000
FXUS66 KPDT 052339
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
439 PM PDT Mon Jun 5 2023

Updated Aviation Discussion

.AVIATION...00z TAFs...Expecting VFR conditions through the
period. Most sites will see clear skies and light, NW/N winds less
than 15 mph. Only possible concern this evening is an outside
chance of thunderstorms impacting BDN/RDM. Largely expecting
storms to remain isolated to higher terrain areas, with a less
than 20% chance of even VCTS for the two sites, but storm activity
has been observed around nearby Prineville. Storm activity should
cease by nightfall, leaving light, terrain-driven winds at all
sites. BDN/RDM should see clearing from current bkn-ovc conditions
overnight. Evans/74

&&

.PREV DISCUSSION... /issued 246 PM PDT Mon Jun 5 2023/

SHORT TERM...Tonight through Wednesday night...An interesting and
complex pattern has set up across the western U.S. with some
challenges in the short term forecast. The forecast area is
sandwiched between three separate upper lows. The first upper low
is large over B.C. that is traveling east and will no longer be a
concern tonight and tomorrow when it moves into Alberta. A much
smaller circulation is decaying and is over central ID at this
time. The third low has intensified over the past 24 hours and is
currently centered off the southern CA coast. This system will be
the main focus for thunderstorm activity in our area over the next
several days.

Scattered thunderstorms have already developed over the southern
half of Oregon, mainly south of the CWA. A few cells developed
along the Ochoco and Malheur National Forests. Storms have been
slow moving in an area of diffluent flow, and there have been a
couple of RAWS locations reporting 0.1-0.25" of rain. Despite the
weak shear of 25 kts or less, some storms have had high
reflectivity cores greater than 50 dBZ indicative of strong
updrafts and hail. No ground truth reports of hail so far. CAMS
shows storms dissipating shortly after 03Z.

The potential for thunderstorms on Tuesday will be the far south
of our CWA and only 20 pct during the evening. The CA low will
creep northward, sending a weak impulse over far southern OR.
Tuesday should be relatively quiet, although it will feel like
mid-July as temperatures climb into the 80s and 90s. The eastern
CR Gorge will be pushing the 100 degree mark as the inverted
surface thermal trough will extend along the Cascades. RHs will be
in the teens. No wind concerns are anticipated, although north
winds sustained at 10-15 mph are forecast for central and north
central OR which could pose problems for fire control where flashy
fuels are present.

Wednesday is looking like an active day for thunderstorms in
eastern OR as the system to the south widens and increases a SSE
flow over the region. SPC has central and northeast Oregon in the
marginal risk for severe thunderstorms. It will be another hot day
with highs in the mid 80s to upper 90s and a few more locations
in the Lower Columbia Basin flirting with 100 degrees. PWATS will
increase to around 0.8", although surface dewpoints will mostly be
in the 40s. SREF probability of bulk shear from 0-6km greater
than 30 kts is around 60% (10% greater than 40 kts). CAPES will be
pushing 1000 J/kg over northeast OR. All of these would indicate
strong updrafts resulting in strong storms...isolated severe.
Wister/85

LONG TERM...Thursday through Monday...Given the complexity of the
longwave pattern, ensemble and deterministic guidance are in
remarkably good agreement through the long-term period with only
small differences in features of interest. Warm to hot temperatures
with locally breezy winds through the Cascade gaps and a slight
chance to chance of showers and thunderstorms, primarily for the
mountains, dominate the forecast. Overall, Thursday appears to be
the hottest day with temperatures 10-15 degrees above normal with
mean temperatures dropping back down to around 5-10 degrees above
normal for Friday through Monday.

Ensemble means are in excellent agreement that the CONUS will be
under the influence of a quasi-omega block with a semi-stationary
deep closed low along the Northeast U.S., an upper-level ridge
draped over the Central U.S. extending up through the Northern
Rockies of Canada, and more transient low pressure over the
Southwest U.S. and Great Basin. As the closed low over the Southwest
transitions to an open wave on Thursday and Friday, shortwave energy
will combine with some instability and an increasingly saturated air
mass with PWATs of 0.8-1.2" to generate the best chance for showers
and thunderstorms across the CWA. The best chances will be over the
eastern mountains where forecast instability is greatest. In the
wake of the open wave, ensemble guidance suggests another closed low
will to take up camp over the Southwest with the overall blocking
pattern remaining in place through the weekend. Ensemble means show
the low over the Northeast finally exiting offshore through Sunday
with another wave from the Canadian Prairies slotting in over the
Midwest. This is where some model differences are apparent with
ramifications for the pattern upstream; ensemble clusters reveal
some variance in the magnitude of the height field over the Midwest
and also the height field offshore of the Pacific Northwest. If the
pattern over the Midwest finally turns progressive, the ridge will
finally break down with ensemble means then favoring northwesterly
flow aloft by mid-week. Plunkett/86

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  52  88  56  92 /   0   0   0   0
ALW  56  93  61  96 /   0   0   0   0
PSC  57  93  61  99 /   0   0   0   0
YKM  55  90  58  96 /   0   0   0   0
HRI  55  93  58  98 /   0   0   0   0
ELN  50  85  53  94 /   0   0   0   0
RDM  50  85  52  88 /  10   0  10  10
LGD  52  86  55  89 /   0   0   0  20
GCD  51  85  53  89 /  10   0  10  30
DLS  55  95  57  97 /   0   0   0   0

&&

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

$$

SHORT TERM...85
LONG TERM....86
AVIATION...74

NWS PDT Office Area Forecast Discussion