Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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208 FXUS66 KPDT 261005 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 305 AM PDT Wed Jun 26 2024 .SHORT TERM...Today through Friday...A passing shortwave trough and cold front along with pockets of favorable instability should allow for areas of showers and some thunderstorms today, with the low associated with this trough then progressing across the PacNW on Thursday, followed by a transient ridge on Friday bringing at least a day of quieter weather across the area. For today, a few showers are already noted moving into the Central Oregon area. Look for activity to see an uptick across both the Cascades and adjacent valleys and eastern slopes, along with the eastern mountains of Oregon and Washington. Activity may even slip into the lower Columbia Basin of Washington at times later this morning, providing a brief shower just west and northwest of the Tri-Cities. The eastern mountains should have pockets of favorable instability for thunderstorm development by this afternoon (around 200-600 J/kg), but overall parameters are unlikely to be supportive of anything noteworthy outside a few lightning strikes and perhaps locally breezy, shifting winds. On the note of winds, a breezy day is in store across the region, but currently anticipate activity should be below highlight level. The NBM shows a broad swath of 40-80% probability of gusts reaching 45+ mph in the Oregon Columbia Basin and into the Foothills of the Blues, with a much higher 50-90% chance in the higher terrain of the Simcoe Highlands as well as a few portions of the higher terrain near the Kittitas Valley. Not seeing enough mixing from the mid levels however, even though pressure gradients are conducive of near advisory level winds, and expectation is that we`ll see an isolated gust or two reaching advisory level of 45+ but not widespread enough to warrant the advisory itself. Breezy again tomorrow as well, though lower with a more limited chance of 45+ gusts from the NBM (30-60% probability) once again for aforementioned areas from above. Widespread gusts otherwise today and tomorrow around the 20-30 mph range. Meanwhile overnight tonight into Thursday, mountain precipitation becomes the dominant activity, mostly along the Cascades as rain shadowing takes over from westerly flow. A few showers may be possible tomorrow morning into the eastern mountains of OR/WA as well, but with PWAT values dropping to around a half inch or less, unlikely to see any exciting rainfall amounts and limited to a tenth of an inch or less in most spots. By Friday our weather tempers down as a transient ridge keeps winds calm and precipitation nil. Finally, temperatures will see a bit of a rollercoaster, with widespread highs for our population centers in the 80`s to low 90`s today, followed by a significant drop into the 70`s and very low 80`s tomorrow behind the cold front, rebounding with the ridge on Friday into the widespread 80`s (confidence high all days, 70-90%). Goatley/87 .LONG TERM...Saturday through Wednesday...Main concerns through the long term forecast will center around a trough passage over the weekend into early next week, with otherwise low concerns the rest of the period. Saturday starts with the PacNW between two synoptic features, upper level trough centered just offshore, and an upper ridge centered along the norther Rockies. Deterministic and ensemble guidance are in good agreement that the forecast area will remain under the influence of the ridge through the afternoon Saturday, resulting in the warmest day in the extended forecast, with low mid 80s to low 90s across the forecast area (confidence 60-70%). While the first half of Saturday will remain dry, a shortwave impulse rounding the upper trough will result in scattered shower chances developing across the Cascade crest and eastern mountains beginning in the evening. The upper trough will then move across the PacNW Sunday through early Monday, reinforcing chances of showers across the Cascade crest and the eastern mountains. Rain accumulations will be fairly light with these shower chances, with the NBM only showing chances of 35-50% for 0.05 inches of rain through Sunday night along the Cascade crest and eastern mountains. That said, a few showers across the higher terrain in the Blues and Wallowas could tap into increasing surface instability (50-65% chance of 150 J/kg CAPE) Sunday afternoon, resulting in isolated thunderstorms capable of gusty winds, small hail, and downpours. Besides precipitation, or lack there of, ensemble guidance points to the development of widespread breezy to locally windy conditions Sunday as the trough moves overhead, as well as Monday as the influences of the trough passage linger throughout the day. For the usually windy locations (i.e. OR Columbia Basin, eastern Gorge, Simcoe Highlands, WA Cascade east slopes, and Kittitas valley) the NBM is showing the probability of peak wind gusts reaching 45mph or greater between 65-85% Sunday, and 50-80% Monday. Late Monday through Wednesday, differences in ensemble mean guidance begin to present itself. While both GFS and ECMWF ensemble guidance place the region under a northwest flow aloft initially, the GFS members favor a broad shallow trough over the PacNW, whereas the ECMWF members favor a zonal flow over the region. In either solution, conditions will remain relatively dry with very little precipitation chances, as well as breezy conditions through the Cascade gap areas through the midweek (confidence 60%). Instead, the impacts will be to temperatures, where the GFS solutions favor temperatures about 5 degrees cooler than the ECMWF solutions. These differences would result in temperatures each afternoon firmly in the 80s across the lower elevations, or mid 70s to lower 80s with the cooler solutions. Lawhorn/82 && .AVIATION...06Z TAFs...VFR conditions are forecast for all sites through the period (>95% probability of occurrence). Increasing mid-level moisture and elevated instability will lead to increasing cloud cover and may facilitate high-based showers and isolated thunderstorms during the overnight hours (10-40% chance, highest across south-central WA). For TAF sites, the best chance of measurable precipitation will be at YKM (30-40%) during the late night and early morning hours. Confidence is lower at all other sites (<30% chance). Afternoon convection may affect KPDT/KPSC/KALW/KYKM Wednesday, but confidence on timing/location precludes mention in the 06Z TAFs. Westerly winds will increase to 12-22 kts with gusts of 20-35 kts for all sites Wednesday morning and afternoon. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 85 52 74 49 / 10 10 10 0 ALW 91 56 78 53 / 20 10 10 0 PSC 93 58 80 54 / 10 0 0 0 YKM 87 51 77 48 / 40 10 0 0 HRI 90 57 79 52 / 10 0 0 0 ELN 81 52 71 51 / 50 10 10 0 RDM 81 45 72 42 / 0 0 0 0 LGD 86 50 69 46 / 20 10 10 0 GCD 90 50 73 45 / 20 0 0 0 DLS 79 57 74 53 / 20 10 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...87 LONG TERM....82 AVIATION...86