textproduct: Pendleton

KEY MESSAGES

- Mountain snowfall will remain across WA Cascades and Blue Mountains today. *Active Winter Weather Advisories*

- Hydro concerns through Sunday, potentially returning midweek. *Active River Flood Warnings*

- Upper ridge moves into our region with mountain precip and breezy winds.

DISCUSSION

Current satellite and radar imagery shows light returns across portions of Foothills-Blue Mtns of OR/WA under mid to high clouds. The remaining locations will have mostly clear skies. As the upper trough moves eastward, the associated cold front began weakening around this late morning that lightened snow rates for WA Cascades and Blue Mountains. However, high temperatures have been struggling to warm since this morning, staying near to below freezing over those mountain areas based on surface observations. Low temps may further plummet tonight where there is snowpack. The ECMWF EFI even signals a decent ensemble agreement (EFI values of -0.5 to -0.7) for minimum temps relative to model climatology for WA Cascades and Blue mountains. With the ongoing light to moderate atmospheric river sagging southward, this will continue some lingering snowfall amounts between 1 and 4 inches for the WA Cascades and Blue mountains through the remainder of today. Given these impacts, Winter Weather Advisory will remain across the Northern/Northwest Blues until 8 PM PDT this evening for elevations above 4000 feet. Since the Puget Sound Convergence Zone started weakening from earlier with light snow rates, this has led to degrading from a Winter Storm Warning to an Winter Weather Advisory for the Upper East Slopes of WA Cascades through 5 PM PDT.

Breezy conditions (25-45 mph) may develop over exposed ridges/hills in portions of the Columbia Basin, Kittitas Valley, Simcoe Highlands and WA Cascades. This is in response of tight surface pressure gradients and the strong jet streak above 80 kts as the upper ridge gradually moves inland from the Pacific Ocean. Both HREF and NBM suggest a 30-50% probability of wind gusts exceeding 35 mph or higher for WA Cascades and Kittitas Valley. Also, there is a 40-60% chance for exposed ridges over the Kittitas Valley to exceed 45 mph during early evening hours.

The additional moisture from the atmospheric river along with melting snow from Northern Blue Mountains led to rises along area rivers. Notable hydro concerns would be the Umatilla River near Gibbon and the Walla Walla River near Touchet, which have crest in minor to moderate flood stage today. Thanks to increased snowmelt combined with recent runoff, this resulted in overflows for other rivers and creeks across portions of the Columbia counties and OR/WA border to Walla Walla River. With that, River Flood Warnings for Umatilla River near Gibson and Walla Walla River near Touchet will remain in effect until Sunday. Other rivers are also remaining forecasted to rise above action/bankfull stage, which includes the Grande Ronde River at Troy, Klickitat River near Pitt, and the Naches River near Naches later today.

An upper ridge will then move across our region Monday into next week with weak warm fronts and potential breezy winds. This could bring light precip over the mountain areas (WA/OR Cascades and Blue mountains). With rising snow levels (7 kft or above) and warmer temps, it is most likely that we may see rain as the precip type for higher elevations. Also, warmer temps will lead to increased snowmelt which will keep rivers and streams elevated. In addition, breezy winds (25-45 mph) may return with the westerly flow. Confidence is 30-50% for gusts to exceed 35 mph for exposed ridges over WA Cascades and Northwest Blues during afternoon and early evening hours. Feaster/97

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Isolated showers in the vicinity of PDT and ALW are expected (90 percent confidence) to dissipate this evening, with dry conditions forecast for other sites. Breezy west to northwest winds of 10-15 kts accompanied by gusts of 15-25 kts should taper off this evening into the overnight hours, followed by light or variable winds through Sunday. Mid- and high-level cloud cover will increase overnight through Sunday. 86

Preliminary Point Temps/PoPs

PDT 27 50 40 65 / 0 10 30 10 ALW 30 49 42 60 / 10 10 50 30 PSC 29 52 39 64 / 0 10 20 10 YKM 28 49 34 63 / 0 10 30 10 HRI 30 52 39 65 / 0 10 20 10 ELN 25 43 32 56 / 0 20 50 30 RDM 24 55 37 71 / 0 10 0 0 LGD 26 49 38 62 / 20 10 60 20 GCD 25 52 38 67 / 0 10 30 10 DLS 33 51 39 66 / 0 20 20 10

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 8 PM PDT this evening for WAZ030. OR...Winter Weather Advisory until 8 PM PDT this evening for ORZ502.