textproduct: Pendleton

KEY MESSAGES

- Red Flag Warning in effect today for the lower Columbia Basin of Oregon (OR691)

- Hot, dry, and breezy Wednesday, then warm, dry and breezy to windy Thursday with continued fire weather concerns

- Cooler, wetter weather pattern likely (90 percent confidence) Friday into the weekend

DISCUSSION

Water vapor imagery shows a shortwave from the Pacific approaching the OR/WA coast early this afternoon. Cirrus is overspreading the forecast area in advance of the wave, and a cumulus field is developing over the central Oregon Cascades and higher terrain of the Blue Mountains. As the shortwave moves overhead later this afternoon through the evening, there is a very low to slight chance (5-15 percent) of high-based showers and thunderstorms across the Cascades, Blues, and Blue Mountain foothills.

Locally breezy northeasterly winds (10-20 mph with higher gusts) coupled with low relative humidity (10-20 percent) have prompted a Red Flag Warning for OR691 (lower Columbia Basin of Oregon) through 8 PM PDT this evening (see Fire Weather section below for additional details).

The Heat Advisory that was in effect for the eastern Columbia River Gorge of Oregon and Washington today was cancelled as temperatures have been a few degrees cooler than previously anticipated, lowering the overall risk of heat-related impacts. That said, widespread Moderate (level 2 of 4) HeatRisk is still forecast across the lower elevations of the forecast area today and tomorrow. This level of heat primarily affects those who are sensitive to heat, especially those without cooling/hydration.

Wednesday, another weak shortwave trough is expected to move over the forecast area. While confidence in exact location is still uncertain, have increased PoPs across the mountains (Cascades and Blues) and Yakima/Kittitas valleys to account for a very low (5-14 percent) to slight chance (15-24 percent) of high-based showers and thunderstorms during the afternoon and evening hours. The best chances will be along the higher terrain of the east slopes of the Washington Cascades (away from the crest).

Breezy westerly winds in tandem with low relative humidity will facilitate another round of fire weather concerns Wednesday afternoon and evening (see Fire Weather section below for details).

By Thursday, the closed low currently developing in the Gulf of Alaska is expected (90 percent confidence) to move southeast along the coast of British Columbia and southeast Alaska. A shortwave wrapping around the base of the low is forecast to move inland over the Pacific Northwest during the afternoon. Breezy to windy westerly winds and low relative humidity are anticipated and fire weather headlines may be needed (see Fire Weather Section below for details).

A transition to a cooler, wetter pattern is likely (90 percent confidence) by Thursday night as a second 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 so stay tuned as details become clearer.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

VFR conditions will persist through the period with light winds less than 12 knots for PDT/YKM/ALW/PSC/DLS. RDM/BDN will see an increase in winds of 10-13G17-21KT before settling to 10kts after 01-04Z respectively. No CIG or VIS issues expected.

Preliminary Point Temps/PoPs

PDT 56 92 59 86 / 0 0 0 0 ALW 61 93 64 88 / 0 0 0 0 PSC 59 96 61 90 / 0 0 0 0 YKM 61 95 59 88 / 0 0 10 0 HRI 58 95 63 88 / 0 0 0 0 ELN 60 91 59 82 / 0 10 10 0 RDM 52 88 48 83 / 0 0 10 0 LGD 54 89 54 86 / 10 0 0 0 GCD 52 91 52 87 / 0 0 0 0 DLS 64 94 62 84 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Red Flag Warning until 8 PM PDT this evening for ORZ691.