491 FXUS66 KPDT 022329 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 329 PM PST Sat Mar 2 2024 .SHORT TERM...Today through Monday...Current radar and visible satellite imagery showing spotty showers developing across the Yakima/Kittitas Valleys, John-Day/Ochoco Highlands and Basin, and the Blue Mountain foothills and east under partly to mostly cloudy skies. There is a slight chance (15-20%) that some of these discrete cells could turn into thunderstorms before 5 PM over the northern Blue Mountains, eastern John-Day/Ochoco Highlands and Basin, and Wallowa/Union Counties, but have not yet observed any cloud flashes as of 3 PM via satellite products. These conditions are in response to the trough, that moved in overnight, broadening and shifting east as a weak shortwave moves onshore. This has caused flow aloft to stay out of the southwest slightly longer than originally expected, leading to less precipitation shadowing by the Cascades as with a more westerly flow aloft pattern. Flow aloft does become more from the west tonight into Sunday to allow drier conditions until the next upper level trough nears the coast into Monday. This system will bring with it the ability for efficient upslope precipitation to occur across our mountain zones, leading to significant snowfall along the Oregon Cascades and the northern Blue Mountains above 4000 feet as the issuance of Winter Weather Advisories for Monday is likely (60-80%) within the next 24 hours. Lower elevation snow will also be possible early Monday morning along the northern Blue Mountain foothills before potentially including much of the Basin Monday night. Confidence is low to moderate (30-50%) for snow at lower elevations as snow levels will be bouncing from the 100-600 foot mark north-to-south Monday morning, to 1200-3000 feet north-to- south in the afternoon, and to 500-2000 feet northwest-to- southeast Monday night. Conditions will dry quickly tonight across the Basin and Central Oregon as the shortwave lifts and pressure increases into Sunday ahead of the next system. Clouds will also clear across the Basin to allow overnight lows to plummet into the mid-to-upper 20s for lower elevations of the Basin and Blue Mountain foothills, and into the low-20s through Central Oregon. Another weak shortwave is poised to move through the area Sunday afternoon as mountain snow is likely (45-75%) and lower elevation rain/snow chances (15-35%) stay confined to Central Oregon, Blue Mountain foothills, and the east slopes of the Cascades. Minimal precipitation amounts are expected in these lower elevations (0.02 of an inch or less of rain), with 3-6 inches of snow above 4000 feet along the Oregon Cascades, 1-4 inches of snow above 4000 feet over the Washington Cascades, and 1-3 inches through the northern Blue Mountains above 4000 feet. Confidence in these snow amounts is moderate to high (60-80%) as the NBM highlights a a 66% chance of 4 inches of snow or more over Santiam Pass, 10-30% chance of 4 inches of snow or more over White and Snoqualmie Passes, and a 10-15% chance of 4 inches of snow at Tollgate in the northern Blue Mountains. A closed low traveling down the British Columbia coast will open as it approaches the Washington coast Monday morning as it brings with it our next substantial weather system. This will provide significant mountain snowfall across the Oregon Cascades and the northern Blue Mountains as winter weather highlights may be warranted. Expected snow values of 4 to 8 inches above 4000 feet along the Oregon Cascades, 5 to 7 inches along the northern Blue Mountains above 4000 feet, and 2 to 6 inches above 4000 feet through the Washington Cascades. Confidence in these snow amounts is moderate (60-70%) as the NBM indicates a 71% of 6 inches of snow or more over Santiam Pass, 35-45% chance of 6 inches or snow or more through the northern Blue Mountains, and a 19% and 22% chance of 6 inches or more over Snoqualmie and White Pass respectively. Mountain snow looks to persist into Tuesday as drier conditions return to the Basin. High temperatures will stay about 5 degrees below normal through Monday as values reach into the mid-to-upper 40s through the Basin and Blue Mountain foothills, and in the upper-30s to low-40s over Central Oregon. Low temperatures will also stay slightly below normal with morning values in the upper-20s to low-30s through the Basin. Winds will also be increasing through the morning before peaking through the afternoon both Sunday and Monday. Wind gusts of between 20-25 mph are expected over Central Oregon, Simcoe Highlands, and the Blue Mountain foothills out of the southwest. 75 .LONG TERM...Tuesday through Saturday...The long term finally becomes quiet as the weather pattern should relax, with light precipitation and warming temperatures bringing us back to near normal. A shortwave trough will be exiting the region on Tuesday, allowing for lingering precipitation that should quickly become relegated to only high elevation activity by Wednesday. A drier northwesterly flow then takes over as ridging builds into the PacNW, shifting eastwards through the end of the week before the next impactful system begins to approach on Saturday allowing this ridge to fully exit the region. This will keep us mostly quiet as any precipitation that does occur will be high elevation and light in nature, with the building ridge allowing for temperatures to gradually warm back to near normal through the end of the period. The NBM has a 10-15% chance of snowfall of 6+ inches in the mountains for the 72 hour period ending Friday evening, reinforcing this period of drier and quieter weather for the region. For warming temperatures, the NBM's 50th percentile for high temperatures on Friday indicates widespread upper 40's to mid 50's, much closer to normal conditions as noted above. Forecast discrepancies are mostly related to the strength of the ridging, with ensemble clusters showing variations in the depth of this feature, but all agree it will be present through the end of the week, leading to moderate to high confidence (60-80%) in expected conditions. Goatley/87 && .AVIATION...00Z TAFs...VFR conditions are expected over the next 24 hours. Winds are on the decline, and by tonight expecting widespread winds 10 knots or less, but strong gusts will continue to be possible through around 03Z or so. Cloud heights continue between 5-10k feet, and will lift to average between 10-25k feet tomorrow. Goatley/87 && .PRELIMINARY POINT TEMPS/POPS... PDT 26 45 28 44 / 10 20 10 30 ALW 29 46 31 45 / 10 20 20 50 PSC 30 49 32 49 / 0 10 0 20 YKM 26 46 26 46 / 10 20 10 20 HRI 28 49 31 49 / 0 10 10 20 ELN 22 41 23 42 / 10 30 10 20 RDM 21 38 23 38 / 10 20 20 50 LGD 22 39 24 39 / 40 40 30 40 GCD 20 38 22 38 / 20 30 40 60 DLS 30 46 31 45 / 10 30 40 50 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...75 LONG TERM....87 AVIATION...87