textproduct: Pendleton

KEY MESSAGES

- Windy through the Grande Ronde Valley and along the slopes of the northern Blue Mountains into tonight.

- Above-normal temperatures today for most, becoming closer to normal Sunday and Monday.

- Mostly dry conditions east of the Cascades until at least late next week.

DISCUSSION

GOES-18 imagery shows an upper-level closed low churning offshore in the northeast Pacific. A well-defined cold frontal boundary is approaching the coast and forecast to move inland tonight into Sunday.

Ahead of the frontal passage, mild temperatures and breezy to locally windy south to southeast winds are ongoing and expected (80 percent confidence) into tonight. Windy conditions along the slopes of the northern Blue Mountains (east of Pendleton) and through the Grande Ronde Valley are anticipated to persist due to a decently strong cross-Blues pressure gradient (~10 mb difference between Pendleton and Ontario).

Cold frontal passage tonight into Sunday will be accompanied by light precipitation and followed by cooler temperatures and breezy westerly to southwesterly winds.

Precipitation chances return Monday, especially late afternoon as a shortwave moves over the Pacific Northwest. Otherwise, cooler, near-normal temperatures are forecast.

Well-above-normal temperatures and periods of breezy to windy southerly to southeasterly winds are forecast again Tuesday through late week, with notable precipitation confined to the Washington Cascades and south-central Washington as ensemble guidance indicates an omega-block will develop (troughing over the East, ridging over the Plains and West, and troughing upstream in the Pacific). Under this pattern, precipitation is largely confined to the Cascades with drier conditions to the east.

Significant uncertainty in the 500-hPa pattern develops in ensemble solutions by late week into next weekend. Roughly half of ensemble solutions develop a closed low offshore in the Pacific and take it south of our forecast area into California or the Southwest, while the remainder show troughing extending from the Northeast Pacific into the Pacific Northwest. The former scenario would be warmer and drier while the latter scenario would be cooler and wetter across the region.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

VFR conditions currently across all sites, which will stay the course through the period. Light showers this evening expected for KDLS/KPDT/KALW with breezy conditions across most sites as gusts of 20-30kts will be possible. High winds aloft will also contribute to 40kt shear at 2kft for KPDT/KALW/KPSC. 75

Preliminary Point Temps/PoPs

PDT 44 57 39 56 / 0 30 20 20 ALW 48 57 42 54 / 0 50 10 20 PSC 40 61 37 55 / 10 20 10 20 YKM 40 59 35 54 / 20 0 10 10 HRI 40 60 38 55 / 0 20 20 20 ELN 34 51 27 49 / 40 10 10 20 RDM 39 54 31 59 / 10 10 0 30 LGD 43 51 37 57 / 0 20 10 10 GCD 41 55 36 61 / 0 10 10 10 DLS 44 57 41 55 / 70 10 20 40

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Wind Advisory until 8 PM PST this evening for ORZ049. Wind Advisory from 4 PM this afternoon to 1 AM PST Sunday for ORZ507.