374
FXUS66 KPDT 082152
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
252 PM PDT Mon Jul 8 2024

.SHORT TERM...Tonight through Wednesday night...Although no
precipitation is in the forecast through Wednesday night, there
are multiple weather concerns--the heat and fire weather. Starting
with the heat, nearly all of the forecast area are under
Excessive Heat Warnings or Heat Advisories. Widespread
temperatures are in the 90s to around 105 at this time, and it
will be even hotter tomorrow. The inverted surface thermal trough
will be directly over us and the 850mb temps will climb from
around 26-30C today to 27-32C tomorrow. There will be locations
pushing 110-113F tomorrow in the Lower Columbia Basin, eastern CR
Gorge, and the John Day Basin. Wednesday will be cooler,
particularly in our western zones, but a 5-10 degree drop in
temperatures still means triple digits with no relief in cooling.
Areas under the Excessive Heat Warning will only cool down into
the 60s to lower 70s at night.

The position of the thermal trough is a key player in the
instability, especially as the upper ridge shifts to the east. The
axis of the surface thermal trough will be along the Cascades
tonight and Tuesday where Red Flag Warnings have been posted. Fire
Weather Watches were issued earlier for the Blue Mountains,
Wallowas, and the John Day-Ochoco Highlands in effect for Tuesday
afternoon through Wednesday. Confidence is about 60-80% for the
atmosphere to become more unstable in these areas. Last night`s
HREF showed several members with isolated returns on the simulated
reflectivity over southeast Oregon late Tuesday. The forecast
soundings also showed high based inverted V. The same CAMs in the
most recent runs were less "impressive" on the reflectivity.
Another tool often used for elevated instability (DIV Q aloft and
theta-e decreasing with height between H7-H5) had little
indication. Due to low confidence in thunderstorms on Tuesday
(<15%), Tuesday will remain as dry throughout the CWA.

The ridge will flatten on Wednesday, increasing the westerly flow
at the surface and aloft. A Fire Weather Watch was issued earlier
for the Kittitas Valley and the WA/OR Basin zones, and confidence
is around 70% for these zones to meet red flag criteria. Based on
the wind forecast for areas along the Columbia Deschutes Plateau,
fire weather highlights may need to be extended down to central
Oregon. Confidence in central Oregon meeting red flag for wind and
RH on Wednesday is currently around 50%. Wister/85



.LONG TERM...Thursday through Monday...
Starting Thursday, the long-lasting ridge will finally lose its
potency as the synoptic pattern becomes zonal through Saturday.
This will support relatively hot conditions along with elevated
fire weather concerns via breezy winds through the Cascade Gaps,
possibly extending into the Basin.

Ensembles are in good agreement through Saturday as the ridge
flattens into a more zonal pattern, which typically supports gap
flows. NBM probabilistic guidance shows high chances (>70%) of wind
gusts at 25-35 mph through our usual areas: the Columbia River
Gorge, Kittitas Valley, Simcoe Highlands, and extending into the
Columbia Basin.

The dry hot environment will allow high temps to remain in the 90s
for a majority of our lower elevation and valley zones. Around
the Columbia Basin, temps will be in the lower 100s. Being said,
RHs are most likely (70-80%) to remain at critical levels in the
teens but around 20s and 30s along the Cascades, suggested by the NBM.
Temps begin to cool Sunday through Monday with the incoming
shortwave trough moving inland of PacNW.

Small differences in the ensembles begin to show starting Sunday
along with the models, as both GFS and Canadian try to bring in a
shortwave trough through the region around Monday. However, it is
still a little too far out to accurately determine how much
moisture this system will bring. Given how dry the environment
will be through the period, dry thunderstorms could also be a
concern (<20% confidence). Feaster/97


&&

.AVIATION...VFR conditions expected throughout this period. Skies
will be clear with terrain-driven winds less than 10 kts.
Feaster/97


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  62 106  69 103 /   0   0   0   0
ALW  64 109  72 106 /   0   0   0   0
PSC  66 109  72 109 /   0   0   0   0
YKM  68 108  70 106 /   0   0   0   0
HRI  64 111  70 108 /   0   0   0   0
ELN  64 108  68 101 /   0   0   0   0
RDM  59 105  61  99 /   0   0   0   0
LGD  58 101  66 100 /   0   0   0   0
GCD  60 104  64 101 /   0   0   0   0
DLS  71 111  72 101 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 10 PM PDT Wednesday for ORZ041-044-
     505-507-508-510-511.

     Red Flag Warning until 11 PM PDT Tuesday for ORZ610-611-639-640.

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

     Heat Advisory until 10 PM PDT Wednesday for ORZ049-050-502-503.

     Fire Weather Watch from Tuesday afternoon through Wednesday
     evening for ORZ642>645.

     Heat Advisory until 10 PM PDT Tuesday for ORZ509.

WA...Excessive Heat Warning until 10 PM PDT Wednesday for WAZ024-
     026>029-521-523.

     Red Flag Warning until 11 PM PDT Tuesday for WAZ694-695.

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

     Heat Advisory until 10 PM PDT Wednesday for WAZ030.

     Fire Weather Watch from Tuesday afternoon through Wednesday
     evening for WAZ692-693.

     Heat Advisory until 10 PM PDT Tuesday for WAZ522.

&&

$$

SHORT TERM...85
LONG TERM....97
AVIATION...97