602 FXUS66 KPDT 242328 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 428 PM PDT Wed May 24 2023 Updated Aviation Discussion .AVIATION...00z TAFs...VFR conditions expected through the period. Expecting primarily NW/N winds during the day with a few clouds 5-10 kft, clearing at night as winds become more terrain-driven. Winds expected to become northerly once again during the day Thursday. Evans/74 && .PREV DISCUSSION... /issued 234 PM PDT Wed May 24 2023/ SHORT TERM...Tonight through Friday Night...An upper trough remains over the Pacific Northwest this afternoon and is expected to remain through Friday night. This will keep weather unsettled through the next few days. Currently the trough has an upper low in northeast Washington radar shows weak thunderstorms rotating around the low. Have added a slight chance of thunderstorms for the rest of the afternoon north of the Tri- Cities just in case of some of the cells drift south of their current location. Other cells are drifting south towards the Washington Cascades, so also have a slight chance of thunderstorms there. Instability is weak and moisture is not too impressive, so just expect brief storms that develop then quickly die off. Rain amounts will be minimal. Storms should end shortly after sundown. Lows tonight will be a few degrees warmer than the last couple of nights with mid 40s to mid 50s and upper 30s to mid 40s in the mountains. Tomorrow, the upper low will have moved into southern British Columbia and this will increase moisture somewhat and instability, while mild, will be a bit stronger than today. Would characterize the coverage from the SREF paintball plot as widely isolated thunderstorms. Have a slight chance of showers and thunderstorms over the Cascades as well as the Elkhorn and Wallowa Mountains. Would not shocked to see a cell or two elsewhere in the eastern mountains, but the probability was too low to include it. Any thunderstorms should be fairly weak due to the weak instability parameters and shear to low to let storms become organized. Once again, showers and thunderstorms will die off in the evening. Rain amounts should be fairly light though a tenth of an inch will be possible with thunderstorms. Temperatures will be up a few degrees tomorrow with highs in the mid 70s to mid 80s and in the mid 60s to lower 70s in the mountains. Friday becomes a little more interesting as instability increases along with precipitable water and shear strengthens a bit. SPC has general thunderstorm coverage over the entire area but have limited it to a chance of showers and a slight chance of thunderstorms in the mountains in the afternoon. Also have a slight chance of showers in the Blue Mountain Foothills. SREF guidance indicates a 5-10 percent chance of strong thunderstorms in Wallowa County and have a chance of thunderstorms there. Rain amounts will mainly be just a few hundredths of an inch with up to a tenth of an inch with thunderstorms. Once again showers and thunderstorms will end in the evening. The warming trend will continue as temperatures warm a couple more degrees to the upper 70s to mid 80s with upper 60s to mid 70s in the mountains. Perry/83 LONG TERM...Saturday through Wednesday...A trough will be over the western CONUS at the start of the period. By Monday into Tuesday, the models remain in very good agreement that an upper low will move south over California and a more zonal flow will move into the Pacific northwest. There is considerable uncertainty by Tuesday into Wednesday, with the GFS developing a ridge and the ECMWF still having a trough. The ensemble clusters also show the agreement, but begin to diverge by Tuesday and Wednesday. On Tuesday, only about 12% of the clusters, show anything but a trough over California. However, by Wednesday, only about 25% show a deep trough, while another about 55% show a weaker trough and another 20% show a ridge. Also across the Pacific Northwest, there are difference with regard to the troughing (or lack thereof), with a fairly even split 56% to 44% supporting the trough moving further south and east. Obviously this does not lend very high confidence in the forecast toward the end of the period. There will be at least some rain/thunderstorm chances over far eastern Oregon/Wallowa County on Saturday. There could be very small chances on Sunday, and then the remainder of the extended period looks dry. High temperatures look to be above normal, but not too hot heading into the holiday weekend. Highs Saturday and Sunday will range from the mid 70s across central Oregon, to the upper 80s in the Columbia Basin. Highs on Monday and Tuesday will be a few degrees warmer, ranging from near 80 degrees in central Oregon to near 90 degrees in the Basin. Wednesday could be even a degree or two warmer, with highs in the lower 80s in central Oregon to around 90 or perhaps lower 90s in the Columbia Basin. Overnight lows will be in the 40s and 50s. && .PRELIMINARY POINT TEMPS/POPS... PDT 47 77 50 80 / 0 0 0 10 ALW 50 81 53 84 / 0 0 0 20 PSC 54 83 56 87 / 0 0 0 0 YKM 51 80 55 82 / 10 10 10 10 HRI 50 82 54 85 / 0 0 0 10 ELN 48 77 51 78 / 10 10 10 10 RDM 42 74 45 76 / 0 0 10 10 LGD 43 73 47 76 / 10 10 10 20 GCD 42 73 45 75 / 10 10 10 30 DLS 53 84 56 87 / 0 10 10 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...83 LONG TERM....77 AVIATION...74