textproduct: Pendleton

KEY MESSAGES

- Multiple Red Flag Warnings in effect for abundant lightning today through tomorrow

- Isolated to scattered thunderstorms and showers will develop over the Cascades and eastern mountains through Saturday, with gusty outflow winds possible

- Smokey conditions will continue while temperatures will be near normal through the week

DISCUSSION

Water vapor imagery shows upper level troughing over the PacNW this afternoon, with a shortwave offshore Vancouver Island poised to drop into the trough later tonight. Area radar and visible satellite imagery shows isolated to scattered thunderstorms developing across portions of central/northeast OR and the WA Cascade east slopes. This activity will continue through this evening across most areas as a shortwave impulse rides the southwest flow aloft. The shortwave will tap into increasing monsoonal moisture (PWATS ~0.75in) and increasing instability (MUCAPE 250-750J/kg and low level lapse rates 9-10C). Convection will continue overnight across the eastern mountains as instability lingers and the shortwave impulse continues to push northeast.

Troughing will slowly push offshore through Saturday, all the while keeping south to southwest flow over the PacNW. Daily shortwave impulses will tap into the increased monsoonal moisture and surface instability, resulting in rounds of isolated to scattered thunderstorms developing over the Cascades and eastern mountains. For tomorrow, the best instability (300-600J/kg, low level lapse rates 9-10C) will be present over the WA Cascade east slopes and from the Elkhorn crest to Wallowa county. Expectation is that abundant lightning and gusty outflow winds will redevelop in these areas, producing a critical fire weather threat. By Saturday, the best activity will be focused over the Blue mountains, but an increase in moisture across the region will result in higher wetting rain potential with any developing showers and thunderstorms. Nonetheless, there is moderate confidence (60-70%) of elevated fire weather conditions developing owing to lightning potential outside of rain cores and gusty outflow winds.

Sunday into the middle of next week, ensemble cluster solutions are still in disagreement on the evolution of the overall synoptic pattern. While there is good agreement (55-65% confidence) in a closed low developing well offshore the PacNW, ensemble clusters either favor the closed low strengthening and reminding offshore through Wednesday, or the low weakening with an open wave trough sliding across the PacNW into the middle of the week. Through Tuesday, either solution still places a mid to upper level southwest flow over the PacNW, which will result in continued chances (15-30%) of isolated to widely scattered showers/thunderstorms over the mountains.

Otherwise, the lack of strong system moving over the region will prevent smoke from clearing out, with smoke from area wildfires to continue to inundate portions of the forecast area into next week. Lawhorn/82

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

VFR conditions with light winds (less than 15 knots sustained) with mostly elevated smoke. Might see some plumes make its way down to the surface in the early morning hours, but nothing to suggest any prolong sub-VFR conditions. There's a 5 to 15 percent chance for any TAF site to experience temporary MVFR conditions until the smoke/haze lifts. Otherwise, the only chance for some precipitation is in BDN with a PROB30 of thunderstorms in the afternoon hours. Might see a small chance of showers near RDM, depending if coverage pushes through. Otherwise, a mostly dry TAF forecast for now.

FIRE WEATHER

Increased surface moisture and instability across the region will bring isolated to scattered thunderstorm threat into the weekend. The abundant lightning threat today will be along the WA Cascade east slopes, central OR, and the eastern OR mountains. The threat will shift out of central OR tomorrow and Saturday, but remain in the other two areas. Gusty outflow winds will also be a concern from stronger storms that develop. Winds will be mostly light to locally breezy through the weekend.

Preliminary Point Temps/PoPs

PDT 54 87 54 89 / 0 0 0 20 ALW 59 89 60 91 / 0 0 0 30 PSC 58 91 57 93 / 0 0 0 10 YKM 60 88 60 90 / 10 10 10 10 HRI 58 90 60 92 / 0 0 0 20 ELN 57 83 56 86 / 20 30 10 10 RDM 48 85 50 86 / 0 10 10 10 LGD 55 86 54 87 / 60 30 10 60 GCD 54 85 54 88 / 70 30 10 30 DLS 63 90 63 90 / 0 10 10 10

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 3 PM PDT Friday for WAZ026>030-521>523. Red Flag Warning from noon to 9 PM PDT Friday for WAZ695. OR...Air Quality Alert until 3 PM PDT Friday for ORZ041-049-050-502- 503-505-506-509>511. Red Flag Warning from 5 AM to 7 PM PDT Friday for ORZ694. Red Flag Warning until 7 PM PDT Friday for ORZ695-697-699. Red Flag Warning until 5 AM PDT Friday for ORZ696-698.