Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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615 FXUS66 KPDT 261654 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 954 AM PDT Thu Sep 26 2024 .Updated for Aviation... .AVIATION... 18Z TAFS...VFR conditions with winds less than 10 kts are expected through the TAF period. && .PREV DISCUSSION... /issued 420 AM PDT Thu Sep 26 2024/ SHORT TERM...Today through Saturday night... Key Messages: 1. Showers return to the Washington Cascades tonight into Friday. 2. Breezy winds tonight through Friday. 3. Above normal temperatures persist into the weekend. Current radar and infrared satellite imagery shows light returns exiting east Wallowa county and lingering over Snoqualmie Pass under clearing skies. This is a result of the departing upper level trough and associated cold front that will continue to depart to our northeast and into southern Alberta by mid-morning on Thursday. In the wake of this system, upper level high pressure over the Desert Southwest will encroach into the Northern Rockies today and Friday to provide zonal flow over the area. The building high pressure will help to deflect a weak, incoming shortwave later this afternoon and evening, leading to rain chances (35-65%) being confined along the Washington Cascade crest as rain amounts of 0.10-0.20" are expected over Snoqualmie Pass between 5PM tonight and 5AM Friday morning. Rain accumulations will stay fairly well confined to the Cascade Crest as only a trace is expected at Cle Elum and dry conditions at lower elevations. Confidence in these rain amounts are high (80-90%) as the HREF and NBM both highlight a 60-70% of 0.10" or greater rain amounts at Snoqualmie Pass, dropping to a 40-50% chance of 0.20" or greater rain amounts. The weak shortwave and associated cold front will pass over the area this evening and into early Friday morning, also attributing to elevated winds along the east slopes of the Washington Cascades and Simcoe Highlands. Sustained winds of 10-20 mph will be possible with gusts of up to 30 mph out of the west, peaking between 11PM Thursday and 5AM Friday. Confidence in these elevated winds is high (80%) as the HREF and NBM both advertise a 70-90% chance of wind gusts of 30 mph or greater and a 60-70% chance of sustained winds of 20 mph over the aforementioned areas. In the wake of this passing weak cold front, a pressure gradient looks to set up Friday afternoon over the Kittitas Valley as suggested by a 4.5-7 mb difference between Everett (PAE) and Pasco (PSC) via the GFS, NAM, and SREF. These values correlate to sustained winds of 15-20 mph and gusts up to 30 mph out of the west, peaking between 2PM and 8PM on Friday. Confidence in these wind values is moderate (60%) as the HREF and NBM suggest a 65-75% chance of sustained winds of 20 mph or greater with only the NBM showing a 67% chance of gusts reaching 30 mph or greater. Persistent west-southwest flow aloft into the early part of the weekend will keep temperatures above normal as highs stay in the upper 70s to low 80s across lower elevations of the Basin. Temperatures are expected to slowly increase into Saturday as flow aloft incurs more of a southerly component due to an approaching shortwave. Near normal high temperatures today will become 5-7 degrees above normal Friday and 6-8 degrees above normal on Saturday. Confidence in highs reaching into the low 80s for areas of the Basin is moderate (60-70%) as the NBM highlights a 45-65% chance of 80 degrees high temperatures on Friday and Saturday for Hermiston, Walla Walla, Pilot Rock, and the Tri-Cities. Temperatures do look to return to near normal over the beginning part of the week. 75 LONG TERM...Sunday through Thursday... Model are in good agreement with the shortwave trough moving into the PacNW Sunday. With increased west-northwesterly flow, gusty winds will develop at 20-30 mph (60-90% probability) at the Kittitas and Yakima Valley including eastern CR gorge. As the trough moves eastward, a upper ridge builds over into the region Monday with winds less than 12 mph (>70% confidence). No major weather impacts will occur for these days. Slight chances (15-30%) of showers could occur Tuesday at the WA Cascades due to the orographic lifting from the cold front. Models are in good agreement with the cold front arriving to the PacNW Tuesday. Wednesday will have breezy winds up to 20 mph as the upper ridge moves inland of the region off OR coast. WA Cascades might have developing showers, but chances are low (<20%) as the upper ridge builds over off OR coast. The PacNW will enter a ridge Thursday with slight chances of evening showers at the WA/OR Cascades. For Thursday night, about 32% total cluster members favor a ridge breakdown whereas 51% members has a ridge over the PacNW with only 18% members favoring a zonal pattern. If the ridge breaks down, chances of showers could increase. But if not, then a upper ridge may stay longer thus returning dry conditions and warm temps. Unfortunately, this can make this weather pattern challenging to forecast, given the uncertainties. Feaster/97 AVIATION...12Z TAFS...VFR conditions are expected through the TAF period. Mid to high (FEW-BKN at 070-250) clouds will prevail for the next 24 hours. Winds will be less then 12 kts. Feaster/97 && .PRELIMINARY POINT TEMPS/POPS... PDT 48 77 47 75 / 0 0 0 0 ALW 53 79 51 80 / 0 0 0 0 PSC 56 80 50 79 / 0 0 0 0 YKM 48 77 44 77 / 0 0 0 0 HRI 52 80 49 79 / 0 0 0 0 ELN 49 73 44 77 / 0 0 0 0 RDM 43 79 43 80 / 0 0 0 0 LGD 48 79 48 86 / 0 0 0 0 GCD 48 84 50 89 / 0 0 0 0 DLS 54 80 52 80 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...75 LONG TERM....97 AVIATION...77