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. Fire Weather Watches in effect Friday morning through Saturday evening for wind and low relative humidity.

- Widespread smoke and haze very likely (99% confidence) to persist through Thursday, then improvement Friday through the weekend except in the vicinity of or downwind of ongoing wildfires.

- Widespread Moderate to locally Major HeatRisk Thursday and Friday.

DISCUSSION

Satellite imagery shows widespread smoke and haze across the forecast area this afternoon, the result of smoke transport from earlier in the week and continued smoke output from ongoing regional wildfires. With regard to the upper-level pattern, water vapor imagery reveals an upper-level ridge axis extending from the Great Basin northwest to just offshore of British Columbia, west of the forecast area. Meanwhile, a low-pressure system is located well offshore in the vicinity of 45N, 144W.

Widespread wildfire smoke is expected (99 percent confidence) to persist across the region through at least Thursday, and air quality headlines issued by air quality agencies remain in effect for our entire CWA until further notice.

Hot temperatures will accompany the upper ridge tomorrow through Friday as its axis shifts inland. Currently, widespread Moderate to locally Major HeatRisk is anticipated due to forecast afternoon temperatures in the 95-100 degree range and lows in the 50s and 60s. That said, wildfire smoke inhibits efficient solar heating so afternoon temperatures may end up being several degrees cooler than currently forecast if smoke is sufficiently dense; similar to yesterday forecast highs were decreased by roughly 2-5 degrees for this afternoon across much of our forecast area to account for how the smoke has affected temperatures. Conversely, the dry air mass (PWATs of 0.2-0.6") should facilitate efficient nocturnal cooling, and smoke does not significantly affect nocturnal cooling. Have opted to hold off on issuing any heat headlines for now, but will continue to assess the need.

Ensemble NWP guidance continues to advertise a change to a quasi-zonal upper-level pattern by late week through the weekend. Ensemble clusters keep the aforementioned upper low to the northwest of the region, but a couple shortwaves are likely (80% confidence) to flatten the ridge Friday through the weekend. This pattern will facilitate 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 will lead to increasing fire weather concerns (see FIRE WEATHER section below). Moreover, breezy to windy westerly winds represent the best chance of scouring the widespread smoke.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Widespread smoke and haze from local and regional wildland fires continue to impact all TAF sites through the next 24-hours. Smoke is dense enough that many sites are seeing MVFR conditions and these conditions are expected to remain through much of the period with brief lifting at DLS/PDT/YKM/PSC between 05-08Z. Winds are to light to clear the smoke from the area.

FIRE WEATHER

Periods of elevated to critical fire weather conditions are anticipated today into the weekend 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 Thursday. Have held off on issuing any Red Flag Warnings for hot, dry, and unstable conditions, but will continue to monitor the need. Additionally, high-resolution weather models (12Z HREF and 12Z REFS) indicate some potential (broadly 30-70%) in overlap of critical wind/RH thresholds in central and east- central Oregon today, expanding to include the Cascade gaps of OR/WA Thursday.

Friday through Saturday, confidence is very high (80 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. Coupled with the dry air mass, forecast elevated to critical fire weather conditions have prompted the issuance of multiple Fire Weather Watches; confidence in the combination of critical winds and relative humidity is high (60-80 percent) for Friday and Saturday.

Persistent weak troughing will likely (70% confidence) keep breezy westerly gap winds in place Sunday into early next week. Confidence in meeting wind/RH criteria is low (40% or less) Sunday and Monday.

Preliminary Point Temps/PoPs

PDT 90 54 97 61 / 0 0 0 0 ALW 93 60 98 67 / 0 0 0 0 PSC 92 58 98 60 / 0 0 0 0 YKM 90 56 98 62 / 0 0 0 0 HRI 93 56 98 64 / 0 0 0 0 ELN 88 55 95 63 / 0 0 0 0 RDM 92 53 98 54 / 0 0 0 0 LGD 94 54 99 61 / 0 0 0 0 GCD 97 56 100 59 / 0 0 0 0 DLS 97 57 99 64 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 5 AM PDT Tuesday for WAZ024-026>030- 521>523. Fire Weather Watch from Friday morning through Saturday evening for WAZ690. OR...Air Quality Alert until 5 AM PDT Tuesday for ORZ041-044-049- 050-502-503-505>511. Fire Weather Watch from Friday morning through Saturday evening for ORZ691-703.