textproduct: Pendleton

KEY MESSAGES

- Hot temperatures through Friday -- Heat Advisories in effect.

- Very low to slight chance (5-20 percent) of high-based showers and thunderstorms Friday and Saturday.

- Widespread breezy to windy westerly winds coupled with low relative humidity Saturday -- Fire Weather Watches in effect.

DISCUSSION

Water vapor imagery shows a large, closed low offshore in the Pacific. Meanwhile, an upper-level ridge of high pressure extends from the Four Corners into the Pacific Northwest. The interaction of these two synoptic-scale features will drive the bulk of our weather over the next several days.

Under the ridge, widespread hot conditions are in place with afternoon high temperatures already in the low/mid-90s early this afternoon. Temperatures are expected to continue climbing into the mid/upper 90s this afternoon, with localized areas exceeding 100 degrees such as in Hells Canyon and Warm Springs area. Heat Advisories have been issued for the majority of our forecast area, in effect through 10 PM Friday. Friday is forecast to be the hotter day across the northeast half of our forecast area from south-central Washington to northeast Oregon, with widespread upper 90s to lower 100s forecast. While uncertainty in precise temperatures does exist due to forecast high clouds and wildfire smoke, confidence remains medium-high (40-80%) in Major HeatRisk (level 3 of 4) for the majority of our population centers within the aforementioned area. This level of heat affects anyone without cooling/hydration. In areas that area not likely (20% chance or less) to see Major HeatRisk, Moderate HeatRisk (level 2 of 4) is forecast (70-90 percent confidence); areas include central Oregon and portions of the Blue Mountain foothills in the southwest half of our forecast area.

Ensemble NWP guidance is in concensus that the upper low will slowly track north-northeast overnight through Friday and remain offshore. This places the forecast area under southerly to southwesterly flow aloft. Synoptic-scale forcing coupled with increasing mid-level moisture may facilitate some high-based showers and thunderstorms overnight through Friday and into Saturday morning, but probabilities are quite low (5-15 percent), highest for the Cascades.

The low is then expected (95 percent confidence) to track inland across northern Oregon and Washington during the day Saturday, morphing into an open-wave trough as it moves inland. Its attendant cold frontal passage during the day will help drive breezy to windy westerly winds through the Cascade gaps as well as across the Columbia Basin and portions of the Blue Mountains. While confidence was only medium (40-60%) in reaching RH thresholds, due to the magnitude of the forecast winds (10-25 mph with gusts of 25-40 mph, locally higher through especially wind-prone areas), have issued Fire Weather Watches due to wind and low relative humidity for the majority of our non-mountain fire weather zones, in effect Saturday afternoon through Saturday evening. Additional headlines may be needed if confidence increases in overlap of critical wind/RH thresholds.

Some breezy conditions are forecast to linger Sunday as the trough exits to the east.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

VFR conditions prevail with lingering elevated smoke in the region. Some sites have a small chance (5 to 15 percent) that elevated smoke will makes it way down to the surface at any TAF sites, bringing MVFR conditions. Greatest chance of occurrence will be the overnight hours and lift in the late morning to afternoon hours. Otherwise, winds will be mostly light in general at less than 12 knots sustained.

Preliminary Point Temps/PoPs

PDT 60 96 64 89 / 0 0 10 10 ALW 65 100 71 92 / 0 0 10 10 PSC 69 100 65 94 / 0 0 10 10 YKM 68 98 69 93 / 0 0 20 20 HRI 67 97 67 91 / 0 0 10 10 ELN 62 95 67 87 / 0 0 20 30 RDM 60 93 54 87 / 0 0 10 0 LGD 58 100 65 94 / 0 0 10 30 GCD 63 100 63 95 / 0 0 10 10 DLS 72 96 66 84 / 0 0 10 10

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 1 PM PDT Friday for WAZ028>030. Heat Advisory until 10 PM PDT Friday for WAZ024-026>030-521- 523. Fire Weather Watch from Saturday afternoon through Saturday evening for WAZ690-691. OR...Air Quality Alert until 1 PM PDT Friday for ORZ041-050-502-505- 506-509>511. Heat Advisory until 10 PM PDT Friday for ORZ041-044-049-050- 502-503-505>508-510-511. Fire Weather Watch from Saturday afternoon through Saturday evening for ORZ691-696-698-700-703.