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Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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583 FXUS66 KPDT 121734 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1034 AM PDT Mon Aug 12 2024 .AVIATION...18z TAFs...Mostly VFR. The exception will be KBDN where smoke from nearby fires has been creating MVFR conditions. Dry conditions expected at terminals today. Surface wind will be gusty to breezy through the afternoon and into the early evening hours with gusts of 20-30 kts forecast at terminals. Wind should weaken between 00z and 06z tonight, with KDLS remaining gusty through the period. Branham/76 && .PREV DISCUSSION... /issued 242 AM PDT Mon Aug 12 2024/ SHORT TERM...Today through Wednesday night...Complex forecast for the next 36 hours with the main concern focused on thunderstorm potential over the eastern mountains. Latest water vapor imagery shows a vorticity maximum off the northern California coast. Models are in good agreement on moving it east and inland initially then turning it northeast across eastern Oregon tonight through midday Tuesday. An area of showers and embedded thunderstorms will accompany this feature. The NAM and NAM Nest have been the most consistent from run to run with this scenario. The CAMS are showing this evolution now too with some variability in the west edge of the precipitation shield. The big question is how much lightning will accompany this activity. The HREF TSTM probabilities are lack luster but peak at 40% over Baker County around 14Z Tuesday....then decrease thereafter. Instability will be weak overnight as well with cool surface temperatures in the 40s and 50s and marginal elevated instability. Thus the current thinking is that the potential for abundant lightning is low (30-40% chance mainly eastern Grant and Wallowa counties) and fire weather highlights will not be issued. Plus precipitable water is forecast to increase to around 1.0 inch tonight and thunderstorms are expected to be accompanied by decent rainfall of .10-.25 inches. There is a small chance (20%) that a stray storm could pop over the northeastern mountains late this afternoon or evening before the main activity arrives overnight. CAMS are hinting at this possibility mainly over Wallowa County. Otherwise today will be warm with high temperatures near 90 in the lower elevations and in the 80s mountains. It will be noticeably cooler on Tuesday with highs in the mid 70s to lower 80s lower elevations and mid 60s to mid 70s mountains. It will be rather cool Wednesday morning with the mountain valleys in central Oregon falling into the mid to upper 30s for lows. Wednesday will be a pleasant day with highs in the 80s except 70s in the mountains. Models are in good agreement on bringing an upper low into the region late Wednesday night. For now kept the forecast dry with pops less than 15% but would not be surprised if slightly higher POPS are introduced in later forecasts. 78 LONG TERM...Thursday through Monday...Much of the period looks cool and wet as ensemble guidance is in good agreement on a closed low enveloping the region next weekend through early next week. The NW origin of this low will allow cooler air to spill in, making for high temps in the 70s and 80s across much of the forecast area, which is about average or just below. Ideally, these conditions will temper fire behavior enough to help put a cap on what`s been a particularly active wildfire season. Thursday looks to be the warmest day of the period as a more SW trough rolls through and provides for a chance of showers and isolated thunderstorms across an area stretching from central Oregon to Wallowa County. Opted to leave storm chances in the forecast even though instability isn`t particularly great as the flow is SW enough to at least produce a marginal chance of orographic storms over the eastern mountains. Once the aforementioned closed low arrives on Friday, however, instability drops off quite a bit, and while shower chances will be persistent across much of the CWA, current thinking is that the pattern just isn`t supportive for storm activity through the weekend. Would say right now that chances for storms from central Oregon through the eastern mountains on Thursday stands at around 15-20%, down to around 10% Friday onward. Moisture will certainly be there, but with a closed low overhead, cloud cover will likely remain persistent across the forecast area. With temps dropping to more seasonal averages, minimum RHs increase toward the 20s and even 30s across even the lowest elevation zones of the forecast area, at least according to the NBM. Winds are expected to pick up with this synoptic pattern, but that shouldn`t be too much of a concern with how wetter the forecast is trending. That, and winds at this time don`t look to be strong enough to cause widespread issues as far as fire spread is concerned. Overall forecast confidence is on the higher end (60-70%) on a cool and wet pattern that many will likely welcome given what`s been a hot, dry, and fiery summer. Evans/74 && .PRELIMINARY POINT TEMPS/POPS... PDT 87 54 79 50 / 0 10 0 0 ALW 91 60 83 56 / 0 10 10 0 PSC 92 60 84 59 / 0 0 0 0 YKM 90 55 83 52 / 0 0 0 0 HRI 91 60 83 57 / 0 0 0 0 ELN 86 57 80 54 / 0 0 0 0 RDM 86 45 78 44 / 0 0 0 0 LGD 90 54 80 49 / 10 40 30 10 GCD 90 53 84 49 / 10 40 10 0 DLS 82 59 77 58 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...78 LONG TERM....74 AVIATION...76