592
FXUS66 KPDT 112350
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
450 PM PDT Thu Jul 11 2024

.AVIATION...00Z TAFs...VFR conditions are expected (>95% chance)
for all sites through the period. While smoke from nearby
wildfires is producing some haze aloft, it is not forecast to
reduce visibility to values below VFR at TAF sites. Aside from
the aforementioned smoke aloft, mostly clear skies are forecast.
Winds will be diurnally driven through the Cascade gaps, strongest
for DLS/BDN/RDM/YKM this afternoon and evening. Otherwise, winds
of predominantly 10 kts or below are forecast for all sites
overnight into Friday morning. Some gusts of 15-20 kts are
anticipated later Friday morning through afternoon, primarily at
DLS. Plunkett/86

&&

.PREV DISCUSSION... /issued 235 PM PDT Thu Jul 11 2024/

SHORT TERM...Tonight through Saturday night...The weather
concerns have briefly relaxed with temperatures about 5-10 degrees
cooler and winds are less compared to yesterday. Breezy winds have
been observed throughout the day in the Kittitas Valley, and it
is now breezy in the eastern CR Gorge. The Red Flag Warning
remains in effect for the Kittitas Valley (WA690) through this
evening where the RH is around 20%. Cooler air has filtered
through the eastern CR Gorge where the RHs are in the mid 20s to
lower 30s. These are gradient driven winds with a tight cross
Cascade gradient rather than associated with an onshore flow.
Visible satellite shows the stratus clouds near the mouth of the
Columbia River but no indications elsewhere. UIL sounding this
morning shows the marine depth less than 2K feet. The inverted
surface thermal trough has shifted eastward towards the ID border,
and this has steepened lapse rates with active behavior observed
with the fires in northern Harney and Malheur Counties, including
the Falls Fire.

Friday`s pattern changes little from today, although the axis of
the thermal trough will be more along the ID border. Winds will be
similar to today and will be locally breezy. This will result in
elevated fire conditions but not expected to meet red flag. There
remains concerns once again for the Kittitas Valley where
sustained winds of 20-25 mph have been observed this afternoon.
The probability of similar magnitudes on Friday is 25% on the NBM
with less likelihood of red flag conditions. High temperatures on
Friday will be in the 80s and 90s...locally around 100.

Fire concerns return on Saturday, and Fire Weather Watches have
been issued for fire zones OR642 and OR644 for thunderstorms
producing abundant lightning. Although the best probability for
storms in our southeast zones will be on Sunday, there is a chance
(20-30%) for storms to develop areas south of John Day and La
Grande as early as Saturday evening. Since this affects the Falls
Fire and Upper Pine, a watch was issued as "heads up". PWATs will
be less than 0.6", therefore any storms that develop will likely
produce less than 0.1". This is associated with a weak shortwave
trough moving north along the CA coast with increased vorticity
over southeast OR. Wister/85

LONG TERM...Saturday through Wednesday...

Bottom Line Up Front

1. Breezy conditions return along Cascade east slopes and through
   the Cascade Gaps could leave to fire weather concerns.

2. Thunderstorm potential Saturday and Sunday.

3. Dry and warm conditions remain in place.

Models continue to be in firm agreement with the upper level high
continuing to be perched over the Four Corners and an upper level
low off the coast of California. This synoptic set up will cause
west to south west flow aloft. This will create the tightening of
the surface pressure gradients across the Cascades. A diurnal wind
pattern will set itself up each day with winds becoming breezy
along the east slopes of the Cascades especially through the
Cascade Gaps. NBM is showing a near 88% probability of the
Columbia River Gorge, foothills of the southern Blues and the
lower Columbia Basin will see daily sustained wind speed averaging
between 10 to 15 mph. 80% of the raw ensembles are in agreement
with what the NBM is showing. Moving on to the Kittitas and Yakima
Valleys, NBM in showing 90% probabilities of sustained winds of
20 to 25 mph with 90 to 100% of the raw ensembles in agreement.
Daily daytime relative humidities will be in the teen with a few
scattered locations being in the 20s. With the elevated winds, dry
RH values and the incoming instability and abundant lightning
from thunderstorms, confidence in fire weather conditions is
moderate 70-80%.

Models remain in firm agreement through the period with the
synoptic pattern with the upper level low remaining off the
coast of California and the upper level high over the Four
Corners. However, models show the low to strengthen just a bit and
the high to move slightly southward a touch. Just enough that
there is some upper level moisture that gets wrapped around the
high and ushered into the region Saturday night with the majority
ushering in Sunday. This set up will allow for thunderstorm
probabilities through central OR and along the Ochoco-John Day
Highlands before spreading across the rest of the eastern
mountains and into Wallowa County. Model derived soundings for
Deschutes and Grant counties show MUCAPE values cresting 600 J/kg,
lapse rates of 9.3 C/km, lifted index of -2 and bulk shear of 43
kts. PWATs within the sounding is 0.65 inches and with the dry
layer beneath the moisture, these thunderstorms on Saturday will
be dry. The ingredients are there for thunderstorms on Saturday,
however, raw ensembles are only showing a probability of 15% due
to the model variances in the amount of moisture that will make
its way into the region. Also, models show the majority of the
moisture to be to the south of the area barley clipping Deschutes
County. Sunday shows a tad more promise with raw ensembles showing
upwards of 25% probabilities for thunderstorms with model derived
soundings showing a much more moist and unstable atmosphere. Model
derived soundings along the eastern mountains have areas where
MUCAPE values are cresting over 800 J/kg with some locations
seeing values as high as 1000 J/kg, lapse rates of 9.5 C/km,
lifted index of -2 to -4 and bulk shear of 45 kts. PWATs are in
the 0.65 to 0.80 inch range and with the continued dry and warm
surface conditions, any rain associated with these storms will be
light to moderate. This has raised some fire weather concerns,
especially around the fires in the far southeastern portion of the
CWA so a fire weather watch for abundant lightning has been
issued with concerns for outflow winds. Model derived downdraft
CAPE values are roughly 400 J/kg higher than the MUCAPE. With this
there are high likelihoods of strong downdraft and outflow winds.

Lastly, even with the synoptic pattern shift, models are still
showing the region to be under dry and warm conditions through the
long term period. EFI is showing temperatures to remain above
normal through the beginning of the long term before slowly
teetering more towards climatological normal by mid work week. 90%
of the raw ensembles have the Pendleton area back in the mid to
upper 90s, 65% has the Basin, Gorge, Yakima Valley and central OR
to be in the upper 90s and into the 100s. Temperatures will
steadily decrease through the long term period before leveling off
by Wednesday. However, if models stay consistent as they are,
temperatures will remain in the 100s in the Basin through the end
of the long term period (50-60% confidence) Bennese/90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  96  60  99 /   0   0   0   0
ALW  64  99  66 102 /   0   0   0   0
PSC  64 100  65 103 /   0   0   0   0
YKM  61  99  63 101 /   0   0   0   0
HRI  63 100  65 103 /   0   0   0   0
ELN  62  98  64  99 /   0   0   0   0
RDM  53  95  54  98 /   0   0   0   0
LGD  58  96  60  98 /   0   0   0   0
GCD  59  99  60 102 /   0   0   0   0
DLS  62  97  64 100 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Saturday afternoon through Sunday
     evening for ORZ642-644.

WA...Red Flag Warning until 8 PM PDT this evening for WAZ690.

&&

$$

SHORT TERM...85
LONG TERM....90
AVIATION...86