Excessive Heat in Oregon, July 25 to 31, 2022

Area Forecast Discussion
National Weather Service Pendleton OR
1025 PM PDT Sun Jul 24 2022

Updated Aviation Discussion

.SHORT TERM...Today through Tuesday night. Area’s sensible
weather concern revolves around the upcoming heat wave and
increased heat risk. Temperatures increase tomorrow though the
peak of the heat wave appears to be mid-late work week. Start to
see level 3 HeatRisk across parts of south central WA into the OR
Lower Basin and Gorge Monday with widespread level 3 across much
of south central WA into the foothills of the Blues and north
central OR. Otherwise, an innocuous surface pattern will largely
prevail under the upper ridge as it builds today in the eastern
North Pacific then shifts to be over the Pacific Northwest
Tuesday. As such, fire weather concerns will be limited given
light surface winds in the short term despite the hot, dry
conditions and poor-fair overnight RH recovery.

Latest water vapor imagery shows the mid-level ridge circulation
well with the ridge building into the eastern North Pacific,
meanwhile increasing 500 mb heights rises spreading across the
interior Pacific Northwest today as a shortwave trough departs and
the upper high builds upstream. Highs will increasing Monday by 4-8
degrees with highs in the upper 90s to 105 across the lower
elevations into central OR. The 24-hr heat risk across parts of
south central WA into the OR Lower Basin and Gorge starts to reach
level 3 in areas Monday owing mainly to daytime highs.

Tuesday highs increase again by another 3-5 degrees or so with
temperatures in parts of the Lower Basin highly likely to read 104-
108 with central OR seeing highs around 100-102. Meantime, the
affect of the heat wave on lows starts to be felt where there will
be an enhancement in the heat as lows are expected to be well
outside normal by 8-12 degrees. Lower elevations are anticipated to
see lows only reach the mid 60s to near 70 in the Basin, Gorge, and
Foothills of the Blues Tuesday morning. Confidence in the short term
temperatures is high. Notably, an atypically warmer than normal air
mass will be in place in the lower troposphere. 850 mb temps seen
aloft this morning at OTX read ~20 C that is near the 90th sounding
per the SPC sounding climatology. Furthermore, confidence is
increased given the hot ensemble 850 mb temperature and the Max T
forecast envelope between the GEFS and EPS. The latter 850 hPa mean
forecasts exceeds the 90th percentile Monday and the 97.5th
percentile Tuesday for this time of year with respective to climo
too. Lastly, the forecast envelope between hi-res guidance from the
HREF and UW hi-res appear reasonable as well. Thus conditions are
favorable for the upcoming heat given the expected ample sunshine,
deep mixing, and anomalously warm temps aloft. 80

.LONG TERM...Wednesday through Sunday...The primary weather
feature of note in the extended period continues to be a long
duration heat event already well underway come Wednesday. High
temperatures are projected to climb near daily records each
afternoon through at least Friday for parts of the CWA like the
lower Columbia Basin accompanied by warm overnight low
temperatures in the 60s and 70s. This combination results in High
to Very High HeatRisk, especially for lower elevation areas, with
the aforementioned multi-day duration a particular cause for
concern. Temperatures finally begin to trend a little lower late
in the period as the ridge slowly deteriorates.

On Wednesday a robust ridge of high pressure will be situated over
the Pacific Northwest, persisting into the early part of the
weekend. Ensemble and deterministic guidance are in a excellent
agreement regarding the overall pattern through Friday although one
noteworthy discrepancy exists regarding a subtle ridge-riding
shortwave moving up from northern California into Oregon on
Wednesday. All the parameters needed to support elevated convection
like 700-300mb moisture and instability appear minimal at best, and
the forcing provided by the wave feature isn’t impressive either.
Still, the NAM and GFS suggest at least a slight chance(10-15
percent) of a high based T-storm developing over central Oregon
Cascades where the previously mentioned convection parameters appear
best aligned. Other guidance like the ECMWF deterministic and
various ensemble systems depict this feature in a weaker state,
thus no activity. Whether anything develops is still to be
determined but a slight chance for T-storms was added to western
Deschutes County for Wednesday afternoon and evening.

Outside of the slight chance for convection Wednesday the focus
remains on the very hot temperatures through the rest of the week.
Guidance has trended a degree or two warmer Wednesday into Friday
with ensembles maintaining a very tight spread between their
individual member projected temperatures around the region;
confidence in this event continues to be high. Exploring GEFS and
ECMWF ensemble systems further, it appears increasing likely parts
of the lower Columbia Basin, particularly near Tri-Cities, may
eclipse 110 degrees for three consecutive days(Wed-Fri).  Excellent
isolation and boundary layer mixing during the daytime hours
combined with exceedingly anomalous temperatures aloft around 850-
600mb support to this scenario as well. With all this in mind heat
related impacts will be a significant concern for the population
centers of the lower Columbia Basin, likely exacerbated due to the
abnormal length of this event and overnight low temperatures in the
70s providing little relief.

Uncertainty begins to grow in the large scale pattern Friday night
into the weekend. Cluster analysis reveals a split between ensemble
systems as to how the ridge breaks down and progresses into early
next week, having ramifications on our eventual transition back to
seasonable temperatures.  Many of the GEFS members along with the
deterministic GFS depict the ridge degrading quicker than the Grand
Ensemble Mean, pushing a shortwave trough into northern Washington
Saturday. This solution likely leads to a more noticeable drop in
temperatures for Saturday afternoon but breezier afternoon winds;
fire danger may become elevated. Conversely a large portion of the
ECMWF members maintain the ridge into early next week which would
extended the heatwave another few days, albeit not to the same
severity as Tuesday-Friday. At the very least all of these ensemble
systems agree on a long-wave trough progressing the large scale
pattern just outside of the extended period. Schuldt/99

&&

.AVIATION...06Z TAFs...VFR conditions to prevail through the
period. High clouds moving over the region from the north will
provide periodic few-sct CIGS AOA 25kft through tonight. Diurnally
driven winds will continue to remain light, less than 12kts,
through the period. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  62 100  65 102 /   0   0   0   0
ALW  65 101  67 105 /   0   0   0   0
PSC  66 103  69 106 /   0   0   0   0
YKM  62 102  65 105 /   0   0   0   0
HRI  64 104  68 106 /   0   0   0   0
ELN  62 100  65 104 /   0   0   0   0
RDM  49  98  57 102 /   0   0   0   0
LGD  56  94  62  98 /   0   0   0   0
GCD  54  97  60 101 /   0   0   0   0
DLS  66 104  69 107 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from 11 AM Monday to 11 PM PDT Friday for
     ORZ041-044.

     Excessive Heat Watch from Tuesday morning through Friday evening
     for ORZ049-502-503-505-507>511.

     Excessive Heat Watch from Wednesday afternoon through Friday
     evening for ORZ050.

WA...Excessive Heat Warning from 11 AM Monday to 11 PM PDT Friday for
     WAZ024-026>028.

     Excessive Heat Watch from Tuesday morning through Friday evening
     for WAZ029-030-520-521.

&&

SHORT TERM...80
LONG TERM....99
AVIATION...82