280
FXUS66 KPDT 182342
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
442 PM PDT Thu Jul 18 2024

.AVIATION...00z TAFs...VFR. Dry conditions persist as the ridge
progresses eastward. Gusty winds will remain present across KDLS,
KRDM, and KBDN this evening in response to a tightened pressure
gradient impacting western Oregon. Wind should weaken at these
terminals after 08z tonight, with generally light wind (less than
15 kts) expected otherwise. Branham/76

&&

.PREV DISCUSSION... /issued 249 PM PDT Thu Jul 18 2024/

SHORT TERM...Tonight through Saturday...A deep high pressure
ridge is expected to only strengthen it`s grip on the inland PacNW
over this weekend, once again burning us up with very warm
temperatures and increased fire weather concerns.

Heat advisories are expiring this evening, and although afternoon
temperatures tomorrow will still be warm, highs should drop by a
couple of degrees and overnight lows will be back into the 50`s to
60`s, allowing enough recovery that heat products will not be
necessary tomorrow. Saturday is a different story though as we see
widespread highs soaring back into the triple digits for our
lower elevation population centers. And with even warmer
temperatures on Sunday combined with overnight lows back into the
upper 60`s to low 70`s, an excessive heat warning has been issued.
The NBM shows all of our population centers at an 80-100% chance
of exceeding 100 degrees on Saturday, giving very high confidence
to this warning.

Meanwhile, as flow turns more southerly from the ridge stretching
into Canada, instability will be on the increase. This shouldn`t
come into effect until once again on Saturday when lapse rates
across Southern and Central Oregon will rise. With relative
humidities nearing the single digits alongside the hot
temperatures and the Falls Fire ongoing, a Fire Weather Watch was
necessary for hot, dry, and unstable conditions for zone OR-642
for the danger of extreme fire behavior. Thunderstorm potential
may begin to materialize into early next week as this instability
continues to overspread and moisture begins to advect back into
the region. Goatley/87

LONG TERM...Sunday through Thursday...A strong high pressure ridge
will prevail over the region on Sunday, before a low to our
northwest noses its way in and breaks down the ridge. We`ll see this
prolonged heat come to an end as this ridge breaks down, but this
will come at the cost of potential critical fire weather conditions,
as the ridge`s breakdown promotes breezy conditions across much of
the forecast area for the early to middle of next work week.

Sunday will be by far the hottest day of the period, with NBM
probabilistic guidance depicting high chances (60-80%) of temps
eclipsing 105 degrees across the Columbia Basin and adjacent
valleys. Moderate odds exist for temps exceeding 110 degrees as
well, primarily for the lower Columbia Basin (40-50%). Elsewhere,
expect triple digit readings outside of our high mountain zones,
with numerous daily high temperature records in jeopardy as a result
of this particularly strong high pressure ridge.

As the aforementioned low pushes into the PacNW, it will orient the
winds aloft more SW, which may inject enough moisture to support
thunderstorm development across primarily central Oregon and up
along the east slopes of the Cascades. The 12z NAM highlights these
areas in particular on Sunday, and seeing a signal this far out does
inspire some confidence in the forecast, albeit on the lower end
still (40%) given how hot and dry we`ll be for the rest of the
weekend. Better chances for storm development look to be on Monday,
as the low really starts to move in and advect more moisture into
the area, with chances spreading towards the eastern mountains as
well (45% confidence).

Ensembles are in good agreement on this low moving in by early next
week, which will cool temperatures down by a good 10 to 15 degrees
by the midweek with highs hovering right around averages for this
time of year. Concern, however, then shifts toward an uptick in
winds that could potentially spurn critical fire weather conditions.
Confidence is only low/moderate based on what models are outputting
for wind speeds (30-40% chance in Red Flag Conditions, at least for
the east slopes of the Cascades and Columbia Basin), but based on
pattern recognition alone, ensembles still key in on a classic ridge
breakdown set-up that generally leads to gusty conditions while RHs
remain below critical values after the heat we`re expecting over the
coming weekend. Evans/74

AVIATION...18z TAFs (Previous Discussion)...VFR conditions
expected, with clear skies and light, terrain driven winds
prevailing, except for BDN, RDM, and DLS which will see breezy
conditions this afternoon with gusts up to 25 kts out of the NW.
Haze will continue to obscure the horizon for many sites across the
forecast area. Evans/74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  62  96  59 102 /   0   0   0   0
ALW  67 100  65 106 /   0   0   0   0
PSC  68 101  65 105 /   0   0   0   0
YKM  62  99  61 103 /   0   0   0   0
HRI  67 101  64 105 /   0   0   0   0
ELN  65  97  62 104 /   0   0   0   0
RDM  53  93  53 100 /   0   0   0   0
LGD  60  95  60 103 /   0   0   0   0
GCD  58  98  59 105 /   0   0   0   0
DLS  64  96  64 105 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from 11 AM Saturday to 8 PM PDT Monday
     for ORZ041-044-049-050-502-503-505-507-508.

     Heat Advisory until 10 PM PDT this evening for ORZ044.

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

     Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for ORZ506-
     510-511.

WA...Excessive Heat Warning from 11 AM Saturday to 8 PM PDT Monday
     for WAZ024-026>030-521.

     Heat Advisory until 10 PM PDT this evening for WAZ026>028.

     Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for WAZ523.

&&

$$

SHORT TERM...87
LONG TERM....74
AVIATION...76