Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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209 FXUS66 KPDT 151107 AAA AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 407 AM PDT Sat Jun 15 2024 Updated Aviation Discussion .SHORT TERM...Today through Monday night...Although no highlights will be issued for the morning package, there are a few weather concerns in the short term. Today will be breezy with isolated to scattered showers and thunderstorms with best probability for lightning (30%) along the WA Cascades. Showers will end tonight, clouds and winds will decrease, and it will be a chilly Sunday morning. The cooling trend continues into Sunday with a 60% chance of showers along the WA and northern OR Cascades. Showers on Monday will mainly occur along the Blue Mountains and Wallowas where PoPs are 40-60%. The PacNW will be under a longwave upper level trough through Monday night. A 120kt polar jet is along the base of the trough with the axis of the jet just south of the WA/OR border. Lapse rates will be steep over eastern WA today where H5 temps will fall to around -28C and mid-level lapse rates will increase to around 7-8 C/km. CAPES will range from 150-200 J/kg. Along the WA Cascade north of Mt. Adams, HREF-calibrated thunder is around 50-60% but probabilities decrease significantly south and east of Mt. Adams. There are no organized fronts or shortwaves enhancing showers, just a westerly flow and orographic lift with channeled vorticity. Therefore, confidence is high that any precipitation amounts greater than 0.25" will be along the Cascade crest while the northern Blue Mtns and Wallowas will receive less than 0.10". Strong winds aloft and a tight MSLP gradient will keep breezy winds for most of the forecast area where gusts of 25-35 mph...locally 45 mph...will be a minor nuisance for outdoor events. Dry grassy areas will be susceptible to fire spread. Surface winds will gradually decouple from winds aloft and diminish tonight. Drier air will spread across the region, and skies will be partly cloudy to mostly clear. Overnight lows will fall into the 30s to mid 40s...locally in the mid 20s in the colder valleys such as Ukiah, Seneca, and Sunriver. Confidence that the Redmond and Bend areas will fall below freezing is around 30-40%, so it will be close. Rather than issue a Freeze Warning for the central Oregon zone (OR511), will give heads up on social media and weather graphics that it will be cold tonight with areas of frost. Models continue to back off on the QPF for Monday. There are some model differences on the position of an approaching closed low, but they all are in agreement that a closed low will dive south- southeast from the coast to eastern Oregon Sunday night and Monday with the position of the low near the OR/ID border. Wallowa County will have the best chance for measurable rainfall. The GFS continues to have the highest QPF compared to the other deterministic models, showing 0.15-0.2" in Wallowa County. Wrap- around moisture often is underestimated in these patterns, so this cannot be ruled out. However, the GFS has backed off considerably on the QPF compared to the previous runs. The NBM also has 20% probability for greater than 0.25", so it doesn`t look to be a big precipitation producer that models advertised several days ago. A slight chance (20%) of thunderstorms is forecast for the northeast mountains associated with steep lapse rates from the cold upper low. Wister/85 .LONG TERM...Tuesday through Saturday...Ensemble clusters are in very good agreement on the 500 mb pattern Tuesday through Friday which will be characterized by a broad trough over the West but with a gradual deamplification of the flow. On Saturday the clusters show some differences in the position of the trough axis but this will have little impact on the sensible weather. For Tuesday the closed upper low that will be impacting the region on Sunday and Monday will be moving quickly across MT into s-cntrl Canada. There may be just enough lingering moisture for a 15-20% chance of showers over Wallowa County during the afternoon. The NBM probability of TSTMS in this area is 10-15% with highest values over eastern Wallowa County. CAPE values are only forecast to be 100-200 J/kg so any TSTMS will be rather brief/weak. From Tuesday night onward the probability of precipitation will be less than 10% except for occasional 15-20% chances for light showers along the immediate WA Cascade crest. High temperatures on Tuesday will be within a few degrees of normal but a warming trend will begin Wednesday through Saturday with high temperatures as much as 10 degrees above normal Friday and Saturday. The ensemble clusters and NBM are depicting lower 90s for highs in the Columbia Basin on Friday spreading to the Yakima Valley and northern foothills of the Oregon and SE Washington on Saturday. The ECMWF ensemble is forecasting 100 degrees for KPSC for Saturday but that seems a bit warm given the 500 mb pattern. With temperatures climbing into the 90s the NWS experimental HeatRisk is forecast to climb into the moderate category which means the expected temperatures can affect those sensitive to heat. Winds will not be a major concern until possibly Saturday when there could be a weak marine push during the afternoon/evening . The ECMWF ensemble members are showing breezy winds for KELN and the NBM is forecasting sustained winds of 20 mph with gusts to 30 mph at KELN 00Z Sunday. Probabilistic NBM is showing the potential for a little stronger winds Saturday with a 30-50% chance of 45 mph gusts in the Simcoe Highlands, Kittitas Valley and portions of n-cntrl ORE. 78 && .AVIATION...12Z TAFS...VFR conditions will prevail through the forecast period. Primary concerns will be the winds across all TAF sites. Winds will increase after 15Z, peaking after 18Z with sustained winds 15-20kt and gusts 25-30kt. Winds will slowly subside this evening. SCT-BKN clouds are expected at 045-070 with BKN-OVC mid cloud above, tending to decrease this afternoon, becoming SKC tonight after 03-06Z. 78 && .PRELIMINARY POINT TEMPS/POPS... PDT 66 40 66 43 / 10 0 0 20 ALW 69 44 69 45 / 30 0 0 20 PSC 72 45 72 48 / 10 0 0 20 YKM 69 37 69 42 / 10 0 10 10 HRI 71 44 72 46 / 10 0 0 20 ELN 64 40 65 43 / 10 0 10 10 RDM 61 33 62 36 / 10 0 0 10 LGD 61 36 62 39 / 20 0 10 30 GCD 64 36 64 38 / 10 0 0 30 DLS 66 46 69 49 / 20 0 0 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...85 LONG TERM....78 AVIATION...78