159
FXUS66 KPDT 131725
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1025 AM PDT Sat Jul 13 2024

Updated Aviation Discussion

.AVIATION...18z TAFs...VFR conditions expected. Sites will see
mostly clear skies and light, terrain-driven winds less than 12
kts, save for DLS which will see gusts up to 25 kts at times this
afternoon. Area haze and smoke may also cause some obscurities in
the horizon as well. Evans/74

&&

.PREV DISCUSSION... /issued 321 AM PDT Sat Jul 13 2024/

SHORT TERM...Today through Monday...

Key Points:

1) Critical fire weather conditions expected throughout the
weekend including dry and unstable conditions and abundant
lightning for southeastern Oregon, and breezy winds/low RH`s for
the Cascade Gaps into the Columbia Basin.

2) Heat remains present with heat advisory continuing throughout
the weekend.

Models indicate the overall pattern will remain fairly consistent
through the weekend into early next week as a deep upper level
high centered over the Four Corners stretches out ridging across
our region while troughing just offshore in the Pacific helps to
produce a westerly to southwesterly flow pattern. This will keep
us hot and dry overall while smaller shortwaves rounding the ridge
will produce both periods of breezy winds as well as the
potential for some isolated thunderstorm activity in southern
Oregon that may be able to work its way up towards our region on
Sunday.

CAMs continue to keep the most plentiful thunderstorm activity
south of our region today and Sunday with the passage of the
shortwave activity. Forecast soundings show very dry conditions
until the 500 mb level as well, but the 700-500 mb lapse rates
today are upwards of 9-9.5 C/km. With plentiful instability, fire
weather concerns have remained high in the Strawberry/Southern
Blue Mountain zones today. By Sunday CAMs present more convection
potential up into our zones with portions of Central OR up through
southern Wallowa County seeing isolated storms at times. But with
low to mid levels still dry, expecting these will be mostly dry
thunderstorms with lightning and gusty outflow winds the possible
hazard. For more information on the fire weather potential, see
Fire Weather section below.

Onto the continued heat, the NBM has widespread 60-95% chance of
highs 100+ for the Yakima Valley, Central Oregon, Columbia Basin,
and foothills of the Blue Mountains. Probabilities do drop on
Sunday as the passing shortwave impulse should help to deter some
of the ridging, but 40-90% chance still remains for the Yakima
Valley, Columbia Basin, and foothills of the Blues. There remains
high confidence in HeatRisk values of moderate to locally major,
giving good confidence to the ongoing heat advisory. Probabilities
drop by Monday, but don`t get too excited - highs still remain
widespread 90`s to near 100 in the Columbia Basin, so relief will
only be by a few degrees at best. Goatley/87

LONG TERM...Tuesday through Saturday...Models continue to be in
good agreement regarding placement of key weather features during
the long term periods. Mainly that the weather pattern over the
western USA will continue to be dominated by a large scale ridge of
high pressure. The center of the ridge will initially be over the
Four Corners area but slowly shift west to be closer to Las Vegas
late in the week. Question becomes whether there will be enough
moisture wrapping around the ridge to become concerned about
possible thunderstorms. As of now the probabilities of thunderstorms
remains less than 10% on any given day over the long term forecast
periods. The ridge placement does guarantee that high temperatures
will continue to run 10 to 15 degrees above normal throughout the
long term period. This will continue to put much of the forecast
area in the moderate HeatRisk category with a low chance (20-30%) of
occasional major HeatRisk.

FIRE WEATHER...Instability continues to remain prevalent across
central and southeastern Oregon with Haines values of 6 widespread
in this region. A red flag warning for hot dry and unstable was
issued for OR-642 to account for this and the Falls Fire ongoing
in this zone; however, any new startups that occur across OR-611,
640, 644, and even 645 will see extreme fire behavior potential as
instability is strong in these regions as well. On Sunday, CAMs
remain scattered on thunderstorm potential, but each show some
form of activity making its way into the region. A fire weather
watch remains in effect for OR-642 for this potential as this is
the most likely zone that storms will be possible in with abundant
lightning.

Winds and RH`s still remain borderline for our fire weather watch
across the Cascade gaps and into the Columbia Basin on Sunday. But
with fuels very dry and RH values into the teens alongside
sustained winds of 15-25 mph, critical fire weather concerns
remain highly plausible. The NBM has a 60-100% chance of sustained
winds 20+ mph from the Cascade Gaps through the Columbia Basin and
even into the foothills of the Blues, which gives moderate to high
confidence (60-70%) that these breezes will coincide long enough
with minimum RH values to have a significant effect on fire
potential. Have continued the fire weather watch for this area
with the expectation it will likely be upgraded today. Goatley/87

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT 100  63  98  59 /   0   0   0   0
ALW 103  68 101  66 /   0   0   0   0
PSC 104  66 102  65 /   0   0   0   0
YKM 102  64 100  61 /   0   0   0   0
HRI 104  66 102  66 /   0   0   0   0
ELN 100  66  96  63 /   0   0   0   0
RDM  99  55  96  54 /   0   0  10   0
LGD  99  61  96  58 /   0   0   0   0
GCD 103  62  98  58 /   0   0  10  20
DLS 100  66  97  64 /   0   0   0   0

&&

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

     Fire Weather Watch from Sunday afternoon through Sunday evening
     for ORZ641.

     Red Flag Warning until 8 PM PDT this evening for ORZ642.

     Fire Weather Watch from Sunday morning through Sunday evening
     for ORZ642.

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

     Fire Weather Watch from Sunday afternoon through Sunday evening
     for WAZ690-691.

&&

$$

SHORT TERM...87
LONG TERM....91
AVIATION...74