textproduct: Pendleton

KEY MESSAGES

- Multiple Red Flag Warnings in effect Today due to breezy winds and low relative humidity

- Cooler, breezy, and showery weather is likely (95 percent confidence) Friday into the weekend

- Chance of thunderstorms for the Blue Mountains on Friday, with a very low chance (5-14 percent) to slight chance (15-24 percent) elsewhere

DISCUSSION

Cooler temperatures are expected this afternoon by 5 to 10 degrees on average as more dense sky cover overspreads the region during the afternoon in advance of an upper level low and westerly jet over the northeast Pacific spreading westerly diffluent mid level flow across the Cascade range. This will bring isolated to scattered mountain showers to the Cascades crest mainly This evening with low enough instability that thunderstorms are not showing up across the HREF members. Broader, stronger surface winds indicated by the NBM showing 25 to 35 knots (roughly 30 to 40 mph) are seen across the Simcoe Highlands, and Lower Columbia Basin/River Gorge This Afternoon, with breezy conditions in all other other zones, barring the eastern mountains. The coolest temperatures of the next 7 days fall over the weekend, as the EC/GFS and Canadian models all drive a second shortwave farther south into SW Oregon/nrn CA helping to carve out the upper low broadly over the Interior NW with unseasonably cool air aloft (560dm 500 mb low). Precipitation probabilities jump to 90% across the Cascades and Eastern Mountains by Friday Afternoon and Evening and begins to back off over the weekend.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

VFR conditions are forecast at all sites for the next 24 hours. CIGs will lower through the day as a low-pressure system approaches from the Pacific, and rain showers are forecast to spread east of the Cascades later this afternoon/early evening into the overnight hours. Cannot rule out sub-VFR CIGs, but confidence is low at less than 30 percent for all sites. Winds will become breezy today with lighter winds returning overnight for most sites.

FIRE WEATHER

Despite increasing cloud cover and not quite as hot temperatures, critical fire weather is possible to likely across several zones This Afternoon. The breezier to gusty winds will be the tipping point as an incoming system aids the development of gap winds and gusty winds across the Lower Columbia Basin. Went ahead and added WA694 to the group of Red Flag Warned zones as eastern sections of this zone came in with 70-80% confidence in 25% or less RH and 15 mph or higher winds this afternoon, especially western sections of the Toppenish Ridge and vicinity. No other changes to previous red flags, which include OR703, OR/WA691 and WA690. For Friday, the breezy winds continue however relative humidity levels drop out of the critical criteria. As the cooler air aloft moves in over the next 2-3 days, increased wetting rain opportunity unfolds Friday Afternoon and overnight into Saturday morning for the higher elevation mountain zones.

Preliminary Point Temps/PoPs

PDT 85 52 75 46 / 0 50 50 30 ALW 87 58 76 52 / 0 30 50 30 PSC 89 56 80 51 / 0 30 20 10 YKM 86 55 79 50 / 0 30 10 10 HRI 87 54 78 49 / 0 50 30 10 ELN 81 50 71 45 / 0 20 30 10 RDM 82 46 71 39 / 0 60 20 30 LGD 85 53 70 47 / 0 50 90 90 GCD 86 51 71 43 / 0 70 90 90 DLS 83 56 75 53 / 0 60 20 10

PDT WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning until 8 PM PDT this evening for WAZ694. Red Flag Warning until 9 PM PDT this evening for WAZ690-691. OR...Red Flag Warning until 9 PM PDT this evening for ORZ691. Red Flag Warning until 8 PM PDT this evening for ORZ703.