Area Forecast Discussion (AFD)
Issued by Portland, OR (PQR)
000 FXUS66 KPQR 161005 AFDPQR Area Forecast Discussion National Weather Service Portland OR 304 AM PDT Mon Sep 16 2019 .SYNOPSIS...Showers and isolated thunderstorms are expected today as a cool upper trough moves over the Pacific NW. A cold front will bring rain and breezy winds to the area on Tuesday, with rain being heavy at times. Another cool upper trough will continue showers and bring another threat for isolated thunderstorms on Wednesday. Drier weather expected late in the week, but temperatures will remain cooler than usual for this time of the year. && .SHORT TERM...Today through Thursday...Isolated thunderstorms are reaching the coast early this morning as a cold upper trough approaches the Pacific NW as isolated to scattered showers cs inland. The threat for isolated thunderstorms remains on the coast through the morning, then shifts inland this afternoon as the upper trough moves inland. The showers will pick up in frequency and intensity this afternoon as the cool upper trough moves over the region. The snow levels will lower to around 6500 feet today for a light dusting of snow in the higher Cascades, but do not expect any winter weather for the Cascade passes. Another strong and moist cold front will bring another round of moderate to heavy rain on Tuesday. The rain will reach the coast early Tuesday morning and spread inland by the early afternoon. This front is very similar to the one that moved through on Sunday, and expect similar rain rates and totals. Rain totals along the coast and higher terrain of 0.75 to 1.5 inches are expected between Tuesday morning and Tuesday evening with 0.5 to 0.75 inch expected for the interior valleys. Winds will be breezy with the front passage on Tuesday with gusts of 40 mph possible along the coast and 30 mph for the Willamette Valley. Temperatures will be much cooler on Tuesday with daytime highs barely making it to 60 degrees. Another cool upper trough follows the Tuesday front that will support showers through Tuesday night and Wednesday. Cold air aloft will destabilize the atmosphere and expect isolated thunderstorms along the coast Tuesday night and inland Wednesday afternoon. The upper trough moves east of the Cascades Wednesday night and showers will decrease. An upper ridge tries to build on Thursday, but a shortwave trough may sneak over the ridge and maintain Cascade showers or marine stratus and drizzle along the coast. Regardless it will be a drier day. Temperatures will warm a bit, but still be well below the seasonal normals. ~TJ .LONG TERM...No Changes. Previous discussion follows...Thursday night through Sunday...Cannot rule out that some stray showers will continue into Friday as weak disturbances move through the upper level flow. There remains quite a bit of uncertainty in the weather towards the end of the week and into next weekend. At this juncture, looks like late Friday and Saturday could be fairly dry, then another upper level trough approaches the region on Sunday bringing a chance of showers. /tw && .AVIATION...Isolated thunderstorms continue over the coastal waters overnight with some even reaching the coast. Chances for thunderstorms will spread inland today as a cool upper trough moves ashore. VFR conditions are expected at the coast today and tonight. However expect spotty MVFR or lower conditions with heavier showers or thunderstorms. For inland areas, widespread MVFR conditions with cigs between 1500 and 2500 ft along with some IFR conditions will affect the terminals this morning. As the cool upper trough moves over the interior and daytime surface heating increases we should see the lower layers begin to lift by mid morning with VFR for most areas 18-20Z. Showers will increase in the afternoon along with chances for showers and thunderstorms with may bring brief MVFR or lower conditions. Thunderstorm chances should end around 04Z Tue. KPDX AND APPROACHES...Cigs around 1200-1500 ft should hold through about 16Z the lift above 2000 feet before breaking to VFR 20Z. Showers will pick up over the valley in the afternoon. Expect mainly VFR conditions Mon afternoon and evening, with the potential for some heavier showers or even a thunderstorm or two to bring brief MVFR or IFR conditions. /mh Pyle && .MARINE...A broad and weak surface low pressure will drop southward across the waters through Monday. This should bring relatively benign winds, though cold air aloft will probably result in some squally showers and thunderstorms today. Expect seas to stay in the 7 to 9 ft range through Monday evening. The next front is expected to bring gale force winds as it crosses the waters late tonight and Tue, so have issued a Gale Warning. It looks like the strongest winds would be brief, lasting about 6 hours during the day early Tuesday morning. Seas will be steep and wind-driven with the front, peaking at 10-11 ft. Winds settle Tuesday night into Wednesday with broad low pressure over the waters, but seas stay in the 8 to 10 ft range with NW swell. High pressure returns to the waters late in the week for a more summer type pattern. /mh Bowen && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Gale Warning from 3 AM to 2 PM PDT Tuesday for Coastal Waters from Cape Shoalwater WA to Florence OR out 60 NM. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland This discussion is for Northwest Oregon and Southwest Washington from the Cascade crest to 60 nautical miles offshore. This area is commonly referred to as the forecast area.