textproduct: Pendleton

KEY MESSAGES

- Mountain snow continues through Thursday morning *Winter Weather Advisory Active*

- Warmer weekend temperatures with light mountain snow persisting

- Active winter weather returns to the mountains next week

DISCUSSION

Current radar and visible satellite imagery shows spotty, light returns moving across the Columbia Basin, more predominately featured across the Blue Mountains, under partly to mostly cloudy skies. This is in response to a second upper level trough dropping along the Washington/Oregon coasts as it follows closely behind the system that brought significant mountain snowfall across the Northern Blue Mountains and Oregon Cascades last night. A weaker frontal system is associated with the upper level feature, which will bring more muted snow amounts across our mountain zones through Thursday morning. However, the Oregon Cascades are still expected to pick up snow amounts of up to 8 inches. These higher amounts are likely over higher terrain, with pass-level elevations expected to receive 5-6 inches through Thursday morning as the NBM advertises a 55-65% chance of 5 inches over Santiam Pass. Thus, a Winter Weather Advisory has been issued across the east slopes of the Oregon Cascades until 10 AM Thursday.

An upper level ridge builds to our east and across the Interior Northwest on Friday as a strong upper level low drops along the Eastern Pacific, promoting southwest flow aloft and the start of a warming trend that will continue through the beginning of next week. High temperatures across the Columbia Basin are expected to break into the low-50s Saturday. The upper level flow will also tap into some moisture that will keep light snow occurring at higher terrain along the Cascades on Saturday. Temperatures peak in the low to mid- 50s across the Columbia Basin and the Blue Mountain foothills Monday with snow levels between 4000-5000 feet. These temperatures are 5-7 degrees above normal for this time of year.

Both the upper level ridge and offshore upper low pressure will weaken on Sunday to promote more west-southwest flow aloft that will return more substantial mountain snowfall across the Cascades, extending into the Northern Blue Mountains and Elkhorns on Monday. Currently, snow amounts are anticipated to peak on Monday associated with the passing of a slow moving cold front, with expected snow amounts of 5-10 inches over the Cascades and 3 to 7 inches over the Blue Mountains and Elkhorns. These amounts do reach advisory criteria. Sunday and Tuesday will also bring additional snowfall in the amounts of 2 to 5 inches both days for the Cascades, with the Northern Blue Mountains potentially receiving 2 to 5 inches on Tuesday. However, confidence in these snow amounts is low to moderate (30-60%) related to the overall strength of the upper level trough and how slow the upper level ridge and surface high pressure departs to our east. This is evident in the overall spread (25th vs. 75th percentile) of snow amounts across the Cascade passes being around 4 inches via the NBM. Thus, scenarios range from sub-advisory to low-end warning snow amounts across our mountain zones. 75

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

All TAF sites in VFR with the exception of some PROB30's of MVFR in DLS/YKM from some passing snow showers. Temporary low level cloud decks could pass through at around 1500-2500 feet. Winds remain light at less than 15 mph.

Preliminary Point Temps/PoPs

PDT 24 41 26 41 / 20 10 30 20 ALW 26 40 27 41 / 20 10 40 40 PSC 26 43 26 45 / 20 0 20 10 YKM 26 39 23 40 / 20 20 20 0 HRI 26 43 26 45 / 20 10 20 10 ELN 23 35 18 36 / 30 30 20 10 RDM 21 37 18 39 / 10 40 10 0 LGD 17 38 21 38 / 20 20 40 40 GCD 18 36 20 36 / 10 30 40 20 DLS 31 43 29 45 / 30 30 20 10

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Winter Weather Advisory until 10 AM PST Thursday for ORZ509.