456 FXUS66 KPDT 272356 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 456 PM PDT Sat Apr 27 2024 .Updated Aviation Discussion. .AVIATION...00Z TAFS...VFR conditions currently at all sites, which will stay the course through the period. Breezy winds are continuing at KPSC/KALW/KPDT/KDLS as gusts of 20-30kts are expected through the early evening before subsiding to 10-15kts overnight. OVernight ceilings will also drop to BKN/SCT060-080 before improving to BKN/OVC100-150 mid-to late morning behind a weak cold front passing through the area. This will also attribute to wind gusts increasing to 20-25kts as winds incur a more northerly component. Shifting wind directions will be more obvious for KRDM/KBDN/KDLS, which will be out of the northwest versus west-southwest elsewhere. 75 && .PREV DISCUSSION... /issued 309 PM PDT Sat Apr 27 2024/ SHORT TERM...Today through Monday...Current satellite shows stratus clouds beginning to slink over the Cascades. Radar shows a few areas with signals with the current observations showing a light amount of rain has fallen in isolated areas along the eastern slopes of the Cascades with only 0.01 inches in the last hour. Winds have also kicked up a bit bringing a few areas of patchy blowing dust just northeast of the Tri-Cities along HWY 395 as called in by a spotter and confirmed on cameras. A few observations in the area show sustained winds near 25 mph and gusts near 35 mph. These breezy winds will continue through the afternoon so be mindful of blowing dust when driving near Tri- Cites. Models are in firm agreement with the upper level low that brought the rain showers across the region yesterday to be down over the Four Corners while the next upper level low slides down the coast of B.C.. This has caused the flow over the region to turn to a more zonal flow or westerly and increasing the winds through the Cascade Gaps. 80-90% of the raw ensembles show that the winds will continue through the late afternoon with sustained speeds of 20-25 mph and gusts to 35 mph. Blowing dust has been spotted along HWY395 and will continue through the afternoon as well. EFI continues to show the region under near normal seasonal temperatures with over 90% of the ensembles showing the Gorge, foothills of the Blues, Basin and adjacent valleys seeing highs in the mid to upper 60s, mid elevations in the mid to upper 50s and the higher terrains in the mid 40s. Sunday models show the pattern begins to shift the upper level low continues to descend into the PacNW sending a shortwave with precipitation out ahead of it. Guidance shows a disturbance will bring enhanced precipitation over the Cascades as well as ensembles showing cooler temperatures as well. NBM shows the snow levels will begin to drop to below pass levels descending as low as 2400 ft overnight Sunday into Monday. EFI shows temperatures to be slightly below normal average along the WA Cascades but near normal elsewhere. 80-90% of the ensembles have the lower elevations cooling to the upper 50s low 60s, mid-elevations cooling to the upper 40s to mid 50s and the higher terrains in the low to mid 30s.With this, precipitation falling across the Cascades will be that of snow. With the highest concentrations above 3500ft in the WA Cascades and 4000ft in the OR Cascades. EFI has picked up on this event and has it marked as an above average seasonal snowfall event with values of 0.81 and a shift of tails nearing 0-1. Not surprised as it is late April. Looking at the raw ensembles and guidance, there is now higher confidence (60-80%) that Snoqualmie and Santiam Pass could see roughly 5-7 inches along the I-90 above 3500 ft and 6-8 inches HWY20, Santiam Pass so a winter weather advisory has been issued for 11PM Sunday night to 11AM Monday morning. Winds will also become a highlight Sunday through Monday as the westerly flow deepens with the incoming upper level low. Guidance shows that surface gradients begin to tighten sharply across the Cascades leading to breezy to windy conditions through the Cascades Gaps and along the foothills of the Blues through portions of the Columbia Basin. Raw ensembles show 80-90% probabilities of 30-35 mph or higher sustained winds with gusts nearing 40 mph through those areas with locally higher gusts. Bennese/90 LONG TERM...Tuesday through Saturday...An active pattern is likely (>95% chance) Tuesday, followed by more uncertainty in pattern details Wednesday through Saturday as ensemble guidance is struggling to resolve the tracks of multiple waves with origins in the vicinity of the Gulf of Alaska. A compact upper-level closed low is anticipated to weaken into a broad upper-level trough Tuesday as it tracks southeast from the Gulf of Alaska into the PacNW. This is the second in a series of two shortwave impulses, the first anticipated Monday. The main weather concern with this trough will be low snow levels facilitating a 30-50% chance of advisory-level snow for the Cascade crest. Chances of accumulating snow are low (~5% chance) for population centers in central OR, the Kittitas Valley, the foothills of the Blue Mountains, and the Simcoe Highlands. Sub- freezing morning low temperatures are possible (50-80% chance) Tuesday morning for the Kittitas Valley. Probabilities of sub- freezing temperatures are lower (20-50% chance) for the Yakima Valley and the foothills of the northern Blue Mtns of OR. Ensemble members depict the trough exiting Wednesday and favor a brief upper-level ridge building into the PacNW from the Pacific. Ensemble clusters vary in strength of the aforementioned ridge with roughly 60% showing an amplified ridge while the remaining 20% suggest weak ridging. Thursday, ensemble clusters are struggling to resolve the track of another closed low from the Gulf of Alaska. Roughly 15% of members depict a deep closed low tracking onshore into WA/OR with widespread precipitation and cool temperatures, while a further ~23% show a weak troughing pattern over the PacNW with precipitation focused more over the Cascades and WA. The remaining members all advertise warmer temperatures as an upper-level ridge axis moves either overhead (37% of members) or remains offshore. The latter two solutions would lead to mostly dry conditions for our forecast area. Friday, clusters show a similar pattern (59% chance of the upper- level ridge, 29% chance of a weaker ridge, and 11% chance of the deep closed low). The trough would result in cool, unsettled weather, while the ridge would be warm and drier. Saturday, ensembles are favoring an upper-level ridge (53% of members) and dry weather, while the remaining are advertising a third system from the Gulf of Alaska with precipitation across the PacNW. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 40 61 39 55 / 10 0 10 40 ALW 45 64 42 57 / 20 10 20 70 PSC 46 66 44 62 / 0 0 0 50 YKM 37 64 36 59 / 0 0 10 30 HRI 42 65 41 60 / 10 0 10 30 ELN 38 58 35 54 / 20 10 20 40 RDM 36 58 32 50 / 10 0 10 40 LGD 39 59 37 49 / 30 20 30 70 GCD 37 61 36 50 / 30 10 20 50 DLS 46 61 42 57 / 30 20 40 60 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory from 11 PM Sunday to 11 AM PDT Monday for ORZ509. WA...Winter Weather Advisory from 11 PM Sunday to 11 AM PDT Monday for WAZ522. && $$ SHORT TERM...90 LONG TERM....86 AVIATION...75