textproduct: Pendleton

KEY MESSAGES

- Upper level high pressure builds back over the region through the midweek with warming temperatures and mostly dry conditions

- Breezy winds return Wednesday, with moderate confidence (55-60%) in elevated fire weather conditions developing Wednesday

- Near seasonable temperatures and diurnally breezy Cascade Gap winds return Thursday into the weekend

DISCUSSION

Water vapor imagery tonight shows an upper level low moving across western WA, while nighttime satellite and radar imagery shows little activity across the forecast area with only scattered showers/thunderstorms across northeast WA. Winds in the lower elevations have mostly weakened, with breezy conditions still reported through the Cascade gaps, portions of the OR Columbia Basin, and the Blue Mountain foothills.

Today through Tuesday: The upper low over western WA will continue to push east through the remainder of today, weakening and becoming an open wave trough during it's transit. On the Backside of the trough, a slight chance (15-25%) of light rain showers will be possible along the WA Cascade crest this morning, but will diminish in the afternoon as the trough pushes into Canada. Breezy winds through the Cascade gaps and portions of the Columbia Basin will remain through the evening hours, as the cross Cascade surface pressure gradient will be slower to weaken.

Late Sunday through Tuesday, an upper level ridge will build over the PacNW and Northern Rockies, producing another warming trend that will persist into Wednesday. From the most recent NBM run, 90th percentile max temperatures remain around the mid 90s, with locally upper 90s in the WA Columbia Basin. Otherwise, while conditions are expected to remain mostly dry across the forecast area, there are less than 10% chances of isolated showers/thunderstorms developing across the southern Blues Monday afternoon, and the northern Blues Tuesday afternoon.

Wednesday through Saturday: While warming impacts from the upper level ridge is expected to persist into Wednesday, there is good agreement amongst ensemble guidance that upper level troughing in the northeast Pacific will drop closer to the PacNW Wednesday, then push inland during the day Thursday (confidence 55-65%). The approach of the upper trough and an attendant surface low will tighten surface pressure gradients along the Cascade crest, resulting in a return to breezy westerly winds developing Wednesday. Fire weather conditions will become elevated to marginally critical across portions of the Columbia Basin/Gorge and adjacent valleys in the afternoon, as relative humidities will be near critical values (confidence 55-60%).

Thursday, ensemble cluster analysis shows the upper trough swinging into southern BC, pushing the upper ridge further east of the region. Near seasonable temperatures will result with a slight increase in relative humidity across the forecast area (confidence 45-55%), while breezy winds persist through the Cascade gaps. Confidence is moderate (45-60%) that fire weather conditions will be elevated, but remain above critical thresholds. Friday into Saturday, ensemble cluster solutions favor upper level troughing continuing to impact the PacNW, though ensemble members are in disagreement on position and strength of the trough. Confidence in forecast details is low- moderate (35-50%) during this period. Lawhorn/82

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

VFR conditions to prevail through the period. Winds will increase to 12-17kts with gusts to around 25kts at sites PDT/ALW late tomorrow morning into the early evening. Winds at site DLS will remain 12-17kts with gusts to 25kts through 2Z, becoming light through the remainder of the period. All other sites are expected to see light winds through the period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 82 48 89 56 / 0 0 0 0 ALW 84 55 92 63 / 0 0 0 0 PSC 86 52 92 56 / 0 0 0 0 YKM 86 56 90 60 / 0 0 0 0 HRI 85 52 91 57 / 0 0 0 0 ELN 77 50 86 57 / 0 0 0 0 RDM 83 45 90 49 / 0 0 0 0 LGD 85 48 93 55 / 0 0 0 0 GCD 87 51 95 56 / 0 0 0 10 DLS 83 58 92 63 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523. OR...Air Quality Alert until noon PDT Monday for ORZ041-044-049-050- 502-503-505>507-509>511.