913
FXUS66 KPDT 032150
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
250 PM PDT Wed Jul 3 2024

.SHORT TERM...Tonight through Friday night...Water vapor imagery
reveals an amplifying upper-level ridge offshore in the Pacific, a
harbinger of the much-advertised upcoming heat wave.

Ensemble guidance is in excellent agreement (100% chance) that
the aforementioned ridge will continue to amplify through the
week, slowly migrating eastward such that mid-level height rises
are anticipated each day over the forecast area. This will support
a warming trend of 5-10 degrees each day through Friday, culminating
in widespread afternoon high temperatures in the 90s to lower
100s by Friday afternoon. NBM probabilities suggest the chance of
exceeding 100 degrees is broadly 20-50% across the lower
elevations, except locally 60-90% in the hottest areas of the
eastern Columbia River Gorge as well as central and north-central
OR. In tandem with modest overnight temperature recovery (lows in
the mid-50s to upper 60s), this will facilitate Moderate to Major
HeatRisk across the lower elevations.

After coordination, we have opted to issue a Heat Advisory for
the Lower Slopes of the Eastern Washington Cascades Crest, valid
noon Friday until 10PM PDT Tuesday. This zone joins our non-
mountain zones (except the Grande Ronde Valley) where existing
heat highlights (Advisory or Warning) are in effect for the same
period. While mountain zones will certainly observe above-normal
temperatures, forecast lows in the 50s preclude HeatRisk values
above Moderate at this time and do not support Heat Advisories.
Should confidence in warmer overnight lows develop, additional
highlights may be needed for these areas.

In terms of fire weather concerns, the combination of a dry air
mass and hot temperatures will induce very low afternoon RHs in
the single digits and teens. However, surface pressure gradients
are not anticipated to be supportive of more than locally breezy
winds each afternoon and evening through the Cascade gaps and
across central OR. Thus, Red Flag conditions are not forecast at
this time.

While heat highlights start Friday afternoon, the bulk of the
heat wave will commence Saturday. More details are given in the
discussion below. Plunkett/86

&&

.LONG TERM...Saturday through Wednesday...There is very good model
agreement with the building of a strong and persistent upper
ridge over the west through the extended (and likely beyond). The
center of the ridge will actually slide southeast through Monday,
and remain over California, then reposition itself and strengthen
further for the early and middle part of next week.

What this means is that very hot temperatures will linger into
next week, with virtually no chance of any precipitation.
Excessive heat warnings and heat advisories have been issued
through Tuesday at this time and will monitor for any possible
extensions.

HeatRisk values will generally be Moderate to Major, with some
locations even reaching the Extreme category. Anyone who is
outside for long period of time, and especially those who are heat
sensitive should take precautions during this extended heat wave,
including adequate hydration and trying to spend some time
indoors.

Highs across the lower elevations will generally be 100 to 105
degrees (90-100%) in most areas with 105 to 110 degrees in the
Columbia Basin (90-100%). These temperatures would be about 20
degrees above normal. Some records temperatures are also expected.

ECMWF EFI values for high temperatures range from 0.6 to 0.9
across the region (generally from west to east) and increasing
though early next week.

The ensembles are in generally good agreement as well and
supportive of the strong ridge solution (>60%) beyond midweek.
The GFS ensembles have at least several members >=110 degrees in
the Columbia Basin Monday through Wednesday. The ECMWF has many
members. The ECMWF may be overdone while the GFS is underdone, but
guidance does indicate at least some potential for high
temperatures >=110 degrees in the Columbia Basin, especially early
next week. At this point the most likely days would be Monday-
Wednesday (with 50% at best at this time).

&&

.AVIATION...18Z TAFS...VFR conditions will continue (100%) through
the next week. Today is likely the last breezy day outside of any
local breezes as strong high pressure builds over the area into
the weekend. DLS will continue to see gusts in the 20 to 25 kt
range through the evening. Some local breeziness is possible
elsewhere, though for the most part they will be 10 kts or less.
All sites will be 10 kts or less on Thursday and beyond.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  54  90  58  95 /   0   0   0   0
ALW  57  93  60  98 /   0   0   0   0
PSC  58  94  62 100 /   0   0   0   0
YKM  54  93  59  99 /   0   0   0   0
HRI  56  95  59 100 /   0   0   0   0
ELN  56  93  59  99 /   0   0   0   0
RDM  48  92  54  98 /   0   0   0   0
LGD  51  87  55  91 /   0   0   0   0
GCD  50  91  55  95 /   0   0   0   0
DLS  59  97  64 104 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from noon Friday to 10 PM PDT Tuesday for
     ORZ041-044-507-508-510.

     Heat Advisory from noon Friday to 10 PM PDT Tuesday for ORZ505-
     511.

WA...Excessive Heat Warning from noon Friday to 10 PM PDT Tuesday for
     WAZ024-026>029-521.

     Heat Advisory from noon Friday to 10 PM PDT Tuesday for WAZ523.

&&

$$

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