textproduct: Pendleton

KEY MESSAGES

- Breezy winds and low relative humidity producing elevated to critical fire weather conditions through this evening

- Drying and warming trend into Friday as upper level high pressure builds over the region, with elevated fire weather concerns due to dry and unstable conditions

- Breezy winds developing Saturday, with uncertainty in timing/extent of thunderstorms/showers Friday through Sunday morning

DISCUSSION

Visible satellite imagery shows mostly clear skies across the forecast area this afternoon, though several smoke plumes are visible across the Cascade east slopes and in the northern Blue mountains. Meanwhile, water vapor imagery shows an upper low offshore western CONUS while a shortwave trough slides into western MT.

The shortwave trough passage through the region has resulted in a strengthening of the cross Cascade pressure gradient today. Breezy gap winds extending into the Columbia Basin will persist through the evening, then decrease with the weakening of the surface pressure gradients overnight. Though several days of thunderstorms moved through the area, dry conditions have settled back into the region, and combined with the breezy winds, will bring elevated to critical fire weather conditions through the evening.

Tomorrow through Thursday, upper level ridging will build into the PacNW resulting in a warming and drying trend with light winds. Daytime temperatures will rise into the lower to upper 90s in the lower elevations by Thursday, with Thursday night lows only cooling into the lower to mid 60s across much of the area (cooler in central OR and mountain valleys/basins). Rising lapse rates (and mixing heights) under the upper ridge will bring elevated fire weather concerns across the high terrain, as the combination of dry and unstable conditions may lead to increased fire behavior through Thursday.

Friday through Sunday, ECMWF and GFS ensemble members are in good agreement that the upper low offshore western CONUS will become an open wave as it lifts into the PacNW, bringing with it rounds of isolated to widely scattered thunderstorms, breezy to locally gusty winds, and cooler temperatures. However, agreement on timing, intensity, and location are poor. GFS ensemble mean shows it's members (and the deterministic) favoring the upper trough coming inland late Friday evening and overnight, triggering nocturnal isolated thunderstorms across the forecast area during that time period. Meanwhile, ECMWF members (and it's deterministic/control) favor a later passage by about 6 to 12 hours, with isolated thunderstorms developing very early Saturday morning across the Cascade east slopes, then late evening thunderstorms developing over the Blues and Wallowa county. Both solutions do favor breezy winds developing through the Cascade gaps Saturday, with ECMWF members favoring stronger winds then those of the GFS members. Forecast confidence is at least moderate (45-60%) in the upper trough passage occurring through the weekend, however there is low confidence (20-25%) in forecast details.

By next Monday, there is moderate confidence (55-60%) in upper level ridging building back over the region with dry and warm conditions with light winds. Lawhorn/82

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

VFR conditions prevail with breezy winds in DLS and PDT. Winds will be generally light at less than 12 knots sustained with elevated smoke in the region. A small chance (5 to 15 percent) exists for some low-level smoke bringing temporary MVFR conditions for all TAF sites.

FIRE WEATHER

Breezy winds through the Cascade Gaps will overlap with low RH in the OR Columbia Basin, eastern Gorge, and around Warm Springs through this evening. Hot, dry, and unstable conditions will develop Wednesday through Thursday as high pressure builds overhead. Friday into the weekend, there is increasing potential for a return of isolated thunderstorms across the area, with breezy to locally windy conditions through the Cascade gaps and Columbia Basin. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 54 90 56 93 / 0 0 0 0 ALW 62 92 63 95 / 0 0 0 0 PSC 57 92 56 96 / 0 0 0 0 YKM 59 92 61 96 / 0 0 0 0 HRI 59 92 59 95 / 0 0 0 0 ELN 59 88 59 92 / 0 0 0 0 RDM 47 91 50 94 / 0 0 0 0 LGD 53 93 56 97 / 0 0 0 0 GCD 55 95 57 99 / 0 0 0 0 DLS 60 91 61 96 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until 1 PM PDT Wednesday for ORZ041-505-506- 509>511. Red Flag Warning until 10 PM PDT this evening for ORZ691-701- 703.