textproduct: Pendleton

KEY MESSAGES

- Red Flag Warning in effect for the Lower Columbia Basin of Oregon (OR690) until 10PM PDT Saturday due to breezy winds and low relative humidity.

- Diurnally breezy westerly winds through the Cascade gaps each afternoon and evening through Saturday.

- Hot, dry conditions early next week with increasing HeatRisk.

- Likely (>60% chance) increase in monsoonal moisture by mid-week.

DISCUSSION

Water vapor imagery shows a closed mid/upper-level low churning in the vicinity of Vancouver Island. This low will continue to track northeast into British Columbia through Saturday, with flow aloft turning from south-southwesterly to west- southwesterly. Monsoonal moisture has largely been pushed to the east of the forecast area, with the only area of lingering higher PWATs (0.7-1.2" per RAP-based mesoanalysis) draped across the northeastern Blue Mountains from the Elkhorns east through Wallowa County. There is a very low chance (5-15%) of showers and thunderstorms across the aforementioned area this afternoon and evening, with dry conditions expected (95% confidence) elsewhere. As of 2PM PDT, only modest CU development has been observed over the Elkhorns, Wallowas, and surrounding sub- ranges of the Blues.

At the surface, diurnally breezy winds are forecast from the Cascade gaps eastward into the lower Columbia Basin this afternoon and evening due to a cross-Cascade temperature and pressure gradient and onshore flow. Neither gradient is nearly as strong as yesterday's, so not anticipating winds to be anywhere close to advisory thresholds, but the combination of locally breezy westerly winds (10-20 mph with gusts of 20-30 mph), low relative humidity (15-25%), and ongoing large wildfires has prompted the issuance of a Red Flag Warning (RFW) for fire weather zone OR691 (Lower Columbia Basin of Oregon) through 10PM Saturday. Winds through the gaps should be a bit stronger on Saturday as winds aloft turn more zonal, and there is medium confidence (30-50%) in hitting critical thresholds of wind/RH for the Kittitas Valley (WA690) and portions of the lower Columbia Basin of Washington (WA691) on Saturday. Did not issue any watches to avoid confusion with the ongoing RFW.

Winds will become lighter on Sunday as a 500-hPa ridge builds into the Pacific Northwest. By Monday, lighter northerly to easterly winds are forecast.

Tuesday through the remainder of the week, ensemble NWP guidance shows the remnants of Tropical Storm Elida tracking northward along roughly 120W and either replacing or getting absorbed by an existing area of low pressure off the Pacific coast. The evolution this low, its interaction with the broad 500-hPa ridge over the Western CONUS, and advection of monsoonal moisture into the region will modulate precipitation chances and temperatures across the forecast area. In general, there are increasing precipitation chances across the region, especially the Blue Mountains, Tuesday through Thursday, with a slight drop on Friday. Chances peak at 25-40% on Thursday for the Blue Mountains, with lower (10-25%) chances elsewhere.

On the topic of heat, chances of Major (level 3 of 4) HeatRisk increase to 10-40% for the Blue Mountain foothills Tuesday through Friday, with higher chances (20-70%) for the lower Columbia Basin and surrounding valleys. This level of heat affects anyone without cooling/hydration as well as heath systems and industries.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

VFR conditions currently across all sites, which is expected to stay the course. However, smoke from nearby wildfires may drop visibilities to MVFR levels tonight for KPDT/KALW/KRDM/KBDN. Breezy winds at KDLS/KRDM/KBDN/KYKM will subside through the evening, picking back up by tomorrow afternoon as gusts of 15-25kts will return. Elsewhere, winds should stay at or below 10kts. 75

FIRE WEATHER

Breezy diurnally driven westerly wind and low relative humidity is expected through the Cascade gaps each afternoon and evening through Saturday, leading to elevated to critical fire weather conditions. A Red Flag Warning has been issued for OR691, the Lower Columbia Basin of Oregon, from 2PM this afternoon through 10PM Saturday. Critical RH is not forecast overnight, but the warning was issued for a two-day event to simplify messaging. Confidence was a bit too low (30-50%) in overlap of critical wind/RH for WA690 (Kittitas Valley), and WA691 (Lower Columbia Basin of Washington) on Saturday to issue any headlines this morning.

There is a very low chance (5-15 percent) of showers and thunderstorms across the northeast Blue Mountains today.

Very warm to hot, and dry conditions are then forecast early next week, followed by a slight chance (15-24 percent) to chance (25-40 percent) of showers and slight chance (15-24%) of thunderstorms Tuesday through the remainder of the week as monsoonal moisture from the Southwest will likely (>60% confidence) return to the region. Highest chances of showers and thunderstorms will be over the mountains, especially the Blue Mountains.

Preliminary Point Temps/PoPs

PDT 57 91 56 92 / 0 0 0 0 ALW 63 93 62 93 / 0 0 0 0 PSC 60 95 59 95 / 0 0 0 0 YKM 57 93 58 94 / 0 0 0 0 HRI 60 94 60 94 / 0 0 0 0 ELN 55 85 56 91 / 0 0 0 0 RDM 49 91 50 92 / 0 0 0 0 LGD 56 94 55 94 / 0 0 0 0 GCD 53 96 55 95 / 0 0 0 0 DLS 59 89 60 94 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Red Flag Warning until 10 PM PDT Saturday for ORZ691. Air Quality Alert until noon PDT Monday for ORZ050-502-503-505- 506-508.