textproduct: Pendleton

DISCUSSION

Satellite and radar imagery tonight show a frontal boundary in the process of stalling across the PacNW, with an associated band of precip draped from southwest OR to southeast WA. North of this band, areas of low stratus along the WA Cascade east slopes and in the Yakima/Kittitas valleys has managed to survive an earlier frontal passage, and are expected to persist in these areas through the morning. Otherwise, light to moderate band of rain will continue to fall along the stalled front.

Today through Monday: Precipitation chances will continue across the forecast area today as a stalled cold front will tap into an accompanying weak plume of moisture. Snow levels will remain above 5.5kft through this morning, resulting in mostly rain falling below the highest peaks across the OR Cascades and the eastern mountains. Bands of rain will also continue to develop across the lower elevations of OR and far southeast WA throughout this morning and the remainder of today. A shortwave arriving to the region the latter half of today will pull the stalled frontal boundary north while dropping snow levels to 3kft to 4.5kft by tonight. This will result in the best chance of snow accumulations across the Cascades and Blues through Monday, with NBM chances of 6 inches of snow between 50-75% for the Blues and OR Cascades above 4.5kft. Otherwise, snow amounts will remain quite meager for the WA Cascades, with only a 20-40% chance of 3 inches of snow accumulations. Prior to the change over to snow, there is a 75-95% chance of at least 0.5 inches of rainfall across the Blues and the OR Cascades. This will result in rises in rivers/streams in the associated drainage basins, though at this time all river forecasts remain below action stage.

The incoming shortwave today will produce breezy winds in the lower elevations and along exposed ridges, with wind gusts between 25 to 40 mph developing this afternoon through Monday morning.

Light snow will continue across the Cascade crest and the interior northern Blues as flow aloft becomes zonal briefly early Monday. By Monday evening, flow aloft will transition into a split flow that will bring dry conditions across most of the region.

Tuesday through Thursday: Ensemble cluster guidance indicates that the split flow pattern will persist through late Wednesday, with transient ridging now developing across the region by early Thursday. Much of the forecast area will remain dry under this pattern, however, cluster and ensemble solutions show moisture rounding a low to the south and clipping portions of central OR, Ochoco-John Day Highlands, and the Strawberrys/Elkhorns/Wallowas Tuesday night and Wednesday morning. Snow levels will be low enough Tuesday night for light snow accumulations across these areas.

Friday and Saturday: By early Friday, ensemble cluster solutions show a trough dropping out of the Gulf of Alaska and setting up offshore the PacNW. However, there remains disagreement in the strength of position of the approaching trough into the weekend. Confidence remains moderate (50-65%) in at least light to moderate snow in the mountains with mostly light rain and overnight rain/snow mixes in the lower elevations. Lawhorn/82

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Variable conditions across all sites, with VFR at KRDM/KBDN/KYKM and MVFR at KDLS/KPDT/KALW/KPSC due to reduced ceilings of 2-3kft and visibilities of 3SM at KDLS. Light rain is currently impacting all sites, which will linger through much of the day before tapering off late this evening. As a result, MVFR conditions are expected to persist today and improve to VFR overnight as ceilings lift to 5-15kft. Winds will stay light and below 10kts through much of the period, but increase to 10-15kts for KPSC and KALW toward the end of the period. 75

Preliminary Point Temps/PoPs

PDT 35 49 30 46 / 100 30 0 0 ALW 37 49 32 47 / 100 40 0 0 PSC 36 54 30 49 / 90 10 0 0 YKM 31 50 28 46 / 70 10 0 0 HRI 36 53 29 46 / 90 20 0 0 ELN 31 45 27 42 / 50 20 0 0 RDM 27 45 23 46 / 60 0 0 0 LGD 33 45 26 46 / 100 50 0 0 GCD 33 43 26 46 / 90 10 0 10 DLS 38 51 34 48 / 80 20 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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