textproduct: Pendleton

KEY MESSAGES

- Red Flag Warnings in effect through 11 PM this evening for abundant lightning and gusty outflow winds for the northern Blue Mountains.

- Breezy to windy westerly winds today will overlap with low relative humidity across much of the forecast area. Red Flag Warnings and Wind Advisories are in effect through this evening.

DISCUSSION

A low-pressure system currently centered near the OR/WA coast will continue to drive an active weather day across the region. Cross-Cascade surface pressure differences have been a bit weaker than anticipated yesterday; observed values in the 7-8 mb range (Portland to Spokane) are a few millibars shy of what we would like to see for widespread windy conditions. That said, NWP guidance shows an increase to 9-11 mb through the remainder of the afternoon and into the evening. Coupled with a 25-35 kt 850-mb jet through the Cascade gaps and across the Columbia Basin, still anticipating widespread breezy conditions, so have retained the previously issued Wind Advisories which remain in effect through this evening. Additionally, have added patchy blowing dust to the forecast for dust-prone locations within the Columbia Basin region. Confidence is low in timing, magnitude, and duration of any visibility reductions, but given the extended dry conditions, forecast winds will be capable of lofting dust.

High-based showers are ongoing across the eastern third of our forecast area, roughly along and east of a line extending from Grant County through Umatilla, Walla Walla, and Franklin counties. Gusty outflow winds in excess of 45 mph have been observed with shower activity in Wallowa County. Additional shower and thunderstorm development will be capable of producing strong, gusty outflow winds due to a deep, well-mixed boundary layer; DCAPE values of roughly 1000-1400 J/kg are in place over the region. CAMs have loosely clustered around the northeastern portion of the Blue Mountains from the Elkhorns north through the northern Blue Mountains for additional thunderstorm development this afternoon. A wide range of solutions remains present among CAMs, many of which produce no significant convection while others initiate and maintain rather robust cells over the aforementioned area. Should robust convection develop, an environment characterized by ample effective shear (30-45 kts) and MUCAPE in excess of 500 J/kg will be capable of maintaining a few strong thunderstorms. Moreover, stronger storms will be capable of producing small hail and severe outflow winds in excess of 60 mph.

The low-pressure system will track inland across northern Washington this evening through Sunday, with low (5-10 percent) precipitation chances into tonight. Breezy westerly winds will continue into Sunday, though not anticipating the need for additional headlines for wind or fire weather.

Ensemble NWP guidance is in subjectively excellent agreement that a ridge of high pressure will rebuild over the Pacific Northwest by Monday, while a pair of closed lows (one in the Gulf of Alaska, and the other farther south in the eastern Pacific) attempt to merge. A low (5-15 percent) chance of showers and thunderstorms is forecast for the southern Blue Mountains on Monday, with otherwise above-normal temperatures and dry conditions.

Later Tuesday through Friday, the then-merged lows (per ensemble mean 500-hPa heights/vorticity and deterministic solutions) will likely (90 percent confidence) track towards the Pacific Northwest (later Tuesday or Wednesday) and eventually inland (Thursday or Friday). This scenario would result in breezy westerly winds through the Cascade gaps and low chances (20 percent or less) of showers and thunderstorms.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

VFR conditions initiate and maintain through the forecast period. DLS/PDT/ALW will see periods of breezy conditions throughout the forecast period with 15 to 25 knot gusts. ALW is forecasted to improve by 00Z while PDT/DLS will see general breezy winds, though not as strong as prior. This should help keep smoke lifted, but ALW/PSC could see a small chance (5 to 15 percent) of MVFR conditions developing overnight with smoke making its way down to the surface.

FIRE WEATHER

A low-pressure system currently centered near the OR/WA coast will continue to produce widespread breezy to windy westerly winds of 15-25 mph with gusts of 25-40 mph, locally stronger, through this evening. Moreover, a very low to slight chance (5-20%) of high-based showers and thunderstorms will continue roughly from Grant and Umatilla counties eastward to Wallowa County through this evening. Any showers and thunderstorms will be capable of producing strong, gusty outflow winds of 40-60 mph. Red Flag Warnings remain in effect for wind and low relative humidity (WA690, WA691, OR691, OR696, OR698, OR700, and OR703) as well as abundant lightning and gusty outflow winds (OR/WA692) through this evening.

Breezy winds will continue overnight into Sunday as the low- pressure system exits to the northeast, but overlap of critical wind/RH thresholds is unlikely (<30% chance).

Preliminary Point Temps/PoPs

PDT 49 82 48 89 / 0 0 0 0 ALW 57 84 55 92 / 0 0 0 0 PSC 58 86 52 92 / 0 0 0 0 YKM 59 86 56 90 / 0 0 0 0 HRI 58 85 52 91 / 0 0 0 0 ELN 54 77 50 86 / 0 0 0 0 RDM 45 83 45 90 / 0 0 0 0 LGD 51 85 48 93 / 10 0 0 0 GCD 53 87 51 95 / 0 0 0 0 DLS 61 83 58 92 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523. OR...Air Quality Alert until noon PDT Monday for ORZ041-044-049-050- 502-503-505>507-509>511.