839
FXUS66 KPDT 200918
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
218 AM PDT Thu Jun 20 2024

.SHORT TERM...Today through Friday...

 Bottom Line Up Front

1. Dry conditions with isolated dry thunderstorms along the eastern
mountains.

2. Hottest day will be Saturday with moderate heat risk.

With the northerly flow in place and the daily run of a surface
thermal trough, dry conditions will prevail through the period.
However, looking at some of the CAMs models, there will be some
instability moving across the eastern mountains. Model derived
sounding are showing MUCAPE values well above 400 J/kg with lifted
indexes of -1 to -4, lapse rates of 8.5 C/kg and bulk shear nearing
40 kts. PWATs are moderate with 0.50-0.65 inches available. Given
the ingredients as well as daytime heating and orographic lift, one
can not rule out the possibilities of some isolated thunderstorms
over the eastern mountains tomorrow afternoon (less than 25%
probabilities). Not only are the ingredients available along the
eastern mountains, but CAMs models show there are decent amounts of
MUCAPE (250 J/kg) along the WA Cascades. However, probabilities of
isolated thunderstorms along the eastern slopes are less than 10%.

Models are in firm agreement with the upper level flow being from
the northwest with a strong surface thermal trough making its way
into the region. Models show Saturday to be the day with the
strongest trough set up which will bring temperatures above Normal.
EFI shows temperatures to be well above normal temperatures with
over 70% of the raw ensembles putting the majority of the region in
low to mid 90s with some isolated areas in the Basin in the high
90s. NBM is showing a moderate heat risk across the majority of the
Basin as well as through the Gorge and portions of the southern
Blues with very isolated locations seeing high risk. If you are out
and about this weekend, please plan appropriately. For more
information go to www.weather.gov/heat. Bennese/90

.LONG TERM...Sunday through Thursday...A dry cold front will result
in gusty winds on Sunday.  Models have consistently advertised this
for at least several days now, so the confidence is high that it
will be breezy to windy. The NBM probability of gusts >= 22 kts is
over 90% for most of the forecast area and the probability of gusts
>= 34 kts is 70-100% in the Lower Columbia Basin, eastern CR Gorge,
Simcoe Highlands, and the Kittitas Valley. For gusts >=41 kts, the
probabilities are around 80% for the Kittitas Valley, 30% for the
eastern CR Gorge, and 15% or less elsewhere. Confidence is also high
that the relative humidity will be in the teens for areas in and
around the Lower Columbia Basin and across south central and
southeast Oregon.  All of the mean ensembles are showing dry air
aloft behind the front...less than 10% at 700mb.  The primary
weather concerns for Sunday will be fire weather, and highlights may
be needed as we approach the weekend.

The westerly flow aloft across the eastern Pacific and the PacNW
will begin to buckle in response to a deep closed low developing off
the Gulf of Alaska.  By Tuesday, a large trough will develop between
130-150W, and the westerly flow over WA/OR will back to the
southwest. Models are not hinting at any convection and all show
very weak or no surface-based instability.  However, there is some
elevated instability looking at the GFS with mid-level theta-e
decreasing with height and DIV Q aloft.  Usually, these are signs of
isolated high based storms.  For now, will not mention thunderstorms
for Tuesday until confidence improves.  At this time, confidence is
only 15%.

There are differences in the model progs for Wed-Thur, but nothing
significant. Main difference is the amplitude of the trough as it
moves inland, but less than 25% of the ensembles from the GEFS,
ECMWF, and GEPS advertise a flat trough. The rest are showing a
fairly organized trough over WA/OR Thursday. Therefore, Thursday is
forecast to be a little cooler with 20-35% chance of showers along
the Cascades and the eastern mountains. Wister/85


&&

.AVIATION...12Z TAFs...VFR conditions expected over the next 24
hours. Winds 10 knots or less except BDN/RDM tomorrow afternoon
when gusts between 10-20 knots possible. SKC overnight but high
level clouds will move over, generally SCT to BKN at 20-25k feet.
Goatley/87


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  87  54  89  56 /   0   0   0   0
ALW  91  57  92  60 /   0   0   0   0
PSC  92  57  94  60 /   0   0   0   0
YKM  88  56  93  59 /   0   0   0   0
HRI  93  56  95  60 /   0   0   0   0
ELN  86  54  90  59 /   0   0   0   0
RDM  83  50  88  53 /   0   0   0   0
LGD  83  53  85  54 /   0   0   0   0
GCD  85  50  89  55 /   0   0   0   0
DLS  92  61  94  63 /   0   0   0   0

&&

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

$$

SHORT TERM...90
LONG TERM....85
AVIATION...87