Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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487 FXUS66 KPDT 111615 AAA AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 915 AM PDT Tue Jun 11 2024 .MORNING UPDATE... Current winds in Ellensburg, The Dalles and along the Blue Mountain Foothills are already at around 20 mph with gusts of 30 to 35 mph, so the expected windy conditions are developing. Wind advisories for the Kittitas Valley and Simcoe Highlands look good and believe the Columbia Basin will remain just below wind advisory levels. The winds, along with very dry soil moisture values in Washington and the Oregon Columbia Basin, will make blowing dust possible today with the higher wind gusts. Have added patchy blowing dust today and this evening to the Kittitas Valley and Simcoe Highlands as well as portions of the Columbia Basin and the Blue Mountain Foothills. Otherwise, the forecast looks good and no other changes were made. Forecast update already out. Perry/83 .SHORT TERM...Today through Thursday... Key Messages: 1. Breezy to windy conditions today. *Wind Advisories Issued* 2. Cooling trend through Wednesday. Current radar and infrared satellite imagery showing dry conditions as pockets of mid-to high level clouds pass across the Columbia and John Day-Ochoco Basins. This is a result from the transient upper level ridge, that brought sunny skies and warm temperatures across the area Monday, continuing to exit to our east. An upper level trough is currently approaching Vancouver Island, and will be passing to our north later today. A dry cold front will be associated with this system and will transect the area, allowing a pressure gradient to develop along the Cascades. This will lead to windy conditions across the Kittitas Valley, Simcoe Highlands, and the Eastern Gorge, as sustained winds of 20-35 mph and gusts of up to 50 mph are anticipated. Thus, a Wind Advisory has been issued for the aforementioned areas between 9 AM and 11 PM today. Confidence is high (80%) in wind gusts reaching advisory criteria, as the GFS and NAM suggest a pressure gradient of 11.5-13 mb will develop between Portland and Spokane (11 mb is normal advisory threshold). Further confidence is gleamed from the NBM, which highlights an 80-95% chance of wind gusts of 45 mph or greater over the earlier mentioned areas, with the ECMWF EFI showing 60-70% of ensemble members indicating above climatological normal wind gust values. A significant temperature gradient of 7-10 degrees will also be setting up along the Cascades as advertised by the ICON, NAM, and HRRR 925 mb temperatures, further enhancing confidence. The only lacking piece of evidence resides with 850 mb winds, which are only around 45 mph as advertised by the GFS, NAM, HRRR, and the ECMWF. Winds will also be breezy across the Lower Columbia Basin and Blue Mountain foothills this afternoon, but are expected to stay below advisory level and hover between 30-40 mph. The NBM showcases a 70-90% chance of wind gusts of 39 mph or greater over the Basin and foothills this afternoon, but this may be a bit inflated when taking into account the lack of 850 mb winds. Thus, it is expected that the higher winds through the Gorge will slow as the terrain becomes less variable in the Basin. Flow aloft will stay predominately out of the west-southwest on Wednesday as another transient upper level ridge builds across the area. This more zonal flow will provide cooler overnight temperatures in the mid-to upper 40s across the Basin, as Wednesday`s high temperatures drop 4 to 8 degrees from Tuesday. Wednesday morning temperatures across Central Oregon will be slightly cooler, with lows dropping into the low to mid-40s. Breezy winds are again anticipated on Wednesday along the Gorge and Kittitas Valley, with gusts of 25-35 mph likely (70-80% confidence). A large upper level low pressure system will approach the British Columbia coast on Thursday, which will steadily increase winds through the day. By the evening hours, wind gusts of 20-30 mph will arrive as a cold front passes. The large approaching system will also lead to flow aloft turning more southwest and enhancing to allow high temperatures to rebound back into the mid-to upper 80s across lower elevations of the Basin and foothills - which is 6-8 degrees above normal. 75 .LONG TERM...Friday through Tuesday...There is excellent ensemble agreement (99-100% chance) that a deep, upper-level closed low centered over the Northeast Pacific Ocean will propagate east- southeastward towards the Pacific Northwest on Friday. In response, onshore-directed pressure gradients will increase resulting in westerly gap flow across the Columbia and Deschutes plateaus. As for precipitation, while areas east of the Cascade crest will be shadowed, there is a chance (25-50%) of light rain along the WA Cascade crest Friday afternoon and evening. Saturday through Tuesday, ensemble concensus loosens regarding the evolution of the aforementioned low, and any attendant shortwaves, as it tracks into the Pacific Northwest. Delving into possible forecast scenarios, Saturday, ensemble clusters range from a deep closed low overhead (10% of members) to a weaker open-wave trough across Washington and southern Canada (35% of members). Sunday, most ensemble members (75%) advertise the upper- level trough over the Pacific Northwest, while the remaining 25% of members suggest the main upper low will track north of the forecast area. The latter scenario would be warmer and drier than the favored outcome (cool and unsettled). The unsettled pattern is still the most likely outcome (75% of members) Monday, though cluster scenarios diverge regarding pattern details; the favored scenario among the range of unsettled patterns is the upper-level closed low overhead (45% of members). This would result in the coolest temperatures and showery weather across the region. Breezy to windy westerly gap winds Friday and Saturday will be the primary instigator of any potential highlights. Both days, NBM probabilities suggest a 30-90% chance (predominantly 30-60% except for climatologically windy locations) of 24-hr maximum wind gusts exceeding advisory magnitude (45 mph) for the lower Columbia Basin of OR, foothills of the northern and southern Blue Mountains of OR, the eastern Columbia River Gorge of OR/WA, the Simcoe Highlands, and the Kittitas Valley. While the system will have the potential to bring rain to the forecast area Friday through Tuesday, chances of wetting rain (0.1" or higher) are low through the period (<35% chance), with the exception of the Cascade crest (35-65% chance, highest for WA). Due to aforementioned ensemble spread leading to uncertainty in exact pattern details, confidence is low (20-40% chance), but the combination of cold temperatures aloft and low PWATs may facilitate a late-season freeze Sunday and Monday mornings in freeze-prone locations of central and northeast OR. Plunkett/86 && .AVIATION...12Z TAFs...VFR conditions are very likely (95-100% chance) at DLS/YKM/PSC/PDT/ALW, and likely (75-85% chance) at BDN/RDM through the period. Should sub-VFR conditions materialize, it would be due to post-frontal BKN-OVC low-level stratus (015-030 AGL) Tuesday evening and night in the wake of a dry cold front. An upper-level low and aforementioned cold front will induce westerly to northwesterly winds of 15-25 kts accompanied by gusts of 25-40 kts this afternoon and evening. Aside from the low probability of low-level stratus, clouds will be limited to FEW-SCT cirrus. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 83 46 77 46 / 0 0 0 0 ALW 86 50 78 49 / 0 0 0 0 PSC 88 52 81 51 / 0 0 0 0 YKM 83 45 79 46 / 0 0 0 0 HRI 86 49 81 49 / 0 0 0 0 ELN 74 45 73 46 / 0 0 0 0 RDM 81 41 76 42 / 0 0 0 0 LGD 82 43 74 44 / 0 0 0 0 GCD 85 45 79 46 / 0 0 0 0 DLS 79 50 80 50 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory from 9 AM this morning to 11 PM PDT this evening for ORZ041. WA...Wind Advisory from 9 AM this morning to 11 PM PDT this evening for WAZ024-026-521. && $$ MORNING UPDATE...83 SHORT TERM...75 LONG TERM....86 AVIATION...86