textproduct: Pendleton

KEY MESSAGES

- Above-normal temperatures through Wednesday as an upper- level ridge of high pressure builds overhead then shifts east to the northern Rockies.

- Very low chance (5-15%) of showers and thunderstorms for the southern Blue Mountains this afternoon/evening, and for the northern Blue Mountains Tuesday afternoon/evening.

- Breezy westerly winds Wednesday, with locally medium-high probability (50-80%) of Red Flag conditions in the eastern Columbia River Gorge and western half of the lower Columbia Basin. Lower probability (<50%) of Red Flag conditions due to wind and low relative humidity elsewhere.

DISCUSSION

Water vapor imagery shows an upper-level ridge of high pressure building over the region. Meanwhile, a large, upper-level closed low is churning off southeast Alaska, and a somewhat smaller and weaker closed low is located to our west in the eastern Pacific. A weak shortwave embedded within southwesterly flow aloft is noted over the northwest Great Basin.

The aforementioned upper-level ridge is forecast to gradually shift east over the northern Rockies through Wednesday. This will result in warming, mostly dry conditions areawide. Above- normal temperatures are anticipated to peak in the 90s to near 100 for most areas on Tuesday, with portions of northeast Oregon seeing similar temperatures on Wednesday. Accompanying HeatRisk looks to peak Tuesday/Wednesday with medium-high (50-100%) probability of Moderate (level 2 of 4) HeatRisk for the majority of our population centers. A few areas of the Columbia Basin have low-medium (10-50%) chances of Major (level 3 of 4) HeatRisk. Moderate HeatRisk affects those who are sensitive to heat, especially those without cooling/hydration, while Major HeatRisk affects anyone without cooling/hydration.

While mostly dry conditions are forecast through Wednesday, would be remiss for not mentioning the low probabilities (5-15%) of convection each day. Ensemble NWP guidance is in excellent agreement that the aforementioned lows will slowly approach the Pacific Northwest, with a weak shortwave embedded in southwest flow aloft passing over northern California and southeast Oregon this afternoon and evening. This will present a low (5-15%) chance of high-based showers and thunderstorms for the far southern Blue Mountains. Any showers and thunderstorms that develop will be capable of producing strong, gusty outflow winds. Tuesday, guidance merges the two offshore lows, and wraps a weak shortwave (the remnants of the smaller low) up the Pacific coast. While the wave is not forecast to move inland across our forecast area, weak synoptic-scale forcing coupled with modest diurnally induced instability, negative mid-level theta-e lapse rates, and very marginal mid-level moisture indicate some potential for afternoon convection. Best chances (5-15%) are for the northern Blue Mountains and the rest of far northeast Oregon.

By Wednesday, guidance shows yet another shortwave swinging around the parent offshore low, with low (5-10%) chances of convection again over the Blue Mountains. There is medium-high confidence (50-80%) in localized overlap of breezy winds and critically low relative humidity in the eastern Columbia River Gorge and western half of the lower Columbia Basin, per NBM probabilities. Elsewhere, there are lower probabilities (<50%) of overlap of wind/rh thresholds.

Thursday through the remainder of the week, anticipating near- to below-normal temperatures and diurnally breezy westerly winds through the Cascade gaps as troughing moves onshore.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

VFR conditions are expected at all terminals with only the possibility of smoke that is not expected to impact visibility to the MVFR category. Light winds under 12 knots continue before gusts (20 to 25kts) develop around DLS/RDM late in the afternoon.

Preliminary Point Temps/PoPs

PDT 55 94 59 92 / 0 0 0 0 ALW 62 95 66 93 / 0 0 0 0 PSC 57 95 61 96 / 0 0 0 0 YKM 61 95 62 95 / 0 0 0 0 HRI 58 95 63 94 / 0 0 0 0 ELN 57 92 61 91 / 0 0 0 0 RDM 50 95 50 91 / 0 0 0 0 LGD 56 97 58 97 / 0 20 20 10 GCD 57 96 58 96 / 0 10 10 0 DLS 65 95 64 89 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until noon PDT Wednesday for WAZ026-028>030- 522-523. OR...Air Quality Alert until noon PDT Wednesday for ORZ044-502-503- 507.