textproduct: Pendleton

KEY MESSAGES

- Red Flag Warnings in effect for abundant lightning threat through this evening for portions of the WA Cascade east slopes and the Northern Blues

- Breezy to gusty winds developing today will overlap with low relative humidity across lower elevation locations through this evening. Red Flag Warnings and wind advisories are in effect

- Mostly dry conditions through the remainder of the week, with a return of breezy to windy conditions Wednesday

DISCUSSION

Water vapor imagery tonight shows an upper level closed low offshore southern OR, while nighttime satellite and radar imagery show weak, light scattered showers pushing north across southeast WA and northeast OR.

Today through Sunday: The upper low offshore southern OR will be the main driver of weather conditions across the PacNW through Sunday night. Today, shower activity with low chances (5-20%) of embedded isolated thunderstorms will be focused along the WA Cascade east slopes, northern Blues, and Wallowa county. The activity will start early this morning along the WA Cascade east slopes, then spread east to the Northern Blues and Wallowa county in the afternoon. Latest CAMs show very weak instability support in the morning (MUCAPE 100-250 J/kg), but by the afternoon show modest instability modest instability (MUCAPE between 250-750 J/kg) developing in the afternoon, with strong low-level lapse rates (9-10 C/km). Thunderstorms through the afternoon will be capable of gusty outflow winds and abundant lightning, which has resulted in the issuance of Red Flag Warnings.

The upper low lifting up the coast today will also result in a cross-Cascade pressure gradient to tighten, with winds strengthening as an associated cooler airmass begins to filter into the intermountain PacNW. Breezy winds 15-30mph with gusts 30-45mph will develop across the lower elevations through the afternoon. The strongest winds (sustained winds 25-35mph and gusts 45-50mph) will develop through the Cascade Gaps into western portions of the OR columbia Basin this afternoon, resulting in wind advisories being issued. Confidence is moderate-high (60-85%) that these strong winds will overlap with critically low relative humidities across most of our non- mountain fire weather zones this afternoon. As a result multiple Red Flag Warnings were issued for the wind/low RH threat across the Columbia Basin/Gorge, adjacent foothills/valleys, central OR, and the John Day Basin through this evening.

Late Saturday through Sunday morning, the upper low will become an open wave trough as it moves inland across WA and northern OR. A slight chance (15-25%) of light showers will be possible across the WA Cascade crest Sunday morning. The upper trough will exit into Canada around the ID/MT border, leaving behind drier and cooler conditions the remainder of Sunday. Breezy winds (15-25mph with gusts up to 40mph) will redevelop through the Cascade gaps through early Sunday evening, with light winds returning Sunday night.

Monday through Friday: Ensemble cluster guidance is in good agreement of upper level ridging building back over the PacNW Monday with dry conditions and a warming trend persisting through Tuesday. By Wednesday, ensemble cluster solutions are in good agreement that an upper trough will lift across the PacNW with a isolated light showers developing along the WA Cascade crest and breezy winds through the Cascade gaps into the Columbia Basin and adjacent valleys/foothills. That said, cluster solutions are in disagreement on passage timing and location of the trough, resulting in low confidence (25-35%) in forecast details. Thursday into Friday, cluster solutions favor a dry southwest flow over the PacNW as broad troughing extends from western Canada into the northeast Pacific. This will keep the region dry overall, with diurnally breezy winds through the Cascade gaps and near normal temperatures. Lawhorn/82

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

VFR to MVFR conditions through the TAF period with isolated showers and thunderstorms moving through the region. Gusty wind of 20-30 kt favored at all terminals today, with wind weakening after 03z this evening. Gusty and erratic wind could accompany any storm development today. Branham/76

FIRE WEATHER

An upper weather system impacting the region today will bring the threat of thunderstorms capable of abundant lightning across WA Cascade crest, northern Blues, and Wallowa county. In most non-mountain zones, breezy winds will overlap with critically low relative humidity this afternoon, resulting in critical fire weather concerns. Multiple Red Flag Warnings are in effect for abundant lightning and for the wind/RH threats. RHs will improve slightly and winds weaken Sunday, though elevated fire weather concerns will remain.

Preliminary Point Temps/PoPs

PDT 90 49 82 48 / 20 0 0 0 ALW 93 57 84 55 / 20 0 0 0 PSC 96 58 86 54 / 20 0 0 0 YKM 95 59 86 57 / 30 0 0 0 HRI 92 58 85 53 / 20 0 0 0 ELN 87 54 78 51 / 30 0 0 0 RDM 89 45 84 46 / 10 0 0 0 LGD 95 51 86 50 / 20 10 0 0 GCD 95 53 87 52 / 20 0 0 0 DLS 85 61 82 59 / 10 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523. Wind Advisory until 11 PM PDT this evening for WAZ024-521. Red Flag Warning until 10 PM PDT this evening for WAZ690-691. Red Flag Warning until 11 PM PDT this evening for WAZ692. Red Flag Warning until 8 PM PDT this evening for WAZ693. Wind Advisory from 2 PM this afternoon to 10 PM PDT this evening for WAZ026. Red Flag Warning until noon PDT today for WAZ695. OR...Air Quality Alert until noon PDT Monday for ORZ041-044-049-050- 502-503-505>507-509>511. Wind Advisory until 11 PM PDT this evening for ORZ041-044-508- 510. Red Flag Warning until 10 PM PDT this evening for ORZ691-696- 698-700-703. Red Flag Warning until 11 PM PDT this evening for ORZ692. Red Flag Warning until 8 PM PDT this evening for ORZ693.