516
FXUS66 KPDT 071025
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
325 AM PDT Fri Jun 7 2024

.SHORT TERM...Today through Sunday...

Key Messages:

1. Warm temperatures through the weekend.

2. Thunderstorm potential each day, peaking Sunday.

Current radar and infrared satellite imagery showing dry
conditions as some high level clouds stream in across the Basin
from the west. These conditions are a result of an upper level
ridge that has built over much of the western CONUS on Thursday,
with a more pronounced ridge developing over the Pacific Northwest
today into early Saturday. Today`s building ridge, coupled with
southwest flow aloft, will attribute to warming conditions through
Saturday. High temperatures on Thursday stayed in the upper 80s
for much of the Basin, with the only exception being The Dalles
which recorded a high of 90 degrees. Highs today will bump up 1
to 2 degrees from yesterday, with Tri-Cities expected to join the
Dalles in the low 90s. Most of the Basin, Central Oregon, and the
Yakima Valley will stay in the upper 80s. Confidence in these
high temperatures is high (90%) as the NBM suggests an 80% chance
at the Dalles, 53% for Tri-Cities, and 30% for Hermiston and
Redmond reaching 90 degrees or above this afternoon. An
approaching upper level trough on Saturday will enhance southwest
flow to increase high temperatures another 2 to 5 degrees, as the
Tri-Cities, Hermiston, the Dalles, and Yakima are all forecast to
reach into the low 90s (which is about 10 degrees above normal).
Confidence is high (90%) in these areas reaching highs in the low
90s, with the NBM highlighting an 87% at Tri- Cities, 86% at the
Dalles, 71% for Hermiston, 61% at Yakima, and 35% for Pendleton
reaching 90 degrees or above Saturday afternoon. Clouds will be
increasing Saturday afternoon and evening as an upper level trough
moves into the region, keeping overnight temperatures mild as
Sunday morning lows only drop into the low to mid-60s through the
Gorge, Lower Columbia Basin, Yakima Valley, and the Blue Mountain
foothills. High temperatures will cool about 2 to 5 degrees on
Sunday as the incoming system keeps clouds overhead and slight
chances for rain develops across Central Oregon and our mountain
zones. This decrease is minimal due to the continued southwest
flow aloft and the overall lack of moisture with the system.

The secondary concern resides with a slight chance (10-25%) of
developing afternoon thunderstorms each day, with the greatest
chance (15-25%) occurring on Sunday. There is also a potential
for overnight thunderstorms Saturday into Sunday over Deschutes,
Crook, and Grant counties. These conditions are a result from a
weak shortwave undercutting the building upper level ridge today,
leading to a slight chance (10%) of isolated thunderstorms over
Deschutes, southern Crook, and southern Grant counties. Conditions
are fairly marginal today, with most unstable CAPE (MUCAPE) of
100-150 J/kg, 10-20 knots of low level shear, and low level lapse
rates of 6-7 C/km via the HREF and RAP. These parameters suggest
low confidence (10%) in developing storms, with any developing
cells being brief and unable to strengthen due to the lack of
shear. The upper level ridge begins to exit to our east on
Saturday, as an upper level trough and associated frontal system
approach the coast. This system will begin to bring rain chances
across Central Oregon by the afternoon before increasing chances
and extending north across the Blue Mountains, Cascades, and
portions of the Basin. Regarding thunderstorm potential for
Saturday, it will begin over Deschutes county early in the
afternoon before extending north and east into Jefferson, Crook,
Grant, and southern Wheeler Counties through the evening.
Conditions are slightly enhanced for thunderstorm development on
Saturday as the HREF suggests MUCAPE of 200-300 J/kg, 35-45 knots
of low level shear, and low level lapse rates of 7-8 C/km via the
HREF and RAP. An incoming surface cold front from the northeast
late Saturday into Sunday will keep MUCAPE elevated at 150-250
J/kg and low level shear between 35 and 45 knots over eastern
Deschutes, Crook, and western Grant counties. These parameters
Saturday and Saturday night provide low confidence (20%) of
isolated thunderstorms forming over the aforementioned areas,
with high confidence (80-90%) in storms staying sub-severe.

The main upper level trough and frontal system passes over the
area on Sunday, bringing the best chances (15-25%) of developing
thunderstorms across Deschutes, Crook, Grant, Union, and Wallowa
Counties. The GFS and NAM both advertise MUCAPE of 400-600 J/kg
and 35-45 knots of low level shear. Low level lapse rates are not
too impressive at 6-7 C/km, but precipitable water of 0.7-0.9"
(100-130%) hint at an advanced trigger for convection and the
potential for moderate to heavy rainfall under any developing
storm cells. Even with these more enhanced thunderstorm parameters
Sunday, confidence is still high (80%) in storm cells staying
sub-severe as isolated, discrete cells are anticipated. However,
there is still a potential for frequent lightning, gusty winds,
and small hail with any developing storms - so stay weather aware
and have multiple ways of receiving weather alerts. 75


.LONG TERM...Monday through Friday....

Key Messages:

1) Cooler pattern in store for the region

2) Breezy to windy conditions also return

The long term looks to be staving off summer heat for a brief
period thanks to a progressive pattern initiated by the system
moving across the region at the end of the short term period.
Models show the system over this weekend departs, leaving a
transient ridge in its wake to start next week. There is high
confidence (70%) that this ridge will be a short lived feature,
and should quickly be swept out by a cold front Tuesday into
Wednesday. Behind this front, flow becomes zonal during the mid-
week period, then southwesterly on Friday in preparation for a
deep low that approaches the West Coast at that time, with
surprisingly good agreement from ensemble members. Still, there
are outliers, and around 19% of members show ridging holding on
rather than the progressive pattern, but the remainder expect some
form of offshore troughing and southwesterly flow.

With this pattern, expect a steady decay to temperatures, dropping
us back to near normal conditions during the mid-week timeframe
(upper 70`s to low 80`s), and then around 5 degrees below normal
for highs by next Friday (upper 60`s to mid to upper 70`s). There
is moderate confidence (60%) in these temperatures, but still
some uncertainty thanks to the around ~20% of outliers in
ensembles expecting ridging to hold off the progressive pattern,
which would keep us seasonably warm. But with a progressive
pattern and changing pressure gradients also comes winds. The NBM
indicates a 60-90% chance of wind gusts of around 40+ mph Monday
night into Tuesday as the cold front approaches, with a more
widespread risk of these winds at a similar chance on Tuesday. The
main areas of concern will be the Kittitas Valley, Simcoe
Highlands, and Columbia Basin/Foothills of the Blues of Oregon.
Once the front has passed and we reach the more zonal flow, winds
should subside for Wednesday and Thursday, but by Friday as the
gradients tighten with the approach of the next system, look for a
similar risk of gusty winds in the aforementioned areas once
again. We got a brief glimpse of summer, but the long term
indicates we`re getting more spring-like conditions once again.
Goatley/87


&&

.AVIATION...12Z TAFs...VFR conditions expected over the next 24
hours with a high probability (90-100%). BDN/RDM have a 10-15% of
seeing a rogue shower or possibly thunderstorm which would bring
conditions down briefly during the afternoon, but this threat is
low and would be quickly over. Otherwise SKC or some high
clouds/cirrus should be dominant. Winds 10 knots or less all sites
except BDN/RDM during the afternoon when a few gusts 15-20 knots
possible. Goatley/87


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  84  55  87  60 /   0   0   0  10
ALW  87  56  90  62 /   0   0   0   0
PSC  90  58  92  64 /   0   0   0   0
YKM  88  55  90  60 /   0   0   0   0
HRI  89  57  92  63 /   0   0   0   0
ELN  84  53  87  60 /   0   0   0   0
RDM  86  53  84  56 /   0   0   0  20
LGD  83  52  84  58 /   0   0   0  10
GCD  88  54  88  57 /   0  20  20  30
DLS  92  61  90  63 /   0   0   0   0

&&

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

$$

SHORT TERM...75
LONG TERM....87
AVIATION...87