textproduct: Pendleton

KEY MESSAGES

- Elevated to critical fire weather conditions through the week due to periods of breezy conditions, low RH, and hot, dry, and unstable conditions. Red Flag Warnings in effect Friday morning through Saturday evening for wind and low relative humidity.

- Widespread smoke persists today, then westerly winds will likely (80% confidence) bring improvement Friday through the weekend, except in the vicinity of or downwind of ongoing wildfires.

- Widespread Moderate to locally Major HeatRisk today and Friday.

DISCUSSION

Similar to the previous few days, satellite imagery shows widespread smoke and haze across the forecast area this afternoon. While some modest improvement in smoke has occurred in central Oregon and south-central Washington, regional wildfires continue to produce significant smoke which is now being transported to the northeast.

Water vapor imagery reveals an upper-level ridge axis extending from the Great Basin through the Pacific Northwest and into British Columbia. Meanwhile, a low-pressure system is located well offshore in the vicinity of 49N, 144W.

Under the ridge, hot temperatures will continue through Friday. Widespread Moderate to locally Major HeatRisk is expected (80% confidence) due to forecast afternoon temperatures in the 95-100 degree range and lows in the 50s and 60s (locally into the lower 70s). Wildfire smoke inhibits efficient solar heating so afternoon temperatures may end up being several degrees cooler than currently forecast where smoke is sufficiently dense; this is most likely beneath the plumes from the Grasshopper Fire and Rowe Creek Complex. Have opted to hold off on issuing any heat headlines.

A couple shortwaves are likely (95% confidence) to flatten the ridge Friday through the weekend, with the strongest expected Saturday afternoon. This pattern will facilitate breezy to windy westerly winds through the Cascade gaps and across the Blue Mountain foothills and Columbia Basin. Wind coupled with low relative humidity will lead to increasing fire weather concerns and Red Flag Warnings have been issued (see FIRE WEATHER section below). Breezy to windy westerly winds will be capable of scouring much of the existing smoke from our forecast area; while widespread improvement is anticipated (80% confidence), smoke is still expected to be present downwind of ongoing wildfires within their respective plumes, so some areas will see continued smoke while others will be much clearer.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

MVFR or lower conditions will prevail through the period. Smoke from area wildfires will continue to impact all sites, resulting in vsby down to IFR conditions and CIGs down to MVFR conditions. Smoke is expected to worsen vsby conditions overnight, especially at sites DLS/ALW/PDT. Otherwise, winds will be light to locally breezy through the period. Lawhorn/82

FIRE WEATHER

Periods of elevated to critical fire weather conditions are anticipated today into at least early next week due to a combination of locally breezy winds and low relative humidity as well as hot, dry, and unstable conditions.

Today through Friday, the combination of dry air and hot temperatures will drive afternoon RHs into the single digits to teens. Predominantly poor to fair overnight RH recovery is forecast through the week, except for locally good to excellent recovery in drainages. Of note, deep mixing across the region coupled with locally breezy winds, especially central Oregon and vicinity, may support plume-dominated fire this afternoon and Friday. Have held off on issuing any zone-wide Red Flag Warnings for hot, dry, and unstable conditions. Additionally, high-resolution weather models (12Z HREF and 12Z REFS) continue to highlight some potential (broadly 30-70% of members) overlap of critical wind/RH thresholds in central and east-central Oregon as well as the Cascade gaps of OR/WA this afternoon and evening, but confidence was too low to issue any zone-wide Red Flag Warnings.

Friday through Saturday, confidence is very high (95 percent) in a return to breezy westerly winds through the Cascade gaps and across the Columbia Basin as a couple weak shortwaves flatten the ridge. The stronger shortwave appears opportunistically timed Saturday afternoon to coincide with afternoon heating to facilitate more widespread breezy winds. Coupled with the dry air mass, forecast elevated to critical fire weather conditions have prompted the issuance of multiple Red Flag Warnings; confidence in the combination of critical winds and relative humidity is high (80 percent) for Friday and Saturday.

Looking ahead, persistent quasi-zonal flow or weak troughing aloft will likely (80% confidence) keep breezy westerly gap winds in place Sunday into at least early next week. Confidence in meeting wind/RH criteria is low (20-50%) Sunday and Monday for wind-prone areas.

Preliminary Point Temps/PoPs

PDT 61 97 59 93 / 0 0 0 0 ALW 67 98 66 95 / 0 0 0 0 PSC 60 99 61 96 / 0 0 0 0 YKM 62 99 62 96 / 0 0 0 0 HRI 64 99 64 95 / 0 0 0 0 ELN 63 94 63 90 / 0 0 0 0 RDM 54 97 52 93 / 0 0 0 0 LGD 61 100 59 96 / 0 0 0 0 GCD 59 100 59 97 / 0 0 0 0 DLS 63 96 64 93 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning from 11 AM Friday to 11 PM PDT Saturday for WAZ690-691. Air Quality Alert until 5 AM PDT Tuesday for WAZ024-026>030- 521>523. OR...Air Quality Alert until noon PDT Friday for ORZ041-044-049-050- 502-503-505>511. Red Flag Warning from 11 AM Friday to 11 PM PDT Saturday for ORZ691-701-703.