FXUS66 KPDT 112357 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 500 PM PDT Sat May 11 2024 Updated Aviation Discussion .SHORT TERM...Tonight through Monday...Satellite imagery this afternoon is showing mainly clear skies across the region, though some cumulus fields have managed to develop across areas of the northeast OR mountains. Temperatures have already managed to climb into the 80s across many lower elevation locations this afternoon, with a few more hours of good daytime heating to go. The upper level ridge of high pressure that has produced these warm temperatures and clear skies will continue to sit over the region through tomorrow morning. That means that tonight may be another great night to watch the aurora, if it does develop again tonight. Tomorrow morning, the upper ridge will push east as a shortwave trough slides across the PacNW later in the day. Afternoon temperatures will decrease 4 to 7 degrees across the area as the ridge axis shifts east, but still expect mostly upper 70s to 80s in the lower elevations. Surface pressure gradients will also begin to tighten across the Cascades in response to the approaching shortwave, resulting in breezy winds 15-25 mph and gusts up to 45 mph through the Cascade gaps and into the Lower Columbia Basin tomorrow afternoon. Sunday night into Monday morning the shortwave trough axis will quickly move across the PacNW, placing the region under a brief northwest flow aloft during the afternoon. By the evening hours, a quick moving shortwave trough will dive across the PacNW. Overall, these systems will be fairly dry, though global deterministic guidance and members of the HREF indicate the development of light, shallow showers across the central WA Cascade crest Monday morning (confidence 25%). Otherwise, breezy conditions will continue through Monday, with westerly sustained winds increasing to 20-30 mph with gusts up to 45mph through the Cascade gaps and into the OR Columbia Basin; winds will be 15-25 mph everywhere else. Winds will be the strongest through the Kittitas valley Monday, with sustained winds of 25-35 mph and gusts up to 50 mph developing in the afternoon (confidence 60%). Lawhorn/82 .LONG TERM...Tuesday through Saturday...Deterministic models and ensembles are in good agreement on the longwave pattern for Tuesday and Wednesday which provides high confidence in the forecast. An upper level ridge will be positioned off the west coast with northwest flow aloft over the region. It will be dry and warm but not as warm as this weekend. The NBM has high temperatures in the mid 70s to lower 80s in the lower elevations on Tuesday and mostly 80s on Wednesday. On Wednesday night there will be a 15-30% chance of light showers along the Washington Cascade crest. Beginning Thursday through Saturday confidence in the forecast decreases. The ensemble clusters are split between a trough and ridge over the area and the GEFS and ECMWF 500 mb ensemble means show NW flow aloft with a tight 500 mb height gradient across the Pacific NW. The deterministic models are similar to the ensemble means. The NBM during this time period shows cooler air filtering into the region with high temperatures lowering into the mid 60s to mid 70s for the lower elevations on Friday and Saturday. This lends credence to the GFS solution which shows a cold frontal passage on Thursday and a surface pressure gradient of up to 14 millibars between Portland and Spokane. Pressure differences this high favor strong and gusty west winds across the lower elevations especially the Cascade gaps. The NBM probabilities of 45+ mph winds are 40-70% across much of the lower elevations for Thursday evening/night. Thursday through Saturday there will be a 10-20% chance of light showers along the Cascade crest and over the northeast mountains with snow levels 5000-7000 feet. The probability of thunderstorms in these areas will be quite low (5-10%). Elsewhere the probability of measurable rain will be 5% or less. 78 && .AVIATION...00Z TAFs...Clear skies for all sites for the next 24 hours. Winds terrain driven and generally less than 10 kt except for 10G20kt at KDLS, KRDM and KBDN this afternoon and early evening. Similar conditions are expected tomorrow. Wister/85 && .PRELIMINARY POINT TEMPS/POPS... PDT 53 82 51 75 / 0 0 0 0 ALW 58 85 54 78 / 0 0 0 0 PSC 58 89 56 82 / 0 0 0 0 YKM 53 86 51 79 / 0 0 0 0 HRI 57 87 54 80 / 0 0 0 0 ELN 52 81 47 71 / 0 0 0 0 RDM 45 77 43 74 / 0 0 0 0 LGD 51 79 46 73 / 0 0 0 0 GCD 46 80 45 75 / 0 0 0 0 DLS 56 84 53 74 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None.