Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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332 FXUS66 KPDT 142136 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 236 PM PDT Fri Jun 14 2024 .SHORT TERM...Tonight through Sunday... Key Points: 1) Very cool temperatures expected this weekend, with highs 10-13 degrees below normal. 2) Overnight lows similarly cool, with a chance at near to below freezing for Central Oregon and all mountain zones. 3) Rain, thunderstorms, and breezy winds expected with the weekend system, but significant weather concerns unlikely. A deep upper low is moving along the Canadian coastline and will slide inland between the US and Canada tonight into Saturday, bringing significantly cooler weather, particularly for this time of year, along with breezy winds and a chance at precipitation. The jet will find itself just south of us, keeping us on the cool side of the system with temperatures the first major article with this system. The forecast calls for highs 10-13 degrees below normal Saturday and Sunday, with highs in the 60`s to low 70`s for our population centers - a likely last hurrah at Spring-like conditions for the region. The NBM even suggests there is nowhere in the region that could see 80 degrees, with probabilities for temperatures greater than or equal to 80 at zero widespread. Meanwhile overnight lows will be very chilly - in the low 40`s to mid 30`s. Portions of Central Oregon and all mountain zones are expected to even see freezing temperatures yet again. Widespread frost for these areas seems certain, but moving onto a freeze risk remains much more uncertain. Confidence is low to moderate (30-40%) that we will see lows reaching 32 for Deschutes County, and if we do it`s unlikely that they`ll be widespread enough to warrant a freeze warning. Moving onto winds, probabilities are low (<30%) that gusts will be strong enough to reach wind advisory levels on Saturday (45+ mph) for a widespread enough region to justify any issuance. The NBM shows a 30-60% chance for portions of the Lower Columbia Basin, Foothills of the Blues, Simcoe Highlands, and Kittitas Valley, with the highest percentage chances in the Simcoes. If any gusts do reach this level, the expectation would be that the higher terrain of these areas and perhaps a localized site or two could reach this threshold, but not enough to warrant the issuance at this time. Finally precipitation does move back into the region, including the return of mountain snow! For snowfall - amounts are light, and limited to only the highest terrain. Several inches may occur for the highest peaks and crests, but expecting little to none by the time you reach the mountain passes and valleys. Showers and some thunderstorms will also be present with this system on Saturday, but ingredients for storms including instability and shear will be lacking in the best environment (generally the Washington side of the CWA), and anticipating at best some thunder in the mountains on Saturday due to orographic enhancement. Finally, QPF just won`t be present to warrant significant rainfall outside of the mountains. Rain shadowing from the Cascades will limit significant accumulations on Saturday outside of the mountains themselves, and then as wrap around moisture brings a bit more widespread chances late Sunday into Monday, PWAT values generally at or below normal (0.25-0.75 inch) won`t promote much in the way of noteworthy accumulations for general late night/early morning showers from Central Oregon up through the Wallowas and foothills of the Blues. Six hour QPF chances from 06-12Z Monday of 0.1 inch or greater are 10% or less. So although we will be active and unusually cool, no other major impacts are anticipated at this time. Goatley/87 .LONG TERM...Monday through Friday...Cool and wet conditions continue into Monday as broad troughing envelops the region. This system will provide for enough moisture advection and instability to support showers and potentially thunderstorms across primarily the eastern mountains of Oregon and Washington, while the western half of the forecast area is left under the trough`s dry slot. Current thinking is that showers will prevail more so than thunderstorms due to how cold the air mass will be, however did leave mention in given the time of year and the trough axis being located right overhead. The colder air pulled down into the PacNW via this trough will allow for more chilly nights, with low temps Monday and Tuesday morning diving down into the 40s and 30s for the entire forecast area. Zones must vulnerable to freezing temps would be central Oregon and the Wallowa Valley, however confidence in this occurring is low (20-30%) as cloud cover and ambient moisture may help prevent temps from bottoming out too much. Ensembles suggest troughing will persist into the midweek, however temps will slowly start to rebound back toward seasonal averages as mid-level flow becomes more zonal, thus cutting off further cold air advection. NBM suggests light PoPs during the afternoon hours for primarily our mountain zones Tuesday into Wednesday as troughing supports instability and the opportunity for weak orographic showers and isolated t-storms to develop, however NBM PoPs waver around 15-25% and the best chances for rain look to be on Monday across the entire period. Ensembles generally depict more benign flow moving in by the end of the work week, either in the form of zonal flow or troughing weak enough to preclude any precip threats. NBM produces a warming trend as a result, with high temps inching back towards the 90s by the end of the period. Confidence in these temps is only low to moderate (40- 45%), however, due to the discrepancies depicted across ensemble members. Evans/74 .AVIATION...18z TAFs (Previous Discussion)...VFR conditions expected for the period. Moderately breezy west winds are expected across all sites, with some areas potentially seeing gusts up to 30 kts at times this afternoon. Sct-bkn high clouds will prevail, before more mid-level clouds build later this evening into the overnight hours. Evans/74 && .PRELIMINARY POINT TEMPS/POPS... PDT 49 66 40 66 / 10 10 0 10 ALW 52 69 43 69 / 20 30 0 10 PSC 55 71 45 72 / 0 10 0 0 YKM 46 68 38 69 / 0 10 0 10 HRI 52 71 43 72 / 10 10 0 10 ELN 45 64 41 67 / 0 10 0 10 RDM 41 61 33 64 / 0 0 0 0 LGD 46 61 37 62 / 10 20 0 10 GCD 43 64 35 64 / 0 10 0 10 DLS 52 66 46 70 / 10 20 0 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...87 LONG TERM....74 AVIATION...74