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 /06Z TAFS THROUGH 06Z THURSDAY/

VFR conditions persist through the period with the exception of RDM which is seeing MVFR conditions and a VIS of 5SM due to low level smoke. The smoke at BDN is expected to persist through 09Z.

Breezy winds are expected DLS through 00Z. Winds will be generally light elsewhere at less than 12 knots sustained with elevated smoke in the region.

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 91 57 93 / 0 0 0 0 ALW 62 92 64 95 / 0 0 0 0 PSC 57 93 58 96 / 0 0 0 0 YKM 59 93 62 97 / 0 0 0 0 HRI 59 93 60 95 / 0 0 0 0 ELN 59 89 59 93 / 0 0 0 0 RDM 47 93 51 95 / 0 0 0 0 LGD 53 94 57 97 / 0 0 0 0 GCD 55 96 57 98 / 0 0 0 0 DLS 60 92 62 97 / 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.