the region remain low
(10-15%), however, if any storms come to fruition, guidance shows
outflow winds will be strong with downdraft CAPE values near 800
J/kg and soundings show very dry low levels.

Last but certainly not least, heat. Raw ensembles show above 70% of
the region will continue to be above 90 degrees while the foothills
of the Blues, Columbia Basin and adjacent valleys will remain above
100 degrees. However, as the first shortwave makes its way over the
top of the ridge, temperatures will decrease slightly with over 60%
of the raw ensembles showing the temperatures to remain the same as
today. EFI continues to show the majority of the region under above
normal temperatures just not as drastically as previously.
Bennese/90

.LONG TERM...Tuesday through Saturday...Much of the long term looks
to remain hot and dry, as ensemble guidance depicts our area wedged
between an amplifying Four Corners high and troughing to our
northwest. Fortunately, being caught in between these two features
will work against temperatures heating up too much, but so long as
these above-average temps persist, RHs will remain very low, making
the thresholds for critical fire weather conditions low as well.

The only real notable feature that shows up in the synoptic pattern
across guidance is the arrival of an upper-level low from our
southwest sometime between late Tuesday and Wednesday. Generally,
our concerns with these types of SW systems would be the chance for
orographic thunderstorms or an increase in winds, but thus far, mid-
level moisture is lacking across deterministic guidance, as is
instability, and the signal for wind gusts is weak outside of the
usual gap flows. This feature is still worth keeping an eye on, but
with how dry the BL will continue to be under these prolonged hot
conditions, am a bit skeptical at this time in how well this system
initiates convection or shower activity of any kind. Current
forecast confidence sits at 20%.

The rest of the week looks benign outside of the heat, with winds
expected to be lax save for the Cascade Gaps. Ensemble clusters keep
us locked in the aforementioned pattern until the tail end of the
period, when the trough to our northwest may begin to encroach upon
the Interior Northwest. With models not depicting this until beyond
a week out, however, forecast confidence is too low to speak of too
many details. Evans/74

&&

.FIRE WEATHER...Instability today has already caused the Falls Fire to
show periods of extreme fire behavior. Webcams show the fire to be
initiating what are commonly called pyro-cumulus clouds, much like
thunderstorm cumulus clouds. This shows that the instability has
moved over the fire and extreme fire behavior is being observed.
Instability remains the primary concern across the southern and
southeastern portion of the region. A Red Flag Warning has been
issued for fire weather zone 642 has been issued for hot, dry and
unstable conditions to account for the ongoing Falls Fire. However,
any new starts in the surrounding fire zones OR611, OR640 and OR644
will see extreme fire behavior. Sunday models continue to show
instability across the southern portion of the region and due to the
continued hot, dry and unstable conditions, the Red Flag Warning has
been extended to cover Sunday as well.

Dry and breezy conditions has lead to Red Flag Warnings being issued
for Sunday for the foothills of the Cascades in OR, Gorge, Simcoe
Highlands, Columbia Basin, Kittitas and Yakima Valleys. Short term
guidance shows an increase in the gap winds as the upper level
shortwave makes its way along the top of the ridge. Winds will see
an increase with sustained winds of 15 to 20 mph with RH values
dipping into the low teens and even single digits. With the ongoing
Larch Creek Fire on the landscape confidence in the Red Flag warning
is high (80-90%). If a fire starts under these conditions, extreme
fire spread will occur. Bennese/90


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  63  98  60  95 /   0   0   0   0
ALW  68 102  66  98 /   0   0   0   0
PSC  66 103  66 100 /   0   0   0   0
YKM  64 100  61  99 /   0   0   0   0
HRI  68 102  65 100 /   0   0   0   0
ELN  66  97  64  96 /   0   0   0   0
RDM  56  97  55  95 /   0   0   0   0
LGD  63  96  57  93 /   0   0   0   0
GCD  64  99  59  96 /   0   0   0   0
DLS  66  97  64  96 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 10 PM PDT Sunday for ORZ041-044-049-503-
     505>508-511.

     Red Flag Warning from 11 AM to 9 PM PDT Sunday for ORZ641.

     Red Flag Warning until 11 PM PDT Sunday for ORZ642.

WA...Heat Advisory until 10 PM PDT Sunday for WAZ024-026>029-521.

     Red Flag Warning from 11 AM to 9 PM PDT Sunday for WAZ690-691.

&&

$$

SHORT TERM...90
LONG TERM....74
AVIATION...97