textproduct: Pendleton

KEY MESSAGES

- Mountain snowfall today

- Widespread windy conditions today

- Warmer, drier conditions return for the weekend

DISCUSSION

Afternoon and evening convection that brought gusty outflow winds, locally heavy rainfall, and isolated lightning to the Blue Mountain foothills and eastern portions of the lower Columbia Basin has exited to the northeast. No additional thunderstorms are forecast early this morning, but there are low (10-15 percent) chances of isolated thunderstorms across the Blue Mountains and their foothills again this afternoon.

Attention now returns to ongoing and forecast snow showers across the mountains as an upper-level low moves over the Pacific Northwest. Winter weather headlines remain in effect for the Cascades today where snow showers are likely (70 percent chance) to result in additional accumulations of 4-6 inches for the Oregon Cascades and 2-4 inches for the Washington Cascades. For the northern Blue Mountains, confidence in advisory-level snowfall associated with wrap-around showers as the low tracks overhead today is low (10-30 percent, highest above 5000 ft), so have held off on issuing any winter weather headlines there.

In addition to the winter weather, widespread breezy to windy conditions are expected (80 percent confidence) today, especially during the afternoon hours, in a well-mixed, post- frontal environment as the upper low tracks overhead and then east of the forecast area. Surface pressure differences between PDX (Portland) and GEG (Spokane) from current deterministic NWP guidance range from 8 to 12 mb. Moreover, a 30-40 kt low-level jet is advertised by the 00Z HREF. Glancing at probabilistic guidance, the NBM is showing medium-high (50-90 percent) probabilities of exceeding advisory-level wind gusts (45 mph or greater) for much of the Columbia Gorge, Kittitas Valley, foothills of the Blue Mountains, and portions of the lower Columbia Basin. Thus, have opted to issue a Wind Advisory for the aforementioned forecast zones, valid 11 AM PDT to 8 PM PDT today.

Looking ahead, ensemble cluster analysis suggests high model concensus (90 percent of members or greater) that upper-level ridging will return Friday in the wake of today's upper low, resulting in dry conditions followed by above-normal temperatures for the weekend into early next week. 86

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Predominantly VFR conditions are forecast at TAF sites, albeit with temporary MVFR CIGs/VSBYs ongoing in snow showers this morning at BDN. Elsewhere, precipitation chances range from low (YKM/RDM/DLS/PSC) to medium (PDT/ALW) with the best chances (30-50 percent) of rain showers at sites ALW/PDT between 21-24Z. Winds are expected (80 percent confidence) to increase to 15-25 kts with gusts of 20-35 kts at all sites through the morning, then winds will diminish later this evening into tonight. 86

Preliminary Point Temps/PoPs

PDT 50 32 59 35 / 50 10 0 0 ALW 50 37 59 39 / 60 20 0 0 PSC 58 35 63 35 / 30 0 0 0 YKM 57 32 62 35 / 10 0 0 0 HRI 55 34 63 35 / 30 10 0 0 ELN 49 32 56 32 / 20 0 0 0 RDM 47 22 62 29 / 40 0 0 0 LGD 45 28 58 33 / 80 40 0 0 GCD 44 25 58 31 / 80 30 0 0 DLS 55 35 64 39 / 30 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 11 AM this morning to 8 PM PDT this evening for WAZ024-026-521. Winter Weather Advisory until 11 AM PDT this morning for WAZ522. OR...Wind Advisory from 11 AM this morning to 8 PM PDT this evening for ORZ041-044-508-510. Winter Storm Warning until 5 PM PDT this afternoon for ORZ509.