textproduct: Pendleton

DISCUSSION

Stratus and patchy fog continue to impact the Columbia Basin and adjacent valleys/foothills tonight thanks to a ridge of high pressure persisting overhead. Areas outside of the Columbia Basin are currently under mostly clear skies, though satellite does show cirrus beginning to cross the Cascade crest at this time. Expect clear skies to be replaced with high to mid level cloud cover through the remainder of the day, while the low stratus and patchy fog in the Basin will persist through the morning hours.

Today through Monday: Precipitation chances will return to the forecast area today as a weak plume of moisture arrives to the PacNW with a surface frontal system. Snow levels will remain above 6kft through tomorrow morning, resulting in mostly rain falling below the highest peaks in the mountain areas. By early Sunday morning, a stalled front will lay northeast to southwest across the forecast area, resulting in steady precipitation falling outside of the WA Cascade east slopes and the Yakima/Kittitas valleys. Snow levels will be 4kft to 5.5kft across central WA, but rising to 5.5kft to 7kft across the remainder of the forecast area, resulting in mostly rain falling through the first half of Sunday. A shortwave arriving to the region the latter half of Sunday will pull the stalled frontal boundary/deformation area north while dropping snow levels to 3kft to 4.5kft Sunday night. This will result in the best chance of snow accumulations across the Cascades and Blues, though the NBM is only showing a 40-65% chance of 4 inches of snow accumulations in these areas through Monday morning.

The incoming shortwave late Sunday will produce breezy winds in the lower elevations and along exposed ridges, with wind gusts between 25 to 35 mph developing Sunday night into 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 the region.

Tuesday through Friday: Ensemble cluster guidance indicates that the split flow pattern will persist through early Thursday before a trough drops south from the Gulf of Alaska and sets up offshore the PacNW. Ensemble cluster solutions are in great agreement that conditions will remain dry under the split flow pattern. But by late Thursday into Friday, disagreement grows with strength and position of the approaching trough. Confidence is at least moderate(45-60%) in a return of light to moderate snow in the mountains, with low confidence (15-25%) in heavy snow along the Cascade east slopes and Blues with more widespread rain/snow mix or rain across the remainder of the forecast area. Lawhorn/82

AVIATION...12Z TAFS

Low stratus and patchy fog will bring MVFR or lower conditions to most sites through this morning, with improvement to VFR expected after 18Z. Currently, the only site with vsby problems is PDT, with vsby IFR or less expected to persist into the morning. A system approaching the region will help to lift CIGs through the afternoon, but as precipitation arrives, CIGs are expected to lower to 3kft-5kft AGL at most sites. Rain impacts have been included either as prevailing or PROB30 groups for sites DLS/PDT/YKM/ALW/PSC this afternoon into the evening. Moderate confidence (60-70%) in more persistent and heavier rainfall developing after 10Z at sites DLS/PDT/ALW/PSC, with lower confidence (20-40%) at sites YKM/RDM/BDN. Winds will be light through the period, except at site BDN where sustained winds of around 12kts will develop in the afternoon. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 43 51 38 50 / 70 90 80 20 ALW 44 50 39 49 / 80 100 90 40 PSC 42 50 38 55 / 70 90 60 10 YKM 38 47 33 50 / 50 70 40 10 HRI 42 50 38 53 / 70 90 60 10 ELN 36 42 31 45 / 60 70 40 10 RDM 40 52 29 47 / 60 90 40 0 LGD 42 50 35 45 / 70 100 100 50 GCD 42 52 34 44 / 50 90 90 20 DLS 44 49 38 52 / 90 90 60 20

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until noon PST today for ORZ506-509.