Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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340 FXUS66 KPDT 070509 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1009 PM PDT Thu Jun 6 2024 .AVIATION....06Z TAFs...VFR conditions are very likely (99-100% chance at DLS/PDT/YKM/ALW/PSC, and 95% chance at BDN/RDM). At BDN/RDM, the low chances of MVFR conditions reflect a low chance of an afternoon shower or thunderstorm initiating over the Cascade crest or adjacent high terrain and propagating over the lower terrain of central OR. Diurnally driven winds of 10 kts or less are anticipated, aside from aft/eve gusts of 15-20 kts at BDN/RDM. Clouds will be limited to FEW-SCT cirrus with the exception of FEW-BKN cumulus over the Blue Mountains and Cascades of OR. Plunkett/86 && .PREV DISCUSSION... /issued 412 PM PDT Thu Jun 6 2024/ SHORT TERM...Tonight through Saturday night...Temperatures have climbed into the mid-70s to mid-80s this afternoon and the heat trend will continue through the short term. Conditions do not warrant any headlines, but many locations in and around the Lower Columbia Basin and the John Day Valley will observe the first 90 degrees of the season. Based on the current position of the inverted surface thermal trough and the models pushing the thermal trough east of the Cascades over the next several days, confidence in the 90+ temps is high (90%). However, the probability of 100 degrees is 15% or less. The thermal trough is not anomalously strong and 850 temps climb to 17-20C on Saturday-- the hottest day of the week. Keep in mind that overnight lows Saturday night will be 60-65F for many of the lower elevations, therefore there will be little relief in the unseasonably hot temperatures. The previous forecast discussion mentioned the slight chance (15%) of thunderstorms this afternoon and evening for our far southeast zones. This was based on some morning convection in Malheur County where there was elevated instability and a weak impulse embedded in a southwest flow aloft. Latest visible satellite and web cams are showing very low tops to the cumulus clouds. Will keep the 15% in the forecast for the next few hours but definitely don`t want to go higher. Similar conditions are forecast for Friday with only a 15% chance of afternoon and evening showers and thunderstorms for our southern zones. I did extend the slight chance to cover southern Deschutes County where some of the HREF ensembles, mainly the ARW and FV3, advertise convective activity in the late afternoon. The westerly flow aloft will keep the isolated showers and thunderstorms mainly south of the forecast area. There has been good run-to-run continuity of the models on Saturday in terms of the potential for showers and thunderstorms. Current PoPs are around 20-40%, so any storms that develop will be isolated but cannot rule out scattered coverage in the afternoon and evening. SPC has general thunderstorms over eastern Oregon. Models have backed off on the CAPES compared to previous runs and now show average SBCAPES around 100-150 J/kg so storms are not looking to be strong or severe at this time. Wister/85 LONG TERM...Sunday through Thursday night... Key Messages: 1. Potential thunderstorms with mountain showers for Sunday. 2. Breezy winds (25-35 mph) throughout this week. 3. Above normal high temperatures during this week. A shortwave trough moves over to the PacNW as the transient ridge exits the area Sunday through Monday late morning. This can bring potential chances of mountain showers and thunderstorms for John Day Basin and then eastern mountains. Developing thunderstorms are likely for Sunday with CAPE values below 500 J/Kg and isolated pockets around 600 J/Kg or above, including lapse rates of 7-8 C/Km. However, confidence is low due to these parameters showing marginal instability (20-30%). There is a 15-30% chance of precip at the Blues and the Cascades and <15% in the Columbia Basin and central OR before decreasing onward. By Monday late morning, conditions should improve when the trough exits further east from the PacNW as another ridge builds in. The models and ensembles are in great agreement with the shortwave trough moving in Sunday into Monday morning thus increasing confidence on this week`s forecast. Chances are high for breezy winds at Yakima Valley, Simcoe Highlands, and Kittitas Valley during this week within 25-35 mph (>70%). Confidence is moderate for wind gusts exceeding up to 40 mph in the Kittitas Valley (50-60%). This is due to the strong surface pressure gradient from the shortwave trough. However, wind gusts will decrease to around 17-25 mph later this week (40% confidence). High temperatures will remain above normal for this week as well in the upper 80s to low 90s in the Columbia Basin and mid to upper 70s across the remaining forecast area. High temperatures could briefly drop a few degrees for Sunday into Monday night as the shortwave trough moves over the PacNW. Feaster/97 && .PRELIMINARY POINT TEMPS/POPS... PDT 54 84 55 88 / 0 0 0 0 ALW 57 86 57 91 / 0 0 0 0 PSC 59 89 58 93 / 0 0 0 0 YKM 52 88 54 90 / 0 0 0 0 HRI 57 89 57 93 / 0 0 0 0 ELN 52 85 54 88 / 0 0 0 0 RDM 50 87 53 85 / 0 0 0 10 LGD 51 83 53 85 / 0 0 0 10 GCD 53 88 55 89 / 10 10 20 20 DLS 58 93 62 89 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...85 LONG TERM....97/90 AVIATION...86