Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
365 FXUS66 KPQR 151830 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 1130 AM PDT Sun Sep 15 2024 Updated Aviation Discussion .SYNOPSIS... A fall-like weather pattern will continue over the next week. Mainly dry on Sunday with increasing sunshine. Dry on Monday with sunshine and warmer temperatures. Rapid change to cool and wet conditions Tuesday into Wednesday as a strong frontal system brings widespread rain to the area. Drier and warmer conditions return again late in the week. && .SHORT TERM...Now through Tuesday night...Mainly dry on Sunday with increasing sunshine. Cannot rule out a stray shower or two at the coast and over the southern Willamette Valley. Locations to the north of that should stay dry through the day. Expect mild temps with highs around 70 degrees across the lowlands. Becoming warmer on Monday with plenty of sunshine as dry northeast flow develops aloft on the backside of a low to the southeast. Monday is still shaping up to be the warmest day of the week, and the latest iteration of the deterministic NBM has ticked up a degree or two. The NBM now suggests highs in the mid to upper 70s, except 60s at the coast. There is still a chance for high temps in the lower 80s (15-30% from Portland to Eugene). Overall Monday will be a great day for outdoor activities, especially given the rapid pattern change to cool and wet weather come Tuesday. This is when models and their ensembles have consistently showed widespread rain developing across all of northwest OR and southwest WA as a stronger frontal system moves over the coastal waters and pushes inland. Chances for rain remain near 100% with this system. Expect rain to begin at the coast Tuesday morning before pushing into the Willamette Valley, Portland/Vancouver metro and Cowlitz Valley during late morning to early afternoon hours. Post-frontal showers will then continue Tuesday night. Total rain amounts will likely wind up between 0.25-0.50 inches, except 0.50-0.75 inches at the coast and 0.50-1.0 inches in the Cascades and Coast Range. Probabilities for rain amounts over one inch are around 10-15% from Kelso to Portland to Salem to Corvallis. Probabilities increase to 30-50% from Junction City to Eugene-Springfield to Creswell and Cottage Grove. 30-50% chance for most locations along the coast, and a 50-65% in the Coast Range and Cascades. Regardless of exact rain amounts, enough will fall to result in a significant damper on fire activity. In regards to temps, highs will struggle to reach the mid 60s on Tuesday, around 10-13 degrees below average for this time of year. -TK .LONG TERM...Wednesday through Saturday...While there will be some showers lingering in the area on Wednesday, suspect convective activity will be on the decrease as weak high pressure builds in behind Tuesday`s weather system. Model soundings depict increasing sunshine Wednesday, allowing temps to warm back to around 70 degrees. Similar temps likely on Thursday and Friday, albeit a few degrees warmer. Most model guidance depicts shortwave ridging late in the week, resulting in dry conditions. NBM PoPs back this up and are under 10-15% both days. Offshore flow attempts to develop Friday night or Saturday, likely bringing even warmer temperatures to the region heading into next weekend. In fact, NBM probabilities for high temps of 80 degrees or warmer climb to 20-25% by next Saturday. -TK && .AVIATION...Some isolated showers linger over the area but clouds are beginning to lift and erode. Areas with the densest and MVFR CIGs are along the southern portions of Washington and along the Cascades. Much of the cloud cover is cumulus signifying the mixing nature of the airmass. Will see VFR conditions persist through the day as high pressure builds. Overnight temperatures are not decreasing enough the fog is a concern inland, but cannot rule it out along the coast. PDX APPROACHES...General VFR through the next 24 hours with a few periods of MVFR CIGs with passing clouds. Will see steady improvement through the day. Winds may become breezy in the afternoon, but gusts not expected to exceed 20 kt. -Muessle && .MARINE... High pressure over the outer waters will build tonight into Sunday. As such, will maintain the northerly pressure gradients, with gusty north winds Sunday night. Small Craft Advisory continues for late this afternoon into Monday, where have gusts 20 to 25 kt. Does appear will get some gusts in similar range closer to shore, but suspect most of these will be stay just offshore. Seems gradients relax early Monday am with Small Craft Advisory winds continuing over the outer zones through the afternoon. Overall, seas stay in 5 to 8 ft through Monday, with highest seas well offshore. Then, a taste of fall arrives Tuesday. A potentially strong front will push across the waters Tuesday as it elongates/weakens over the coastal waters. Winds not really turning to southerly (as do with most fronts), but may briefly get burst of west to southwest winds of 20 to 25 kt with the frontal passage. Models still vary some on the timing/strength of this system, so will see how things shape up as get closer in time to Tuesday. && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Monday for PZZ252-253. Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Monday for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland