Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
606 FXUS66 KPQR 032215 AFDPQR Area Forecast Discussion National Weather Service Portland OR 315 PM PDT Mon Jun 3 2024 .SYNOPSIS...Another disturbance will bring rain to much of SW Washington and portions of NW Oregon tonight into Tuesday, with lighter shower activity continuing elsewhere. Temperatures begin a steady upward trend on Wednesday, peaking with high in the upper 80s to low 90s in the interior lowlands Friday and Saturday. && .DISCUSSION...Radar imagery shows scattered shower activity ongoing across northwest Oregon and southwest Washington this afternoon in moist onshore flow as one system departs into the northern Rockies and another approaches from the eastern Pacific. This next system is currently centered approximately 600 miles off the BC coast, with a 150 kt jet streak at the base of the upper level trough taking aim on Vancouver Island and the Washington coast. At the surface, a frontal system arcing southeastward towards the Washington and Oregon coastal waters will approach the area tonight into Tuesday morning and bring the next round of steadier precipitation. As most of the energy from this next system will be focused north of the area, there will be a fairly sharp gradient of precipitation across the area, with heavier rain focused over southwest WA and far northwest OR and lighter shower activity persisting south of a roughly Tillamook-Portland-Mt Hood line. In terms of QPF, guidance is in line with previous forecast cycles, depicting another 0.25-0.50" of rain through tomorrow morning from northern coastal areas to the Willapa Hills and south WA/north OR Cascades, with lesser amounts of a tenth or two for lowland locations including Portland. However, some of the exposed west slopes of the Coast Range and Cascades could pick up another 1.00-1.25" where orographic support is maximized. Meanwhile, locations farther south from Salem to Eugene will likely be limited to less than a tenth of an inch through Tuesday. Shower activity will then gradually wind down across the area Tuesday night into Wednesday morning as the system departs to the east. The shift back to a warmer and drier pattern will commence on Wednesday as a ridge of high pressure begins to build east of the Cascades, setting the stage for above for well above normal temperatures by the end of the week. Guidance shows good agreement on highs rebounding to near seasonal norms in the 70s in the lowlands on Wednesday and then into the 80s by Thursday. Heat will peak across the area Friday into Saturday as the ridge continues to strengthen. Models continue to converge on highs in the upper 80s to low 90s, with NBM probabilistic guidance indicating a 50 percent chance for temperatures to reach 90 degrees in Portland on Friday, decreasing with southward extent to around a 10 percent chance in Eugene. However, chances to reach 95 degrees are only around 10 percent in Portland and near zero in Eugene, underscoring the increasing confidence on the range of temperature outcomes. Probabilities decrease on Saturday, with around a 20 percent chance to hit 90 at PDX and lower probabilities elsewhere. Given that the ridge is setting up a bit farther east than in previous forecast cycles, the other forecast concern in this timeframe will be the potential for a few thunderstorms to develop along the Cascades Friday and Saturday afternoon as the region remains in southwest flow aloft, allowing a few embedded disturbances to brush the area. Currently carrying a slight chance of thunderstorms in the Lane County Cascades on Friday and as far north as Mount Jefferson on Saturday. Temperatures trend back downward as the ridge breaks down on Sunday, but guidance does keep temperatures above seasonal norms into early next week as WPC ensemble clusters continue to favor ridging nosing back into the area from the Pacific in the extended term. /CB && .AVIATION...Northwesterly flow aloft becoming westerly as moist onshore flow persists through Tuesday. Predominately VFR in the post frontal environment with scattered showers and gusty southwest winds at the surface. Showers gradually diminishing this afternoon, but the next frontal system begins to push in this evening with light rain and lowering CIGS. Expect conditions to deteriorate to MVFR along the coast after 00Z, and inland by around 04Z Tuesday. Winds are expected to remain breezy, though backing to more southerly direction. Strongest winds expected along the coast with gusts up to 30 kt. May see some low level wind shear develop overnight into Tuesday morning between 06Z-18Z as southwest winds increase to around 35-40 kt at 2000 feet. PDX AND APPROACHES...VFR with decreasing rain showers this afternoon. Conditions expected to deteriorate to MVFR late this evening as another frontal system brings rain and lower CIGS. Chances for MVFR increase to above 50% after 04Z Tuesday, continuing through Tuesday morning. Southwest winds around 12-16 kt expected through this evening, then becoming more southerly with gusts up to 20 kt. Low level wind shear also possible after 06Z Tuesday as southwest winds around 2000 ft increase to around 40 kt. /DH && .MARINE...Another frontal system quickly approaching the coastal waters will bring increased southerly winds with gusts up to 35 kt overnight into early Tuesday morning. Will maintain the Gale Warning for coastal waters north of Cape Foulweather, including the Columbia River Bar. Small Craft Advisories continue for the zones south of Cape Foulweather through Tuesday night. Seas remain steep and choppy at around 10 to 12 feet through Tuesday. An incoming northwesterly swell will likely cause seas to build to around 12 to 14 feet Tuesday night through Wednesday. High pressure builds midweek for more settled conditions. Expect a summer type pattern with high pressure offshore and a thermal trough along the coast, bringing northerly winds gusting to 25 kt at times through the end of the week. Seas around 8 to 10 ft on Thursday likely to subside to around 6 ft on Friday. /DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210- 251-252-271-272. Gale Warning from 11 PM this evening to 8 AM PDT Tuesday for PZZ210-251-252-271-272. Small Craft Advisory until 5 PM PDT Tuesday for PZZ253-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland