textproduct: Pendleton

KEY MESSAGES

- Showers and isolated thunderstorms along the Cascade crest Friday and Saturday

- Breezy Cascade Gap winds today will spread to the lower elevations Friday and Saturday

- Dry conditions Sunday before an active weather pattern returns through the middle of next week

DISCUSSION

Today through Saturday: Satellite imagery today shows mostly clear conditions while surface observations report breezy winds through the Cascade gaps.

Dry conditions with locally breezy conditions will continue through the remainder of the day as the PacNW sits under a quasi-zonal flow. Flow aloft will gradually gain a southerly component tonight through tomorrow morning as an upper low drops out of the Gulf of Alaska, with the low arriving just offshore Vancouver Island by tomorrow afternoon. The low arrival will bring rain showers to the WA Cascade crest, while a tightening cross-Cascade pressure gradient will result in breezy winds (15-25 mph with gusts up to 40 mph) through the Cascade gaps and lower elevation areas. While fire weather concerns will overall remain low, there will be elevated conditions in the WA Columbia Basin as afternoon RHs dip below 25% and sustained winds will near 20 mph (confidence 30-50%).

Saturday, the upper low will swing across the PacNW, but limited moisture associated with this system will confine shower chances to the Cascade crest. Increasing surface instability with increased low to mid level lapse rates across the Cascade crest/east slopes will also allow for slight chances (15-25%) of isolated thunderstorms in the afternoon and early evening. Otherwise, breezy westerly winds will continue across the lower elevations through Saturday evening.

Sunday through Wednesday: By Sunday morning, mostly dry conditions and light winds will develop across the region as the upper low departs to the east and a transient ridge moves over the PacNW.

Early to mid next week, ensemble guidance is in good agreement that the PacNW will be under a prolonged troughing pattern that will bring widespread shower chances as the trough meanders across the region. There is some disagreement in the strength of the trough as it moves across the PacNW; about 25% of members favoring a closed low, which would result in higher precipitation amounts and better thunderstorm chances in the mountains Tuesday into Wednesday. Disagreement in position/timing of the trough/low passage also grows into the middle of next week, as ~30% of ensemble members favor the trough and showers exiting the region Wednesday afternoon, while the remaining members show showers and the trough still over the region. Confidence in precipitation chances through this period is moderate (60-70%), however confidence in timing is low (25-35%). Lawhorn/82

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

VFR conditions currently across all sites, which will stay the course through the period. 8-12kt wind overnight will increase to 20-30kts across all terminals through the morning and persist through the evening. Cloud cover will also increase and lower from 25kft to around 10kft by mid-to late morning. 75

FIRE WEATHER

Dry conditions and mostly locally breezy winds will persist today. A system approaching the region will bring widespread breezy winds tomorrow through Saturday. This will lead to elevated fire weather concerns in the WA Columbia Basin in the afternoon (30-50% chance of wind/RH criteria being met). Showers and isolated thunderstorms will develop along the Cascade crest tomorrow through Saturday, with dry conditions and light winds returning Sunday. An active weather pattern returns next week.

Preliminary Point Temps/PoPs

PDT 47 72 44 66 / 0 0 0 0 ALW 52 74 50 67 / 0 0 0 0 PSC 49 77 48 71 / 0 0 0 0 YKM 47 74 44 68 / 0 0 0 20 HRI 50 74 46 69 / 0 0 0 0 ELN 43 66 39 60 / 0 0 0 40 RDM 39 73 38 62 / 0 0 0 0 LGD 43 74 43 63 / 0 0 0 0 GCD 41 79 41 64 / 0 0 0 0 DLS 51 71 49 66 / 0 0 10 30

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.