textproduct: Pendleton

KEY MESSAGES

- Elevated to locally critical fire weather conditions Tuesday

- Widespread smoke and haze through at least mid-week

- Widespread Moderate to locally Major HeatRisk middle to late week.

DISCUSSION

Satellite imagery shows widespread smoke and haze across the forecast area this afternoon. Upper-level troughing has exited to the east over the Northern Great Plains, and an amplifying upper-level ridge is noted offshore in the Pacific. This pattern has set up a classic West Coast thermal trough (WCTT) to the west of the Cascades, leading to an offshore-directed pressure gradient and ample southward and westward smoke transport from the wildfires to our north in northern Washington and Canada.

Wildfire smoke is expected (99 percent confidence) to persist across the region through at least mid-week as the upper-level ridge amplifies and slowly tracks eastward. Winds will remain diurnally and terrain-driven and supportive of continued advection of smoke into the region. Air quality headlines have been issued by Oregon Department of Environmental Quality, the Washington State Department of Ecology, Benton Clear Air Agency, and the Yakima Regional Clean Air Agency, valid until further notice.

The ridge axis will move inland Wednesday through Friday, with increasingly hot temperatures forecast during the period. Currently, widespread Moderate to locally Major HeatRisk is forecast due to afternoon temperatures in the 95-100 degree range and lows in the 50s and 60s. That said, note that wildfire smoke inhibits efficient solar heating so afternoon temperatures may end up being several degrees cooler than currently forecast if smoke is sufficiently dense. Conversely, the dry air mass (PWATs of 0.2-0.6") should facilitate efficient nocturnal cooling, and smoke does not significantly affect nocturnal cooling.

The upper-level pattern will likely change (70 percent chance) by late week, mostly likely Friday through the weekend, to a quasi-zonal pattern as ensemble clusters indicate some flavor of upper-level low or shortwave trough will track inland over British Columbia. This solution would lead to a reversal of surface pressure gradients and result in breezy to windy westerly winds through the Cascade gaps and across the Blue Mountain foothills and Columbia Basin. Wind coupled with low relative humidity in this scenario would lead to increasing fire weather concerns (see FIRE WEATHER section below). Moreover, the westerly wind represents the best chance of scouring the widespread smoke.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Variable conditions currently across sites, with IFR at KRDM, MVFR at KPDT/KYKM/KALW, and VFR conditions at KDLS/KPSC. IFR and MVFR conditions are expected to persist through the evening associated with decreased visibilities and ceilings related to smoke from nearby wildfires. Winds are expected to stay light and below 10kts for all sites through the period. 75

FIRE WEATHER

Elevated to locally critical fire weather conditions are forecast Tuesday as locally breezy east to northeast winds overlap with dry air; dropped the Fire Weather Watches due to low confidence in widespread overlap of critical conditions.

By mid-week, the combination of dry air and hot temperatures will drive afternoon RHs into the single digits to teens. Poor to fair overnight RH recovery is forecast through the week, except for locally better recovery in drainages.

Late week, confidence is high (70 percent) in a return to breezy westerly winds through the Cascade gaps and across the Columbia Basin as a low-pressure system will likely (70 percent) approach or move into British Columbia. Confidence in the combination of critical winds and relative humidity late Thursday is low-medium (20-50 percent) with medium-high confidence (40-80 percent) for Friday.

Preliminary Point Temps/PoPs

PDT 49 88 53 93 / 0 0 0 0 ALW 53 90 57 96 / 0 0 0 0 PSC 51 91 54 96 / 0 0 0 0 YKM 55 90 58 95 / 0 0 0 0 HRI 52 90 55 95 / 0 0 0 0 ELN 54 88 57 93 / 0 0 0 0 RDM 42 88 47 95 / 0 0 0 0 LGD 48 88 51 96 / 0 0 0 0 GCD 47 90 51 98 / 0 0 0 0 DLS 58 92 61 98 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 5 AM PDT Tuesday for WAZ024-026>030- 521>523. OR...Air Quality Alert until 5 AM PDT Tuesday for ORZ041-044-049- 050-502-503-505>507-509>511.