227 
FXUS66 KPDT 300958
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
258 AM PDT Fri Jun 30 2023

.SHORT TERM...Today through Sunday Night...Current radar and 
infrared satellite imagery showing dry conditions under mostly 
clear skies as an upper level ridge continues to build in from the
southwest. This ridge will peak in intensity today, providing the
hottest day in the forecast before a very slight cool down takes 
effect through the holiday weekend. High temperatures this 
afternoon will break into the mid to upper 90s across the Basin, 
Yakima Valley, and Blue Mountain foothills, with low to mid 90s 
across Central Oregon. Some of our higher populated areas in the 
Basin may reach triple digits later today, as the NBM hints at a 
51% chance of high temperatures of 100 degrees for the Tri-Cities 
area and a 41% chance for Hermiston. A widespread moderate (2 out 
of 4) HeatRisk exists across the entire Lower Columbia Basin, 
Yakima/Kittitas Valleys, and John Day Basin, which affects most 
individuals sensitive to heat - especially those without effective
cooling and/or adequate hydration. If you are planning outdoor 
activities today, try to avoid peak heating hours and drink plenty
of fluids. 

An upper level trough and associated low pressure will be nearing 
the British Columbia coast tonight, tightening pressure gradients 
against the existing ridge to provide an increase in winds across 
the Eastern Gorge and the Kittitas Valleys this evening. Peak 
west/northwest wind gusts of 30-35mph will be possible after 8PM and 
slowly subside through the early morning hours on Saturday. This 
will be a brief respite before the trough axis slides just to our 
north, flattening the present ridge and reinvigorating winds through 
the aforementioned areas during the afternoon and evening as 30-
40mph wind gusts out of the west/northwest are expected. This trough 
will also lead to flow aloft shifting from southwest to more west-
northwest, advecting a drier air mass across the Pacific Northwest 
that will elevate fire weather concerns beginning late Saturday 
morning and extending through the evening. H8 to H5 RH values will 
drop from 25-50% Friday to 10-20% Saturday with precipitable 
Water (PW) values of 0.25-0.50", which is 30-60% below normal. 
Good (55- 70%) overnight RH recoveries Friday night will become 
more moderate (30-55%) Saturday night as afternoon minimum RH 
values on Saturday will plummet into the mid-teens through the 
Lower Columbia Basin and the upper-teens to low 20s for the 
Eastern Gorge and Yakima/Kittitas Valleys. These concerns have 
warranted the issuance of a Fire Weather Watch for the Eastern 
Gorge, Lower Columbia Basin, and Yakima/Kittitas Valleys Saturday 
afternoon/evening. High temperatures will be 3-5 degrees cooler on
Saturday than on Friday, with highs reaching back into the low to
mid 90s across the Lower Columbia Basin. The upper level trough 
continues to progress east into Alberta late Saturday into Sunday 
to allow for pressure gradients to slacken and high temperatures 
to cool slightly (1-3 degrees). Afternoon RH values will also 
rebound back into the upper- teens to low-20s through the Basin as
locally breezy winds of 20-25 mph will be possible for the 
Kittitas Valley, Eastern Gorge, and Central Oregon. These lower 
winds coupled with the slightly increased RH values are expected 
to alleviate fire weather concerns on Sunday. 75



.LONG TERM...Monday through Friday...Weather concerns during the 
long term period are relatively minor and will be the above seasonal 
temperatures and occasionally breezy winds.  Monday's high 
temperatures in the 80s to mid 90s for most of the CWA will be 
around 5-10 degrees above seasonal average.  The high temperatures 
the remainder of the week will be about 10-15 degrees above seasonal 
average, and there will be a few areas in and around the Lower 
Columbia Basin that will observe 100-105.  The NBM has been 
consistent that temperatures exceeding 105 is less than 10%.  There 
will not be much recovery in overnight cooling for the lower 
elevations as 60-65F low temperatures are expected. This will not be 
a major heat wave but one that will continue to be addressed in 
social media posts and wx graphics. 

Next week will be met with a westerly flow aloft that will keep the 
850mb thermal ridge and surface thermal trough suppressed.  Surface 
winds during the daytime will predominantly come from the NNW due to 
the position of the surface thermal trough to the south.  Just about 
all forecast zones will have a 75% chance of observing gusts 15-25 
mph during the week with the strongest winds through the typically 
windy areas of the eastern CR Gorge and Kittitas Valley but also 
over central and north central OR along the Columbia Deschutes 
Plateau.  Although the wind gusts will not be anything substantial, 
gusts at 15-25 mph will pose problems for fire control in dry grassy 
fuels. Outdoor burning should really be avoided.

Models are in very good agreement through Thursday.  There are hints 
of a weak shortwave trough along the southern OR and northern CA 
coast by Friday.  Nearly 90% of the Canadian ensemble members show a 
well defined trough and are more aggressive with the breakdown of 
the upper ridge, while only 35% of the GEFS and 20% of the ECMWF ENS 
members cluster towards this solution.  The NBM keeps a dry forecast 
for now which looks reasonable due to uncertainty for the Day 8 
forecast.  Models do, however, point towards more instability by the 
end of next week.   Wister/85


&&

.AVIATION...06Z TAFs...VFR conditions are expected (99-100% 
chance) for all TAF sites over the next 24 hours. Mostly clear skies 
and terrain-driven winds of less than 10 kts are forecast overnight 
for all sites. Friday, winds of 10 kts or less with brief afternoon 
and evening gusts to 15 kts are forecast for all but KDLS where 
winds of 15 kts with gusts of 25 kts are anticipated. Plunkett/86


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  94  60  91  55 /   0   0   0   0 
ALW  98  63  94  60 /   0   0   0   0 
PSC  99  65  96  61 /   0   0   0   0 
YKM  95  61  91  57 /   0   0   0   0 
HRI  98  64  95  59 /   0   0   0   0 
ELN  90  58  84  58 /   0   0   0   0 
RDM  92  55  90  51 /   0   0   0   0 
LGD  91  59  89  54 /   0   0   0   0 
GCD  93  57  90  54 /   0   0   0   0 
DLS  93  61  90  59 /   0   0   0   0 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Saturday morning through Saturday 
     evening for ORZ639-641.

WA...Fire Weather Watch from Saturday morning through Saturday 
     evening for WAZ690-691.

&&

$$

SHORT TERM...75
LONG TERM....85
AVIATION...86