533
FXUS66 KPDT 072311
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
411 PM PDT Sun Jul 7 2024

.Updated for Aviation...


&&

.PREV DISCUSSION... /issued 257 PM PDT Sun Jul 7 2024/

SHORT TERM...Tonight through Tuesday night...Water vapor imagery
reveals the axis of an anomalously strong mid/upper-level ridge
over the West Coast. Meanwhile, visible imagery shows mostly clear
skies across the region.

Ensemble and deterministic guidance are in excellent agreement
(100% chance) that the ridge axis will propagate eastward through
Tuesday night such that the ridge will be directly overhead on
Tuesday. Hottest temperatures of this long-duration heatwave are
anticipated Tuesday afternoon, while the warmest overnight lows
are expected Tuesday morning or Wednesday morning, depending on
location within our CWA.

To provide an idea of how hot the region may get, NBM
probabilities of exceeding 110 degrees range from 20-70% for much
of the eastern Gorge, Columbia Basin, and adjoining valleys and
foothills on Tuesday. Meanwhile, probabilities of overnight low
temperatures at or above 70 degrees range from 50-95% across the
same region Tuesday and Wednesday, especially for areas subject to
westerly winds that will keep the lower levels of the atmosphere
mixed overnight, thus limiting radiational cooling. Heat
Advisories and Excessive Heat Warnings are in effect during the
period.

Regarding fire weather concerns, a subtle vorticity maximum and
mid-level shortwave are increasingly apparent in NWP guidance for
Tuesday afternoon into Wednesday. While mid-level moisture in
forecast soundings appears meager to marginal, negative mid-level
theta-e lapse rates coupled with modest synoptic lift may
facilitate isolated afternoon and overnight convection (<10%
chance). Convection, if any, would begin across central Oregon
Tuesday afternoon and propagate northeastward across eastern
Oregon overnight. Have opted to forgo any Fire Weather Watches for
lightning due to low confidence. That said, the very dry air mass
coupled with some instability over central Oregon on Tuesday
afternoon will result in enhanced fire weather potential for any
new fires that develop. Additionally, locally breezy northerly
winds coupled with very low afternoon RHs will lead to a 30-50%
chance in Red Flag criteria across central and north-central OR
during Tuesday afternoon and evening. Plunkett/86

LONG TERM...Wednesday through Sunday...

Key Points:

1) Heat continues through the period, though may lightly decrease
enough that heat products, or at least excessive heat warnings,
are not necessary.

2) Breezy conditions and critical RH`s will coincide on Wednesday
to produce enhanced fire weather concerns.

3) Fire weather concerns relax on Thursday through the weekend,
but areas of locally breezy winds may be possible.

Models indicate the overall synoptic pattern as follows: high
pressure will continue its slow progression eastwards through the
end of the week, centering over the Four Corners region by
Saturday. The ridge will still attempt to extend over our region
and control the overall weather pattern, but various shortwave
troughs will try and break through the stubborn high with mixed
results between the major ensembles. By the end of the period
Sunday night into Monday, ensembles are coming together that a
deep trough just offshore may finally be the feature to break up
the monotony.

Confidence remains high (70-80%) in warm temperatures through the
period, as afternoon highs start off very hot on Wednesday
(95-105, locally approaching 110 in the Columbia Basin), dropping
by around 3-8 degrees then on Thursday as a shortwave helps to
flatten the pressure gradient and lightly cool us off. While the
region will remain warm (90s to low 100s), overnight lows are
expected to descend back down into the 50s to 60s, helping to
reduce overall HeatRisk and perhaps dial back the need for heat
related products. These temperatures should continue through the
end of the period, though perhaps warming 1-2 degrees through the
weekend as the ridging tries to regain control.

Fire weather concerns are on the rise for Wednesday as the
approaching system is expected to tighten our pressure gradient
and bring breezy winds across the Cascade gaps and into the lower
Columbia Basin. The NBM shows 55-100% probability of sustained
winds 25+ mph from Pendleton across to the Columbia Gorge and up
through the Cascade Gaps including both the Yakima and Kittitas
Valley. With RH values still critically low, widespread teens for
the day, probabilities are becoming moderate to high (60-80%) that
elevated fire weather conditions will occur. Conditions should
decline by Thursday, but winds may remain enhanced enough through
some of the Cascade gaps to warrant another day of concern.
Goatley/87

AVIATION...
00Z TAFS...VFR conditions are expected through the TAF period.
There could be some gusty winds to around 20 kts at DLS, BDN and
RDM for a few hours late this afternoon/early evening. Otherwise
all site will have winds less than 10 kts.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  59 102  62 106 /   0   0   0   0
ALW  62 105  64 108 /   0   0   0   0
PSC  64 105  66 110 /   0   0   0   0
YKM  65 105  68 108 /   0   0   0   0
HRI  63 106  64 111 /   0   0   0   0
ELN  62 105  64 108 /   0   0   0   0
RDM  54 101  59 104 /   0   0   0   0
LGD  53  98  58 102 /   0   0   0   0
GCD  56 100  60 106 /   0   0   0   0
DLS  67 108  71 111 /   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.

     Heat Advisory from noon Monday to 10 PM PDT Wednesday for ORZ049-
     050-502-503.

     Heat Advisory from noon Monday to 10 PM PDT Tuesday for ORZ509.

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

     Heat Advisory from noon Monday to 10 PM PDT Wednesday for WAZ030.

     Heat Advisory from noon Monday to 10 PM PDT Tuesday for WAZ522.

&&

$$

SHORT TERM...86
LONG TERM....87
AVIATION...77