textproduct: Pendleton

KEY MESSAGES

- Hot temperatures will continue to bring areas of Major HeatRisk today, but area smoke may limit daytime heating potential

- Shortwave impulse today will tap into monsoonal moisture and increased instability to produce isolated to scattered thunderstorms across the Blue mountains to the ID border

- Upper level troughing offshore will produce breezy winds in the Cascade Gaps and Columbia Basin late this afternoon through the weekend.

DISCUSSION

Satellite imagery tonight shows remnant cloud cover from earlier convective activity over far eastern OR/WA and across the WA Cascades, while radar does show light showers about to exit the central WA Cascade crest at this time. At the surface, moderate to heavy smoke is impacting areas of central OR, mountain valleys across the Blues, and the Blue mountain foothills.

Sensible weather concerns today continue to revolve around a an upper level ridge over the PacNW producing hot temperatures in and around the Columbia Basin; another shortwave impulse riding up the ridge will tap into monsoonal moisture and increasing instability, producing isolated to scattered thunderstorms from the Blue mountains to the ID border.

Today, the PacNW will remain under the influence of an upper level ridge of high pressure while a deep southerly flow persists aloft. Hot temperatures will continue across the lower elevations, with the brunt of the heating expected in the Columbia Basin/Gorge and adjacent foothills/valleys this afternoon. Portions of the OR/WA Columbia Basin and the eastern Gorge are forecast to see high temperatures between 100 to 103 degrees this afternoon, with the Blue Mountain foothills, Yakima/Kittitas valleys, portions of north central Oregon, and portions of the John Day Basin reaching around 100 degrees (confidence 70-90%). While model guidance depicts the warming temperatures, regional smoke density and timing of winds through the Cascade gaps increase uncertainty in the effectiveness of daytime heating. Between elevated afternoon and overnight temperatures, HeatRisk values across much of the lower elevations will be in the moderate to major categories again today, resulting in Heat Advisories through this evening across the Columbia Basin/Gorge, Yakima Valley, and the northern Blue Mountain foothills.

Monsoonal moisture will continue to linger across the PacNW through this evening, with PWATS between 0.75 to 1.25 inches. A weak shortwave impulse riding up the southerly flow will tap into the moisture and increasing instability to help initiate isolated to scattered thunderstorms. Today, the main thunderstorm activity will be focused across areas of the Blue mountains to the ID border. Conditions in these areas will be favor thunderstorm activity, with MUCAPE between 500-1250J/kg, low level lapse rates 8-10 C/km, and 0-6km shear between 20-40kts. These conditions will be more than enough for thunderstorms to develop in the afternoon and become organized as they propagate northeast. Expect at least small hail, gusty outflow winds, frequent lightning, and a few storms to produce heavy downpours.

Later today through the weekend, there is good agreement amongst ensemble cluster guidance that upper troughing will develop off the coast of the PacNW while upper level ridging pushes east and south. Southwest flow aloft will prevent monsoonal moisture from advecting into the region, resulting in drying conditions across the forecast area. The proximity of the upper trough later today into Friday will also result in breezy west to northwest winds(15-25mph with gusts 25-35mph) through the Cascade gaps and across the Columbia Basin. Saturday, a shortwave will eject across northwest WA into BC, bringing breezy to windy conditions (gusts up to 50mph) through the Cascade gaps, with breezy conditions across the remainder of the forecast area. Friday, there is moderate confidence (60-75%) that peak winds will overlap with critically low RHs in portions of the Columbia Basin and Cascade Gaps. On Saturday, there remains moderate confidence (60-70%) winds and low RHs will overlap in areas of the Columbia Basin and eastern mountains. Otherwise, the shortwave passage will also result in light rain showers developing along the WA Cascade crest through Sunday morning (confidence 55-65%). Sunday through Wednesday, the forecast area will remain under a mild, dry southwest flow aloft with diurnally driven breezy winds, near to below normal temperatures, and dry conditions (confidence 55-60%). Lawhorn/82

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Mostly VFR conditions to prevail through the period. Smoke impacts are expected to prevail at sites RDM/BDN through the morning, with lowered vsby anticipated to develop at sites PDT/ALW due to smoke. Winds will increase to 10-15kts with gusts to around 21kts at sites PDT/RDM/BDN this afternoon. Site DLS will see prevailing winds 12-22kts with gusts up to 35kts through the period. Winds will otherwise be light through the period. Lawhorn/82

FIRE WEATHER

Hot and dry conditions remain across the region today, especially across the Columbia Basin and adjacent valleys/foothills. Lingering monsoonal moisture and increased instability will result in another round of isolated to scattered thunderstorms this afternoon and evening, with chances (20-50%) focused from the Blues mountains to the ID border. Thunderstorms will be capable of frequent lightning, gusty outflow winds, small hail, and brief heavy downpours. Winds will increase through the Cascade Gaps and Columbia Basin Friday, and are expected to overlap with near to critically low RHs, resulting in elevated fire weather conditions. A weak system passage Saturday may result in breezy conditions area wide, with peak winds overlapping with critically low RHs in the eastern mountains and portions of the Columbia Basin in the afternoon. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 96 62 97 63 / 0 0 0 0 ALW 99 69 99 68 / 10 0 0 0 PSC 101 66 100 66 / 10 0 0 0 YKM 100 64 99 64 / 10 0 0 0 HRI 99 66 100 67 / 0 0 0 0 ELN 94 61 95 60 / 20 0 0 0 RDM 93 57 95 55 / 0 0 0 0 LGD 99 63 101 61 / 50 10 10 0 GCD 99 59 100 58 / 10 0 0 0 DLS 91 66 97 65 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory until 9 PM PDT this evening for WAZ024-027>029. Air Quality Alert until 9 AM PDT Friday for WAZ028>030. OR...Heat Advisory until 9 PM PDT this evening for ORZ041-044-507. Air Quality Alert until noon PDT Friday for ORZ044-049-050-502- 503-505-506-508-509-511. Red Flag Warning from 11 AM this morning to 8 PM PDT this evening for ORZ694-695-697>699.