textproduct: Pendleton

KEY MESSAGES

- Above-normal temperatures Monday 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 on Monday, and for the northern Blue Mountains on Tuesday.

- Breezy westerly winds Wednesday, with low-medium probability (20-60%) of Red Flag conditions in the Columbia Basin and Cascade gaps.

DISCUSSION

Water vapor imagery shows an upper-level low exiting the region to the east over southern Canada and the northern Rockies. Meanwhile, a large, upper-level closed low is churning in the Gulf of Alaska, and a somewhat smaller and weaker closed low is located to our west in the eastern Pacific.

At the surface, widespread breezy conditions are present beneath dry zonal flow in the wake of the low, with the most notable winds through the Cascade gaps, Columbia Basin, and Blue Mountain foothills. Temperatures are seasonably cool, a few degrees below normal.

An upper-level ridge of high pressure is forecast to build overhead tonight into Monday and 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 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 (10-45%) 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 Monday 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 by later Monday, with a weak shortwave embedded in southwest flow aloft passing over northern California and southeast Oregon late 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 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 (5-15%) chances of convection again over the Blue Mountains. There is higher confidence (20-60%) in overlap of breezy winds and critically low relative humidity in the Columbia Basin and Cascade gaps Wednesday, per NBM probabilities.

Thursday through the remainder of the week, anticipating near- normal temperatures and diurnally breezy westerly winds through the Cascade gaps.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Slightly breezy winds at PDT/ALW/DLS Today with gusts (20-25kts) tapering off around 7 or 8 pm. Elsewhere lighter (under 12 knot) winds at YKM/PSC/RDM/BDN, with VFR at all terminals.

Preliminary Point Temps/PoPs

PDT 49 90 54 94 / 0 0 0 0 ALW 55 93 61 95 / 0 0 0 0 PSC 53 93 57 96 / 0 0 0 0 YKM 57 91 61 95 / 0 0 0 0 HRI 53 92 58 95 / 0 0 0 0 ELN 51 87 57 93 / 0 0 0 0 RDM 45 91 49 94 / 0 0 0 0 LGD 49 93 56 97 / 0 0 0 10 GCD 52 95 57 96 / 0 0 0 0 DLS 59 94 64 97 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523. OR...Air Quality Alert until noon PDT Monday for ORZ041-044-049-050- 502-503-505>507-509>511.