Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
747 FXUS66 KPQR 151029 AFDPQR Area Forecast Discussion National Weather Service Portland OR 329 AM PDT Sat Jun 15 2024 .SYNOPSIS...Low pressure brings cool and showery weather with a chance of thunderstorms today and Sunday. The best chances will be in the afternoon across northern portions of the forecast area. Cool and showery conditions last into Monday, then warmer and drier weather returns Tuesday through the end of next week. && .SHORT TERM...Now through Monday Night...The pattern change is well underway this morning as an upper level low centered over Vancouver Island brings about a shift to cooler and wetter weather which will persist through the next few days. Water vapor imagery depicts a well defined shortwave embedded within the larger scale trough swinging across western Oregon and spurring an increase in shower activity across our area as a weak surface front approaches the coast. Upper level troughing will maintain widespread showers across much of the area today in the post frontal air mass, with coverage generally decreasing with southward extent and becoming a little spottier in nature around Eugene by this afternoon. Model QPF amounts remain on track from previous runs, depicting 0.50-0.75" and locally higher amounts across the north Oregon and south Washington Cascades through late this evening, but generally a quarter inch or less across most other locations. Rain amounts will be somewhat variable across the area given the hit or miss nature of the activity, with locally higher amounts possible in heavier showers. Abundant cloud cover will help to hold temperatures 7-10 degrees below seasonal norms across the area today, with highs struggling to reach the mid 60s in most locations. Both NBM and SREF probabilistic guidance remain rather bullish on thunderstorm potential as colder air filtering into the region aloft serves to steepen mid level lapse rates. Have tempered these expectations somewhat in the forecast as this potential will be at least in part dependent on getting some breaks of sun and resulting surface heating to generate sufficient instability. Additionally, the most favorable jet dynamics and upper level support are somewhat mistimed as they will be departing the area by later this morning, and no upstream lightning strikes have been noted in association with these features thus far overnight. Despite those caveats, a few rumbles of thunder are certainly possible across the area through this evening. While the best chances will generally be focused along and north of the Columbia River into southwest Washington, a few strikes will be possible as far south as Eugene through this afternoon. The cool and showery weather will persist over the region on Sunday as upper level troughing remains in place, with highs across the area similar to today. Shower activity will increase again in the afternoon as the main upper low shifts southeast across Washington and Oregon, bringing a renewed chance of thunderstorms across the north through early evening. The area will begin to dry out but remain cool on Monday as northwest flow takes hold behind the trough departing into the Rockies, with light shower activity mostly confined to the higher terrain and winding down through Monday night. /CB .LONG TERM...Tuesday through Friday...Warmer weather looks to return Tuesday through the end of next week as WPC ensemble clusters agree on the weakening of the trough over the western CONUS and subsequent increasing 500 mb heights across the Pacific Northwest. Guidance suggests temperatures will rebound back above normal into the upper 70s to low 80s by Tuesday as this occurs. Wednesday and Thursday then appear to be the hottest days of the coming week as most deterministic solutions depict a weak Rex Block developing with a low amplitude ridge over western Canada and an open trough over northern California. This results in rather high confidence in NBM temperature spreads showing highs in the mid to upper 80s for areas away from the coast both Wednesday and Thursday, with only around a 25 percent chance to reach 90 from Portland to Salem and closer to a 10 percent chance around Eugene. /CB && .AVIATION...A front is currently in the process of pushing through the area, allowing for intermittent rain showers and the possibility of brief lowering of ceilings to MVFR, mostly at the coast. Inland terminals should mostly see low-end VFR conditions once the front fully pushes in by 14-15z Sat; chance of MVFR or lower ceilings is around 15-25% for all inland terminals. While the front is pushing in, all terminals could see a low chance of an isolated thunderstorm or two, though chances are even lower south of KCVO. Chances will generally be 10-20% of a thunderstorm at most terminals north of there, with threat ending around 3z Sun. Any thunderstorms will have the potential to produce small hail along with gusty and erratic winds. Weak southwesterly winds will gradually turn westerly and slightly strengthen throughout daytime hours Saturday, but gusts should top out around 15-20 kts. Winds will become light and variable over Saturday night again. PDX AND APPROACHES...Scattered cloud decks will turn to low-end broken clouds once the front fully pushes in around 13-14z Sat. The chance of ceilings dropping to MVFR or lower is around 15-30%, and the majority of the TAF period should remain VFR. The front fully moves through the area by 20z Sat, and VFR conditions will remain locked in place afterwards. There will be a low chance of thunderstorms from 12z Sat to 3z Sun, with highest chances Saturday afternoon; chance of a weak isolated thunderstorm is around 25%. /Jliu && .MARINE...Fairly innocuous conditions for the near future. Seas remain around 5 to 7 ft at 9 to 11 seconds. A front is currently passing through, allowing for slightly stronger west winds no stronger than 20 kt through daytime hours Saturday. These decrease again going into Saturday night. Late Sunday/early Monday strong northwesterly winds will return and will likely bring marginal Small Craft Winds to all waters. There is still some uncertainty in the timing and strength of the Monday system /42/JLiu && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland