textproduct: Pendleton

KEY MESSAGES

- Rivers continue running high

- A front Tuesday will bring high mountain snow and low elevation rain Tuesday and Wednesday

- Fire Weather Risk Low

DISCUSSION

An atmospheric river modeled with compact, up to 800 kg/ms IVT, will spread inland Tonight impinging on the WA Cascades and Columbia Basin. Mountain rain/snow overnight is expected to be followed by rain chances Tuesday as increasing snow levels and warmer temperatures in the mid 60s across the lowlands is expected to be common. Cooler temperatures are anticipated on Wednesday (low 50s across the low lands and reaching around 60s across some of the lower basin (Columbia, John Day).

NBM mean PoPs drop to zero by Thursday evening. The synoptic system bringing the weather regime change will present some weak momentum transfer in a westerly surface flow, mixing out diurnally more gusty winds Tuesday and Wednesday however far from widespread and obvious advisory levels. As typical in these setups, windiest conditions should be found across the Simcoe Highlands, not to mention the higher terrain of the Eastern Slopes of the OR/WA Cascades. In many of these areas the 25th to 75th percentiles of the NBM ensemble members range from gusts of 20 to 35 mph Tuesday. Wednesday looks more interesting as the same statistics suggest 35 to 45 mph common across the Lower Columbia Basin and the Yakima Valley, perhaps inching a little closer to to advisory criteria.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

VFR conditions are forecast at all sites for the next 24 hours. CIGs will gradually lower to 8-12 kft AGL by tonight as moisture arrives from the Pacific. Confidence is low (10-20 percent) in light rain developing overnight at RDM/BDN, with low confidence (10-30 percent) in light rain spreading to all sites by Tuesday morning.

Winds of 10 kts or less are currently forecast through tonight. That said, there is medium (40-60 percent) confidence in periods of southwesterly sustained winds of 10-15 kts accompanied by gusts of 15-25 kts at RDM/BDN/PSC by Tuesday morning. By late Tuesday morning and afternoon, winds are expected (80 percent confidence) to increase to 10-15 kts at all sites except DLS. Gusts of 20-30 kts are likely (80 percent confidence) to accompany the aforementioned sustained winds.

By Tuesday afternoon, rain chances increase for all sites. Highest chances (60-80 percent) are at DLS/PDT/YKM/ALW with lower (30-50 percent) chances at RDM/BDN/PSC. 86

FIRE WEATHER

Minimum Relative humidity this week will be generally the lowest on Thursday and Friday, largely across the the John Day/Ochoco Highlands. The upside here is the winds are not going to be particularly strong, with light and variable winds on Thursday, and a more breezy setup by Friday.

HYDROLOGY

The Naches River is forecast to fall below the minor Flood stage late This Afternoon. Additional precipitation across the WA Cascades Tonight and Through the day Wednesday might have the river crest once again near or around the flood stage of 17.8 late Wednesday Morning, as the deterministic forecast takes it to 17.7 feet. HEFS probabilities suggest about a 10% chance of reaching about 18.1 feet or about a third of a foot above minor flood stage midday Wednesday. Rivers and tributaries along the Yakima system will continue to run high through the middle to late week.

Preliminary Point Temps/PoPs

PDT 44 66 42 56 / 0 60 60 30 ALW 47 63 44 56 / 0 80 80 50 PSC 46 65 45 61 / 0 50 40 10 YKM 42 62 36 55 / 0 70 30 10 HRI 45 66 43 60 / 0 50 40 10 ELN 38 55 34 48 / 0 80 30 20 RDM 41 66 37 53 / 10 30 30 10 LGD 45 65 42 54 / 10 60 80 60 GCD 43 67 46 58 / 10 40 40 40 DLS 45 60 42 57 / 10 80 70 40

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.