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 (99 percent confidence) Friday into the weekend

- Chance (25-35 percent) of thunderstorms for the Blue Mountains on Friday, with a very low chance (5-14 percent) to slight chance (15-24 percent) elsewhere

DISCUSSION

Water vapor imagery shows a closed low moving southeast along the coast of British Columbia and southeast Alaska. Meanwhile, a shortwave wrapping around the base of the low will continue to track inland over the Pacific Northwest during the afternoon and overnight hours, with precipitation expected to accompany the wave.

Breezy to windy westerly winds and low relative humidity are present across much of the region and Red Flag Warnings have been issued for multiple fire weather zones (see Fire Weather Section below for details).

A transition to a cooler, wetter pattern is likely (99 percent confidence) by tonight as the shortwave moves overhead, followed by the parent closed low over the weekend. Cluster analysis of 00Z ensemble members shows relatively small differences in timing/location and magnitude of the low during the period, so confidence is high in the current forecast of below-normal temperatures Friday through the weekend. However, even small differences in the track/timing of the low can have a significant impact on precipitation; the trend in ensemble guidance has been to keep the lower elevations relatively dry with precipitation focused over the mountains. The latest NBM shows a 10-30 percent chance of a wetting rain (0.10" or greater) across the Columbia Basin, a medium chance (40-60 percent) along the Blue Mountain foothills, and a high chance (70-100 percent) for the Cascade and Blue mountains as well as the valleys and basins within the Blue Mountains.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

VFR conditions to prevail through the period. A low-pressure system moving through the area will bring rain shower impacts to this evening into the overnight hours. Another round of showers may be possible (30-40% chance) at sites PDT/ALW after 19Z tomorrow. Breezy winds will continue to develop at sites late this afternoon, becoming light overnight. Breezy winds will return at sites DLS/RDM/BDN by tomorrow afternoon. Lawhorn/82

FIRE WEATHER

Fire weather concerns are present today, focused primarily across fire weather zones OR691, WA691, WA690, OR703, and WA694 as breezy to windy westerly winds (10-20 mph with gusts of 20-35 mph) overlap with low relative humidity of 10-20 percent.

Cooler, breezy, and showery weather with isolated to scattered thunderstorms (mainly for the mountains) is then forecast Friday through the weekend as an upper-level closed low pressure system moves over the Pacific Northwest. While isolated to scattered thunderstorms are forecast over the Blue Mountains, have not issued any fire weather headlines for a couple reasons. First, many of the fire weather zones which are forecast to receive lightning have not yet been declared ready for Red Flag Warnings this season. Second, anticipating the majority of the thunderstorms over the Blue Mountains to either produce a wetting rain (0.10" or more) or be preceded and/or followed by a wetting rain overnight through the weekend (70-95 percent chance). Elsewhere, the chance of wetting rain is low (10-30 percent) for the Columbia Basin to medium (40-60 percent) along the Blue Mountain foothills.

Preliminary Point Temps/PoPs

PDT 52 75 46 69 / 50 50 30 10 ALW 58 76 52 70 / 30 50 30 10 PSC 56 80 51 75 / 30 20 10 0 YKM 55 79 50 74 / 30 10 10 0 HRI 54 78 49 73 / 50 30 10 0 ELN 50 71 45 66 / 20 30 10 10 RDM 46 71 39 62 / 60 20 30 20 LGD 53 70 47 63 / 50 90 90 40 GCD 51 71 43 62 / 70 90 90 60 DLS 56 75 53 70 / 60 20 10 10

PDT WATCHES/WARNINGS/ADVISORIES

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