232
FXUS66 KPDT 021719
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1019 AM PDT Tue Jul 2 2024

Updated Aviation Discussion

.AVIATION...18z TAFs...VFR conditions expected. Outside of some
moderate winds out of the W/NW, aviation impacts are expected to
be limited over the next 24 hours. Skies will remain clear, with
PDT and DLS most vulnerable to breezy conditions, where gusts
could exceed 25 to 30 kts at times. Evans/74

&&

.PREV DISCUSSION... /issued 448 AM PDT Tue Jul 2 2024/

SHORT TERM...Today through Thursday night...Limited concerns in
the short term period. The main sensible weather highlights
include:
- Prevailing near seasonable high temperatures today and tomorrow.
- Elevated fire weather concerns today stemming from dry and
  breezy to locally windy condition with the strongest winds
  across the Cascade gaps, eastern Columbia Gorge spilling into
  north central OR and Kittitas Valley.
- Hot temperatures with highs 6-12 degrees above normal on
  Thursday.

A shift from a large scale cyclonic flow regime to an anticyclonic
flow regime will take place in the short term. Northwest flow
aloft currently overhead with an extensive upper-level trough over
the northwest and north central CONUS will give way to an upper
ridge in the eastern North Pacific with the ridge axis evolving
east to be near/over the PacNW coast by Thursday. Guidance is in
very good agreement with the overall synoptic pattern. Of which,
the ECMWF ensemble mean 500 mb height forecast for the center of
the upper high is forecast to fall outside model climo for this
time of year from now through Thursday night with these anomalous
heights and ridge axis extending north across the PacNW coast by
Thursday. A shortwave trough apparent in water vapor imagery west
of Haida Gwaii that is embedded in the background flow is expected
to rotate and move into northeast WA/northern ID today. This will
provide large scale forcing for ascent outside the area to the
far north and northeast. Of which, the combination of scant
moisture with the best forcing outside our area and weak lapse
rates will preclude any threat for precip/storms. High confidence
(>90%) with the latest HREF bolstering this outcome that shows
the best chances for dBZ >40 dBZ and 4-hr prob of thunder confined
to extreme northeast WA into western MT. Otherwise, little to
slight uptick in temperatures Wednesday that will give way to
above average highs by Thursday. Limited heat risk signal on
Thursday with highs 6-12 degrees above normal, greatest departures
across central OR, Kittitas Valley, eastern Gorge, and the Lower
Basin.

A modest cross-Cascade gradient sharpening today in tandem with
increasing flow aloft with an enhanced belt of 700 hPa winds
moving in will promote breezy to locally windy conditions late
today into early tonight. Current thinking is the strongest winds
will be most likely along the Kittitas breezeway with KELN likely
peaking 35-45 mph. While cannot rule out an isolated ~45 mph gust
(50-70% chance) there, thinking the frequency and coverage does
not necessitate a wind advisory at this time.

LONG TERM...Friday through Tuesday...The first heat wave of the
summer looks to be more likely than not with triple digit
temperatures forecast widely across lower elevations Friday-
Tuesday, albeit with some increasing spread early next week. The
main highlights include:
- High-level moderate HeatRisk (category 2) to major HeatRisk
  (Category 3) Friday through Tuesday with the greatest confidence
  in triple digits this weekend - a good chance for some pockets
  of extreme HeatRisk (category 4) as well.
- Less relief by way of mild, elevated overnight lows starting
  Friday night with lows 6-12 degrees above normal across the
  lower elevations.
- Dry and light breezes through the weekend.

Increased confidence in anomalous high temperatures affecting the
region. Latest ECMWF extreme forecast index showing unusual
temperatures highly likely (values of 0.6-0.8) based on forecast
agreement amongst ensemble members through Monday. ECMWF ensemble
mean 500 mb height forecast keeps the upper-ridge over the PacNW
Sunday, albeit its 500 mb height forecast not as impressive
compared to earlier in the period with its forecast still
exceeding the 99th percentile by Sunday and then diminishing
further on Monday. These less anomalous height forecasts speaks
somewhat to the uncertainty and increasing spread in the
temperature forecast starting early next week. Clustering
scenarios show the potential for weak shortwave trough/disturbance
affecting the area by way of lower heights along the eastern
periphery of the upper-ridge Sunday and Monday. That said, this
possibility appears low (less than 30%) but bears monitoring,
alongside a very low threat for isolated precip/storms late in
the long term. By Tuesday, there is an increased possibility of
the upper-ridge weakening in magnitude and/or shifting more east.
That said, odds still favor the heat to continue into early next
week.

Chances for exceeding 100 F peaks on Saturday and Sunday across
the lower elevations with chances commonly seen to be greater than
80%. These chances start to decline Monday with the Lower Basin
and foothills of the Blues falling to 50-70% for exceeding 100 F,
and fall around 5-10% again on Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  83  55  83  54 /   0   0   0   0
ALW  86  57  86  57 /   0   0   0   0
PSC  89  59  89  58 /   0   0   0   0
YKM  87  55  89  54 /   0   0   0   0
HRI  88  58  89  56 /   0   0   0   0
ELN  78  55  85  55 /   0   0   0   0
RDM  82  46  84  48 /   0   0   0   0
LGD  79  50  78  50 /   0   0   0   0
GCD  81  48  83  49 /   0   0   0   0
DLS  82  56  87  59 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...91
LONG TERM....80
AVIATION...74