Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
480 FXUS66 KPQR 141004 AFDPQR Area Forecast Discussion National Weather Service Portland OR 300 AM PDT Sat Sep 14 2024 .SYNOPSIS...A fall-like weather pattern will continue over the next week. Chances for light showers this weekend, however much of the time will be dry. Dry and mild conditions on Monday will give way to cool and wet conditions Tuesday into Wednesday as a strong frontal system brings widespread rain to the area. Trending dry again late in the week with slightly warmer temps. && .SHORT TERM...Now through Monday night...Radar, satellite and surface weather observations from 3 AM Saturday morning depicted mostly cloudy skies across northwest OR and southwest WA with areas of virga associated with a weak upper level impulse. The exception to that was over the Long Beach Peninsula and Willapa Hills where at least some light rain has reached the ground with passing showers, albeit not much. Chances for light showers will spread inland late Saturday morning into the afternoon, but most of the day will be dry, especially south of Salem. Temps should be very similar to what was observed on Friday. Cool, dry and calm conditions Saturday night will give way to another chance of light showers on Sunday as an elongated upper level low moves southward down the Washington and Oregon coast towards northern California. Models continue to suggest precipitation with this low will be light, spotty and disorganized. As such, most locations will wind up mainly dry or completely dry on Sunday, especially over the Willamette Valley and southwest WA. Any showers that do develop over the area on Sunday will diminish Sunday night, giving way to widespread dry conditions Monday through Monday night as dry northeast flow aloft develops on the backside of the aforementioned low. Monday is shaping up to be the sunniest and warmest day of the week with high temps most likely in the mid 70s, except 60s at the coast. That said, cannot rule out temps a bit warmer than that as the NBM is showing a 10-25% chance for highs near 80 degrees. Monday will be an excellent day for outdoor activities, especially given the rapid change to cool and wet weather expected the following day. This system is discussed below in the long term discussion. -TK .LONG TERM...Tuesday through Friday...Conditions will deteriorate quickly on Tuesday as a stronger frontal system brings more significant moisture into the region. Confidence is very high widespread rain will occur across all of western WA/OR during that time as every single ensemble member from the GEFS/GEPS/ENS are showing QPF and NBM PoPs are over 90%. Despite high confidence for rainy conditions, confidence is still lower in regards to exact rain amounts. A large degree of model spread remains for QPF, however ensemble member clustering is evident between 0.25-0.50 inches for the lowlands. The latest NBM probabilities for 24-hr rain amounts over 0.5 inches have decreased a bit from 70-80% to 50-70%, which makes sense given less ensemble member clustering evident between 0.5-0.75 inches when compared to yesterday`s guidance. Despite the decrease, probabilities are still fairly high, especially for 24-hr rain amounts over 0.25" as these values range between 70-90%. This means a soaking rain capable of putting a significant damper on wildfire activity is very likely to occur regardless of uncertainty on exact rain amounts. This system will also bring temps around 10-15 degrees below average for this time of year with highs likely in the low to mid 60s on Tuesday. Expect post-frontal showers on Wednesday with conditions drying out Wednesday night into Thursday. From there, temperatures will rebound to near seasonal averages for interior lowland valleys heading into next weekend. -TK && .AVIATION...West flow continues aloft as a shortwave trough settles into the region. This system to bring widely scattered showers with mid and high clouds. However, at the coast expect to see increasing MVFR cigs spreading north to south along the coast. As of 09Z KAST & KHQM has low VFR to MVFR cigs with VFR to the south. HREF indicating 60-80% chance for MVFR CIGS or lower 09-21Z Sat, with probabilities decreasing there after. For inland terminals VFR conditions remain with mid and high clouds although CIGS gradually lower in the morning hours. There is a 20-40% chance in high-end MVFR cigs around the broader Portland metro to Salem area 15-19z Sat. Higher confidence in VFR cigs/vis during the afternoon through tonight. PDX APPROACHES...VFR with mid and high clouds today, but there is a 30-40% chance for high-end MVFR CIGS (3-3.5kft) between 15-19z. Winds become variable near sunrise Saturday morning before turning northerly around midday. /mh -Schuldt && .MARINE...Rather benign weather today as a weakening front on the waters dissipates as it moves ashore later this morning. Another weak trough moves to the waters later tonight into early Sunday morning. Pressure gradients increase Sunday as high pressure strengthens offshore for gusts to 25 kt mainly over the outer zones (10-60NM). Lower forecast confidence for gust to 25 kt for the nearshore zones. Overall seas stay in 3 to 6 ft range today and tonight, then 6 to 8 ft Sunday, Monday. Then a front will push across the waters Tuesday as it elongates/weakens over the coastal waters. Models vary some on the timing/strength of this system, so will see how things shape up as get closer in time to next Tue. /mh /Rockey && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory from 5 PM Sunday to 11 AM PDT Monday for PZZ272-273. && www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland