195
FXUS66 KPDT 031215 CCA
AFDPDT

Area Forecast Discussion...CORRECTED.
National Weather Service Pendleton OR
511 AM PDT Wed Jul 3 2024

.SHORT TERM...Today through Thursday...A dry northwesterly flow
will remain with a ridge of high pressure offshore of the region.
Wind gusts (20-30 mph) will occur along the Columbia River Gorge
and Kittitas valley now through early this morning. Wind
conditions should decrease to light around 10 mph or less starting
Wednesday afternoon hours (80-100% confidence). Otherwise, the
overall pattern and conditions will be constant with persistent
conditions for temperatures and winds.

As the ridge continues over PacNW, starting Thursday will be the
beginning of a long hot dry period into next week. High temperatures
will increase to the lower to mid 90s across the lower elevations
and 80s in the mountains. Few clouds could pass by but overall clear
skies throughout this period, providing easy viewing of evening
firework displays for Independence Day. Dry conditions will persist
with low relative humidity in the teens to lower 20s. Feaster/97

.LONG TERM...Thursday night through Wednesday...A period of very
unusually hot temperatures and warm overnight lows is the main
sensible weather concern. Highs approaching 20 degrees above
normal will reign beginning Friday and prevail into early next
week. Meantime, lows will be 10-15 degrees above seasonable
normals. The combination of daytime highs with limited relief
overnight will promote an increased risk of heat-related impacts
with Major (category 3) to locally Extreme (Category 4) HeatRisk,
notably across the lower elevations of the Lower Columbia Basin,
south central WA, eastern Gorge, and north central OR into the
foothills of the Blues. An Excessive Heat Warning was issued
starting Friday through Tuesday, though there is some uncertainty
with the duration of the heat event with potential to extend it
possibly. The limited relief overnight there will enhance the heat
wave. Of note, Tri-Cities are forecast to hit or exceed 105 F five
times in a row starting Saturday (Sat to Wed) which would rank third
(tied with 2021 and 1898) for the number of consecutive days greater
than or equal to 105 F.

Hot conditions extend into central Oregon and the John Day Basin,
however, modest overnight relief is expected at this time thus a
Heat Advisory was issued Friday-Tuesday. This stems from low
temperatures being cooler and contributing less to the overall
heat stress. Mountains will see warmer than normal temperatures
too, but the level of heat will affect mostly those heat-
sensitive or without cooling/hydration with more adequate relief
overnight.

Ensemble guidance is in good agreement with the large scale
pattern starting Thursday night with an upper-level ridge expected
to be just offshore the West Coast and anticyclonic flow
dominating. ECMWF ensemble mean 500 mb height forecasts at the
center of the upper high continue to fall outside climo Thursday
night. Little movement in the upper ridge anticipated by Sunday
with it then over the West Coast with mean 500 mb heights
forecast to still exceed the 99.5th percentile. Guidance shows the
upper ridge then evolves eastward Monday and Tuesday with the
upper ridge more over the Northern Intermountain West by the
latter day. Limited differences in guidance that affect our
sensible weather this weekend through Monday based on clustering
scenarios with very unusually highs forecast. This is supported by
increasing ECMWF EFI for MaxT over the weekend through Tuesday
with the Sunday-Tuesday looking to hold the hottest temperatures
in the lower elevations/Lower Basin (EFI values of 0.7-0.9). Of
note, clustering highlights a potential open wave disturbance
that could knock down highs (~20%) Tuesday. However, much of the
synoptic outcomes favor a prolonged heat wave with continued
support for heat extending to Wednesday (confidence 70-80%).

&&

.AVIATION...12Z TAFS...VFR conditions with clear skies throughout
the day. Gusty northwesterly winds will arrive for KDLS around 25
kts early afternoon before decreasing tonight (high confidence).
Elsewhere, winds at other terminals will be 10 kts or less.
Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  83  54  90  55 /   0   0   0   0
ALW  87  57  93  57 /   0   0   0   0
PSC  90  58  95  60 /   0   0   0   0
YKM  89  54  94  56 /   0   0   0   0
HRI  89  56  95  57 /   0   0   0   0
ELN  86  56  92  56 /   0   0   0   0
RDM  85  48  92  51 /   0   0   0   0
LGD  80  51  87  52 /   0   0   0   0
GCD  83  50  91  52 /   0   0   0   0
DLS  88  59  97  64 /   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.

&&

$$

SHORT TERM...97
LONG TERM....80
AVIATION...97

CORRECTED TYPO FOR THE NUMBER OF CONSECUTIVE 105 DEGREE DAYS AT TRI-
CITIES