textproduct: Pendleton

KEY MESSAGES

- Widespread rain showers and breezy to windy conditions will develop throughout today, with an isolated thunderstorm or two in the Washington Cascades

- Wind Advisories in effect today from Central Oregon to the Lower Columbia Basin

- Dry conditions and light winds return over the weekend, then a return of periodic light showers in the Cascades next week

DISCUSSION

Satellite and radar imagery tonight show a surface low and upper trough swinging into the PacNW, with a cold front pushing a band of rain across the Cascade east slopes.

Today through Sunday: The north/south oriented band of rain leading the cold front and surface low will continue to push east this morning and exit in the afternoon. Post frontal showers will continue across the Cascade crest and east slopes thanks to support from the upper trough passage, but will diminish through the evening hours as the trough exits to the northeast. There remains a widespread 60-90% chance of at least measurable rain across much of the forecast area today, with only a 30-45% chance of 0.25 inches in the northern Blues and a 65-95% chance of 0.5 inches along the Cascade crest and east slopes. In addition to precipitation, the upper trough and surface low passage will bring increasing west to southwest winds across the forecast area. Winds will be 25-35 mph with gusts 35-50 mph through the Cascade gaps, central OR, and into the Columbia Basin and adjacent foothills/valleys. Winds 15-25 mph and gusts up to 35 mph are expected in most other locations, with stronger winds along the Cascade Crest. Surface winds will be supported by a 40-50kt low level jet that will mix down across portions of the Columbia Basin this afternoon. Wind advisories are in effect across central/north central OR, Columbia Basin/Gorge, Yakima Valley, and the Blue Mountain foothills from 8AM to 11PM today.

Shower activity and windy conditions will diminish tonight into Saturday as the upper trough and surface low exit to the northeast. Deterministic and ensemble guidance continue to depict weak broad troughing developing offshore the PacNW Saturday, then sliding across the region through Sunday. The trough passage will lack moisture and mid to upper level jet support, resulting in dry conditions with light winds. It will however continue to support below normal temperatures across the region, with afternoon highs in the 60s. While widespread overnight freezing temperatures (outside of the mountain zones) are not expected to develop, areas of the Wallowa valley and central OR will see a 25-65% chance of freezing morning temperatures Saturday. The make or break for freezing temperatures will be cloud cover in the overnight and early morning hours, though confidence is low (25-35%) in extent of cloud cover for tomorrow morning.

Monday through Thursday: Ensemble guidance is in good agreement of mostly zonal flow developing over the PacNW as an upper trough develops over AK and northern BC and ridging out in the eastern Pacific through Tuesday. While Monday will remain mostly dry, ensemble cluster solutions hint at a shortwave and attendant weak frontal passage bringing light rain showers to the Cascade crest and east slopes throughout Tuesday, though about 30-45% of cluster members bring light rain to the northern Blues latter half of Tuesday. Winds are favored to remain light to locally breezy with the system passage Tuesday (confidence 60-65%).

Disagreement grows amongst ensemble members mid week in the evolution of the synoptic pattern. Solutions range from ridging Wednesday then upper trough passage Thursday to slow moving troughing Wednesday into Thursday. Either solutions would favor more mountain precipitation, but with plenty of disagreement amongst the members, confidence is low (20-25%) in extent, timing, and amounts of precipitation next week.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

VFR conditions to prevail through the period. Cold front passage will continue to bring rain shower impacts to all sites this morning, with showers expected to end in western sites around 13-14Z, and showers to impact sites PSC/PDT/ALW between 12Z to 16-18Z.

Winds will increase through this morning and persist through the afternoon, with winds generally 15-25kts and gusts 30-40kts. Winds will decrease in the evening across most sites, though sites PDT/ALW will see breezy winds persist to around 6-8Z. While not included in the current TAF, there is a chance (50-70%) that gusts may periodically reach 40kts or greater at site PSC between 18Z-00Z. Will continue to monitor incoming guidance, as an airport weather warning may be warranted during that period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 69 40 65 41 / 90 0 0 0 ALW 69 45 66 44 / 90 10 0 0 PSC 72 43 69 41 / 70 0 0 0 YKM 65 40 64 40 / 30 0 0 0 HRI 72 43 68 40 / 80 0 0 0 ELN 61 36 60 36 / 50 10 0 0 RDM 59 31 64 33 / 10 0 0 0 LGD 66 38 64 38 / 60 0 0 0 GCD 66 37 67 40 / 50 0 0 0 DLS 66 45 68 45 / 60 10 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 8 AM this morning to 11 PM PDT this evening for WAZ024-027-521. Wind Advisory from 11 AM this morning to 11 PM PDT this evening for WAZ028-029. OR...Wind Advisory from 8 AM this morning to 11 PM PDT this evening for ORZ041-044-507-508-510. Wind Advisory from 8 AM this morning to 5 PM PDT this afternoon for ORZ511.