textproduct: Pendleton

KEY MESSAGES

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

- Red Flag warning in effect for portions of the Blue Mountains, WA Cascade east slopes, and Wallowa County today and tomorrow

- Isolated mountain thunderstorms continue through early next week with a return of breezy winds through the Cascade Gaps

DISCUSSION

Water vapor imagery this afternoon shows a pronounced upper low circulation offshore the CA/OR border with upper level troughing extending north across the PacNW. Much like yesterday, area radar and visible satellite imagery show isolated to scattered showers/thunderstorms that have developed across the Cascade east slopes, central/southern Blue mountains, and around the Wallowa mountains. Thunderstorm activity will continue through this evening as a weak shortwave impulse pushes northeast across the PacNW, with thunderstorm activity mainly staying mainly across the mountainous terrain. The shortwave will be supported by modest MUCAPE (250-750 J/kg), low level lapse rates 9-10C, and PWATS around 0.75 inches. By late tonight into early tomorrow morning, another shortwave will rise north across the PacNW, with light showers developing as a result. CAMs are also showing low MUCAPE (around 100-250J/kg) lingering across central and northeast OR, which will bring a low chance (~15%) of showers producing infrequent lightning strikes.

The shortwave will continue to lift across the PacNW through the early evening, bringing yet another round of isolated to scattered thunderstorms across the Cascades, Blues, and Wallowa county. Modest MUCAPE and low-level lapse rates will aid in thunderstorm development through the afternoon, especially across the Blue mountains and Wallowa county. The biggest change will be the increase in monsoonal moisture, with PWATs approaching 1 inch across portions of northeast OR and southeast WA, allowing thunderstorms to produce heavy rain. That said, abundant lightning will still be a threat outside of the main rain cores across the mountainous terrain.

Sunday and Monday, a developing upper level low will retrograde into the northeast Pacific, stretching upper level troughing over the PacNW. This will result in mainly isolated thunderstorms/showers across the mountains in the afternoons. At the surface, the cross-Cascade pressure gradient will begin to tighten, resulting in breezy west winds developing through the Cascade gaps. Winds will strengthen in the afternoons, with the stronger winds (15-20mph with gusts up to 35mph) developing Monday afternoon.

Late Monday through Tuesday, there is good agreement that a shortwave trough diving out of BC will clip the PacNW, bringing with it increased westerly winds through the Cascade gaps, but mostly dry conditions.

Wednesday through Thursday, ensemble clusters are in good agreement of the upper level trough/low remaining offshore, but are split on the development of upper level ridging extending into the area. The solutions range from mainly diffluent to zonal flow persisting over the PacNW with continue dry and mild conditions, to south to southwest flow which would signal the potential for isolated shower/thunderstorm activity over the mountains but continued near seasonable temperatures. Confidence is low (25-35%) in the afternoon forecast for those days. Lawhorn/82

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Smoke will continue to have a marginal impact on the visibilities at area terminals this TAF period, Light winds under 12 knots are expected through the fore cast. Earlier concerns of convection around the central Oregon terminals appears muted at this point based on radar trends and weaker normalized CAPE values around RDM/BDN. MVFR cat vsbys in smoke may develop around the BDN/PDT terminals this evening, improve overnight and return Saturday morning.

FIRE WEATHER

Increased monsoonal moisture and instability across the region will continue to bring an isolated to scattered thunderstorm threat through Saturday. Abundant lightning and gusty outflow wind threat will be across the WA Cascade east slopes and eastern mountains today, then across the Blue Mountains and Wallow County Saturday. Isolated mountain storm chances (15-25%) will continue Sunday and Monday. Breezy winds through the Cascade gaps will return Monday and Tuesday next week.

Preliminary Point Temps/PoPs

PDT 55 87 56 89 / 0 30 0 0 ALW 60 89 62 91 / 0 30 10 0 PSC 57 91 57 93 / 0 20 0 0 YKM 59 90 60 92 / 0 10 10 0 HRI 59 90 59 92 / 0 30 0 0 ELN 56 85 58 86 / 10 20 10 0 RDM 50 85 49 87 / 20 10 10 0 LGD 55 87 54 89 / 20 60 20 30 GCD 55 88 54 91 / 20 20 10 10 DLS 64 90 62 92 / 10 10 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523. Red Flag Warning from noon to 9 PM PDT Saturday for WAZ692-693. Red Flag Warning until 9 PM PDT this evening for WAZ695. Air Quality Alert until noon PDT Saturday for WAZ027-521. OR...Air Quality Alert until noon PDT Monday for ORZ041-503-505-506- 508>511. Red Flag Warning until 7 PM PDT this evening for ORZ694-695- 697-699. Red Flag Warning from noon to 9 PM PDT Saturday for ORZ692>695- 699.