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 /06Z TAFS THROUGH 06Z SATURDAY/

VFR conditions persist through the forecast period with lingering elevated smoke in the region. RDM/ALW is 4SM and MVFR due to the smoke settling and is expected to lift in the next few hours. OTherwise there is a small chance (5-10%) that elevated smoke will makes it way down to the surface at the remaining sites. Winds will be mostly less than 12 knots sustained.

Preliminary Point Temps/PoPs

PDT 60 96 63 90 / 0 0 10 10 ALW 65 101 70 93 / 0 0 10 10 PSC 69 100 66 95 / 0 0 10 10 YKM 68 98 70 95 / 0 0 10 20 HRI 67 97 68 92 / 0 0 10 10 ELN 62 96 67 88 / 0 0 10 30 RDM 60 93 54 88 / 0 0 10 0 LGD 58 101 65 95 / 0 0 10 20 GCD 63 100 63 95 / 0 0 10 10 DLS 72 96 66 85 / 0 10 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. Fire Weather Watch from Friday evening through Saturday afternoon for WAZ695. 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.