059
FXUS66 KPDT 151721
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1021 AM PDT Sat Aug 15 2026

.KEY MESSAGES...
1. Isolated to scattered thunderstorms with abundant lightning and
   gusty outflow winds
                 *Red Flag Warning In Effect*

2. Sunday continued southwest flow will bring chances of
   thunderstorms and showers through Monday.

3. Increased Gap winds Tuesday

&&

.DISCUSSION...
Current nighttime satellite shows some mid level clouds lingering
over the region. Radar shows a few returns along the eastern slopes
of the Cascades but no thunderstorms within the cells. Overnight
temperatures will be in mostly in the 50s with isolated areas in the
Basin seeing low 60s.

Southwest flow aloft will continue over the region with a trough
just off the coast. Models show a shortwave will make its way into
the region bringing with it increased moisture form the southwest. T
his will lead to increased chances of thunderstorms and showers over
the Cascades as well as the eastern mountains again today. Looking
at forecasted NAM soundings, there are MUCAPE values between 250-750
J/kg with isolated pockets of near 1000 J/kg, LIs of -3 to -4, lapse
rates between 1-10 C/km and effective bulk shear of 18-22 kts. HREF
lightning density paintball shows much of the lightning forming
along the crest and east slopes of the Cascades as well as across
the eastern mountains beginning with highest density being after 1
PM. NBM raw ensembles show 30-40% chances of thunderstorms occurring
in those same region. Even with the increased chances of showers
accompanying these storms, there is moderate confidence (60-70%) of
elevated fire weather conditions developing due to lightning
potential outside of rain cores and gusty outflow winds. Therefore a
Red Flag Warning has been issued for these areas through 9 PM
tonight.

Sunday through Monday models show an upper level low off the coast
moving towards the south and deepening the southwest flow across the
region. Models do show some moisture being swept up into the region
leaving slight chances (10-20%) of showers and thunderstorms
occurring Sunday afternoon, especially along the Wallowa Mountains.
There are also chances (10-15%) of thunderstorms in central OR as
well as the WA Cascades. Monday also shows slight chances (10-15%)
of thunderstorms along the same areas.

Tuesday models show a bit of split flow across the region as an
upper level shortwave moves south out of B.C. bringing northwest
flow aloft across the northern portion of the CWA while the trough
remains just off shore and is pushing southwest flow into the
southern portion of the CWA. The northwest flow aloft will allow for
breezy gap winds to form Tuesday with NBM raw ensembles showing
sustained winds speeds between 15-20 mph with 50-70% of the
ensembles in agreement.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...VFR conditions to
prevail through a majority of the period, with MVFR conditions
possible through the remainder of the morning into the early
afternoon. An upper weather system moving through the area early
this morning continues to produce showers/thunderstorms that
are impacting sites PDT/ALW/PSC. These storms should clear out
from PDT around 18Z, then clear ALW/PSC between 19Z-20Z.
Thunderstorms will continue to be possible along the WA Cascade
east slopes and the Blue mountains through the afternoon and
evening. There is a low chance (~15%) of shower/thunderstorm
impacts at sites PDT/ALW between 21Z-00Z.

Winds will increase to 12-20kts with gusts 20-30kts at site DLS
this afternoon, becoming light around or after 05Z. Breezy winds
will develop at sites RDM/BDN with gusts up to 20kts this
afternoon, becoming light late in the evening hours. Winds will
otherwise remain light through the period at all other sites.
Lawhorn/82

&&

.FIRE WEATHER...
Continued monsoonal moisture will bring thunderstorm
chances across the region again today with 30-40% chances for the
Blues Mountains and Wallow Mountains. Eastern slopes of the WA
Cascades will see 10-15% chances for thunderstorms today as well.
Sunday and Monday will also continue to see 10-15% chances of
thunderstorms for the eastern mountains s well as the WA Cascades. A
slight pattern shift Monday night into Tuesday will bring breezy gap
winds of 15-20 mph sustained.

&&

.Preliminary Point Temps/PoPs...
PDT  87  56  88  58 /  20   0   0   0
ALW  90  62  90  64 /  30  10   0   0
PSC  92  57  93  59 /  20   0   0   0
YKM  89  60  91  61 /  20  10   0   0
HRI  90  60  91  62 /  20   0   0   0
ELN  85  58  86  59 /  20  10   0   0
RDM  85  49  86  52 /  20  10   0   0
LGD  86  54  89  57 /  70  20  10   0
GCD  88  54  91  56 /  40   0   0   0
DLS  90  63  89  62 /  20   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523.
     Red Flag Warning until 9 PM PDT this evening for WAZ692-693.
     Air Quality Alert until noon PDT today for WAZ027-521.
OR...Air Quality Alert until noon PDT Monday for ORZ041-503-505-506-
     508>511.
     Red Flag Warning until 9 PM PDT this evening for ORZ692>695-
     699.

&&

$$

DISCUSSION...90
AVIATION...82
FIRE WEATHER...90