textproduct: Pendleton

KEY MESSAGES

- Isolated to scattered mountain showers this morning

- Diurnally breezy winds through the Cascade gaps through Friday

- Dry with near-seasonal temperatures Thursday through Saturday, then warmer Sunday into early next week

DISCUSSION

Water vapor imagery shows a shortwave trough draped over northern Washington and southern British Columbia. This feature will slide over the Pacific Northwest through the day, resulting in continued mild temperatures, breezy westerly winds, and isolated to scattered rain showers for the mountains.

Near-seasonal temperatures and dry weather are then forecast Thursday and Friday as an amplifying ridge of high pressure offshore combines with downstream troughing to create quasi- zonal flow over the Pacific Northwest. Diurnally breezy westerly winds will develop through the Cascade gaps each afternoon and evening. Probabilistic guidance from the NBM indicates a low (10 percent or less) chance of Red Flag conditions (combination of wind and low relative humidity) for the lower Columbia Basin.

By late Friday and Saturday, ensemble guidance shows some spread in the location/amplitude of the offshore ridge and troughing over the northern Rockies and northern Great Plains. While confidence in isolated precipitation is currently low (20 percent or less), the approaching shortwave (should it develop) coupled with the offshore ridge and warming temperatures west of the Cascades would induce a flip in wind direction to offshore (easterly) for Saturday and Sunday. Probabilistic guidance from the NBM suggests low, but noteworthy, chances (5-30 percent) of Red Flag conditions (combination of breezy winds and low relative humidity) for the Columbia Basin both days. Given the low probabilities and uncertainty in the 500-hPa pattern, confidence is much too low for any fire weather headlines at this time, but will continue to monitor closely.

As the ridge eventually moves inland (Monday and Tuesday based on latest 00Z ensemble NWP guidance), temperatures are forecast to rise to above normal. The NBM places a 30-80 percent chance of exceeding 90 degrees across all of the lower elevations on Monday, with chances increasing to 60-95 percent on Tuesday. Moreover, there is a 5-30 percent chance of reaching 100 degrees for the lower elevations of the Columbia Basin on Tuesday. Probabilistic HeatRisk guidance indicates a 5-30 percent chance of Major (level 3 of 4) HeatRisk for the majority of our population centers within the greater Columbia Basin region Monday and Tuesday, a decrease from yesterday's guidance. This level of heat affects anyone without cooling/hydration.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

VFR conditions and breezy winds are forecast at all sites today, followed by winds of 10 kts or less tonight. Skies will become mostly clear by later this evening.

Preliminary Point Temps/PoPs

PDT 69 41 78 49 / 10 0 0 0 ALW 70 47 79 53 / 20 0 0 0 PSC 75 44 82 50 / 0 0 0 0 YKM 74 44 82 51 / 0 0 0 0 HRI 73 43 81 51 / 0 0 0 0 ELN 65 40 76 47 / 0 0 0 0 RDM 68 34 81 43 / 0 0 0 0 LGD 63 38 78 44 / 50 0 0 0 GCD 65 36 81 43 / 0 0 0 0 DLS 71 47 82 54 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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