textproduct: Pendleton

KEY MESSAGES

- Red Flag Warning in effect for the Lower Columbia Basin of Oregon 2PM PDT this afternoon until 10PM PDT Saturday due to breezy winds and low relative humidity.

- Breezy conditions through Saturday, especially for the Columbia Basin, Gorge, Kittitas Valley, Simcoe Highlands.

- Temperatures will be a bit cooler today and Saturday then will rise Sunday into next week and widespread Moderate HeatRisk returns as well with some 30 to 50 percent probabilities of Major HeatRisk in the Basin and Yakima Valley by midweek.

DISCUSSION

Latest radar showed isolated showers and a few thunderstorms mainly from Tri-Cities eastward early this morning. These developed in some lingering instability. Guidance suggests these showers and thunderstorms should hang around through the morning before dissipating.

The upper low off the Washington coast continues to move northward. By late afternoon, it should move into British Columbia. As the low moves further into British Columbia and eventually further east around the periphery of high pressure, its associated trough will weaken and be absorbed into the large flow. This will permit the strong ridge over the Rockies to move westward.

As this happens early next week, temperatures are expected to rise. Exactly how hot we get is still a bit in question but both the GFS and ECMWF ensembles put the Columbia Basin at or above 105 degrees Tuesday through Thursday, and at least 10 percent of the members are 110 degrees. Widespread Moderate HeatRisk will return and the potential for Major HeatRisk, especially across the Columbia Basin reaches 30 to 50 percent, and could end up being higher. Ultimately, the position of the high and smoke from any wildfires will play into the equation as well.

Winds will be a bit breezy, especially across the Gorge, Basin, Kittitas Valley and Simcoe Highlands through Saturday, then should decrease as the high builds in. RH values will be in the teens through Saturday, but wind gusts should be in the 20 to 30 mph range. Elevated fire weather conditions can be expected, but the wind criteria will have to be watched, but looks to be just shy of what is needed for any headlines.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Predominantly VFR conditions are anticipated through the period, with mostly clear to clear skies. However, smoke from area wildfires will drive significant uncertainty in VSBY forecasts (and to a lesser degree CIG forecasts) at RDM/BDN/PDT/ALW. Confidence was too low in timing/magnitude of any VSBY reductions to include anything below 6SM in the 18Z TAFs, but confidence is high (80%) that periods of sub-VFR VSBYs will occur in FU and HZ.

Winds will be diurnally and terrain-driven, breezy in the afternoon and evening hours and strongest at DLS.

FIRE WEATHER

Breezy diurnally driven westerly wind and low relative humidity is expected through the Cascade gaps each afternoon and evening through Saturday, leading to elevated to critical fire weather conditions. A Red Flag Warning has been issued for OR691, the Lower Columbia Basin of Oregon, from 2PM this afternoon through 10PM Saturday. Critical RH is not forecast overnight, but the warning was issued for a two-day event to simplify messaging. Confidence was a bit too low (<60%) in overlap of critical wind/RH for WA690, the Kittitas Valley, on Saturday to issue any headlines this morning.

There is a slight chance (15 percent) of showers and thunderstorms across the northeast Blue Mountains today.

Very warm to hot, and dry conditions are then forecast early next week, followed by a slight chance (10-20 percent) of showers and thunderstorms over the mountains by mid-week.

Preliminary Point Temps/PoPs

PDT 90 57 91 56 / 0 0 0 0 ALW 93 63 93 62 / 0 0 0 0 PSC 95 60 95 59 / 0 0 0 0 YKM 94 57 93 58 / 0 0 0 0 HRI 93 60 94 60 / 0 0 0 0 ELN 88 55 85 56 / 0 0 0 0 RDM 89 49 91 50 / 0 0 0 0 LGD 94 56 94 55 / 0 0 0 0 GCD 96 53 96 55 / 0 0 0 0 DLS 87 59 89 60 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Red Flag Warning from 2 PM this afternoon to 10 PM PDT Saturday for ORZ691.