textproduct: Pendleton

KEY MESSAGES

- 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

DISCUSSION

Slowly building ridging through Friday across the Interior Northwest while the upper flow across the PAC NW become more southerly with time. A large area of 500 mb low pressure near 35N and -137W is the system that will pivot toward the PacNW coast by Friday Night and Saturday time-frame, effectively breaking down the ridge over the Interior of WA/OR and bringing at last a small risk for showers and thunderstorms to the mountains, and overall cooler temperatures each afternoon through the weekend. An abrupt increase in surface winds is likely by Friday through any of the the Gaps and most pronounced across the Columbia River Gorge and Lower Basin though the entirety of Saturday night until the upper low exits northeast as a trough into the Canadian Rockies.

Thursday and Friday will be the hottest days of the next 7 , with temperatures in the 90s across the Columbia Basin, Central Oregon, and the other valley floors. Thursday , HeatRisk reaches an elevated moderate (orange) levels across parts of the Yakima/Kittitas valleys, north central Oregon, and southeast Washington, but not widespread or high enough for heat advisories. Showers are forecast across the Cascade crest on Friday, and RRFS shows some lightning potential late afternoon Friday along the Cascade crest. Uncertainty remains as the NBM Dry lighting chances are still under a 10% chances even across the across the Blue Mountains, and the EC/GFS have differing timing solutions with the incoming wave. At this time the best chances for Thunderstorms are about 15% across the Eastern Blues on Saturday afternoon coinciding with max heating.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

VFR conditions (except for the DLS which sets at 5 SM initially). Lingering smoke in the area will bring small chances (5 to 15 percent) of MVFR conditions developing for all TAF sites. Greatest chances of surface smoke settling will be in the late evening to overnight hours, with daytime mixing lowering those chances.

FIRE WEATHER

Low relative humidity will be expected each day though Friday, with winds that are light (under 10 mph) and variable. Winds become much more significant around Friday Night and on Saturday as an upper wave influences the region, while not as hot temperatures temper the low relative humidity in these more wind prone areas. At this time the need for a fire weather watch is low as chances for dry thunder remain less than 10% based on NBM members on Friday and no critical humidity and wind thresholds overlap.

Preliminary Point Temps/PoPs

PDT 91 56 94 61 / 0 0 0 0 ALW 92 64 96 67 / 0 0 0 0 PSC 93 56 96 61 / 0 0 0 0 YKM 93 61 97 64 / 0 0 0 0 HRI 93 59 96 63 / 0 0 0 0 ELN 89 60 93 63 / 0 0 0 0 RDM 93 50 95 55 / 0 0 0 0 LGD 94 57 97 61 / 0 0 0 0 GCD 96 57 98 61 / 0 0 0 0 DLS 92 62 97 65 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until 1 PM PDT this afternoon for ORZ041-505- 506-509>511.